ZnSnO3 nanocubes (ZSNCs) with various Pt concentrations (1at%, 2at%, and 5at%) were synthesized by the high-yield and facile one-pot hydrothermal method. The microstructures of the obtained products were characterized by XRD, FESEM, TEM, EDS and XPS. The results showed that the ZSNCs with perovskite structure are approximately 600 nm in side length, and this size was reduced to 400 nm after Pt doping. PtOx (PtO and PtO2) nanoparticle with the diameter of about 5 nm were uniformly coated on the surface of ZSNCs. NO2 sensing properties showed that 1% Pt-ZSNCs exhibited the highest response to NO2 than pure ZSNCs and Pt-ZSNCs with other Pt concentrations. The maximum response of 1 at% Pt-ZSNCs to 500 ppb NO2 was 16.0 at the optimal operating temperature of 125 °C, which was over 11 times higher than that of pure ZSNCs. The enhanced NO2 sensing mechanisms of Pt-ZSNCs were discussed in consideration of catalytic activities and chemical sensitization of Pt doping.
A computational fluid dynamics (CFD) model was developed to accurately predicate the flash reduction process, which is considered to be an efficient alternative ironmaking process. Laboratory-scale experiments were conducted in drop tube reactors (DTRs) to verify the accuracy of the CFD model. The reduction degree of ore particles was selected as a critical indicator of model prediction, and the simulated and experimental results were in good agreement. The influencing factors, including the particle size (20–110 μm), peak temperature (1250–1550 °C), and reductive atmosphere (H2/CO), were also investigated. The height variation lines indicated that smaller particles (50 μm) had a longer residence time (3.6 s). CO provided a longer residence time (~1.29 s) compared with H2 (~1.09 s). However, both the experimental and analytical results show that the reduction degree of particles in CO atmosphere only reached 60%, significantly lower than that in H2 atmosphere, even at the highest temperature (1550 °C). The optimum experimental particle size and peak temperature for the preparation of high-quality reduced iron were found to be 50 μm and 1350 °C in H2 atmosphere and 40 μm and 1550 °C in CO atmosphere, respectively.
Selective laser melting technology has a dominant position in the preparation of porous titanium implants with complex structure and precise size. However, the processing characteristics of rapid melting and solidification lead to the products accumulate residual stress easily. Hereby, an in situ method was demonstrated to restrain the residual stress and improve the mechanical strength of porous titanium alloys during laser additive manufacturing. Porous Ti6Al4V was prepared by a SLM 3D printer equipped with a double laser system that rescan each layer immediately after molten powder had solidified, reducing the temperature gradient and avoiding rapid melting and cooling. The results indicate that double scanning process can provide a stronger bonding condition for the cellular structure, and improve the yield strength and elastic modulus of the alloy. Rescanning with 75% energy density result in 33.5%-38.0% reduction of residual stress. In terms of pore structure and morphology, the porosities of double-scanned specimens are 2%-4% lower than that of single-scanned specimens. This inconsistency increases with the increase of sheet thickness due to the anabatic balling phenomena. It is suggested that the rescan laser power should be turned down during the preparation of porous titanium with thick cell walls to ensure dimensional accuracy.
Two new refractory high-entropy alloys, CrHfNbTaTi and CrHfMoTaTi, deriving from the well-known HfNbTaTiZr alloy by principal element substitutions, were prepared by vacuum arc-melting. Their phase components, microstructures, and compressive properties in the as-cast state were investigated intensively. The results showed that both alloys are mainly composed of a BCC and cubic laves phase. In terms of the mechanical properties, the yield strength increased remarkably from 926 MPa of HfNbTaTiZr to 1258 MPa of CrHfNbTaTi, meanwhile a promising ductility of around 24.3 % elongation was retained. The morphology and composition of the network-shape interdendritic regions were closely related to the improvement in mechanical properties deduced by elemental substitution. Whereas, dendritic surrounded by the incompact interdendritic shell at the case of the incorporation of Mo deteriorates the yield strength, and results in a typical brittle feature.
Stellite-21/WC nanopowders were deposited on Inconel using vibration-assisted laser cladding through different laser parameters. To study about the microstructural and mechanical behaviors, optical and scanning electron microscopes, hardness measurements, and wear characterizations were employed. The results showed that the variation of cooling rate resulted in remarkable effects on the microstructure of the as-cladded composites. Moreover, increasing the laser power from 150 W to 250 W increased the heat input and the dilutions. Also, in the higher power of the laser (i.e. 250 W), dilution was affected by two factors that were scanning rate and powder feeding rate. Through the addition of WC nanoparticles as the reinforcement, the dilution magnitude intensified while the hardness value surprisingly increased from 350 to 700 HV. The wear characterizations indicated that the composites containing 3 wt% WC nanoparticles possessed the highest wear resistance.
The utilization of novel materials, high Tc superconductors in particular, is essential in order to pursue the United Nations Sustainable Goals as well as the increasing worldwide demand for clean and carbon-free electric power technologies. Superconducting magnets have proven to be beneficial in several real-life applications such as transportation, energy production, MRI, drug delivery system etc. To achieve high performance, it is crucial to develop uniform large-grain infiltration-growth processed bulk YBa2Cu3Oy (Y-123) super-magnets. In this paper, we are reporting the magnetic and microstructural properties of large-grain top-seeded infiltration growth processed Y-123 pellet of 20 mm in diameter and 6 mm in height, produced utilizing the liquid Yb-123+Ba3Cu5O8 as liquid source. All samples cut at the top of the bulk have a sharp superconducting transition (~ 1 K wide) with the onset Tc around 90 K. On the other hand, in the samples cut from the bottom surface, the onset Tc values slightly decreased to values between 88 K and 90 K, still with a sharp superconducting transition. The top and bottom samples exhibited the highest remnant value of Jc at 77KH//c-axis of 50 kA/cm2 and 55 kA/cm2, respectively. The remnant Jc and irreversibility field values significantly fluctuated, being quite low in some bottom samples. Scanning electron microscopy (SEM) identified nanometer-size Y-211 secondary phase particles dispersed in the Y-123 matrix. The energy dispersive spectroscopy (EDS) clarified that the decreased critical temperature (Tc) and critical current density (Jc) for the bottom samples were due to liquid phase dispersion within Y-123 phase.
The present investigation deals with the improvement in microstructure, physical, and mechanical properties of die-cast A308 alloy subjected to mechanical vibration during solidification. The different frequencies (0, 20, 30, 40, and 50 Hz) at constant amplitude (31 μm) were employed using a power amplifier as the power input device. X-ray diffractometer, optical microscopy, and scanning electron microscopy were used to examine the morphological changes in the cast samples under stationary and vibratory conditions. Metallurgical features of castings were evaluated by ImageJ analysis software. The average values of metallurgical features, i.e., primary α-Al grain size, dendrite arm spacing (DAS), avg. area of eutectic silicon, aspect ratio, and percentage porosity were reduced by 34, 59, 56, 22, and 62% respectively at 30 Hz frequency compared to stationary casting. The mechanical tests of cast samples showed that yield strength, ultimate tensile strength, elongation, and microhardness were increased by 8, 13, 17, and 16%, respectively, at 30 Hz frequency compared to stationary casting. The fractured surface of tensile specimens exhibited mixed-mode fracture behavior due to the appearance of brittle facets, cleavage facets, ductile tearing, and dimple morphologies. The presence of small dimples showed some plastic deformation occurred before fracture.
In this work, NH4ZnPO4 powders were synthesized by a simple precipitation method at room temperature. The effect of PVP, PVA, sucrose and CTAB solution on the morphology and structure of the prepared samples was investigated. The phase composition and morphology of the prepared samples were characterized by using X-ray diffraction and scanning electron microscopy, respectively. Depending on the polymer sources, the hexagonal structure prepared by using non-surfactant of water completely changed to monoclinic structure when CTAB was added into the process. X-ray absorption near edge structure (XANES) and X-ray photoelectron spectroscopy (XPS) was used to study the local structure and surface electronic structure of the prepared samples confirming that the oxidation states of P and Zn ions are 5+ and 2+, respectively. By using ICP-OES technique, our NH4ZnPO4 powders can be classified as a slow-release fertilizer where less than 15% of the ions was released in 24 h. This study shows that a simple precipitation method using water, PVP, PVA, sucrose and CTAB as a template can be used to synthesize NH4ZnPO4 powders. In addition, this method may be extended for the preparation of other oxide materials.
The hot ductility of a Fe-0.3C-9Mn-2Al medium Mn steel was investigated by using a Gleeble3800 thermo-mechanical simulator. Hot tensile tests were conducted at different temperatures (600~1300 oC) under a constant strain rate of 4 × 10-3 s-1. The fracture behavior and mechanism of hot ductility evolution were discussed. The results showed that the hot ductility exhibited a decreasing trend with temperature decreasing from 1000 oC. The reduction of area (RA) decreased rapidly tested below 700 oC and the value was lower than 65% for specimen tested at 650 oC. Mixed brittle-ductile fracture feature is reflected by the coexistence of cleavage step, intergranular facet and dimple at the surface. The fracture belonged to ductile failure for specimens between 720~1000 oC. Large and deep dimples could delay the crack propagation. The change of average width of dimples was in positive proportion with the change of RA. The wide austenite-ferrite intercritical temperature range was crucial for the hot ductility of medium Mn steel. The formation of ferrite film on austenite grain boundaries led to the strain concentration. Yield point elongation occurred at the austenite-ferrite intercritical temperature range during hot tensile test.
Reaction-bonded B4C-SiC composites are highly promising materials for many advanced technological applications. However, their microstructure evolution mechanism remains unclear. Herein, B4C-SiC composites were fabricated by the Si melt infiltration process. The influence of sintering time and B4C content on the mechanical properties, microstructure, and phase evolution were investigated. X-ray diffraction results showed the presence of SiC, boron silicon, boron silicon carbide, and boron carbide. Scanning electron microscopy results showed that with the increasing of boron carbide addition, the amount of Si content decreased and the amount of unreacted B4C increased. Unreacted B4C diminished with increasing sintering time and temperature. The further microstructure analysis showed a transition area between B4C and Si, with a C concentration marginally higher in the transition area than in the Si area. It indicates that after the silicon infiltration，diffusion mechanism is the primary sintering mechanism of the composites. As the diffusion process progresses, the hardness increases. The maximum values of the Vickers hardness, flexural strength, and fracture toughness of the reaction bonded B4C/SiC ceramic composite with 12wt% B4C content sintered at 1600℃ for 0.5 h are 2600 HV, 330 MPa, and 5.2 MPa·m0.5, respectively.
In order to investigate the oxidation behavior of a nickel-based superalloy containing high hafnium content (1.34 wt%), isothermal oxidation tests were performed at 900, 1000 and 1100°C for up to 200 h. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS) were applied to study the oxidation behavior. Weight gain of the experimental superalloy exhibits a parabola-like curve and no spallation of the oxide scale was observed in the oxidation tests. The alloy presents excellent oxidation resistance and no HfO2 is observed in the oxide scale at 900°C. Elevating the oxidation temperature up to 1000°C, HfO2 particles form in the spinel phases of the scale, and “pegs” HfO2 is observed within and beneath the inner layer of Al2O3 after 200 hours. As the oxidation temperature elevated to 1100°C, “pegs” HfO2 is observed at the early stage of oxidation test (within 25 hours). Formation mechanism of HfO2 and the impact on oxidation resistance are investigated based on the analysis of oxidation tests results at different temperatures.
As a part of the fundamental study related to the reduction smelting of both spent lithium-ion batteries and polymetallic sea nodules based on MnO-SiO2-based slags, the activity coefficient of nickel oxide in SiO2 saturated MnO-SiO2 slag and Al2O3 saturated MnO-SiO2-Al2O3 slag at 1623 K was investigated with controlled oxygen partial pressure of 10-7, 10-6, and 10-5 Pa. The results show that the solubility of nickel oxide in the slags increased with increasing the oxygen partial pressure. The nickel in both MnO-SiO2 slag and MnO-SiO2-Al2O3 slag existed as NiO under experimental conditions. The addition of Al2O3 in the MnO-SiO2 slag decreased the dissolution of Ni in the slag, and increased the activity coefficient of NiO. Furthermore, the activity coefficient of NiO, referred to solid NiO, can be calculated as: γNiO=8.58(wt% NiO in slag) + 3.18 (SiO2 saturated MnO-SiO2 slag, 1623K);γNiO=11.06(wt% NiO in slag) + 4.07 (Al2O3 saturated MnO-SiO2-Al2O3 slag, 1623K).
Multicomponent Al20Cr20Fe25Ni25Mn10 alloys were synthesized using spark plasma sintering at temperatures (800 °C, 900 °C and 1000 °C) and holding times (4, 8 and 12 minutes), with aim to develop a high entropy alloy (HEA). The characteristics of spark plasma synthesized (SPSed) alloys were experimental explored through investigation of microstructures, microhardness and corrosion using scanning electron microscope coupled with energy dispersive spectroscopy, Vickers microhardness tester and potentiodynamic polarization respectively. Also, X-ray diffractometry characterization was employed to identify the phases formed on the alloys developed. The EDS results revealed that the alloys consist of elements selected in this work irrespective of varying the sintering parameters. Also, the XRD, EDS and SEM collectively provided evidence that the fabricated alloys are characterized by globular microstructures exhibiting FCC phase formed on a basis of solid solution mechanism; this implies that SPSed alloy shows features of HEAs. The alloy produced at 1000 °C and holding time 12 minutes portrayed an optimal microhardness of 447.97 HV, however, this microhardness decreased to 329.47 HV after heat treatment. The same alloy showed outstanding corrosion resistance performance. Increase in temperature resulted in Al20Cr20Fe25Ni25Mn10 alloy with superior density, microhardness and corrosion resistance over other alloys developed at different parameters.
The composition and structure of substrate material have an important influence on the coating performances, especially the bonding strength and coating hardness,which determines whether the coating can be used. In the paper, the TiAlN coating was deposited on the TC with 0-20wt.% WC by arc ion plating. The influence of cermet substrates characteristics on the structure and properties of TiAlN coating was researched. The results show that TiAlN coating deposited on TC substrates has columnar grain structure. With the increasing of WC, the strength ratio of I(111)/I(200) of TiAlN and the adhesion gradually increases. When there is no WC in the substrate, the preferred orientation of TiAlN coating is (200). As the contents of WC go up, the preferred orientation of TiAlN coating becomes (111) and (200). The biggest difference between the adhesion strength of coating and substrate is the microstructure and composition of the substrate. Scratching results show that the adhesion of TiAlN coating gradually increases from A1 to A5 respectively 53N, 52 N, 56 N, 65 N, 58 N. The coating on the TC substrate with 15wt.% WC has the highest H/E and H3/E2, which indicating the best wear resistance. The failure mechanisms of coated tools are coating peeling, adhesive wear, and abrasive wear. As the cutting speed increases, the amount ofthe flank wear increases, and the durability decreases accordingly. Accompanied by the increasing of WC, the flank wear of coated cermet insert decreases first and then increases.
The purpose of this paper is to investigate the role of graphene oxide (GO) on mechanical and corrosion behaviors, antibacterial performance, and cell response of Mg-Zn-Mn (MZM) composite. MZM/GO nanocomposites were made with various amounts of GO (0.5, 1.0, and 1.5 wt.%) by the semi powder metallurgy method. The GO influence on the MZM composite was analyzed by hardness, compressive and corrosion tests, and antibacterial and cytotoxicity tests. According to the experimental results, increasing the GO amount increased hardness values, compressive value, and antibacterial performance of the MZM composite, while cell viability and osteogenesis level presented reversed trends. It was shown, based on the electrochemical examination, which the corrosion behavior of the MZM alloy was significantly enhanced after encapsulation of 0.5 wt.% GO. Taken together, the antibacterial and mechanically MZM nanocomposites reinforced with GO to be used for implant applications.
This study aims at providing systematically insights into the impact of cathodic polarization on the stress corrosion cracking (SCC) behavior of 21Cr2NiMo steel. Slow stress tensile test demonstrated that 21Cr2NiMo steel is highly sensitive to hydrogen embrittlement at strong cathodic polarization. The lowest SCC susceptibility is presented at -775 mVSCE whereas the SCC susceptibility increased remarkably below -950 mVSCE. SEM and EBSD revealed that cathodic potential decline causes a transition in fracture path from transgranular mode to intergranular mode. The intergranular mode transforms from bainite boundaries separation to prior austenitic grain boundaries separation when more cathodically polarized. Furthermore, corrosion pits promoted the nucleation of SCC cracks. In conclusion, the SCC mechanism transforms from the coexistence of hydrogen embrittlement mechanism and anodic dissolution mechanism to typical hydrogen embrittlement mechanism with applied potential decreases.
For purpose of improving the properties of Babbitt alloys, Ni-coated-graphite reinforced Babbitt metal composite specimens were prepared by selective laser melting (SLM) process, and their microstructures, mechanical and tribological properties were studied using scanning electron microscope (SEM), shear test and dry-sliding wear test, respectively. The results show that most of NCGr particles distribute at boundaries of laser beads in the cross-section of the SLM composite specimens. Microcracks or microvoids form at boundaries of laser beads where NCGr particle accumulating. Both shearing strength and the friction coefficient of the SLM composite specimens decrease with increasing NCGr content. The shearing strength and the friction coefficient of the SLM composite sample with 6% NCGr decrease by around 20% and 33% compared with the NCGr-free sample. Friction mechanism changes from plastic shaping furrow to brittle cutting with increasing NCGr content. A practical Babbitt material with a lower friction coefficient and proper strength could be expected if the dispersion of the NCGr particles is controlled by choosing NCGr particles with thicker Ni layer and precisely controlling laser energy input during SLM process.
Peirce-Smith copper converting involved complex multiphase flow and mixing. In this work, the flow zone distribution and the mixing time in a copper PSC were investigated in a 1:5 scaled cold model. Flow field distribution including dead, splashing and strong-loop zones were measured and a dimensionless equation was developed to correlate the effects of stirring and mixing energy with an error less than 5%. Four positions in the bath including injection, splashing, strong-loop and dead zones were selected to add the hollow salt powders tracer and measure the mixing time. The injection of the quartz flux through the tuyeres or into the backflow point of the splashing wave through a chute is recommended, instead of adding it through a crane hopper from the top of the furnace, to improve the slag-making reaction.
Wood-based panels containing urea-formaldehyde resin result in the long-term release of formaldehyde and threaten human health. To obstruct formaldehyde release, inorganic aluminosilicate coatings prepared by combining metakaolin, silica fume, NaOH and H2O, were applied to the surfaces of wood-based panels. The Si/Al, Na/Al, and H2O/Na2O molar ratios of the coatings were regulated to investigate their effects on the structure and formaldehyde-resistant barrier properties of coatings. The results showed that as the Si/Al molar ratio increased from 1.6 to 2.2, the cracks present in the coatings gradually disappeared and the formaldehyde-resistance rates of the barrier increased. This value also increased as the Na/Al molar ratio increased from 0.9 to 1.2 due to the improvement of the degree of polymerization. As the H2O/Na2O molar ratio increased from 12 to 15, the thickness of the dry film decreased gradually and led to the reduction in the formaldehyde-resistance rate. When the Si/Al, Na/Al and H2O/Na2O molar ratio were 2.2, 1.2, and 12 respectively, the inorganic aluminosilicate coating showed the good performance as a formaldehyde-resistant barrier and its formaldehyde-resistance rate could reach up to 83.2%.
21Cr2NiMo steel is widely used to stabilize offshore oil platforms, however, it suffers from stress corrosion cracking (SCC). Herein, we studied the SCC behavior of 21Cr2NiMo steel in SO2-polluted coastal atmospheres. Electrochemical tests revealed that the addition of SO2 increases the corrosion current. Rust characterization showed that the SO2 addition densities the corrosion products and promotes pitting. Furthermore, the slow strain rate tests demonstrated high susceptibility to SCC at high SO2 contents. Fracture morphologies revealed that the stress-corrosion cracks initiated at corrosion pits and the crack propagation showed transgranular and intergranular cracking modes. In conclusion, the SCC is mix-controlled by anodic dissolution and hydrogen embrittlement mechanisms.
In this work, nanoparticles of potassium ferrite (KFeO2) were synthesized by a simple egg-white solution method upon calcination in air at different temperatures of 500, 600, and 700ºC for 2 h. The effects of calcination temperature on structural and magnetic properties of the synthesized KFeO2 nanoparticles were investigated. By varying the calcination temperature, X-ray diffraction (XRD) and transmission electron microscopy (TEM) results indicated the changes of crystallinity and morphology including particle size, respectively. Significantly, the reduction of particle size of the synthesized KFeO2 was found to have a great influence on the magnetic properties. At room temperature, the synthesized KFeO2 nanoparticles prepared at 600ºC exhibited the highest saturation magnetization (MS) of 26.24 emu•g-1. In addition, the coercivity (HC) increased from 3.51 to 16.89 kA•m-1 with increasing calcination temperature up to 700ºC. The zero-field-cooled (ZFC) results showed that the blocking temperatures (TB) of about 125 and 85 K were observed in the samples calcined at 500 and 600ºC, respectively. Therefore, this work shows that the egg-white solution method is a simple, cost effective, and environmental-friendly for the preparation of KFeO2 nanoparticles.
It is challenging to synthesize atom-precise silver nanoclusters (NCs), which is essential for the development of NCs. In this study, we report the synthesis of atom-precise silver NCs in high purity by a kinetically controlled strategy. The silver NCs were prepared using a mild reducing agent via a one-pot method. The as-prepared silver NCs were confirmed to be Ag49(D-pen)24 (D-pen: D-penicillamine) based on the discussion of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) and thermogravimetry (TG) characterizations. Interface structures of the silver NCs were illustrated by both 1H-NMR and FTIR spectroscopy. The silver NCs were supported on the active carbon (AC) to form the Ag NCs/AC which displayed excellent activity for the catalytic reduction of 4-nitrophenol with the kinetic reaction rate constant k of 0.21 min−1, outperforming several catalysts reported previously. Besides, the catalytic activity of Ag NCs/AC kept almost constant after six times of recycle, suggesting its good stability.
Iron carbon agglomerates (ICA) is considered to be an innovative charge to realize low carbon blast furnace (BF) ironmaking. In this study, the central composite Design (CCD) based on response surface methodology (RSM) was used to synergistically optimize the compressive strength, reactivity and post-reaction strength of ICA. The results show that the iron ore ratio has the most significant influence on compressive strength, reactivity and post-reaction strength. There are significant interactions on the compressive strength and reactivity between the iron ore ratio and carbonization temperature or the iron ore ratio and carbonization time, while the three variables do not interact with each other on the post-reaction strength. In addition, the optimal process parameters are iron ore ratio of 15.30%, carbonization temperature of 1000℃ and carbonization time of 4.27 h, and the model prediction results of compressive strength, reactivity and post-reaction strength are 4026 N, 55.03% and 38.24% respectively, which are close to the experimental results and further verifies the accuracy and reliability of the models.
This paper presents experimental investigation of the mechanical and tribological properties of Cu-GNs nanocomposites. We employed electroless coating process to coat GNs with Ag particles to avoid their reaction with Cu and formation of intermetallic phases. We studied the effect of GNs content on structural, mechanical and tribological properties of the produced nanocomposites. The results showed that the coating process is an efficient technique to avoid reaction between Cu and C and the formation intermetallic phases. The addition of GNs should be done wisely since the mechanical and tribological properties improved with increasing GNs up to a certain threshold values. The optimum GNs proved is 0.5%, at which hardness, wear rate and coefficient of friction are improved by 13%, 81.9% and 49.8%, respectively, compared to Cu- nanocomposite. These improved properties are due to the reduced crystallite size, presence of GNs and homogenous distribution of constituents.
The effect of Al2O3 on the viscosity of the CaO-SiO2-Al2O3-8wt% MgO-1wt% Cr2O3 (CaO/SiO2=1.0, Al2O3=17-29wt%) slags was investigated in the present work. The results indicated that the viscosity of the slag increased gradually with the increasing of Al2O3 content within the range of 17 to 29wt%, due to the role of Al2O3 acting as a network former in polymerizing the aluminosilicate structure of the slag. The apparent activation energy of the slags increased from 180.85 to 210.23 kJ/mol with increasing the Al2O3 content from 17 to 29wt%, which was consistent with the variation of the critical temperature. It was indicated that the polymerization degree of the present slag was increased with the addition of Al2O3. The Iida’s model was applied to the prediction of the slag viscosity due to the existence of Cr2O3, and it was found that the calculated viscosity values fitted well with the measured ones when both of the temperature and Al2O3 content were at relatively low level in the present study.
The aim of this investigation is to prepare geopolymeric precursor using vanadium tailing (VT) by thermal activation and modification. The homogeneous blend of VT and sodium hydroxide is calcinated at elevated temperature for activation and then was modified with metakaolin to assemble geopolymeric precursor. During the thermal activation, the VT is corroded by sodium hydroxide, and then forms sodium silicate on the particles surface. After water is added, the sodium silicate coating is dissolved to release silicon species and create alkaline solution environment, and then the metakaolin dissolved in the alkaline environment to provide aluminum species, followed by geopolymerization. Meanwhile, the VT particles are connected together by gel produced from geopolymerization, resulted in geopolymer with excellent mechanical performance. This investigation not only improves the feasibility of geopolymer technology in large-scale and in-situ applications, but also benefits the utilization of VT and other silica-rich solid wastes.
In this paper, a series of laboratory investigations are carried out to explore the effect of flocculant type on the spatial morphology and microstructural characteristics of flocs in the flocculation and settling of tailings. Four types of flocculants (ZYZ, JYC-2, ZYD and JYC-1) are considered in this study. The fractal characteristics and internal structure of tailings flocs with different flocculant types and settlement heights are analyzed through scanning electron microscopy (SEM) and X-ray microtomography (μCT) scanning experiments based on fractal theory. Results show that unclassified tailings flocs are irregular clusters with fractal characteristics, and the flocculation effect of flocculants has the following trend: ZYZ > JYC-2 > ZYD > JYC-1. The size and the average gray value of tailings flocs decrease as the settlement height decreases. The average gray values at the top and bottom are 144 and 103, respectively. The settlement height remarkably affects the pore distribution pattern, as revealed in the constructed three-dimensional pore model of tailings flocs. The upper part of the flocs has good penetration, while the bottom part is mostly dispersed pores. The number of pores increases exponentially as the settlement height increases, whereas their size initially increases and then decreases as settlement height increases.
The trouble-free and efficient operation of paste thickeners requires optimal design and cooperation of each component. When the underflow discharging is suspended, alleviating vast torque that the remaining solids within thickeners may place on rakes mainly lies in the circulation unit. In this work, the mechanism of this unit was analyzed and a mathematical model was developed for description of the changes in underflow solids concentration and yield stress. The key parameters of the circulation unit, namely the height and flow rate, were varied to test its performance in the experiments with a self-designed laboratorial thickening system. The results show that the circulation unit is valid in reducing underflow solids fraction and yield stress to a reasonable extent, and the model could be used to describe its efficiency at different heights and flow rates. A suitable design and application of the circulation unit contributes to a cost-effective operation of paste thickeners.
Frequent offshore oil spill accidents, industrial oily sewage and the indiscriminate disposal of urban oily sewage have caused serious impacts on human living environment and health. The traditional oil-water separation methods not only cause easily environmental secondary pollution, but also waste of limited resources. Therefore, in this work, 3D graphitic carbon sphere foams (3D-foams) possessed three-dimensional porous structure with pore size distribution of 25~200 μm, and high porosity of 62% were prepared for oil adsorption via foam-gel casting method using graphitic carbon spheres as starting materials. The resulted indicated that the water contact angle of as-prepared 3D-foams was 130°. The contents of graphitic carbon spheres (GCS) greatly influenced the hydrophobicity, water contact angle (WCA) and microstructure of the as-prepared samples. The adsorption capacities of as-prepared 3D-foams for paraffin oil, vegetable oil and vacuum pump oil were about 12~15 g/g, which were 10 times of that graphitic carbon spheres powder.
The present study explores the fabrication of Fe-based amorphous coating by air plasma spraying and its dependency on the coating parameters (plasma power, primary gas flow rate, stand-off distance and powder feed rate). XRD of the coatings deposited at optimized spray parameters showed the presence of amorphous-crystalline phase. Coatings deposited at lower plasma power and moderate gas flow rate exhibited better density, hardness and wear resistance. All coatings demonstrated equally good resistance against corrosive environment (NaCl). Mechanical, wear and tribological studies indicate that a single process parameter optimization cannot provide good coating performance but instead, all process parameters are having their unique role in defining better properties to the coating by controlling the in-flight particle temperature and velocity profile followed by the cooling pattern of molten droplet before impingement on the substrate.
Functionalized ionic liquids (FILs) as extractants were employed for the separation of tungsten and molybdenum from a sulfate solution for the first time. The effects of initial pH, extractant concentration, metal concentrations in the feed, etc., were investigated in detail. The results showed that tricaprylmethylammonium bis(2,4,4-trimethylpentyl)phosphinate ([A336][Cyanex272]) could selectively extract W over Mo at an initial pH of 5.5, and the best separation factor βW/Mo of 25.61 was obtained for a solution with low metal concentrations (WO3: 2.49 g/L, Mo: 1.04 g/L). The [A336][Cyanex272] system works well for solutions of different W/Mo molar ratios and different concentrations of metal ions in the feed. The chemical reaction between [A336][Cyanex272] and W followed the ion association mechanism, which was further proven by the FTIR spectra of loaded [A336][Cyanex272] and free extractant. The stripping experiments indicated that 95.48% W and 100.00% Mo were stripped by a 0.20 mol/L sodium hydroxide solution. Finally, selective extraction of W from Mo was obtained for two synthetic solutions of different high metal concentrations, and the separation factor βW/Mo reached 23.24 and 17.59, respectively. The results suggested the feasibility of [A336][Cyanex272] as an extractant for the separation of tungsten and molybdenum.
Recently, lead halide perovskites have received much attention and be a candidate material for various optoelectronic field for their high performance as light absorbers. Here we report the growth of CsPbI3 nanoblet via a solution process. The single-crystalline CsPbI3 nanobelt have a high yield with uniform in morphology by controlling the PbI2 amount. The single-crystalline CsPbI3 nanobelt possess a mean width, length and thickness of 100 nm, 5 µm and 20 nm respectively. Based on this, the photodetectors (PDs) based on individual CsPbI3 nanobelt were constructed and have a good performance with an external quantum efficiency and responsivity of 2.39×105 % and 770 A·W-1, respectively. More importantly, the PDs show a high detectivity up to 3.12×1012 Jones, which is on par with that of Si PDs. It exhibits as a promising candidate applied in various optoelectronic nanodevices.
Nano-sized silicon carbide (SiC; 0, 1wt%, 2wt%, 4wt%and 8wt%) reinforced copper (Cu) matrix nanocomposites were manufactured, pressed and sintered at 775 and 875°C in argon atmosphere. Both X-ray diffraction (XRD) and scanning electron microscope (SEM) were carried out to characterize microstructural evolution. The density, thermal expansion, mechanical and electrical properties were studied. XRD analyses showed that by increasing SiC contents, the microstrain and dislocation density increased, while crystal size decreased. It was found that the coefficient of thermal expansion (CTE) values of nanocomposites samples were lower than that of Cu matrix. The improvement of CTE with increasing sintering temperature may be due to the densification in their microstructure. Moreover, the mechanical properties of these nanocomposites showed noticeable enhancement by the addition of SiC and sintering temperatures where microhardness and apparent strengthening efficiency of nanocomposites contain 8 wt% SiC and sintered at 875 °C were 958.7 MPa and 1.07 1/vol%, respectively. Electrical conductivity of these samples slightly decreased with the addition of SiC contents and increased with sintering temperature. Based upon the aforementioned results, we can conclude that the prepared Cu-SiC nanocomposites possess good electrical conductivity, high thermal stability and excellent mechanical properties.
Interface characteristics of cyanide tailings are very different compared with those of raw ore. Valuable elements could not be comprehensively recovered via flotation from cyanide tailings originating from Shandong province, China. Herein, the interface and floatability of these tailings were investigated. The chalcopyrite in the cyanide tailings investigated herein was fine with a porous surface. The floatability of 68% chalcopyrite was similar to galena in the presence of a collector. This part of chalcopyrite was compactly wrapped in a layer of fine galena particles. The recovery of chalcopyrite sharply decreased as the nonpolar oil residue in cyanide tailings was removed through alcohol extraction; however, this removal had no effect on galena. The other chalcopyrite in the flotation tailings was covered with an oxidation layer consisting of O, Fe, S, Pb, Cu, Zn, and Si.
We report the electrochemical performance of Ni(OH)2 on gas diffusion layer (GDL) substrate owning to the fact that different current collectors resulting in different electrochemical performances. The Ni(OH)2 working electrode was successfully prepared by a simple method and its electrochemical performance was investigated in 1M NaOH electrolyte. The electrochemical results show that Ni(OH)2 on GDL substrate provides the maximum specific capacitance value of 418.11 F•g-1 at 1 A•g-1. Furthermore, the Ni(OH)2 electrode delivers a high specific energy of 17.25 Wh•kg-1 at specific power of 272.5 W•kg-1 and the cyclic stability retains about 81% after 1000 cycles. Clearly, SEM coupled with EDS results imply that sodium deposition occurring after long-time cycling causes the reduction of the specific capacitance. The present work suggests that light-weight of GDL could be considered as a promising current collector in electrochemical studies of Ni-based electroactive materials for energy storage applications in order to overcome the problem of oxide layer on metal-foam substrates.
Fe-Ni36 alloy was prepared by a one-step electrolysis of mixed oxides precursor in molten Na2CO3-K2CO3 eutectic melt at 750 °C, where a porous Fe2O3-NiO pellets served as cathode and a Ni10Cu11Fe alloy was an inert anode. During the electrolysis, NiO was preferentially electro-reduced to Ni, then Fe2O3 was reduced and simultaneously alloyed with nickel to form Fe-Ni36 alloy. Different cell voltages were applied to optimize the electrolytic conditions, and a relatively low energy consumption of 2.48 kW h/(kg-FeNi36) was achieved under 1.9 V with a high current efficiency of 94.6%. It was found that the particle size of the alloy was much smaller than that of the individual metal. This process provides a low-carbon technology for preparing Fe-Ni36 alloy by molten carbonates electrolysis.
Low O2- diffusion rate in the electro-deoxidation of titanium-containing compound process, either in OS process or FFC process, leads to low reaction speed and low current efficiency. In this study, Ca3Ti2O7 was used as precursor to improve reduction speed of titanium. Due to more “diffusion channels” created in cathode as Ca2+ liberates from Ca3Ti2O7 precursor in the electro-deoxidation process, O2- diffusion rate was improved significantly by using Ca3Ti2O7 instead of CaTiO3 as precursor. Parallel constant voltage electrolysis (3.2 V) confirms that Ca3Ti2O7 and CaTiO3 reduced simultaneously due to their similar crystal structure. However, the reduction area of Ca3Ti2O7 spreads much faster than that of CaTiO3 indicated that difference in O2- diffusion rate. Cyclic voltammetry (CV), constant voltage and theoretical analysis of crystal structure were also carried out to comparing the difference between Ca3Ti2O7 and CaTiO3. Results indicate that by using precursor with more soluble cations, titanium reduction speed can be greatly improved in the electro-deoxidation process. At last, a new electrolysis method was also proposed to converting and recycling of excess CaO from the Ca3Ti2O7 precursor.
In the present work, the impact energy prediction model of low carbon steel was investigated based on the industrial data. A three layer neural network, extreme learning machine and deep neural network were compared with different activation functions, structure parameters and training functions. To determine the optimal hyper-parameters of deep neural network, Bayesian optimization was applied. The model with best performance was applied to investigate importance degree of process parameter variables on impact energy of low carbon steel. The results show that deep neural network obtains better prediction results than that of shallow neural network due to the multiple hidden layers improving the learning ability of the model. Among all the models, the Bayesian optimization deep neural network achieves the highest correlation coefficient of 0.9536, lowest mean absolute relative error of 0.0843 and lowest root mean square error of 17.34 J for predicting the impact energy of low carbon steel. Among all the variables, the main factors affecting the impact energy of low carbon steel with final thickness of 7.5 mm are the thickness of the original slab, the thickness of intermediate slab and rough rolling exit temperature on the specific hot rolling production line.
The effect of nanosized NbC precipitates on hydrogen induced cracking (HIC) of high-strength low-alloy steel was investigated using slow strain rate tensile (SSRT) test with a continuous hydrogen charging and fracture analysis. The results showed that the HIC resistance of the Nb-bearing steel is obviously superior to that of the Nb-free steel, and the fractured Nb-bearing steel in SSRT test shows the less reduction ratio of plasticity (Iδ), but as the hydrogen traps induced by NbC precipitates approach hydrogen saturation, the effect of precipitates on HIC resistance shows an attenuating trend. The highly dispersed nanosized NbC precipitates were speculated to act as irreversible hydrogen traps, and hinder the accumulation of hydrogen at the potential crack nucleation site. In addition, as same as the Nb-free steel, the Nb-bearing steel presents both H-solution strengthening and HIC.
In the Collaborative Research Centre 761 "Steel ab initio - quantum mechanics guideddesign of new Fe based materials", scientists and engineers from RWTHAachen University and the Max Planck Institute for Iron Research have conductedresearch on mechanism-controlled material development with the particularexample of high manganese alloyed steels. From 2007 to 2019, a total of 55 partprojects and 4 transfer projects with industrial participation (some runninguntil 2021) have dealt with material and process design as well as materialcharacterization. The basic idea of the Collaborative Research Centre was todevelop a methodologically new approach for the design of structural materials.
This paper focuses on selected results with respect tothe mechanical properties of high manganese steels, the underlying physicalphenomena, and on specific characterization and modelling tools for this newclass of materials. It is worked out that these steels have a microstructurethat has to be characterized with modern methods on the nm-scale. Regarding theprocess routes, the generation of segregations must be taken into account.Finally, the mechanical properties show a characteristic temperature dependenceand contain peculiarities in the fracture behavior. The mechanical propertiesand especially the bake hardening are affected by short-range ordering phenomena.The strain hardening can be adjusted in a so far not possible scope which makethese steels attractive for demanding sheet steel applications.
Two kinds of ultralow carbon steel weld metals with and without added Cu-Nb were prepared by using gas metal arc welding (GMAW) to investigate the correlation between microstructure and mechanical properties of weld metals. Results of microstructure characterization show that weld metal without Cu-Nb is mainly composed of acicular ferrite (AF), lath bainite (LB), and granular bainite (GB). In contrast, adding Cu-Nb to weld metal causes an evident transformation of martensite and causes grain coarsening. Both weld metals have high tensile strength (more than 950 MPa) and more than 17% elongation; however, their values of toughness deviate greatly with a difference of approximately 40 J at -50℃. Analysis of morphologies of fracture surfaces and secondary cracks further revealed the correlation between microstructure and mechanical properties. The effects that adding Cu and Nb have on microstructure and mechanical properties of weld metal are discussed; the indication is that adding Cu-Nb increases both hardenability and grain size of weld metal and thus deteriorates the toughness.
In the present study, the carbothermic reduction of vanadium titanomagnetite concentrates (VTC) with the assistance of Na2CO3 was carried out in argon atmosphere between 1073 K and 1473 K. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to investigate the phase transformations during the reaction process. By investigating the reaction between VTC and Na2CO3, it was concluded that molten Na2CO3 could break the structure of titanomagnetite by combining with the acidic oxides (Fe2O3, TiO2, Al2O3, and SiO2) to form the Na-rich melt, and release FeO and MgO. Therefore, Na2CO3 could accelerate the reduction rate. In addition, the addition of Na2CO3 was also beneficial for the agglomeration of iron particles and the slag-metal separation by decreasing the viscosity of slag. Thus, the Na2CO3 assisted carbothermic reduction will be a promising method to treat VTC at low temperatures.
In the present research, the hot compression tests were performed on AISI 321 austenitic stainless steel in the deformation temperature range of 800-1200˚C and constant strain rates of 0.001, 0.01, 0.1, and 1 s-1. The hot flow curves were utilized for determination of the strain hardening exponent, strain rate sensitivity exponent and construction of the processing maps. Variation of the strain hardening exponent with strain was used for prediction of the microstructural evolutions during hot deformation. Four types of variations were distinguished which reflect the occurrence of dynamic recovery, single and multiple peak dynamic recrystallization and the interaction between dynamic recrystallization and precipitation. Also, the strain rate sensitivity variations at the applied strain of 0.8 and strain rate of 0.1 s-1 was compared with microstructural evolutions and the results demonstrated the existence of reliable connection between this parameter and evolved microstructures. Furthermore, the power dissipation map at the applied strain of 0.8 was compared with the resultant microstructures at some predetermined deformation conditions. It was concluded that the microstructural evolutions is shifted from complete to partial dynamic recrystallization and dynamic recovery with increasing the power dissipation ratio.
Gangue minerals inadvertently dissolution frequently plays a detrimental role on the flotation of valuable minerals. In this paper, the effect of conditioning time on the flotation separation of brucite and serpentine was investigated. By analyzing the Mg2+ concentration, the relative content of elements, and pulp viscosity, the effect of mineral dissolution on the brucite flotation was studied. The artificial mixed mineral flotation results (with -10 μm serpentine) showed that, with the conditioning time extended from 60 s to 360 s, a large amount of Mg2+ on the mineral surface gradually dissolved into the pulp, resulting in a decrease of brucite recovery (from 83.83% to 76.79%), whereas the recovery of serpentine increased from 52.12% to 64.03%. Moreover, the SEM observation was applied to analyze the agglomeration behavior of brucite and serpentine, which clearly demonstrated the difference of adhesion behavior under various conditioning time. Finally, the total interaction energy that carried out by extended DLVO (E-DLVO) theory also supports the conclusion that the gravitational force between brucite and serpentine increases significantly with the increase of conditioning time.
In this study, an ammonia-based system was used to selectively leach Co from an African high-silicon low-grade Co ore. In this process, other elemental impurities were prevented from leaching; hence, the subsequent process was simple and environmentally friendly. The results revealed that the leaching ratio of Co can reach 95.61% using (NH4)2SO4 as a leaching agent under experimental conditions, which involved a (NH4)2SO4 concentration, reductant dosage, leaching temperature, reaction time, and liquid–solid ratio of 300 g/L, 0.7 g, 353 K, 4 h, and 6:1, respectively. The leaching kinetics of Co showed that the apparent activation energy of Co leaching was 72.97 kJ/mol (i.e., in the range of 40–300 kJ/mol). This indicated that the leaching of Co from the Co ore was controlled using an interfacial chemical reaction. The reaction orders of the particle size and (NH4)2SO4 concentration during leaching were 0.21 and 1.5, respectively. The leaching kinetics model of the Co developed in this study can be expressed as 1-(1-α)1/3 = 28.01 × 103×r0-1 × [(NH4)2SO4]1.5 × exp(-72970/8.314T).
The critical influence of in-situ nanoparticles on the mechanical properties and hydrogen embrittlement (HE) of high-strength steel is investigated in this study. The mechanical strength and elongation of the quenched and tempered steel (919 MPa yield strength, 17.11% elongation) are higher than those of the hot-rolled steel (690 MPa yield strength, 16.81% elongation) due to the strengthening effect of Ti3O5–Nb(C,N) in-situ nanoparticles. The HE susceptibility is substantially mitigated to 55.52%, which is approximately 30% lower than that of steels without in-situ nanoparticles (84.04%) and is attributed to the heterogeneous nucleation of Ti3O5 nanoparticles increasing the density of carbides. Meanwhile, compared with hard TiN inclusions, the spherical and soft Al2O3–MnS core–shell inclusions that nucleate on the in-situ Al2O3 particles could also suppress HE. The in-situ nanoparticles generated by trace-element regional supply have strong potential in the development of high-strength and hydrogen-resistant steels.
The effect of 2-Mercaptobenzothiazole concentration on the sour corrosion behavior of API X60 pipeline steel in an environment containing H2S at 25 °C and at the presence of 0, 2.5, 5, 7.5 and 10 g/L of 2-Mercaptobenzothiazole inhibitor was investigated. In order to examine the sour corrosion behavior of API X60 pipeline steel, Open Circuit Potential (OCP), potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) tests were used. The Energy Dispersive Spectroscopy (EDS) and Scanning Electron Microscopy (SEM) were also used to analyze corrosion products. The results of OCP and potentiodynamic polarization both showed that 2-Mercaptobenzothiazole reduces the speed of both anodic and cathodic reactions. Assessment of the Gibbs free energy of the inhibitor showed that it has a value of more than –20 kJ.mol−1and less than –40 kJ.mol−1. Therefore, the adsorption of 2-Mercaptobenzothiazole on the surface of the API X60 pipeline steel was occurred both physically and chemically. The latter was particularly intended to be adsorbed. Also, as the Gibbs free energy of the inhibitor took a negative value, it was concluded that the adsorption of 2-Mercaptobenzothiazole on the surface of the pipeline steel occurs spontaneously. The results of the EIS indicated that with increase of 2-Mercaptobenzothiazole inhibitor concentration, the corrosion resistance of API X60 steel is increased.An analysis of the corrosion products revealed that iron sulfide compounds are formed on the surface. In sum, the results showed that the increase of the inhibitor concentration results in a decrease in the corrosion rate and an increase ininhibitory efficiency (%IE). Additionally, it was found that 2-Mercaptobenzothiazole adsorption process on the API X 60 steel surfaces in a H2S-containing environment follows the Langmuir adsorption isotherm.And the adsorption process is carried out spontaneously.
To improve the separation capacity of uranium in aqueous solutions, 3R-MoS2 nanosheets were prepared with molten salt electrolysis and further modified with polypyrrole (PPy) to synthesize a hybrid nanoadsorbent (PPy/3R-MoS2). The preparation conditions of PPy/3R-MoS2 were investigated and the obtained nanosheets were characterized with SEM, HRTEM, XRD, FTIR, and XPS. The results show that PPy/3R-MoS2 exhibited enhanced adsorption capacity towards U(VI) compared to pure 3R-MoS2 and PPy; the maximum adsorption was 200.4 mg/g. The adsorption mechanism was elucidated with XPS and FTIR: 1) negatively charged PPy/3R-MoS2 nanosheets attracted UO22+ by electrostatic attraction; 2) exposed C, N, Mo, and S atoms complexed with U(VI) through coordination; 3) Mo in the complex partly reduced the adsorbed U(VI) to U(IV), which further regenerated the adsorption point and continuously adsorbed U(VI). The design of the PPy/3R-MoS2 composite with high adsorption capacity and chemical stability provides a new direction for the removal of radionuclide.
In the present work, sodium dicyanamide (SD) was used as a leaching reagent for gold recovery, and the effects of SD dosage and solution pH on gold leaching performance were investigated. It was found that a gold recovery of 34.8% was obtained when SD was used as the sole leaching reagent at a dosage of 15 kg/t. It was also found that in the presence of a certain amount of potassium ferrocyanide (PF) in the SD solution, the gold recovery increased from 34.8% to 57.08%. The leaching kinetics of SD with and without PF was studied using the quartz crystal microbalance with dissipation (QCM-D) technique. According to the QCM-D results, the gold leaching rate increased from 4.03 ng/cm²∙min-1 to 39.99 ng/cm²∙min-1 when the SD concentration increased from 0 to 0.17 mol/L, and from 39.99 ng/cm²∙min-1 to 272.62 ng/cm²∙min-1 when 0.1 mol/L of PF was used in combination with SD. The pregnant solution in the leaching tests was characterized by X-ray photoelectron spectroscopy (XPS) and ESI-MS. The results indicated that Au and (N(CN)2)ˉ in the SD solution formed a series of metal complex ion, [AuNax(N(CN)2)(x+2)]ˉ (x = 1, 2, 3, or 4).
This study addresses the liquid-liquid extraction behavior of phosphorus from a sulfuric acid solution using benzyl-di-methyl amine (BDMA) in kerosene. The extraction equilibria investigated with varied BDMA concentration could reveal the formation of ¯(3[BDMA].[H3PO4]) into the organic phase. The thermodynamic properties determined at the different temperatures indicated that the process exhibits exothermic nature with a calculated enthalpy (ΔH°) of −24.0 kJ/mol. The organic-to-aqueous phase ratio (O/A) was varied to elucidate the quantitative extraction of phosphorus. The McCabe–Thiele diagram plotted for the extraction isotherm was validated for the requirement of three counter-current stages in extraction at an O/A ratio, 2.0/3.5. The back-extraction of phosphorus from the loaded organic phase was quantitatively achieved by contacting 4.0 mol/L H2SO4 solution in three stages of counter-current contact at an O/A ratio, 3/2. The study can potentially be applied to phosphorus removal from sulphuric acid leach solution of monazite processing and many other solutions.
The Ca-Pb electrode couple was considered to be one of the lowest cost (~36 $ kWh−1 ) among various optional materials for liquid metal battery. The electrochemical properties of Ca-Pb alloy in the Ca| LiCl-NaCl-CaCl2|Pb cell were investigated in this paper. The electrode potential maintains a linear relationship in the current density range from 50 to 200 mA cm-2, which indicates that the alloying and dealloying process of Ca with Pb have the rapid charge transfer and mass transport in the interface between the liquid electrode and liquid electrolyte. The Ca-Pb electrode exhibits great properties with a high discharge voltage of 0.6 V, a small self-discharge current density (< 2 mA cm-2 at 600°C) and a high coulombic efficiency (> 99%). The post-mortem analysis shows that the intermetallics CaPb3 and CaPb were uniformly distributed in the electrode, which indicates that the nucleation of solid intermetallics will not hinder the diffusion of Ca in the electrode. It is noted that this invesitgation on Ca-Pb electrode sheds light on further research and design of electrode for Ca based liquid metal battery.
Evaluating the recyclability of powders in the additive manufacturing field has been a long-term challenge, and in this work, the microstructure and mechanical property of a nickel-based superalloy fabricated by laser powder-bed fusion (LPBF) using recycled powders were investigated. Re-melt surface, satellite, and deformed layer were found on the recycled powders combined with a high oxygen-containing surface layer. The increasing oxygen content led to the formation of high-density oxide inclusions, and the printing-induced cracks widely existed and mainly formed along the grain boundary in the as-built LPBF nickel-based superalloys using recycled powders. Changing the Si or Mn contents a little did not increase the hot cracking susceptibility of the printed parts, while the changed aspect ratio and surface damage of the recycled powders might contribute to the increasing density of cracks. Moreover, the configuration of cracks in the as-built parts led to the anisotropic mechanical properties, mainly resulting in an extremely low ductility vertical to the building direction, and the cracks mainly propagated along the cellular boundary due to the existence of a brittle precipitation phase.
The effect of calcination temperature on the pozzolanic activity of maize straw stem ash (MSSA) was evaluated. The MSSA samples calcined at temperature values of 500, 700, and 850 °C were dissolved in portlandite solution for 6 h, and the residual samples were obtained. The MSSA and MSSA residual samples were analyzed using FT-IR, XRD, SEM, and XPS to determine the vibration bonds, minerals, microstructure, and Si 2p transformation behavior. The conductivity, pH value, loss of conductivity with dissolving time of the MSSA-portlandite mixed solution were determined. The main oxide composition of MSSA were silica and potassium oxide. The dissolution of Si4+ content of MSSA at 500 °C were high compared to those of the other calcination temperatures. The conductivity and loss of conductivity of MSSA at 700 °C were high compared to those of the other calcination temperatures at a particular dissolving time due to the higher KCl content in MSSA at 700 °C. C-S-H was easily identified in MSSA samples using XRD, and small cubic and nearly spherical particles of C-S-H were found in the MSSA residual samples. In conclusion, the optimum calcination temperature of MSSA having the best pozzolanic activity is 500 °C but avoid excessive agglomeration.
In this paper, the properties of γ-ray reduced graphene oxide (GRGOs) samples are compared to hydrazine reduced graphene oxide (HRGO) sample. Characterization techniques FTIR, XRD, Raman spectra, Brunauer-Emmett-Teller (BET) surface area analysis, TGA, electrometer, and cyclicvoltemety were used for the verification of the reduction process, structural changes & defects, and measure the thermal, electrical, and electrochemical properties of samples. It was concluded that γ- Irradiation distorts the structure of GRGOs with massive defects owing to the greater formation of new smaller sp2 - hybridized domains compared to HRGO. The thermal stability of GRGOs was higher than HRGO indicating the more efficient removal of thermally-labile oxygen species by γ-ray. Furthermore, RRGOs showed a pseudocapacitive behavior compared to the electrical double layer behavior of HRGO. The most interesting obtained results are the enhanced specific capacitance of GRGOs to nearly three times in comparison to HRGO which indicates the preference for radiation reduction method in energy storage applications.
To probe the coupling effect of the electron and Li ion conductivity in Ni-rich layered materials (LiNi0.8Co0.15Al0.05O2, NCA), lithium lanthanum titanate (LLTO) nano fiber and carbon-coated LLTO fiber (LLTO@C) materials were introduced to polyvinylidene difluoride, respectively, in the cathode. The enhancement in the conductivity was indicated by the suppressed impedance and polarization. Both at 1C and 5C, the cathodes with coupling conductive paths had a more stable cycling performance. The coupling mechanism was analyzed based on the chemical state and structure evolution of NCA after cycling for 200 cycles at 5C. In the pristine cathode, the propagation of lattice damaged regions, which consist of high density edge-dislocation walls, destroyed the bulk integrity of NCA. In addition, the formation of a rock-salt phase on the surface of NCA was responsible for the capacity loss. In contrast, in the LLTO@C modified cathode, although the formation of dislocation-driven atomic lattice broken regions and cation mixing occurred, they were limited to a scale of several atoms, which retarded the generation of the rock-salt phase and resulted in a preeminent capacity retention. Only NiO phase “pitting” occurred. A mechanism based on the synergistic transport of Li ions and electron was proposed.
A new method for the recovery of Mn is proposed via direct electrochemical reduction of LiMn2O4 from the waste lithium-ion batteries in NaCl-CaCl2 melts at 750℃. The results show the reduction process of LiMn2O4 by electrochemical methods on the coated electrode surface are in three steps, Mn(IV) → Mn(III) → Mn(II) → Mn. The products of electro-deoxidation are CaMn2O4, MnO, (MnO)x(CaO)1-x and Mn. Metal Mn appears when the electrolytic voltage increased to 2.6 V. Increasing the voltage could promote the deoxidation reaction process. With the advancement of the three-phase interline(3PI), the electric deoxygenation gradually proceeds from the outward to core. With the high voltage, the kinetic process of the reduction reaction is accelerated, and double 3PI in different stages are generated.
Abstract: Solid oxide membrane-assisted electrolytic reduction of solid Cr2O3 to Cr in molten CaCl2 was performed using a sintered porous Cr2O3 cathode paired with an yttria-stabilized-zirconia (YSZ) tube anode containing carbon-saturated liquid copper alloy. Analyses of the reduction mechanism, ion migration behavior, and effects of cathode pellet porosity and particle size on electrolysis products and reduction rate identified cathode microstructure and electrolytic conditions as key factors of influence. Optimal results were obtained for high porosity and small particle size, as this combination aided ion migration, and good electrochemical activation was observed for cathode pellets prepared by 4 MPa molding followed by 2 h sintering at 1150°C. The electrode reduction process (Cr3+ → Cr2+ → Cr) was promoted by high electrode voltages to efficiently form Cr metal. As the proposed method did not require expensive pre-electrolysis or generate any harmful by-products, it was concluded to be well-suited for electrolytic Cr production.
Extraction of gold from refractory gold ores without side effects is an extremely motivating goal. However, most refractory gold ores contain large amount of sulfide, such as pyrite. Herein, investigation of the influence of sulfide on gold leaching process is important for utilization of refractory gold ores. For this purpose, the effects of pyrite on the stability of the thiourea system were systematic investigated under different parameters. The results showed that the decomposition rate of thiourea was accelerated sharply by the pyrite. As further proof, the effect of pyrite on gold recovery with thiourea leaching systems was verified by a series of experiments. The decomposition efficiency of thiourea reduced by 40% and the recovery efficiency of Au increased by 56% after being removed the sulfide by roasting. Under the optimal condition, the gold recovery efficiency was 83.69% with the decomposition of thiourea of only 57.92%. Finally, we postulated that the high consumption of thiourea may be not only due to the adsorption by mineral particles, but also the catalytic decomposition by some impurities in the ores, such as pyrite and soluble ferric oxide.
The novel cast irons of nominal chemical composition (wt.%) 0.7C-5W-5Mo-5V-10Cr-2.5Ti were fabricated with the additions of 1.6 wt.% B and 2.7 wt.% B. The aim of this work was a study of the boron’s effect on the alloys’ structural state and phase elemental distribution with respect to the formation of wear-resistant structure constituents. It was found that the alloy containing 1.6 % B was composed of three different eutectics: (a) “M2(C,B)5+ferrite” having a “Chinese Script” morphology (89.8 vol. %), (b) “M7(C,B)3+Austenite” having a “Rosette” morphology, and (c) “M3C+Austenite” having a “Ledeburite”-shaped morphology (2.7 vol. %). With a boron content of 2.7 wt.%, the bulk hardness increased from 31 HRC to 38.5 HRC. The primary carboborides M2(C,B)5 with average microhardness of 2797 HV appeared in the structure with a volume fraction of 17.6 vol.%. The volume fraction of eutectics (a) and (b, c) decreased to 71.2 vol.% and 3.9 vol. %, respectively. The matrix was “ferrite/austenite” for 1.6 wt.% B and “ferrite/pearlite” for 2.7 wt.% B. Both cast irons contained compact precipitates of carbide (Ti,M)C and carboboride (Ti,M)(C,В) with a volume fraction of 7.3-7.5 vol. %. The elemental phase distributions, discussed based on EDX-analysis and the appropriate phase formulae, are presented.
Flower-like ZnO microstructures were successfully obtained by hydrothermal method employing ZnSO4/(NH4)2SO4 as raw material.The operating parameters including hydrothermal temperature, OH-/Zn2+ molar ratio, time and additive amount of dispersant on the phase structure and micromorphology of ZnO particles were investigated. The synthesis conditions of flower-like ZnO microstructures were hydrothermal temperature of 160ºC, OH-/Zn2+ molar ratio of 5:1, reaction time of 4 h, dispersant of 4 mL. Flower-like ZnO microstructures are comprised of hexagon shape ZnO rods arranged in the form of radiative way. The degradation experiments of Rhodamine B (RhB) with a degradation efficiency of 97.6% exposure for 4 h showed that flower-like ZnO microstructures exhibited an excellent photocatalytic capacity in sunshine. The growth mechanism of flower-like ZnO microstructures was schematically presented.
The aim of this study was to investigate the phase transformation and kinetics of the solid-state reaction of CaO-V2O5, which is the predominant binary mixture involved in the vanadium recovery process. Thermal analysis, X-ray diffraction, scanning electron microscope and energy dispersive spectrometry were used to characterize the solid-state reaction of the samples. The extent of the solid reaction was derived using the preliminary quantitative phase analysis of the X-ray diffractograms. The results indicate that the solid reaction of CaO-V2O5 mixture is significantly influenced by the reaction temperature and CaO/V2O5 mole ratio. The transformation of calcium vanadates goes through a step-by-step reaction of CaO-V2O5, CaO-CaV2O6, and CaO-Ca2V2O7 depending on the CaO/V2O5 mole ratio. The kinetic data of the solid reaction of CaO-V2O5 (1:1) mixture was found to follow second order reaction model. The activation energy (Eα) and the pre-exponential factor (A) were determined to be 145.38 kJ/mol, and 3.67×108 min-1, respectively.
In this study, the butt welds of 4 mm thick 5A06 aluminum alloy plates were produced by the developed adjustable-gap bobbin tool friction stir welding at three welding speeds of 200, 300, 400 mm/min. The microstructure was studied by using an optical microscope and electron backscatter diffraction (EBSD). Tensile tests and microhardness measurements were performed to identify the effect of welding speed on the joint mechanical properties. It is revealed that sound joints could be produced at a welding speed of 200 mm/min while voids are present at different positions of the joints as the welding speed increases. The EBSD result shows that the grain size, high angle grain boundaries (HAGBs) and density of geometrically-necessary dislocations (GNDs) in different regions of the joint vary depending on the recovery and recrystallization behavior. Specific attention was given to the relationship between the local microstructure and mechanical properties. Microhardness measurements show that the average hardness of the SZ is higher than that of the base material, which is almost not affected by the welding speed. The tensile strength of the joint decrease with increasing the welding speed, and the maximal strength efficiency reaches 99%.
Recently, the recycling of spent LiFePO4 batteries has received extensive attention due to their environmental impact and economic benefit. In the pretreating process of spent LiFePO4 batteries, the separation of the active materials and the current collectors determines the difficulty of recovery process and the quality of product. In this work, a facile and efficient pretreating process is first proposed. After only freezing the electrode pieces and immersing it in boiling water, LiFePO4 materials have been basically peeled from Al foil. Then, after roasting in an inert atmosphere and sieving, all of the cathode and anode active materials were separated from Al and Cu foils easily and efficiently. The active materials were subjected to acid leaching and the leaching solution further prepared FePO4 and Li2CO3. Finally, the battery-grade FePO4·and Li2CO3 were used to re-synthesize LiFePO4/C via the carbon thermal reduction method. Re-synthesized LiFePO4/C cathode exhibits good electrochemical performance, which satisfies the requirement for middle-end LiFePO4 batteries. The whole process is found to be environmental and have great potential for industrial-scale recycling of spent lithium-ion batteries.
Steel matrix composites (SMCs) reinforced with WC-particles were fabricated via selective laser melting (SLM) by employing various laser scan strategies. A detailed relationship between the SLM strategies, defect formation, microstructural evolution as well as mechanical properties of SMCs was established. The laser scan strategies can be manipulated to deliberately alter the thermal history of SMC during SLM-processing. Particularly, the involved thermal cycling encompassing multiple layers strongly affects the processing quality of SMCs. S-shaped scan sequence combined with interlayer offset and orthogonal stagger mode can effectively eliminate the metallurgical defects and retained austenite within the produced SMCs. However, due to large thermal stress, microcracks, perpendicular to the building direction, are generally formed within the SMCs. By employing the checkerboard filling (CBF) hatching mode, the thermal stress arising during SLM can be significantly reduced, so that the evolution of interlayer microcracks can be prevented. The compressive properties of the fabricated SMCs can be tailored at a high compressive strength (~3031.5 MPa) and fracture strain (~24.8%) by adopting the CBF hatching mode combined with optimized scan sequence and stagger mode. This study demonstrates great feasibility of tuning the mechanical properties of SLM-fabricated SMCs parts without varying the set energy input, e.g. laser power and scanning speed.
Copper bearing biotite is a typical refractory copper mineral on the surface of Zambian copper belt. Aiming to treat this kind of copper oxide ore with a more effective method, ultrasonic-assisted acid leaching was conducted in this paper. Compared with regular acid leaching, ultrasound could reduce leaching time from 120 min to 40 min, and sulfuric acid concentration could be reduced from 0.5 mol•L-1 to 0.3 mol•L-1. Besides, leaching temperature could be reduced from 75℃ to 45℃ at same copper leaching rate of 78%. Mechanism analysis indicates that ultrasonic wave can cause delamination of copper bearing biotite and increase the specific surface area from 0.55 m2•g-1 to 1.67 m2•g-1. The results indicate that copper extraction from copper bearing biotite by ultrasonic-assisted acid leaching is more effective than regular acid leaching. This study proposes a promising method for recycling valuable metals from phyllosilicate minerals.
Sn3O4, as a typical two-dimensional semiconductor photocatalyst, can absorb visible light. However, owing to its rapid recombination of photogenerated electron-hole pairs, it is not high enough for practical application. In this work, a Sn nanoparticles/Sn3O4-x nanosheets heterostructure was prepared by in-situ reduction of Sn3O4 under H2 atmosphere. The Schottky junction formed between Sn and Sn3O4-x can enhance the photogenerated carrier separation ability. And during the hydrogenation process, a portion of the oxygen in the semiconductor can be carried away by hydrogen to form water, resulting in an increasing in oxygen vacancies in the semiconductor. The heterostructure showed clear abilities for the removal of Rhodamine B. At the same time, the cell cytocompatibility experiments proved that Sn/Sn3O4-x can significantly enhance cell compatibility and reduce the harm to organisms. Our work provides a new train for fabrication of Schottky junction composite photocatalyst rich in oxygen vacancies with enhanced photocatalytic performance.
Electrorefining is an effective way to separate metals from corresponding alloys. To obtain Nd from Cu6Nd alloy, cyclic voltammetry and square wave voltammetry were conducted to investigate the reduction behaviour of Nd3+ and the anode dissolution behaviour of Cu6Nd in NaCl-KCl-0.5mol% NdCl3 melt at 1023 K. According to the analysis of the electrochemical behaviour, the cell voltage was determined to be between 0.3 V and 1.2 V for separating Nd from Cu6Nd. After electrolysis at 0.6 V for 4 h, the Nd was found at the surface of the Mo cathode without any Cu. For Fe cathode, the deposition with atom ratio Nd:Fe=1:1 was formed on the surface of the Fe electrode. However, in the experiment terms, the low current density of separation is still a great challenge and needs to be solved.
To provide one more cost-effective structural materials for the ultra-high temperature molten salt thermal storage systems, the explosion-welded technology was induced to manufacture the GH3535/316H bimetallic plates in the present work. The microstructures of the bonding interfaces have been extensively investigated by scanning electron microscope, energy dispersive spectrometer, and electron probe micro-analyzer. It was discovered that the bonding interfaces possess the periodic wavy morphology and are adorned by peninsula- or island-like transition zones. At higher magnification, matrix recrystallization region, fine grain region, columnar grain region, equiaxed grain region, and shrinkage porosity can be observed in the transition zones and the surrounding area. The analysis of electron backscattered diffraction demonstrated that the strain in the recrystallization region of the GH3535 matrix and transition zone is lower than the substrate. Strain concentration occurred at the interface and the solidification defects in the transition zone. The dislocation substructure in 316H near the interface was characterized by the electron channeling contrast imaging. The results showed that a lot of dislocations network was formed in the grains of 316H. Microhardness tests showed that the micro-hardness decreased as the distance from the welding interface increased, and the lowest hardness value was inside the transition zone.
Ceria (CeO2) nanoparticles have been successfully synthesized via a simple complex-precipitation route, which employs cerium chloride as cerium source and citric acid as precipitant. The elemental analysis results of carbon, hydrogen, oxygen and cerium in the precursors were calculated, and the results revealed that the precursors were composed of Ce (OH)3, [Ce(H2Cit)3] or [CeCit]. X-ray diffraction (XRD) analysis showed all ceria nanoparticles prepared to be face centered cubic structure. As n value was 0.25 and pH value was 5.5, the specific surface area of the sample reached the maximum value of 83.17 m2/g. Ceria nanoparticles were observed by scanning electron microscope (SEM). Selected electron diffraction patterns of some samples were obtained by transmission electron microscope (TEM), and the crystal plane spacing of each low-exponential crystal plane was calculated. The UV-vis transmittance curve shows that it has the ability to absorb ultraviolet light and pass through visible light. Among all samples, the minimum of the average transmittance of UVA (TUVA) is 4.42%, and the minimum of the average transmittance of UVB (TUVB) is 1.56%.
In this article, Cu-Gr composite thin films are prepared by electrodeposition route using in-house synthesized graphene sheets. Graphene sheets are synthesized by the electrochemical exfoliation route using 1M HClO4 acid as electrolyte. Graphene sheets have been confirmed by XRD, FTIR, FESEM and TEM microscopy. The (002) plane of graphene sheets are observed at 2θ of 25.66⁰. The (002) plane confirms the crystal structure of carbon peaks. The stretching vibration of C=C bond at a wavelength of 1577 cm-1 and other functional groups of carboxyl and epoxide groups have been observed from FTIR. TEM microscopy confirms the transparent structure of graphene sheets. The prepared graphene sheets were used as reinforcement in concentration of 0.1 g/L and 0.3 g/L with a copper matrix to synthesize Cu-Gr composite. The prepared composite thin films have been characterized by XRD, SEM and EDS for morphological and analytical study. The presence of graphene sheets in Cu-Gr composite was confirmed by EDS analysis. The prepared Cu-Gr nanocomposite thin film shows higher corrosion resistance as compared to pure copper thin films in 3.5% NaCl as confirmed by Tafel plots. EIS also compliments the above results, which shows that 0.3 g/L composite film has highest film resistance.
In order to obtain better bioleaching efficiency, bacterial community dynamics and copper leaching with applying forced aeration were investigated during low-grade copper sulphide bioleaching. Results illustrated appropriate aeration yielded improved bacteria concentrations and enhanced leaching efficiencies. The highest bacteria concentration and Cu2+ concentration after 14-day leaching were 7.61×107 cells•mL-1 and 704.9 mg•L-1, respectively, when aeration duration was 4 h•d-1. The attached bacteria played a significant role during bioleaching from day 1 to day 7. However, free bacteria dominated the bioleaching processes from day 8 to day 14. This is mainly caused by the formation of passivation layer through Fe3+ hydrolysis along with bioleaching, which inhibited the contact between attached bacteria and ore. Meanwhile, 16S rDNA analysis verified the effect of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidanson on bioleaching process. The results demonstrate the importance of free and attached bacteria in bioleaching.
Carbon nanofiber, CNF, is regarded to be a promising material due to its excellent physical and chemical properties. Herein, a novel way to transform CO2 into heteroatom-doped CNFs is proposed, with the introduction of Fe, Co and Ni as catalyst. When electrolyte contained NiO, Co2O3 and Fe2O3 is employed, sulfur doped CNFs in various diameter are obtained. With the introduction of catalyst Fe, the obtained sulfur doped CNFs show the smallest and tightest diameter distribution. The obtained sulfur doped CNFs have high gravimetric capacitance (achieved by SDG-Fe) which could reach 348.5 F/g at 0.5 A/g, excellent cycling stability, and good rate performance. For comparison purposes, both stainless steel and nickel cathode were tested, where the active metal atom at their surface could act as catalyst. In these two situations, sulfur doped graphite sheet and sulfur doped graphite quasi-sphere were the main products, respectively.
In this study, Mg-9Al-1Si-1SiC (wt%) composites were processed by multi-pass equal-channel angular pressing (ECAP) at various temperatures, and the microstructure evolution and strengthening mechanism were explored. The results indicate that the as-cast microstructure was composed of an α-Mg matrix, discontinuous Mg17Al12 phase, and Chinese script-shaped Mg2Si phase. After solution treatment, almost all of the Mg17Al12 phases are dissolved into the matrix, while the Mg2Si phases are not. The subsequent multi-pass ECAP at different temperatures results in more complete dynamic recrystallization and uniform distribution of Mg17Al12 precipitates when compared with the multi-pass ECAP at a constant temperature. A large number of precipitates can effectively improve the nucleation ratio of recrystallization through a particle-stimulated nucleation mechanism. In addition, the nano-scale SiC particles are mainly distributed at grain boundaries, which can effectively prevent dislocation movement. The excellent comprehensive mechanical properties are mainly attributed to grain boundary strengthening and Orowan strengthening.
Layered double hydroxides (LDHs) can be very interesting materials in corrosion inhibition applications as LDHs stops the corrosive elements by its ability of double layer formation and locking them between its layers. In this work, Zn-Mg based LDHs are grown over copper substrate by hydrothermal method. Two types of Zn-Mg based LDHs have been prepared based on hydrothermal reaction time. Both LDHs have been characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, high resolution scanning electron microscopy, energy dispersive X-ray analysis, atomic force microscopy and X-ray diffraction patterns. The results show that LDHs are successfully grown on copper; however, they are found different in terms of thickness and structural configuration. Corrosion testing of LDHs has been executed both in 0.1 M NaCl and 0.1 M NaOH by ac impedance measurements and Tafel polarization curves. The results show that L48 gives more than 90% protection to copper, which is higher than protection provided by L24. However, it is evident that both LDH (L24 and L48) is more effective in NaCl, in terms of reduction of corrosion. This information indicates that LDH is more efficient to exchange Cl- ions than OH- ions.
To rapidly remove the copper impurity from bismuth-copper alloy melts, a green method of super-gravity separation was investigated, which has the characteristics of enhancing the filtration process of bismuth and copper phases. In this study, the influence of super-gravity on the removal of copper impurity from bismuth-copper alloy melts was discussed. After super-gravity separation, the liquid bismuth-rich phases were mainly filtered into the lower crucible, while most of the fine copper phases were remained in the opposite direction. With optimized conditions of T = 280℃, G = 450, and t = 200 s, the purity of the filtered bismuth phase exceeded 99.7wt%, and the mass proportion of the separated bismuth of Bi-2wt%Cu and Bi-10wt%Cu alloys reached 96.27wt% and 85.71wt% respectively, which indicated the little loss of bismuth in the residual. Simultaneously, the removal rate of copper impurity went to 88.0% and 97.8%, respectively. Furthermore, the separation process could be completed rapidly, environmentally friendly and efficiently.
Effect of welding current mode in resistance spot welding process (RSW) on the microstructure and mechanical properties of the advanced high strength steel dual phase 590 (DP590) sheets have been investigated. It were found that fine martensitic structure was formed in the weld zone of the sample welded by single-pulse mode, while the microstructure in the heat-affected zone consists of a very fine martensitic microstructure and rough ferrite. However, using secondary pulse mode has led to the formation of tempered Martensite in the weld zone. The maximum load and the energy absorption to failure in the samples employing the secondary pulse cycle were higher, as compared to the sample employing the single pulse mode. Based on the fractography results, using the secondary pulse mode could significantly change the mode of failure upon shear tension testing. Therefore, the obtained results are some evidence that shows the use of secondary pulse mode can improve the microstructural feature and mechanical properties of the DP590 advanced high strength steel welds.
A reductant counts for much in the hydrometallurgical recycling of valuable metals from spent lithium-ion batteries (LIBs). There is limited information about SnCl2 as a reductant with organic acid (maleic acid) to recover value metals from spent LiCoO2 material. The leaching efficiencies were 98.67% and 97.59% for Li and Co with 1 mol L-1 of maleic acid and 0.3 mol L-1 of SnCl2 at 60°C and 40 min. And the kinetics and thermodynamics of the leaching process were inquired in the article to study the mechanism of leaching process clearly. According to the comparison of H2O2 on the leaching efficiency, optimal leaching parameters and the activation energy, it is feasible to replace H2O2 with SnCl2 as a leaching reducer in the leaching process. In addition, when SnCl2 is used in the acid-leaching process, Sn residue in leachate may has a positive effect on the re-synthesis of nickel-rich cathode materials. Therefore, the present study can provide a new direction for reductants selection for the hydrometallurgical recovery of valuable metals from spent LIBs
The microstructure evolution and performance of Diamond/Al composites during thermal cycling, which is important for their wide application, has been rarely investigated. In the present work, the thermal stability of Diamond/Al composite during thermal cycling up to 200 cycles has been explored: thermal conductivity of the composites was measured, and SEM observation of the marked-out area of the same sample was carried out to achieve quasi-in-situ observation. The interface between (100) plane of diamond and Al matrix was well bonded with zigzag morphology and extensive needle-like Al4C3 phases. However, the interfacial bonding between (111) plane of diamond and Al matrix was rather weak, which was debonded during thermal cycling. The debonding length was initially increased rapidly within the initial 100 cycles, which was then increased slowly in the following 100 cycles. The thermal conductivity of the Diamond/Al composite was primarily decreased very abruptly within initial 20 cycles, increased afterward, and then further decreased monotonously with the increase of thermal cycles. The decreased thermal conductivity of the Al matrix and corresponding thermal stress concentration at the interface caused by the thermal mismatch stress is suggested as the main factor especially in the initial period rather than the interfacial debonding.
To remediate heavy metal ions, an Al2O3-SiO2 composite aerogel is prepared via a sol-gel and an organic solvent sublimation drying (Sol-Gel-OSSD) method. XRD and FTIR suggested that the aerogel is composed of mainly Al2O3 and minor SiO2. It has high specific surface areas (~827 m2/g) and high porosities (~90%) with pore diameters at ~20 nm. It microstructures showed that the distribution of Al, Si and O is homogeneous. The aerogel can remove ~99% Cu2+ within ~40 min and reach its equilibrium uptake afterwards (~69 mg/g). Preliminary calculations show that the Cu2+ uptake by the aerogel follows kinetics of the pseudo second order where chemical sorption may take effects owing largely to the high surface areas, high porosity, and abundant functional groups in the aerogel network such as Al-OH and Si-OH. This aerogel may afford an efficient absorbent for removing Cu2+ ions.
In this study, Al2O3 nanoparticles, as well as MCrAlY/nano-Al2O3 nanocomposite powder were produced using a high-energy ball-milling process. In addition, the MCrAlY/nano-Al2O3 coating was deposited by selecting an optimum nanocomposite powder as feedstock using high-velocity oxy-fuel (HVOF) thermal spraying technique. The morphological and microstructural examinations of Al2O3 nanoparticles, as well as the commercial MCrAlY and MCrAlY/nano-Al2O3 nanocomposite powders, were investigated using X-ray diffraction (XRD) analysis, field emission scanning electron microscope (FESEM) equipped with electron dispersed spectroscopy (EDS) analysis and transmission electron microscope (TEM). The structural investigations and Williamson-Hall results demonstrated that the ball-milled Al2O3 powder after 48 h has the smallest crystallite size and the highest amount of lattice strain compared to all other as-received and ball-milled Al2O3 owing to its optimal nanocrystalline structure. Besides, in the case of developing MCrAlY/nano-Al2O3 nanocomposite powder, with increasing mechanical-milling duration, the particle size of the nanocomposite powders was decreased.
Cobalt modified brownmillerite KBiFe2O5 [KBiFe2(1-x)Co2xO5 (x= 0, 0.05)] polycrystalline is synthesized following solid-state reaction route. Rietveld refinement of X-ray diffraction (XRD) data reveals the phase purity of KBiFe2O5 (KBFO) and KBiFe1.9Co0.1O5 (KBFCO). The optical band gap energy (Eg) of KBFO is observed to be decrease from 1.59 eV to 1.51 eV by Co substitution. The decrease in band gap attributes to the tilting in the Fe-O tetrahedral structure of KBFCO. The observed room temperature Raman peaks of KBFCO are shifted by 3 cm-1 towards lower wavenumber in comparison with KBFO Raman peaks. The shifting of Raman active modes can be attributed to the change in the bond angles and bond lengths of Fe-O tetrahedral and modification in oxygen deficiency in KBFO due to Co doping. The frequency-dependent dielectric constant and loss of KBFCO also decrease with respect to KBFO at room temperature, which is a consequence of the reduction in oxygen migration and modification in vibrational modes present in the sample.
The mechanism of the formation of bonding between compound cast Al/Ti bimetal during a heat treatment regime is investigated by casting commercially pure Al melt on a Ti bar in a steel tube and heat treating the compound cast Ti/Al bimetal for different periods of time, after the Al melt was solidified. No bonding was observed between the two metals after the initial casting. This was attributed to the presence of oxide films on the liquid Al and solid Ti alloys and the trapped atmosphere between them. The effect of these layers in preventing the formation of bonding was eliminated after heat treating the cast part at 973 K (700 oC) for at least 15 min and the metals started to bond with each other. A detailed mechanism for this bonding is presented in this paper.
Abstract: X-ray powder diffraction, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetry, differential scanning calorimetry and mass spectrometry have been used to study the products of nickel-containing pyrrhotite tailings oxidation by the oxygen in the air. The kinetic triplets of oxidation, such as activation energy (Ea), pre-exponential factor (A) and reaction model (f(α)) being a function of the conversion degree (α), were adjusted by the regression analysis. In case of a two-stage process representation, the first step proceeds under autocatalysis control and ends at α = 0.42. The kinetic triplet of the first step can be presented as Ea = 262.2 kJ/mol, lgA = 14.53 s-1, f(α) = (1 – α)4.11(1 + 1.51·10–4α). For the second step, the process is controlled by the two-dimensional diffusion of the reactants in the layer of oxidation products. The kinetic triplet of the second step: Еa = 215.0 kJ/mol, lgA = 10.28 s-1, f(α) = (–ln(1 – α))–1. The obtained empirical formulae for the rate of pyrrhotite tailings oxidation reliably describe the macro-mechanism of the process and can be used to design automatization systems for roasting these materials.
In this study, a family of novel steel-Ti(C,N) composites were fabricated by spark plasma sintering (SPS) method and subsequent heat treatment. The hardness, indentation fracture resistance, and wear behaviour of the steel-Ti(C,N) composites were compared with that of unreinforced samples and their potentials were assessed by traditional cermet/hardmetal systems. The results show that with the addition of 20wt% Ti(C,N), wear rates of the newly examined composites are reduced by about 2 to 4 times and comparable to that of cermets and hardmetals. The martensitic transformation of steel matrix and the formation of in-situ carbides induced by heat treatment meliorated the wear resistance. Although excessive in-situ carbide improves the hardness, the low IFR (Indentation Fracture Resistance) value results in brittle fracture, which in turn results in poor wear property. The operative wear mechanisms were studied. This study provides a practical and cost-effective way to prepare steel-Ti(C,N) composites as potential wear-resistant materials.
The present work initially studies the kinetics of microwave-assisted grinding and flotation in a porphyry copper deposit. The kinetics tests were carried out on the untreated and microwave irradiated samples by varying the exposure time from 15-150 sec. Optical microscopy, energy-dispersive X-ray spectroscopy and scanning electron microscopy were used for determining the mineral liberation, particle surface properties and mineralogical analyses. Results disclosed that the ore’s breakage rate constant monotonically increased by increasing the exposure time particularly for the coarsest fraction size (400 µm) owing to the creation of thermal stress fractures alongside grain boundaries. Exceeded irradiation time (>60 sec) led to the creation of oxidized and porous surfaces along with a dramatic change of particle morphologies resulting in a substantial reduction of both chalcopyrite and pyrite’s flotation rate constants and ultimate recoveries. We concluded that MW-pretreated copper ore was ground faster than untreated one but their floatabilities were somewhat similar.
In this work, the fusion of leaching and purification steps is realized by directly using microemulsion as the leaching agent. The DEHPA/n-heptane/NaOH microemulsion system has been established to directly leach vanadates from sodium roasted vanadium slag. The effect of leaching arguments on the leaching efficiency is investigated, including the molar ratio of H2O/NaDEHP (W), the DEHPA concentration of, solid/liquid ratio, stirring time, and leaching temperature. In optimal situations, the vanadium leaching efficiency could attain 79.57%. Both the XRD characterization of the leaching residue and the Raman spectrum of the microemulsion before and after leaching demonstrate the successful entrance of vanadates from sodium roasted vanadium slag into the microemulsion. The proposed method has realized the leaching and purification of vanadates in one step, which significantly reduces the production cost and environmental pollution. It affords new ways of thinking about the greener recovery of valuable metals from solid resources.
Four types of meager coal and meager-lean coal and one type of high-quality anthracite are selected based on the safety requirements of blast furnace coal injection. The analysis of the organic macerals and inorganic macerals, and the chemical composition of the selected coal samples indicate that the four types of meager coal and meager-lean coal have low volatilization, low ash content, and low sulfur. These qualities are suitable for blast furnace injection and high-quality anthracite. The grindability test was conducted on the four types of meager coal and meager-lean coal, and anthracite mixed coal samples. The results indicate that the mixture of meager coal and meager-lean coal is beneficial to improve the grindability of pulverized coal. The explosive test revealed that the selected coal samples were non-explosive or weak explosive coal samples. When the mixing ratio of meager coal and meager-lean coal was less than 40%, the mixed coal powder would not explode during the blowing process. The minimum ignition temperature test determined the minimum ignition temperatures of the four types of meager coal and meager-lean coal, and anthracite as 326, 313, 310, 315, and 393℃, respectively.
How to cost-effectively reduce NOx emission of iron ore sintering process is a new challenge for iron and steel industry at present. The effects of proportion of mill scale and coke breeze on the NOx emission, strength of sinter and sinter indexes were studied by combustion tests and sinter pot tests. Results showed that the fuel-N’s conversion rate decreased with increasing of the proportions of mill scale. Because NO was reduced to N2 by Fe3O4, FeO and Fe in mill scale. The strength of sinter reached a highest value at 8.0 wt% mill scale due to the formation of low melting point minerals. Meanwhile, the fuel-N’s conversion rate slightly increased and total NOx emission significantly decreased with the proportions of coke breeze increased. Because CO formation and contents of N element in sintered mixture decreased. However, the strength of sinter was also decreased since the decreasing of the melting minerals. In addition, results of sinter pot tests indicated that NOx emission obviousely decreased and sinter indexes have good performances when the proportions of mill scale and coke breeze were 8.0 wt% and 3.70 wt% in sintered mixture.
The composite electrodes prepared by cation exchange resins and activated carbon (AC) were used to adsorb V(IV) in capacitive deionization (CDI). The electrode made of middle resin size (D860/AC M) has the largest specific surface area and mesoporous content than other two composite electrodes. Electrochemical analysis showed that D860/AC M presents higher specific capacitance and electrical double layer capacitor, and significantly lower internal diffusion impedance, thus it exhibits the highest adsorption capacity and rate for V(IV) among three electrodes. The intra-particle diffusion model fits well the initial adsorption stage, while the liquid film diffusion model is more suitable for the fitting at the later stage. The pseudo-second-order kinetic model is fit for the entire adsorption process. The adsorption of V(IV) on the composite electrode follows the Freundlich isotherm, and thermodynamic analysis indicates that this is an exothermic process with entropy reduction and the electric field force plays a dominant role in the CDI process. This work is conducive to peep at the ions adsorption behaviors and mechanisms on the composite electrodes in CDI.
In the present research, effect of graphene nanoplates (GNPs) and carbon nanotubes (CNTs) addition into the Al7075 matrix through the stir casting method on the microstructure and mechanical properties of fabricated composites was investigated. XRD results represented that by addition of reinforcements into Al7075, the dominant crystal orientation changed from a weak (002) to a strong (111). By increasing of reinforcements, the fraction of porosity increased and among the two mentioned reinforcements, addition of GNPs in to the Al7075 matrix led to create a higher fraction of porosity. Addition of reinforcements into Al7075 matrix owing to agglomeration of reinforcements and formation of porosities did not change the experimental Yield strength (YS) considerably. Theoretical calculations to determine the contributions of strengthening mechanisms in the enhancement of YS revealed that by addition of reinforcements, the grain size of matrix did not decrease, so Hall-Petch was not activated. By addition of self-lubricant GNPs and CNTs into the matrix, the wear rate values decreased and the lowest friction coefficient and the highest wear resistance belonged to Al7075/0.53 wt. % CNTs. In Al7075/GNPs, the dominant mechanisms were adhesion and delamination and a little abrasive occurred.
Thermal barrier coatings are widely used for surface modifications. Surface modifications are performed to enhance the surface properties of the material and protect the same from surface degradation such as erosion and corrosion. To increase the wear resistance, the ceramic based coatings are highly recommended in the industrial sector. In this paper, alumina-titania ceramic powder is deposited on the aluminium alloy using atmospheric plasma spray (APS) technique. Experimental investigations are performed to study the material behavior and its erosion rate. Solid particle erosion studies are performed by varying particle velocity and particle flow rate. The angle impingement and stand-of-distance are maintained constant for comparison. The behavior of base metal has clinging effect and the mass change found negative at a maximum particle flow rate of 4g/min. At the same process condition coated sample has lost his life and reached a maximum erosion rate of 0.052 (Δg/g). From the solid particle erosion studies, it has been confirmed that the behavior of as cast aluminium alloy has severe surface damage with erodent reinforcement when compared to coated samples. The influence of particle velocity and the particle flow rate were analyzed. The influence of input process parameter was also identified.
As ore grades constantly decline, more copper tailings that still contain a considerable amount of unrecovered copper are expected to be produced as a byproduct of froth flotation. This research reveals the occurrence mechanism of copper minerals in a typical copper sulfide tailing using quantitative mineral liberation analysis (MLA) integrated with scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The results show that copper minerals are highly disseminated within coarse gangue particles, and more than 90% of them are accumulated in the size fractions less than 106 μm. The predominant copper-bearing mineral is chalcopyrite, which is closely intergrown with orthoclase and muscovite rather than quartz. The flotation tailing sample still contains 3.28wt% liberated chalcopyrite and 3.13wt% liberated bornite because of their extremely fine granularity. The SEM-EDS analysis further demonstrate that copper minerals mainly occurred as fine dispersed and fully enclosed structures in gangue minerals. The information obtained from this research could offer useful references for recovering residual copper from flotation tailings.
A facile approach was developed to construct Fe2O3-modified ZnO micro/nanostructures with excellent superhydrophobicity and photocatalytic activity. The impacts of stearic acid (SA) and Fe2O3-modified on the morphology, water contact angle (WCA) and photocatalytic degradation were investigated. The superhydrophobic results showed increased of WCA from 144 ± 2° to 154 ± 2° when SA weight increase from 5 mg to 20 mg due to formation of hierarchical or rough structure. Furthermore, Fe2O3-modified ZnO micro/nanostructures surface before and after treatment with SA (20 mg) chosen to evaluate the photocatalytic of Methylene blue (MB) dye by supporting visible-light. The results showed degradation of MB after 80 min of irradiation with photodegradation efficiency 91.5% for superhydrophobic state and 92% for the hydrophilic state. This improvement in photocatalytic activity at both states may be attributable to an increase of surface area and improve charge carriers separation.
The effects of chromium on γ-austenite to α-ferrite phase transformation in Nb Microalloyed steel was observed using ultra high-temperature confocal laser scanning microscopy. It is indicated that the starting temperature of the γ→α phase transformation decreases with increasing the Cr content. The hot ductility of Nb microalloyed steel is improved by adding 0.12wt% Cr. Chromium atoms inhibit the diffusion of carbon atoms, which leads to the reduction of grain boundary ferrite thickness. The proportion of high angle grain boundaries is increased by adding chromium. In particular, the proportion is up to 48.7% when the Cr content is 0.12wt%.The high angle grain boundaries hinder the crack propagation and improve the ductility of Nb microalloyed steel.
In this study, the aim is to draw the exact boundary for microstructural and mechanical behaviors in terms of pulsed plasma nitriding conditions. The treatment is applied to AISI 304 austenitic stainless steel at different temperature and durations. The nitrided depth increases with increasing the process temperature and duration. Remarkable increase is observed on the nitrided depth for the conditions of 4750C-8h and 5500C-4h. The austenite structure is transformed into metastable nitrogen oversaturated S-phase for the lower temperature of plasma nitriding. S-phase is converted to CrN precipitation within the conditions of 4750C-8h and 5500C-4h. Plasma nitriding achieves the surface hardness and fatigue limit increase regardless of the condition. The best performance for surface hardness and fatigue limit is obtained with 5500C-4h due to the existence of CrN precipitation.
The current article compares the microstructure and mechanical characteristics of AA6061-T6 joints made by friction stir welding (FSW), friction stir vibration welding (FSVW), and tungsten inert gas welding (TIG) processes. FSVW is a modified version of FSW in which the joining specimens are vibrated normal to the welding line while FSW is carried out. The results indicated that weld region grains for FSVW and FSW were equiaxed and they were smaller than grains for TIG and additionally, weld region grains for FSVW were finer than those for FSW. The results also showed that strength, hardness, and toughness values of joins made by FSVW were higher than those of other joints made by FSW and TIG. It is believed that vibration during FSW enhances the dynamic recrystallization (DR) and as a result, finer grains are developed. The weld efficiency of FSVW is approximately 81%, whereas this ration is about 74% and 67% for FSW and TIG, respectively.
α-MoO3 have been prepared into nanosheets full of mesopores on the surface. The effect of mesopores on the nanosheet surface on the electrode performance remains challenging by far. Our obtained MoO3 nanosheets have exhibited great battery performance, including good capacity, elongated recycling life cycles, and excellent rate performance, e.g. above 800 mAh/g when charged under super high current-density of 1000 mA/g. The material demonstrates excellent stability, keeping the capacity of 1189 mAh/g after 20 cycles, and 1075 mAh/g after 50th cycles from decreasing sharply under density of 100 mA/g. The obtained MoO3 nanosheets is of high purity, well-organized, and dense mesopores on the surface, determining the host electrode materials have exhibited good electrode performance, e.g. battery life and capacity and so on. Setting mesopores, or active sites, on the electrode surface should be an alternative way to stable electrode in the furture.
Acid mine drainage has been an important threat to cementitious structures. To improve the acid resistance of cementitious composites used under acid mine drainage attack, this study is aimed at investigating the effect of cellulose nanocrystals (CNCs) on the acid resistance of cementitious composites. CNCs were added to the mortar mixtures as additives at cement volume ratios of 0.2%, 0.4%, 1% and 1.5%. After 28 days of standard curing, the samples were immersed in sulfuric acid with a pH of 2 for 75 days. The unconfined compressive strength (UCS) test, density, absorption and voids test and thermo-gravimetric analysis (TGA) were carried out to investigate the properties of CNC mixtures before sulfuric acid immersion. It was found that the addition of CNC reduced the volume of permeable voids and increased the hydration degree and mechanical strength. Changes in mass and length were monitored during immersion to evaluate the acid resistance of mixtures. The mixture with 0.4% CNC showed improved acid resistance due to the reduced mass change and length change after brushing.
Bimetal materials derived from transition metals can be good catalysts in some reactions. When supporting on graphene (GP), those catalysts have a remarkable performance in hydrolysis of sodium borohydride. To obtain such catalysts easily and efficiently, herein, a simple thermal reduction strategy has been used to prepare NixCo10-x series bimetal catalysts. Among all of these catalysts, Ni1Co9 is the best catalysts in catalytic performance. The turnover frequency (TOF) related to the total atoms number within the bimetallic nanoparticles reaches 603.82 mLH2·mmolbimetal-1·min-1 at 303 K. Furthermore, graphene is introduced as supporting frame. In additon, Ni1Co9@Graphene (Ni1Co9@GP) makes a large surface area and high TOF, 25534 mLH2·mmolbimetal-1·min-1 at 303 K. The Ni1Co9@GP exhibits efficiently catalytic properties for H2 generation in an alkaline solution because of their high specific surface area. Kinetic studies a high kinetic isotope effect disclosed using D2O lead to the suggestion of an oxidative addition of a O-H bond of water in the rate-determining step.
Aurivillius Bi5Ti3FeO15 (BTFO) ceramic is synthesized by the generic solid-state reaction route. The room temperature X-ray diffraction (XRD) study confirms that the compound is having single-phase without any impurity. Surface morphology of the prepared sample ensures that the presence of microstructural grains with size around 0.2 to 2 µm is observed. Dielectric properties of sample are investigated as a function of frequency of about 100 Hz to 1 MHz at various temperatures (303 K ≤ T ≤ 773 K). The Nyquist plots of impedance data exhibit a semi-circular arc in high temperature region, which is explained by the equivalent electrical circuit (R1C1) (R2QC2). Our results indicate that resistance as well as capacitance of grain boundary is more prominent over the grains. Analysis of ac conductivity data is done by using Jonscher universal power law (σac=σdc+Aωn) which confirms that the conduction process is dominated by the hopping mechanism. The activation energies calculated for relaxation and conduction processes are very close to each other (0.32 eV to 0.53 eV) by which we conclude that the same type of charge carriers are involved in both the processes.
A solidification model of a continuous casting slab with non-uniform cooling condition was established with the ProCAST software. The model was verified by the results of the nail shooting tests and the infrared temperature measurement equipment. It was found that the final solidification position was 220 to 440 mm away from the edge of the slab width for 200 mm × 2300 mm section based on the simulation results. In addition, four characteristic parameters were defined to evaluate the uniformity of the shape of slab solidification end. Then the effects of casting speed, superheat and secondary cooling strength on these four parameters were discussed. Moreover, the central-line segregation of slab produced with and without the soft reduction process were investigated. The results show that, the transverse flow of molten steel with low solid fraction had an important effect on the central-line segregation morphology under the soft reduction.
In order to obtain the purified dendritic hafnium metal, the cathodic redution mechanism of Hf (IV) ions in NaCl-KCl-NaF-K2HfF6 fused salt system were studied in various NaF concentrations at 1073 K. The results of cyclic voltammetry and square wave voltammetry indicate that the reduction process is two steps of Hf (IV)→Hf (II) and Hf (II) →Hf at lower NaF concentrations (0<[F-/Hf4+]<17.39), and one step Hf (IV) →Hf at higher NaF concentrations (17.39< [F-/Hf4+] <23.27). The structure and morphology of the deposits obtained by potentiostatic electrolysis at one step reduction process were analysised and verifyed by XRD, SEM and EDS. At one-step reduction process, the disproportionation reaction between hafnium metal and hafnium complex ions was inhibited, and large dendrite hafnium metal was achieved in molten salt electrorefining.
The chemical binder is one of critical factors that affecting ore agglomeration behavior and leaching efficiency. In this study, the effect of types of binders and mass fraction of H2SO4 solution on curing, soaking and leaching behavior of agglomerations were conducted. The results showed that the Portland cement (3CaO·SiO2, 2CaO·SiO2, 3CaO·Al2O3) was the optional binder to obtain well-shape, stable structure of agglomeration. A higher extraction rate was reached using Portland cement instead of sodium silicate, gypsum and acid-proof cement. The excessive geometric mean size is not conducive to well-shaped agglomerations and desirable porosity. Relied on Computed Tomography (CT) and MATALB, the porosity of 2-D CT images in L1~L3 increased at least 4.5 % after acid leaching. Ore agglomerations started to be heavily destroyed and even disintegrate if sulfuric acid solution was higher than 30 g/L, it was caused by undesirable accumulation of reaction products and residuals.
The reduction behavior and metallization degree of magnetite concentrate with agave bagasse were investigated in an inert atmosphere. The influence of temperature, biomass content and residence time on reduction experiments and metallization degree were investigated by X-ray diffraction and scanning electron microscopy. The results show advantages compared to other kinds of biomass, such as lower content of nitrogen, sulphur, and ash. X-ray diffraction analysis showed that an increase of temperature and biomass content result in higher metallization degree. At 1100°C for 30 minutes with 65:35 and 50:50 magnetite concentrate:agave bagasse ratios, complete metallization was achieved. These results demonstrate that agave bagasse promotes the efficient metallization of magnetite concentrate without external addition of reducing agent. Therefore, the use of this biomass is a technical suitable alternative to replace the fossil fuels in steelmaking process.
Aluminum storage system with graphite as cathode, due to ultra-stable cycling stability, high capacity and good safety, is greatly promoting the development of state-of-the-art rechargeable aluminum battery in the last 5 years. In this work, it confirms that flake graphite stacked with noticeably small and thin graphene nanosheets exhibits high capacity and fare good rate capability in low-cost AlCl3-NaCl inorganic molten salt. The battery can achieve high capacity of ~219 mAh•g-1 over 1200 cycles at high current density of 5 A•g-1, with Coulombic efficiency of 94.1%. Moreover, a clear understanding about reaction mechanism is demonstrated that flake graphite with small and thin graphene nanosheets and high mesopore structures consists of not only the intercalation of AlCl4- anions between graphene layers, but also the adsorption of AlCl4- anions within mesopores; whereas well stacked and highly parallel layered large-size expandable graphite mainly involves the intercalation of AlCl4- anions.
The effect of multiple passes of friction stir processing (FSP) and the addition of Mg powder on different parts of the microstrcuture processed including the stir zone (SZ), the heat-affected zone (HAZ), and the thermo-mechanically affected zone (TMAZ) were investigated. The results of the microstructural observations revealed that although the grain size of the SZ decreased in both the non-composite and composite samples, the grain size increased in the TMAZ and the HAZ of the non-composit sample with increasing the numer of FSP passes. Besides, the addition of Mg powder resulted in much more significant grain refinement. Moreover, increasing the number of the FSP passes resulted in a more uniform distribution of Al-Mg intermetallic compounds in the in-situ composite sample. The results of the tensile testing showed that the four- passes FSPed non-composite sample exhibited a higher elongation percentage with a ductile fracture compared with those of the base metal and the four-pass composite sample while lattermost sample exhibited a brittle fracture and a higher tensile strength value than the base metal and the four-pass FSPed non-composite sample. The fabrication of composite samples resulted in noticeable enhancement of hardness compared with the base metal and the non-composite FSPed samples.
Pt/CeO2-C catalysts with CeO2 pre-calcined at 300~600 °C were synthesized by combining hydrothermal calcination and wet impregnation method. The effects of the pre-calcined CeO2 on the performance of Pt/CeO2-C catalysts for methanol oxidation have been investigated. The Pt/CeO2-C catalysts with pre-calcined CeO2 at 300~600 °C have shown an average particle size of 2.6-2.9 nm, and exhibited better methanol electro-oxidation catalysis activity than the commercial Pt/C catalyst. Specifically, the Pt/CeO2-C catalyst with pre-calcined CeO2 at 400 °C displayed the highest electrochemical surface area (ECSA) value at 68.14 m2 g−1Pt and If/Ib ratio at 1.26, which are far larger than that of the commercial Pt/C catalyst at 53.23 m2 g−1Pt and 0.79 respectively, implying the greatly enhanced CO tolerance performance.
The formation of a rust layer on the surface of iron and steels accelerates their degradation and eventually causes the failure of materials. In addition to fabricating a protective layer or using a sacrificial anode, repairing or removing the rust layer is another way to reduce the corrosion rate and extend the lifespan of iron and steels. Herein, an electrochemical deoxidation approach is employed to repair the rust layer in molten Na2CO3-K2CO3. The rust consists of oxides which can be electrochemically reduced to metals/alloys, releasing oxide ions into the molten salt. The electrochemical method uses electrons to convert oxide to metal rather than remove the entire rust layer away. Due to the fluidity of the molten salt electrolyte, the electrochemical derusting approach is not constrained by the shape of the objects. The rusty layer of iron rods and screws was electrochemically converted to iron by molten salt electrolysis. Thus, the high-temperature molten salt electrolysis may be an effective way to metalize iron rust and be used for repairing cultural relics and healing the rust layers on other metals.
Near eutectic 12.6SiAl alloy has been developed with 0 wt%, 2 wt. %, 4 wt.% and 6 wt.% Al-5Ti-1B master alloy. Microstructural morphology, hardness, tensile strength, elongation and fracture behaviour of the alloys have been studied. The unmodified 12.6SiAl alloy has an irregular needle and platy eutectic silicon (ESi) and coarse polygonal primary silicon (PSi) particles in the matrix-like α-Al phase. The PSi, ESi and α-Al morphology and volume fraction have been changed due to the addition of Al-5Ti-1B master alloy. As an effect of microstructure modification, hardness, UTS and % elongation improved. Nano-sized in-situ Al3Ti particles and ex-situ TiB2 particles are the cause of microstructural modification. The fracture images of the developed alloys exhibit a ductile and brittle mode of fracture at the same time. The Al-5Ti-1B modified alloys have a more ductile mode of fracture and dimples compared to the unmodified one.
The direct semi-solid isothermal treatment (DSSIT) process is proposed to process the cold-rolled ZL104 aluminum alloy to manufacture the semi-solid billet. The influence of two process parameters (i.e. maintained temperature and duration time) on the microstructure and hardness of the semi-solid billet (ZL104 aluminum alloy) were experimentally examined. Results revealed that the average size of grains enlarged and the shape factor was improved with an elevation in the maintained temperature. The shape factor increased with the increase in the duration time while the average grain size enlarged when the duration time was prolonged from 5 to 20 min at 570 °C. The hardness of the studied aluminum alloy decreased due to the increase in the average size of grains with raising of either the maintained temperature or the duration time. The optimal maintained temperature was obtained as 570 °C while the duration time was found as 5 min for preparing the semi-solid ZL104 aluminum alloy. Under the optimal process parameters, the average size of the grain, the shape factor, and the hardness were obtained as 35.88 µm, 0.81 and 55.24 MPa, respectively. The coarsening rate constant in the Lifshitz-Slyozov-Wagner relationship at 570 °C was found at 1357.2 μm3/s.
In the present study, manganese (Mn) has been leached out from a low-grade manganese ore (LGMO) using banana peel as a reductant in a dilute sulfuric acid (H2SO4) medium. The effects of banana peel amount, H2SO4 concentration, reaction temperature and time on Mn leaching from the complex LGMO were studied. The leaching efficiency of ~98% was achieved at 2h leaching time, 4 g banana peel amount, 120oC leaching temperature, 5 g manganese ore amount and 15 vol.% sulfuric acid concentration. The phase, microstructural and chemical analyses of LGMO samples before and after leaching confirmed that a high Mn content (~18 wt.%) has been successfully leached out. Furthermore, the leaching process follows the shrinking core model (SCM) and the leaching rate was controlled by the surface chemical reaction (1 - (1-x)1/3 = kt ) mechanism with an apparent activation energy (Ea) of 40.19 kJ.mol-1.
The effect of picosecond Nd:YAG laser irradiation on chemical and morphological surface characteristics of the commercially pure titanium (CP-Ti) and Ti-13Nb-13Zr alloy in the air and argon atmosphere was studied for different laser output energy values. During the interaction of laser irradiation with investigated materials, part of the energy was absorbed on the target surface influencing the surface modifications. Laser beam interaction with the target surface resulted in various morphological alterations and as a result crater formation and presence of microcracks and hydrodynamic structures were observed. Moreover, different chemical changes on the target materials surfaces were induced resulting in the titanium oxide formation in the irradiation affected area and consequently increasing the irradiation energy absorption. Due to the higher energy absorption at the site of the interaction, the dimensions of the surface damaged area increased. Consequently, surface roughness increased. Appearance of the surface oxides also leads to the increase of the material hardness in the surface-modified area. Observed chemical and morphological changes were more pronounced after laser irradiation of the Ti-13Nb-13Zr alloy surface.
The presence of silver ions (Ag (I)) in wastewater has detrimental effect to living organism. Removal of these soluble silver is a challenging issue, particularly if it is in low concentration. This paper presents the use of β-MnO2 particles as photocatalyst to remove Ag (I) ions selectively from the aqueous solution at various pH. ICP-MS, XRD, FESEM, TEM and XPS were used to determine the removal efficiency and to characterize the deposition of silver onto the surface of β-MnO2 particles. The optimum pH for the removal of Ag (I) ions was found to be at pH 4 with 99 % of removal efficiency under one hour of visible light irradiation. This could be explained from the perspective of electrostatic attraction between β-MnO2 particles and Ag (I) ions as well as the suppression of electron-hole recombination in the presence of H%2B ions.
Ti3AlC2 reinforced Ag-based composites are used as sliding current collectors, electrical contacts and electrode materials, which shows remarkable performance. However, the interfacial reactions between Ag and Ti3AlC2 significantly deteriorate the electrical and thermal properties of the composite. To alleviate the interfacial reactions, carbon-coated Ti3AlC2 particles (C@Ti3AlC2) were fabricated as reinforcement. Ag-10wt.% C@Ti3AlC2 composites with carbon layer thickness of 50-200 nm were prepared. Compared with the uncoated Ag-Ti3AlC2 composite, Ag-C@Ti3AlC2 exhibits a better distribution of Ti3AlC2 particles. With the increase of carbon layer thickness, the Vickers hardness and relative density of Ag-C@Ti3AlC2 decline gradually. The lowest resistivity of Ag-C@Ti3AlC2 reaches 29.4×10-9 Ω·m with the carbon layer thickness of 150 nm, half of the Ag-Ti3AlC2 (66.7×10-9 Ω·m). The thermal conductivity of Ag-C@Ti3AlC2 reaches a maximum value of 135.5 W·m-1·K-1 with a 200-nm carbon coating (~1.8 times over that of the Ag-Ti3AlC2). These results indicate that carbon coating method is a feasible strategy to improve the performance of Ag-C@Ti3AlC2 composites.
Monoclinic SrAl2Si2O8 ceramics for the immobilization of Sr were prepared by a liquid-phase sintering method. The sintering temperature, mineral phase composition, microstructure, flexural strength, bulk density, and Sr ions leaching characteristic of SrAl2Si2O8 ceramics were investigated. A crystalline monoclinic-SrAl2Si2O8 phase was formed by liquid phase sintering at 1223 K. The introduction of four different flux agents (B2O3, CaO·2B2O3, SrO·2B2O3 and BaO·2B2O3) to the SrAl2Si2O8 ceramics not only reduced the densification temperature and decreased the volatilization of Sr during high-temperature sintering, but also impacted the mechanical properties of the ceramics. The product consistency tests showed that the leaching concentration of Sr ions in sample SAS-B with flux agents B2O3 was the lowest and the leaching concentration of Sr ions in sample SAS-B2B with flux agents BaO·2B2O3 was the highest. These results show that the leaching concentration of Sr ions depends largely on amorphous phase in the ceramics. Meanwhile, the formation of mineral analog ceramic containing Sr is an important factor to improve the immobilization of Sr.
The effect of cold rolling and post-rolling heat-treatment on the microstructural and electrochemical properties of the 316L stainless steel is investigated. The two passes and four passes cold-rolled stainless steel specimens were heat-treated by annealing at 900 ⁰C followed by quenching in water. The microstructure of the as-rolled specimens transformed from austenite to strain-induced α'-martensite due to the significant plastic deformation that also resulted in significant grain elongation (~28 to ~54 µm). The hardness of the heat-treated specimens decreased from 190 to 146 HV due to the recovery and recrystallization of the austenite grain structure. The cyclic polarization scans of the as-rolled and heat-treated specimens were obtained in 0.9% NaCl solution. The pitting potential of the four passes rolled specimen was significantly increased to 930.5 mV from 322.3 mV after post-rolling heat treatment. The beneficial effect of the heat treatment process was evident from ~10 times lower corrosion current density and two orders of magnitude lower passive current density of the heat-treated specimens compared to as-rolled specimens. Similarly, appreciably lower corrosion rate (0.013 mpy) and higher pitting resistance (1115.5 mV) was exhibited by the post-rolled heat-treated specimens compared to as-rolled 316L stainless steel specimens.
To discuss the potential role of the iridium (Ir) nanoparticles loaded under conditions at atmospheric and high pressures, we have proceeded to prepare a series of catalysts with the same active phase, but different content of 10, 20, and 30 wt% on gamma alumina for the decomposition of hydrazine. Under atmospheric pressure, the performance of the catalyst was better when using 30 wt% of iridium nanoparticles with chelating agent with a more selectivity of about 27%. The increase of the reaction rate of 175 h-1 to 220 h-1 at the higher iridium loading (30 wt%) is due to a good dispersion of high number active phases rather than an agglomeration surface. On the other hand, as a satisfactory result of this investigation at high pressure, it was found that iridium catalysts with different weight percentages showed the same stability against crushing and activity with a characteristic velocity about 1300 m/s.
In the ironmaking process, adding organic binder replaces a portion of bentonite is a potential solution to improve the performance of the pellets. The interaction between the original bentonite (OB) and the organic binder was investigated. The results illustrate that the micro-morphology of the organic composite bentonite (OCB) became porous and the infrared difference spectrum was a curve. Additionally, the residual burning rates of OB and organic binder were measured, which were 82.72% and 2.30%, respectively. Finally, the influence of OCB on the properties of pellets were studied. The compressive strength of OCB-added green pellets (14.7 N/pellet) was better than that of OB-added pellets (10.3 N/pellet), and the range of melting temperature (173℃) was narrower than that of OB-added pellets (198℃). The compressive strength of OCB-added pellets increased from 2156 N/pellet to 3156 N/pellet with the roasting temperature increased from 1200℃ to 1250℃.
Copper matrix composites reinforced by in situ-formed hybrid TiB whiskers and TiB2 particles were fabricated by powder metallurgy. Microstructure observations showed that there was a competitive precipitation behavior between TiBw and TiB2p, where the relative contents of the two reinforcements varied with sintering temperature. Based on thermodynamic and kinetic assessments, the precipitation mechanisms of the hybrid reinforcements were discussed, and the formation of both TiB whiskers and TiB2 particles from the local melting zone was thermodynamically favored. The precipitation kinetics were mainly controlled by a solid-state diffusion of B atoms. By forming a compact compound layer, in situ reactions were divided into two stages, where Zener growth and Dybkov growth prevailed, respectively. Accordingly, the competitive precipitation behavior was attributed to the transition of the growth model during the reaction process.
Pyrolysis of the Ta2O5/melamine mixture in molten chlorides is herein demonstrated as a facile and controllable method to nitride and functionalize the Ta2O5. The influence of Ta2O5/melamine stoichiometry and composition of molten salts on the nitridation process is rationalized for controllable preparation of Ta3N5 and Ta3N5/TaON. The characterization results including scanning electron microscope (SEM), transmission electron microscopy (TEM), elements mapping and X-ray photoelectron spectroscopy (XPS) as well as photoluminescence spectra all confirm the existence of heterojunction in the Ta3N5/TaON, in which the TaON nanoparticles are closely anchored to the Ta3N5 nanorods. Benefiting from the merits in composition and structure, the Ta3N5/TaON composites show an enhanced photocatalytic activity for degradation of methylene blue. The present study highlights that the molten salt method using a solid nitrogen source can be a new way to the rational design of nitrides and oxynitrides.
The effects of tempering holding time at 700 ℃ on the morphology, mechanical properties, and behavior of nanoparticles in Ti-Mo ferritic steel with different Mo contents were analyzed using scanning electron microscopy and transmission electron microscopy. Equilibrium solid solution amount of Mo, Ti, and C in ferrite at various temperature were calculated. The variation in the sizes of nanoparticles with time at different Mo contents was analyzed. The experiments and calculations were in good agreement with one other, which showed that the change in the nanoparticle size of MNF steel was the smallest during the aging process. Higher Mo contents inhibited the maturation and growth of nanoparticles, but when the Mo content exceeded 0.37 wt%, no obvious inhibition effect was observed. The tensile strength and yield strength decreased continuously with the tempering time. The analysis of the strengthening and toughening mechanism showed that the different mechanical properties between the three was mainly determined by the grain refinement strengthening (the difference range was 30-40 MPa) and precipitation strengthening (the difference range was 78-127 MPa). MNF steel with an ideal chemical ratio had the highest thermodynamic stability, and LNF and HNF have relatively similar thermodynamic stabilities.
In this study, the effect of carburizing on tensile strength and wear resistance of AISI 8620 steel were investigated. Firstly, the alloy with 0.25 %C content was pressed at 700 MPa and sintered at the temperature of 1300°C, 1400°C and 1500°C for 1 hr. After determination of ideal sintering temperature, the carburizing process was applied to Alloy 1 and Alloy 2 (0.2 C% and 0.25%C) at 925°C for 4 h. The microstructure of the samples was characterized by Optical microscopy(OM), scanning electron microscopy (SEM). The mechanical and wear behavior of carburized and non-carburized samples were investigated by hardness, tensile and wear tests. The increase in ultimate tensile strength for Alloy 1 and Alloy 2 after carburizing was calculated as 134.4% and 138.1%, respectively.However, the decrease in elongation % for Alloy 1 and Alloy 2 after carburizing was determined as 62.6 % and 64.7 %, respectively. It is reported that the wear depth values of Alloy 2 for non-carburized and carburized conditions under load of 30 N is 231.2 µm and 100.1 µm, respectively. It is observed that oxidative wear changed to abrasive wear for the transition from load of 15N to load of 30N for Alloy 1 and Alloy 2.
Refill friction stir spot welding (RFSSW) was applied to join the 2-mm-thick AZ91D-H24 magnesium alloy sheets successfully, and the effect of tool plunge depth on the microstructure and fracture behavior of the joints were investigated in detail. The sound surface formation of the joints can be obtained as the plunge depths were 2.0 mm and 2.5 mm. The plunge depth significantly affected the height of hook, and the higher plunge depth corresponded to the more severe upward bend of hook whose morphology compromised the tensile-shear properties of the joints. The hardness reached a minimum at the TMAZ due to the precipitation phases of this zone dissolved into the α-matrix during the welding process. The fracture modes of RFSSW joints can be divided into three types: shear fracture, plug fracture and shear-plug fracture. Among them, the joint under shear-plug fracture had the best tensile-shear load of 6400 N.
The AA6061 Al and commercial pure Ti were welded by ultrasonic spot welding (USW). The focus of this investigation is the interface microstructure and joint formation. The Al-Ti USW joints were welded at the welding energy of 1100 J~ 3200 J. The joint appearance and interface microstructure were observed mainly by Optical microscope (OM) and field emission scanning electron microscope (SEM) The results indicated that good joint only can be achieved with proper welding energy of 2150 J. No significant intermetallic compound (IMC) was found under all conditions. The high energy barriers of Al-Ti and difficulties in diffusion were the main reasons for the absence of IMC according to kinetic analysis. The heat input is crucial for the material plastic flow and bonding area which plays an important role in the joint formation.
Natural magnetite formed by isomorphism substitutions of Fe, Ti, Co, etc. was activated by mechanical grind followed by H2 reduction. Temperature-programmed reduction of hydrogen (H2-TPR) and temperature-programmed surface reaction of carbon dioxide (CO2-TPSR) were carried out to investigate the processes of oxygen loss and CO2 reduction. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and so on. It was found that the stability of spinel phases and oxygen-deficient degree were obviously increased after natural magnetite was mechanically milled and reduced in H2 atmosphere. Meanwhile, the activity and selectivity of CO2 reduction into carbon were enhanced. The deposited carbon on activated natural magnetite was confirmed as amorphous. The amounts of carbon after CO2 reduction at 300℃ for 90 min over the activated natural magnetite attained to 2.87wt% relative to natural magnetite.
A new method for separating and recovering tin from a low-grade tin middling with high Si content and low Fe content by roasting with anthracite coal was researched by investigating the reaction mechanism and conducting an industrial test, in which the Sn was sulfurized into SnS (g) and then collected using a dust collector. The Fe-Sn alloy can be formed at roasting temperatures over 950°C, and the Sn content and “Sn” activity in this Fe-Sn alloy decrease as the roasting temperature increases. Moreover, more FeS can be formed at higher temperatures and then the formation of FeO-FeS with low melting point is promoted, as a result of which this low-grade tin middling is sintered more seriously. Thus from the viewpoint of thermodynamics and kinetics, the Sn volatilization decreases at excessively high roasting temperatures. The results of the industrial test, which was carried out in a coal-fired rotary kiln, show that the Sn volatilization rate reaches 89.7wt% and the Sn is concentrated at a high level in the collected dust, indicating that the tin can be separated and recovered effectively from the low-grade tin middling with high Si content and low Fe content through a reduction-sulfurization roasting process.
The effect of Cr/Mn segregation on the abnormal banded structure of high carbon bearing steel was studied by reheating and hot rolling. Utilizing optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and electron-probe microanalyzer (EPMA), the segregation characteristics of alloying elements in cast billet and their relationship with hot rolled plate banded structure were revealed, and the formation reasons of abnormal banded structure and the elimination methods were analyzed. The results indicated that there was serious positive segregation of C, Cr and Mn alloy elements in the billet. Even distribution of Cr/Mn elements could not be achieved after 10 h of heat preservation at 1200 ℃, and the spacing of element aggregation area increased, but the segregation index of alloy elements decreased. There are obvious alloying element segregation characteristics in the banded structure of the hot-rolled plate. This distinct white band is composed of martensitic phases. The reason for the formation of this abnormal pearlite/martensite banded structure is the interaction between the undercooled austenite transformation behavior of hot-rolled metal and the segregation of its alloying elements. Under the condition of air cooling after rolling, controlling the segregation index of alloy elements can reduce or eliminate the abnormal banded structure.
In this paper, reaction behaviors of Pb-Zn sulfates during reduction roasting of the zinc leaching residue and flotation of the artificial sulfide minerals were deeply investigated. The reaction behaviors of Pb-Zn sulfates were characterized by chemical analyses, X-ray diffraction (XRD), Scanning electron microscopy-Energy dispersive spectroscopy (SEM-EDS) and particle size analyses. Chemical analyses results showed that the transformation ratios of PbSO4 and ZnSO4 reached 65.51wt% and 52.12wt%, respectively, after the reduction roasting. The introduction of sulfidation agent further improved their transformation ratios. SEM-EDS analyses revealed that the temperature obviously affected the particle size, crystal growth and morphology of the artificial Pb-Zn sulfide minerals. Particle size analyses presented that particle size of the material increased after the roasting. Flotation results showed that a flotation concentrate, assaying 12.01wt% Pb, 27.78wt% Zn and 697.54 g/t Ag, was obtained with their respective recoveries of 60.54wt%, 29.24wt% and 57.64wt%. It was proposed to preferentially recover the generated Pb-Zn sulfide minerals and the Ag-containing minerals by flotation from the zinc leaching residue after the reduction roasting.
Graphite materials are widely used as electrode materials for electrochemical energy s torage. N-doping is expected as a promising method to improve the electrochemical properties of graphite. A novel method for one-step N-doping to complete and compact carbon paper was proposed by molten salt electrolysis in LiCl-KCl-Li3N system. The results show that graphitization degree of carbon paper can be improved by molten salt electrolysis, particularly at 2.0 V. Nitrogen gas was produced on anode and nitrogen atoms will replace carbon atoms of carbon paper at different sites to realize nitrogen doping during electrolysis process. The doping content of N in carbon paper is up to 13.0wt%. Three kinds of nitrogen atoms, i.e. quaternary N(N-Q), pyrrolic N(N-5), and pyridinic N(N~6), existed in N-doping carbon paper. The N-doping carbon paper as cathode of Al-ion battery exhibits good charge-recharge properties.
The oxidation pathway and kinetics of titania slag powders in air were analyzed through differential scanning calorimetry (DSC) and thermogravimetry (TG). The oxidation pathway of titania slag powders in air is divided into three stages according to three exothermic peaks and three corresponding mass gain stages displayed in the non-isothermal DSC and TG curves respectively. The isothermal oxidation kinetics of high titania slag powders with different sizes were analyzed through ln-ln analysis method. The entire isothermal oxidation process includes the following two stages. The kinetic mechanism of first stage is described as f(α)=1.77(1-α)[-ln(1-α)]((1.77-1)/1.77),f(α)=1.97(1-a)[-ln(1-a)]((1.97-1)/1.97), and f(α)=1.18(1-α)[-ln(1-α)]((1.18-1)/1.18); whereas the kinetic mechanism of second stage for all samples can be described as[1-(1-α)(1/3)]2=kt. The activation energies of titania slag powders with different sizes (d1 < 0.075 mm, 0.125 < d2 < 0.150 mm, and 0.425 < d3 < 0.600 mm) at different reaction degrees are calculated. Under the current experimental conditions, the rate-controlling step at the first oxidation stage of all samples is a chemical reaction. The rate-controlling steps at the second oxidation stage are the chemical reaction and internal diffusion (d1<0.075 mm) and the internal diffusion (0.125 < d2 < 0.150 mm and 0.425 < d3 < 0.600 mm).
High-voltage pulsed discharge (HVPD) pretreatment was applied to strengthen the leaching effect of Carlin-type gold ore containing arsenic in this work. The optimal results of pretreatment experiments was obtained at the operating conditions of spherical gap spacing 20 mm, pulse numbers 100, and input voltage 90 V. The leaching rate of gold were increased by 15.6% via HVPD pretreatment. The mass fraction of -0.5+0.35 mm and -0.35+0.1 mm were increased by 11.0% and 6.8% compared with untreated samples, respectively, and the Au grade of -0.1 mm was increased by 22.8%. However, the superiority of HVPD pretreatment would be weakened by prolonging grinding time. Scanning electron microscope (SEM) results indicated that the pretreated products presented in the state of melting and then condensation, accompanying by some pore formation. More micro-cracks were generated in the interface of ore and the original crack were expended via pulsed discharge pretreatment, with the contact area between leaching reagent and ore were enlarged, and the leaching reaction rate were enhanced and the leaching effect was strengthened.
The method to produce ferronickel at lower temperature (1250-1400℃) was applied since 1950s at Nippon Yakin Oheyama, Japan. Limestone was used as an additive to adjust the slag composition for lowering slag melting point. The ferronickel product was recovered by means of magnetic separator from semi-molten slag and metal after water quenching. In order to increase the efficiency of magnetic separation, bigger particle size of ferronickel is desired. Therefore, in this study, the influences of CaO, CaF2 and H3BO3 additives on the evolution of ferronickel particle at temperature ≤ 1250℃ were investigated. The experiments were conducted at 900-1250℃ with the addition of CaO, CaF2, and H3BO3. The reduction processes were carried out in a horizontal tube furnace for 2 h under argon atmosphere. The results showed that at 1250℃ with the CaO addition of 10% of the ore weight, the size of ferronickel particles of 20 μm was obtained. The ferronickel particle size can be increased to 165 μm by adding 10% CaO and 10% CaF2. The addition of boric acid further increased the ferronickel particle size to 376 μm as shown by the experiments with the addition of 10% CaO, 10% CaF2 and 10% H3BO3.
Certain inclusions in high-strength 60Si2Mn-Cr spring steel render poor resistance to localized corrosion. In this work, accelerated corrosion tests in 3wt% FeCl3 solution for different time were performed to study the effect of inclusions on the localized corrosion behavior of spring steel. The results show that severe corrosion occur in areas of clustered CaS inclusions. Sulfide inclusions containing Ca and Mg induce the strongest localized corrosion susceptibility. The ability of inducing localized corrosion susceptibility is ranked as MgS > CaS > MnS for the case of (Ca,Mn,Mg)S inclusions. CaS, (Ca,Mn)S, and (Ca,Mn,Mg)S inclusions are mainly responsible for inducing environmental embrittlement.
Graphene is an ideal reinforcing phase for high-performance composite filler, which is of great theoretical and practical significance for improving the wettability and reliability of filler. However, the poor adsorption characteristic between graphene and silver base filler seriously affects the application of graphene-filler in the brazing field. It is a great challenge to improve the adsorption characteristic between graphene and silver base filler. To solve this issue, we studied the adsorption characteristic between graphene and silver with first principle calculation. The effects of Ga, Mo, and W on the adsorption properties of graphene were explored furtherly. There are three possible adsorbed sites, including the hollow site (H); the bridge site (B) and the top site (T). Our research found that the top site is the most preferentially adsorbed site for Ag atom, and there is a strong interaction between graphene and Ag atom due to the doped of metal elements. The doped of metal elements enhances local hybridization between C or metal atoms and Ag. Furthermore, compared with other doped structures (Ga and Mo), W atom doped is not only the most stable adsorption structure but also can improve the effectively adsorption characteristic performance between graphene and Ag.
In this study, continuous drive rotary friction welding (FW) is performed to join cylindrical specimen of carbon steel (EN24) and nickel based superalloy (IN718). The microstructures of three distinguish weld zones such as weld interface (WI)/thermo mechanically affected zone (TMAZ), heat affected zone (HAZ), and base metals were examined. The joint was observed to be free from defects with uneven flash formation. Electron Back Scattered Diffraction (EBSD) analysis shows substantial changes in high angle grain boundaries, low angle grain boundaries and twin boundaries in TMAZ and HAZ areas. Also significant refinement in grain size (2-5μm) was observed at WI/TMAZ with reference to base metals. The possible causes of these are discussed. The microhardness profile across welded joint shows variation in hardness. The changes in hardness were ascribed to grain refinement, phase transformation, and dissolution of strengthening precipitates. The tensile test results reveal that joint efficiency as much as 100% can be achievable by this method.
A 3-D model applying the temperature and carbon concentration-dependent material properties was developed to describe the scrap melting behavior and carbon diffusion under natural convection. The simulated results agreed reasonably well with the experimental ones. The scrap melting was subdivided into four stages of "① formation of a solidified layer; ② rapid melting of the solidified layer; ③ carburization; and ④ carburization + normal melting". The carburization stage could not be ignored at low temperatures as the carburization time for the sample investigated was 214 s at 1573K compared to 12 s at 1723K. The thickness of the boundary layer with significant concentration difference at 1573K increased from 130 μm at 5 s to 140 μm at 60 s. The maximum velocity caused by natural convection decreased from 0.029 m·s-1 at 5 s to 0.009 m·s-1 at 634 s because the differences in temperature and density between the molten metal and scrap decreased with time.
In the present study, open cell steel foams were successfully fabricated through powder metallurgy route using urea granules as water leachable space holder. The influence of different amounts of phosphorus (0, 0.5, 1, 2, and 4 wt.%) was investigated on the cell morphology, porosity percentage, microstructure of cell walls, and mechanical properties of steel foams. The cell morphology and microstructure of cell walls were evaluated using an optical microscope (OM) equipped with image processing software and a scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). In addition, the compression tests were conducted on the steel foams using a universal testing machine. Based on microscopic images, porosities consist of spherical cells and irregularly shaped pores which are distributed in the cell walls. Results indicated that by increasing the phosphorus content, porosity percentage increases from 71.9 to 83.2 percent. The partially distributed ferrite and fine pearlite was observed in the microstructure of cell walls and α-Fe and Fe3P eutectic extended between the boundaries of agglomerated iron particles. Furthermore, elastic and long saw-toothed plateau regions was observed before fracture in the compressional stress-strain curves. According to the results, by increasing the phosphorus content from 0 to 4 wt.%, the plateau region of the stress-strain curves shifts to the right and upward. Therefore, increasing phosphorus content causes improvement in the mechanical properties of steel foams.
Several special mechanical properties such as the dilatancy and compressibility of cemented paste backfilll (CPB) are controlled by the internal microstructure and its evolution. To explore the mesocosmic structure changes of CPB during the development process. Based on the scanning electron microscopy (SEM) and mechanical test results of CPB, the particle size information of CPB was extracted, and a two-dimensional (2D) particle flow code (PFC) model of CPB was established to study the evolution rule of mesoscopic parameters during CPB development. The FISH language of the PFC was used to develop a program for establishing a PFC model according to SEM results. The mesoscopic parameters of CPB samples at different curing times, such as the coordination number (Cn), contact force chain, and rose diagram were obtained by recording and loading; these were used to analyze the intrinsic relationship between mesoscopic parameter variations and macroscopic mechanical response during CPB development. It is of great significance to establish the physical model of CPB by using PFC to reveal the mesoscopic structure of CPB.
The computational simulation and the high temperature measurement of velocities near the mold surface based on the rod deflection method are carried out to study the effects of operation parameters on the flow field in the slab continuous casting mold with narrow width for the production of automobile exposed panels. Reasonable agreement between the calculated results and the measured subsurface velocities of liquid steel is obtained under the different operation parameters of continuous casting process. Based on the simulated results, the flow field on the horizontal plane of 50 mm away from the meniscus can be used as the characteristic flow field for optimizing the flow field of molten steel in the mold. The increased casting speed can increase the subsurface velocity of molten steel and shift down the position of vortex core in the downward circulation zone. The flow field of liquid steel can be improved by a relatively larger Ar gas flow rate of 7 l·min-1 in the slab CC mold with 1040 mm narrow width and 1.7 m·min-1 casting speed. The Double-Roll-Flow (DRF) pattern tends to be stabilized with the 170 mm immersion depth of SEN under the present experimental conditions.
Nanoparticles of Ni0.6-xZn0.4CoxFe2O4 were prepared by aqueous sol-gel auto-combustion route. Ni-Zn-Ferrite system was doped with Co to improve the magnetic properties for application purposes. Structural determination of the phase and crystallite size were found using X-ray diffraction technique. Spinel cubic (single-phase) nanoparticles were formed at some specific x compositions, while at other compositions partial hematite (α-Fe2O3) secondary phase was formed. The tuned values of saturation magnetization directly depend upon the concentration of hematite phase, at this point the value of magnetic saturation become smaller which causes high spin canting effect resulting in decrease in net magnetic moment of the structure. Further doping of Co2+ ions enhances the magnetic properties due to its high magnetic moment and distributions. To cross-check the experimental findings, theoretical analysis was performed using most suitable proposed cations distribution and it supports well. The observed structural and magnetic findings would contribute effectively in electromagnetic-interference-shielding and magnetic-recording-device applications.
Material flow and microstructure evolution during refill friction stir spot welding of alclad 2A12-T4 aluminium alloy are experimentally investigated using the stop-action technique. There are two material flow components, i.e., the inward or outward-directed spiral flow on the horizontal plane and the upward or downward-directed flow on the vertical plane. In the plunge stage, the flowing of plasticized metal into the cavity is similar to a stack where the upper layer is pushed by the lower layer. While in the refill stage, such a process reverses. Therefore, the vertical plasticized metal flow between adjacent layers is unobvious. The welding leads to coarsening of S in the thermo-mechanically affected zone and diminishing of S in the stir zone. Continuous dynamic recrystallization causes formation of fine equiaxed grains in the stir zone, while this process occurs more difficult in the thermo-mechanically affected zone due to the lower magnitude of deformation rate and the pinning action of S precipitates on the dislocations and sub-grain boundaries, leading to high low-angle grain boundaries fraction in this zone.
In order to simulate the wear and corrosion behavior of high-strength EH47 hull steel in a complicated marine environment in which seawater, sea ice, and sea sand coexist, the accelerated wear and corrosion tests were performed in laboratories using a tribometer. The effect of large loads on behavior of abrasion and corrosion in the 3.5wt%NaCl solution with ice and sand to simulate marine environment were investigated. The experimental results showed that the friction coefficient decreases with increased working loads, meanwhile, the loading force and sand on the disk have an greatly influence on the COF. The mechanisms of friction and the coupling effect of abrasion and corrosion in the 3.5wt%NaCl solution with sand were the wear and corrosion mechanisms, furthermore, wear mechanism had the predominant effect.
A NH4HCO3 conversion followed by HCl leaching process was performed and was proved to be effective in extracting lead and strontium from zinc extracted residual. The mechanism of NH4HCO3 conversion and operation conditions, including molar ratio of NH4HCO3 to zinc extracted residual, NH4HCO3 concentration, conversion temperature, conversion time, and stirring velocity were discussed, and the operation conditions were optimized by orthogonal test. The experimental results indicated that NH4HCO3 conversion process in temperature ranging from 25℃ to 85℃ followed the shrinking unreacted core model and was controlled by the inner diffusion through the product layer. The extraction ratios of lead and strontium reached 85.15% and 87.08% under the optimized conditions, respectively. The values of the apparent activation energy E were 13.85 kJ·mol-1 for lead and 13.67 kJ·mol-1 for strontium, respectively.
The present study sought to assess the reductive leaching of indium from indium-bearing zinc ferrite by using oxalic acid as reducer in sulfuric acid solution. The effect of more main factors affecting the procedure on process rate, including the ratio of oxalic acid to sulfuric acid, stirring rate, grain size, temperature and the initial concentration of synergic acid was precisely evaluated. The results confirmed the acceptable efficiency of dissolving indium in the presence of oxalic acid, representing that shrinking-core model with chemical reaction controlling step can describe the kinetics of indium dissolution correctly. Based on the apparent activation energy of 44.55 KJ/mole and reaction order with respect to the acid concentration of 1.14, it was found that the presence of oxalic acid reduces sensitivity to temperature changes and increases the effect of changes in acid concentration. Finally, the equation of kinetic model based on the factors under study was presented.
The research of the fatigue properties of ceramic hard coatings started late, however, with the wide application of coating materials in aerospace and other fields, its safety under fatigue conditions in service is very important. Until now, there is no unified standard to evaluate the fatigue life of the hard coating-ductile substrate system. Even in the research reports, there are different opinions on whether the coating can improve or reduce the fatigue life of the substrate. In this paper, the influence of ceramic coating properties on fatigue performance is reviewed, and the coating effects on the fatigue crack initiation mechanism in the substrate are discussed. The purpose of this review is to help readers understand the fatigue behavior of the hard coating-ductile substrate system.
Molten salts play multiple important roles in the electrolysis of solid metal compounds, particularly oxides and sulfides, for extraction of metals or alloys. Some of these roles are positive in assisting the extraction of metals, such as dissolving the oxide or sulfide anions, and transporting them to the anode for discharging, and offering the high temperature to lower the kinetic barrier to break the metal-oxygen or metal-sulfur bond. However, there are also unfavourable effects, including electronic conduction and significant capability of dissolving oxygen and carbon dioxide gases. In addition, although molten salts are relatively simple in terms of composition, physical properties and decomposition reactions at inert electrodes, in comparison with aqueous electrolytes, the high temperatures of molten salts may promote unwanted electrode-electrolyte interactions. This article reviews briefly and selectively research and development of the FFC Cambridge Process in the past two decades, focusing on observations, understanding and solutions of various interactions between the molten salts and the cathodes at different reduction states, including perovskitisation, non-wetting of molten salts on metals, carbon contamination to products, formation of oxychlorides and calcium intermetallic compounds, and oxygen transfer from air to the cathode product mediated by oxide anions in the molten salt.
Iron and steel making lasts for several thousand years and is based on changing technologies. The driving forces for those changes are economical or disposability of raw material and energy sources. In this paper three challenges for the newly development in iron and steel metallurgy are highlighted: Continuous casting strand size increase, solidification behaviour of new steel grades, and suppression of CO2-emission during iron making. Examples underline the recent process of technological changes. 40 years of Sino German university cooperation in metallurgy are part of those technological development.
Magnesium (Mg) alloys, as the lightest metal engineering materials, have a wide application prospect. However, the strength and ductility of traditional Mg alloys are still relativity low, especially it is difficult to be improved simultaneously. Refining grain size by deformation process is one of the feasible strategies to prepare Mg alloys with high strength and good ductility, based on the grain boundary strengthening and the transition of deformation mechanisms. In this review, effects of grain size on the strength and ductility of Mg alloys are summarized and the fine-grained Mg alloys with high strength and good ductility developed by various severe plastic deformation technologies and improved traditional deformation technologies are introduced. It is demonstrated that although some achievements have been made, effects of grain size on various Mg alloys are rarely discussed systematically and some key mechanisms are not clear, lacking of direct microscopic evidences. This review is expected to be helpful for further developing high-performance fine-grained Mg alloys.
Advanced high strength steels have been widely used to improve crashworthiness and lightweight of vehicles. Hot forming of boron alloyed steels, like 22MnB5, could produce ultrahigh strength steel parts with no springback and accurate control of dimensions, which is very difficult for the popular cold stamping process. Moreover, the hot forming of recently developed medium-Mn steels could have many advantages over the hot formed 22MnB5, e.g. better mechanical properties and lower production cost. In this paper, the hot forming process in automotive industries, the hot formed steel grades, medium-Mn steel grades and their application in hot forming have been all reviewed in depth. In particular, the adaptability of both medium-Mn steels and the present popular 22MnB5 into the hot forming process has been compared thoroughly. Finally, the future researches are suggested on the hot forming of medium-Mn steels for succeeding in commercialization.
Recently, Ni3Al-based alloys have drawn much attention as candidates for high-temperature structural materials due to its excellent comprehensive properties. The microstructure and corresponding mechanical properties of Ni3Al-based alloys are known to be susceptible to the heat treatment. Thus, it is of significance to employ various heat treatments to get the desirable mechanical properties of the alloys. This paper briefly summarized the recent advances about the microstructure evolution which occurs during the heat treatment of Ni3Al-based alloys. Besides of γ' phase and γ phase, the precipitations of β phase, α-Cr precipitates and carbides are also found in Ni3Al-based alloys with various addition of alloying elements. The evolution in morphology, size and volume fraction of various types of secondary phases during heat treatment are reviewed, involving γ' phase, β phase, α-Cr precipitate and carbides, and the kinetics of the growth of precipitates are also analyzed. Furthermore, the influences of heat treatment on the mechanical properties of Ni3Al-based alloys are discussed.
Molten salt is viewed as an excellent medium for chemical reaction, energy transfer, and storage. Molten salt innovative technologies should be developed to recover metals from secondary resources to reserve metals from the primary natural sources. Among these technologies, molten salt electrolysis is an economic and environmentally friendly method for extraction of metals from waste materials. From the perspective of the characteristics of molten salt, the application of molten salt should be comprehensively elaborated in chemistry, electrochemistry, energy, thermal storage, etc. This review discusses further directions for the research and developments of molten salt electrolysis and their use for metal recovery from various metal wastes such as magnet scrap, nuclear waste, and cemented carbide scrap. More attention is placed on the development of various electrolysis methods for different metal containing wastes, overcoming some problems in electrolytes, electrodes, and electrolytic cells. Special focus is given to the future development directions for current associated processing obstacles.
Climate changes because of global warming caused by increasing amounts of greenhouse gases (GHGs) released into the atmosphere, are alarming. Control over greenhouse gas emissions is critically important for the current and future status of mining activities. The mining industry is one of the significant contributors to greenhouses gases. In essence, the anthropogenic greenhouse gases are emitted directly during the actual mining as well as indirectly released by the energy-intensive activities associated with mining equipment, ore transport, and processing industry. Therefore, we reviewed both the direct and indirect GHGs emissions to analyze how mining contributes to climate change. Additionally, we showed how climate change impacts mineral production. This assessment was performed using a GHG inventory model for the gases released from mines undergoing different product life cycles. We also elucidate the key issues and various research outcomes to demonstrate how the mining industry and policymakers can mitigate GHGs emission from the mining sector. The review concludes with an overview of GHG release reduction and mitigation strategies.
The demand for lithium-ion batteries (LIBs) for vehicles is increasing. LIBs use valuable rare metals such as cobalt and lithium and environmentally toxic reagents. LIBs are also necessary to utilize for a long period and to recycle useful materials. The 3R (reduce, reuse, and recycling) of spent LIBs becomes more important considering the circular economy. In this paper, the flowsheets of LIBs treatment process for 3R has been proposed. The reduction of resources, design considering 3R, and reuse method are described. Next, the several technological processes for LIBs for reuse and recycling are introduced from many published papers. The technologies include discharge, sorting, crushing, binder removal, physical separation, pyrometallurgical and hydrometallurgical process. Each process is mainly listed on the tables including the physical, chemical, and biological treatments. Finally, the trend and subject for 3R of LIBs are described.
Strengthening mechanisms in the reduced activated ferritic/martensitic (RAFM) steels have been reviewed. High-angle grain boundaries, subgrain boundaries, nanosized M23C6 and MX carbide precipitates effectively hinder dislocation motion and increase high temperature strength. M23C6 carbide is easy to coarsen under high temperatures and the ability of blocking dislocations is then weakened. The improvement of creep property mainly relies on the reduction of the M23C6 carbide, thus the loss of strength must be compensated by other strengthening mechanisms. The recent progress in development of the RAFM steel is also outlined. To increase creep life, a design strategy of the oxide dispersion strengthened steel is to prevent M23C6 precipitation by reducing the C content, and to introduce high density of nanosized oxide precipitates to offset the reduced strength. Another approach is to apply severe plastic deformation methods, as both subgrains and MX carbides can be substantially refined in the steel. Thermal deformation strengthening of the RAFM steel mainly relies on the thermo-mechanical treatment process to increase the MX carbide and subgrain boundaries, leading to an increase of ~20 times in creep life for the TMT 9Cr-1W-0.06Ta steel compared with the F82H and Eurofer 97 steels under 550℃/ 260 MPa.
Abstract: The purpose of this review is to discuss the application and development of 3D printing technology in the field of rock mechanics and the mechanical behaviors of the 3D-printed specimens based on various available printing materials. This review begins with a brief description of the concepts and principles associated with 3D printing and subsequently systematically elaborates the five major applications of 3D printing technology in the field of rock mechanics, namely, the preparation of rock (including preflawed rock) specimens, joints, and geophysical models, reconstruction of complex rock structures, and bridging experimental testing and numerical simulation. Meanwhile, the mechanical performance of 3D-printed specimens created using six different printing materials, such as polymers, resin, gypsum, sand, ceramics and rock-like geological materials, are reviewed in detail. Afterwards, some improvements that can make these 3D-printed specimens closer to natural rocks and some limitations of 3D printing technology in rock mechanics application are discussed, and some prospects that are required to be investigated in the future are proposed. Finally, a brief summary is presented. This review suggests that 3DP technology, especially when integrating other advanced technologies, such as, computed tomography (CT) scanning, 3D scanning, play great potential in rock mechanics field.
Electroslag remelting (ESR) combines liquid metal refining and solidification structure control in one set. Desulfurization is one of the typical aspects of liquid metal refining during ESR for producing advanced steel and alloy. It involves two patterns, i.e., slag-metal reactions and gas-slag reactions (gasifying desulfurization). This paper reviews the advances in the desulfurization practices of ESR. The effects of processing parameters including the initial sulfur level of consumable electrode, remelting atmosphere, deoxidation schemes of ESR, slag composition, melting rate and electrical parameters on the desulfurization during the ESR are assessed. The interrelation between the desulfurization and the sulfide inclusion evolution during ESR is discussed. The current state of the art in the production of sulfur-bearing steel at a high sulfur level during ESR is also reviewed. The remaining challenges for future work are proposed and discussed in this article.
Recycled concrete aggregate (RCA) derived from demolition waste has been widely explored for use in civil engineering applications. One of the promising strategies globally is to utilize RCA in concrete products. However, the use of RCA in high performance concrete such as self-consolidating concrete (SCC) has only been studied in the past decade. This paper summarizes recent publications on the use of coarse and/or fine RCA in SCC. The high-water absorption and porous structure of RCA, as expected, have been a challenge to produce high fluidity mixture. According to the analysis of published data, a lower strength reduction (within 23% regardless of coarse RCA content) is noticed in SCC as compared with vibrated concrete, possibly attributed to the higher paste content in the SCC matrix which enhances the weak surface layer of RCA and interfacial transition zone. Similarly, SCC tends to become less durable with RCA substitution, though the deterioration can be minimized by using treated RCA through removal and strengthening the adhered mortar. To date, the information reported on the role of RCA on the long-term performance of SCC is still limited, hence a wide range of studies are needed to demonstrate the feasibility of RCA-SCC in field applications.