In this research, high calcium-fly ash (HCFA) collected from the Mae Moh electricity generating plant in Thailand was utilized as a raw material for ceramic production. The main compositions of HCFA characterized by XRF mainly consisted of 28.55 wt% SiO2, 16.06 wt% Al2O3, 23.40 wt% CaO and 17.03 wt% Fe2O3. Due to high proportion of calcareous and ferruginous contents, HCFA was used for replacing the potash feldspar in amounts of 10-40 wt%. The influence of substituting high-calcium fly ash (0-40 wt%) and sintering temperatures (1000-1200 οC) on physical, mechanical, and thermal properties of ceramic-based materials was investigated. The results showed that the incorporation of HCFA in appropriate amounts could enhance the densification and the strength as well as reduce the thermal conductivity of ceramic samples. High proportion of calcareous and ferruginous constituents in fly ash promoted the vitrification behavior of ceramic samples. As a result, the densification was enhanced by liquid phase formation at optimum fly ash content and sintering temperature. In addition, these components also facilitated a more abundant mullite formation and consequently improved flexural strength of the ceramic samples. The optimum ceramic properties were achieved with adding fly ash content between 10-30 wt% sintered at 1150-1200 οC. At 1200 οC, the maximum flexural strength of ceramic-FA samples with adding fly ash 10-30wt% (PSW-FA(10)-(30)) was obtained in the range of 92.25-94.71 MPa when the water absorption reached almost zero (0.03%). In terms of thermal insulation materials, the increase in fly ash addition had a positively effect on the thermal conductivity, due to the higher levels of porosity created by gas evolving from the inorganic decomposition reactions inside the ceramic-FA samples. The addition of 20-40 wt% high-calcium fly ash in ceramic samples sintered at 1150 οC reduced the thermal conductivity to 14.78-49.25%, while maintaining acceptable flexural strength values (~ 45.67-87.62 MPa). Based on these promising mechanical and thermal characteristics, it is feasible to utilize this high-calcium fly ash as an alternative raw material in clay compositions for manufacturing of ceramic tiles
In this study, the effect of Mg replacement with Al on the discharge capacity of Mg2Cu powder mixture is investigated. The mixture of nanocrystalline powder is prepared via mechanical alloying (MA) technique with a high energy planetary ball mill. In addition, different moles of Al are substituted to Mg2Cu powder (0.05, 0.1, 0.15, 0.2, and 0.3). X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are used to analyze changes in structure, morphology, and grain size. The obtained powder is utilized as an anode in a nickel-metal hydride battery (Ni-MH). In the specimens with 0.05 M Al content, the orthorhombic structure of Mg2Cu is emerged after 5 hours milling. The results reveal that more than 0.2 M Al substitution leads to an appearance of MgCu2 peaks. Al substitution does not affect microstructure uniformity; however, it causes a decrease in crystalline size and lattice parameters. The SAD pattern elucidates that the electrode with the Mg1.9Al0.1Cu chemical composition and 20 hours milling has the maximum discharge capacity.
Effectively extracting lithium from the pyrometallurgical slag of spent lithium-ion batteries at a relatively low temperature remains a great challenge. Herein, potassium carbonate/sodium carbonate (K2CO3/Na2CO3) which could form eutectic molten salts at 720°C were used as the roasting agents for extracting lithium from the pyrometallurgical slag. The lithium is successfully extracted from slag by K2CO3/Na2CO3 roasting followed by water leaching. According to the theoretical calculation results, lengths of Li-O bonds increase after adsorption of K+/Na+, resulting in easily release of Li+ from the lattice of LiAlSi2O6 after roasting with K2CO3/Na2CO3. Moreover, the TG-DSC results indicate that the eutectic phenomenon of K2CO3 and Na2CO3 is observed at 720°C and the reaction of slag and eutectic molten salts happens above 720°C. The X-ray diffraction results suggest that Li+ in slag is exchanged by K+ in K2CO3 which is accompanied by the formation of KAlSiO4, while Na2CO3 is mainly employed as a fluxing agent. The lithium extraction efficiency can reach 93.87% under the following optimal conditions: roasting temperature of 740°C, roasting time of 30 min, leaching temperature of 50°C, leaching time of 40 min and water/roasted samples mass ratio of 10:1. This work provides a new system for extracting lithium from the pyrometallurgical slag of spent lithium-ion batteries.
The effectiveness of Ca or Gd addition on ductility and formability of Mg-Zn-Zr based dilute alloys in deep drawing has not been systematically compared previously. In this study, formable Mg-Zn-Gd-Zr and Mg-Zn-Ca-Zr sheet alloys are produced by hot rolling. These sheets have similarly weakened basal texture, but the sheet of the Mg-Zn-Gd-Zr alloys has higher ductility and formability than that of Mg-Zn-Ca-Zr alloys. The combined addition of 0.2 wt.% Ca and 0.4 wt.% Gd to the Mg-1Zn-0.5Zr (wt.%) alloy leads to a Mg-1Zn-0.4Gd-0.2Ca-0.5Zr alloy that has even better ductility and its formability during deep drawing is comparable to the benchmark Al6016 sheet. An increase in Ca concentration from 0.2 wt.% to 0.5 wt.% leads to decreased sheet ductility and formability, predominantly due to grain boundary embrittlement.
Understanding the structural and electronic properties of calcium silicates is crucial to reveal their difference in hydration reactivity. Here we presented a comprehensive comparison of β-C2S and M3-C3S. The structural properties and Bader charge of β-C2S and M3-C3S in the unit cell, during surface reconstruction and after single water adsorption were investigated using density functional theory. We identified different types of atoms in β-C2S and M3-C3S considering the bonding characteristics and Bader charge. For β-C2S, Ca atoms were divided into two groups and O atoms into four groups. For M3-C3S, Ca atoms were divided into four groups, O atoms into four groups, and Si atoms into three groups. The valance electron distribution on the surface was more uniform than that of the unit cell, indicating some atoms became more reactive after surface relaxation. During water adsorption, electrons of β-C2S and M3-C3S were transferred from the surface to the adsorbed water molecules through position re-distribution and bond formation/breaking. And on this basis, we explored the reason why β-C2S and M3-C3S had activity differences. A type of O atom with special bond characteristics (no O-Si bonds) and high reactivity was observed in the unit cell of M3-C3S. As revealed by Bader charge analysis, the reactivity of Ca and O atoms was generally higher in M3-C3S than in β-C2S. The average valence electron number of Ca/O atoms in β-C2S was 6.437/7.550, while in M3-C3S it was 6.481/7.537. Moreover, the water molecules in M3-C3S gained more electrons at the surface compared to β-C2S. The average valence electron variation of H2O on β-C2S was 0.041 while that on M3-C3S was 0.226.
Cr3+-activated far-red and near-infrared phosphors have drawn much attention owing to their adjustable emission wavelengths and wide applications. Herein, we report a series of Cr3+-doped phosphors with β-Ca3(PO4)2-type structure, of which Ca9Ga(PO4)7:Cr3+ possesses the highest far-red emission intensity due to its strong absorption band of Cr3+ ion. Under the excitation of 440 nm, Ca9Ga(PO4)7:Cr3+ phosphors exhibit a broad emission band ranging from 650 to 850 nm peaking at 735 nm and superimpose two sharp lines centered at 690 and 698 nm. The optimal sample, Ca9Ga0.97(PO4)7:0.03Cr3+, has the internal quantum efficiency of 55.7%. The luminescence intensity of Ca9Ga0.97(PO4)7:0.03Cr3+ phosphor obtained at 423 K can maintain 68.5% of that at room temperature, demonstrating its outstanding luminescence thermal stability. Finally, a phosphor-conversion light-emitting diode was fabricated, indicating that Ca9Ga(PO4)7:Cr3+ phosphor has potential applications in the field of indoor plant cultivation.
Lithium-rich materials possess ultra-high specific capacity, but the redox of oxygen is not completely reversible, resulting in voltage attenuation and structural instability. A stepwise co-precipitation method is used for the first time in this paper to achieve the control of the two-phase distribution through controlling the distribution of transition metal elements and realize the modification of particle surface structure without the aid of heterologous ions. The results of characterization tests show that the content of LiMO2 phase inside the particles and the content of Li2MnO3 phase on the surface of the particles are successfully increased, and the surface induced formation of Li4Mn5O12 spinel phase or some disorderly ternary. The electrochemical performance of the modified sample is as follows: LR (pristine) shows specific discharge capacity of 72.7 mA h g-1 after 500 cycles at 1C, while GR (Modified sample) shows specific discharge capacity of 137.5 mA h g-1 at 1C, and the discharge mid-voltage of GR still remains above 3 V when cycling to 220 cycles at 1C (mid-voltage of LR remains above 3 V when cycling to 160 cycles at 1C). Therefore, deliberately regulating the local state of the two phases is an successful way to reinforced the material structure and inhibition the voltage attenuation.
Self-assembled process for device functional layers is a simple, feasible and energy-saving strategy. In mesoporous PSCs, compact and scaffold TiO2 films generally function as the hole blocking and electron transporting layers, respectively. However, they are both typically generated through high-temperature annealing. Here, we deposited TiO2 compact films by a room-temperature self-assembled process, which were conducted as an effective hole blocking layer for perovskite solar cells. The thickness of TiO2 compact films can be easily controlled by the deposition time. By optimizing the TiO2 compact films (80 nm), the power conversion efficiency of mesoporous perovskite solar cells without and with hole conductor layers was up to 10.66% and 17.95%, respectively. Interestingly, an all-low-temperature planar perovskite solar cell with the self-assembled TiO2 layer achieve power conversion efficiency of 16.42%.
A diatomite-based porous ceramic support has been prepared using solid-phase sintering and low-temperature calcination processes. Using diatomite as the main raw material, adding appropriate amount of tourmaline and sintering aids to the glaze, and combining different heat treatment temperatures of the glaze layer, tourmaline/diatomite-based interior wall tiles are prepared. The glaze layer under different heat treatment temperatures is characterized by thermogravimetric-differential thermal analysis, X-ray diffraction and scanning electron microscope. The influences of heat treatment temperature on the microscopic morphology and structure of the glaze layer are analyzed. Taking formaldehyde as the target degradation product, the effects of tourmaline/diatomite-based interior wall tiles on the removal of formaldehyde under different heat treatment temperatures of the glaze layer are investigated. The results show that with the increase of heat treatment temperature, the original pores of diatomite decreases, and the specific surface area, and the structure of tourmaline changes. The surface structure of the material is slightly damaged at 850℃, the strength is increased, and the removal effect of formaldehyde is better. In a 1 m3 environmental chamber, the formaldehyde removal rate reaches 73.6% in 300 min. When the temperature is increased to 950℃ and above, diatomite and the structure of tourmaline are destroyed, and the ability of the material to adsorb and degrade formaldehyde decreases.
The mica was used as a supporting matrix for composite phase change materials (PCMs) because of its distinctive morphology and structure in this work. Mica-based composite PCMs were prepared by vacuum impregnation method using mica as supporting material and polyethylene glycol (PEG) as phase change material. Fourier transform infrared (FTIR) and X-ray diffraction (XRD) analysis confirmed that the addition of PEG had no effect on the crystal structure of mica, and no chemical reaction between PEG and mica during the vacuum impregnation process, and no new substance was formed. The maximum load of mica stabilized PEG is 46.24%, the phase change temperature of M400/PEG is 46.03°C, and the latent heat values of melting and cooling are 77.75 J g-1 and 77.73 J g-1, respectively. The thermal conductivity of M400/PEG is 2.4 times that of pure PEG. The thermal infrared images indicated that the thermal response of M400/PEG was improved compared with that of pure PEG. The leakage test confirmed that mica could stabilize PEG, and M400/PEG had great form-stabilized property. These results demonstrate that M400/PEG has potential in the field of building energy conservation.
In this paper, hot deformation behavior of Mn18Cr18N and Mn18Cr18N+Ce high nitrogen austenitic stainless steel at 1173~1473 K and 0.01~1 s-1 are investigated by thermal compression tests. Influence mechanism of Ce on the hot deformation behavior is analyzed by Ce-containing inclusions and segregation of Ce. The results show that, after adding Ce, large, angular, hard and brittle inclusions (TiN-Al2O3, TiN and Al2O3) can be modified to fine and dispersed Ce-containing inclusions (Ce-Al-O-S and TiN-Ce-Al-O-S). During the solidification, Ce-containing inclusions can be used as heterogeneous nucleation particles to refine as-cast grains. During the hot deformation, Ce-containing inclusions can pin dislocation movement and grain boundary migration, induce dynamic recrystallization (DRX) nucleation, and avoid the formation and propagation of micro cracks and gaps. In addition, During the solidification, Ce atoms will enrich at the front of solid-liquid interface, resulting in composition supercooling and refining the secondary dendrites. Similarly, during the hot deformation, Ce atoms tend to segregate at the boundaries of DRX grains, inhibiting the growth of grains. Under the synergistic effect of Ce-containing inclusions and Ce segregation, although the hot deformation resistance and hot deformation activation energy are improved, DRX is more likely to occur and the size of DRX grains is significantly refined, and the problem of hot deformation cracking can be alleviated. Finally, the microhardness of samples was measured. The results showed that, compared with as-cast samples, the microhardness of hot-deformed samples increases significantly, and with the increase of DRX degree, the microhardness decreases continuously. In addition, Ce can affect the microhardness of Mn18Cr18N steel by affecting as-cast and hot deformation microstructure.
The effect of anodic polarization on plastic deformation behavior and formability of FeSi6.5 steel at room temperature was experimentally investigated through uniaxial tensile and drawing of wire specimen in sulfuric acid solution with current densities of 0-40 mA/cm2. The formability of the FeSi6.5 steel was significantly improved after the anodic polarization. The plastic elongation of the specimen as an anode in the electrochemical environment was 4.4-7%, but 2.7% in the air. The drawing force under the anodic polarization decreased by 12.5-26% compared to that in deionized water. The softening is mainly attributed to the relief in work hardening caused by surface atomic dissolution. The work hardening mechanism of the FeSi6.5 steel wires under anodic polarization condition was analyzed using Hollomon equation and Voce relation combined with the K-M approach. These data support the view that the surface atom dissolution facilitates dislocation slip. FeSi6.5 steel wires were obtained using electrochemical cold drawing and presented a smooth surface and good ductility without crack after five-pass drawing with a total cross-section area reduction of 88%. The drawing with the assistance of anodic polarization is a promising technology for processing hard and brittle metal materials.
In this work, a low-alloyed Mg-2Zn-0.8Sr-0.2Ca matrix composite reinforced by TiC nano-particles is successfully prepared by semi-solid stirring under the assistance of ultrasonic and then the as-cast composite is hot extruded. The results indicate that the volume fraction of dynamical recrystallization and the recrystallized grain size have a certain decline at lower extrusion temperature or rate. The finest grain size of ~0.30 µm is obtained in the sample extruded at 200℃ and 0.1 mm/s. The as-extruded sample displays a strong basal texture intensity, and the basal texture intensity increases to 5.937 mud while the extrusion temperature increases from 200℃ to 240℃. The ultra-high mechanical properties (ultimate tensile strength of 480.2 MPa, yield strength of 462 MPa) are obtained after extrusion at 200℃ with a rate of 0.1 mm/s. Among all strengthening mechanisms for the present composite, grain refinement contributes the most to the increase in strength. A mixture of cleavage facets and dimples are observed in the fracture surfaces of three as-extruded nanocomposites, which explain a mix of brittle-ductile fracture way of the samples.
Transition metal phosphides (TMPs) have exhibited decent performance for oxygen evolution reaction (OER), which is a kinetic bottleneck in many energy storages and conversion systems. However, most reported catalysts are composed of three or fewer metallic components, and the investigation of Multicomponent TMPs with more than four metallic components is hindered by their intrinsic complexity in rationally design the structure and fundamentally comprehension in the component-activity correlation. Here, we reported a facile strategy for combining TMPs with tunable elemental compositions (Ni, Fe, Mn, Co, Cu) on a two-dimensional titanium carbide (MXene) flake through a hydrothermal growth and subsequent phosphorization. The obtained TMPs/MXene hybrid nanostructures present homogeneously distributed elements, high electrical conductivity, and strong interfacial interaction, resulting in an accelerated reaction kinetics and long-term stability. OER performance of catalysts with different components was compared and the results show that NiFeMnCoP/MXene is the most active one with a low overpotential of 240 mV at 10 mA cm-2, a small Tafel slope of 41.43 mV dec-1, and a robust long-term electrochemical stability. The electrocatalytic mechanism investigation revealed that the enhanced OER performance of NiFeMnCoP/MXene results from a strong synergistic effect of the multi-elemental composition. Our work, therefore, provides a scalable synthesis route for multi-elemental TMPs and a valuable guideline for designing efficient MXene-supported catalysts.
The ordinary cemented tailings backfill (CTB) was a cement-based composite prepared from tailings, cementitious materials and water. In this study, a series of laboratory tests including uniaxial compression, digital image correlation (DIC) measurement and scanning electron microscope (SEM) characteristics of fiber-reinforced CTB (FRCTB) was conducted to obtain the uniaxial compressive strength (UCS), failure evolution and microstructural characteristics of FRCTB specimens. The results have shown that: adding fibers could increase the UCS values of the CTB by 6.90 to 32.76%. The UCS value of the FRCTB increased with the PP fiber content increased. Besides, the reinforcement effect of PP fiber on the CTB was better than that of glass fiber. Besides, the addition of fiber could increase the peak strain of the FRCTB by 0.39 to 1.45%. And the peak strain of FRCTB increased with the glass fiber content increased. The failure pattern of FRCTB was coupled with tensile and shear failure. The addition of fiber effectively inhibited the propagation of cracks, and the bridging effect of cracks by the fiber effectively improved the mechanical properties of the FRCTB. The findings in this study can provide a basis for the backfilling design and optimization of backfilling method mining.
The objective of this work is to study the improvement effect of Sm on Mn-based catalysts for selective catalytic reduction (SCR) of NO with NH3. A series of SmxMn0.3–xTi catalysts (x = 0, 0.1, 0.15, 0.2, 0.3) were prepared by co-precipitation. The activity tests indicated that the Sm0.15Mn0.15Ti catalyst showed superior performances with NO conversion of 100% and N2 selectivity above 87% at 180–300°C. The characterizations showed that the doping of Sm suppressed the crystallization of TiO2 and Mn2O3 phases, and increased the specific surface area and acidity. Especially, the surface area increased from 152.2 m2·g−1 of Mn0.3Ti to 241.7 m2·g−1 of Sm0.15Mn0.15Ti. These all contributed to the catalytic activity. The XPS results indicated that the relative atomic ratios of Sm3+/Sm and Oβ/O of Sm0.15Mn0.15Ti were 76.77% and 44.11%, respectively. The existence of Sm contributed to the increase of surface absorbed oxygen (Oβ) and the decrease of the surface concentration of Mn4+, which improved the catalytic activity. In the results of H2-TPR, the presence of Sm induced higher reduction temperature and lower H2 consumption (0.3 mmol g–1) of Sm0.15Mn0.15Ti catalyst than that of Mn0.3Ti catalyst. The decrease of Mn4+ weakened the redox property of the catalysts, and increased the N2 selectivity by suppressing the formation of N2O from both NH3 oxidation and nonselective catalytic reduction reaction. The results of in situ DRIFT spectra revealed that the NH3-SCR of NO over Sm0.15Mn0.15Ti catalyst mainly followed the Eley-Rideal mechanism. The Sm doping increases surface absorbed oxygen and weakens the redox property to improve the NO conversion and N2 selectivity of Sm0.15Mn0.15Ti catalyst.
The Shima yield criterion used in finite element analysis for nickel-based superalloy powder compact during hot isostatic pressing (HIP) was modified through uniaxial compression experiments. The influence of cylindrical capsule characteristics on FGH4096M superalloy powder compact deformation and densification behavior during HIP was investigated through simulations and experiments. Results reveals the simulation shrinkage prediction fitted well with the experimental shrinkage including a maximum shrinkage error of 1.5%. It was shown that the axial shrinkage was 1.7% bigger than radial shrinkage for a cylindrical capsule with the size of Φ50 mm × 100 mm due to the force arm difference along the axial and radial direction of the capsule. The stress deviated from the isostatic state in the capsule led to the uneven shrinkage and non-uniform densification of the powder compact. The ratio of the maximum radial displacement to axial displacement increased from 0.47 to 0.75 with the capsule thickness increased from 2 mm to 4 mm. The pressure transmission was related to the capsule thickness and the capsule material performance, and physical parameters in the HIP process.
The dissolution kinetics of Al2O3 in CaO-Al2O3-SiO2 slags was studied using high-temperature confocal scanning laser microscope at 1773 to 1873 K. The results show that the controlling step during the Al2O3 dissolution was diffusion in the molten slag. It was found that dissolution curves of Al2O3 particles was hardly agreed with the traditional boundary layer diffusion model with the increase of the CaO/Al2O3 of slag. A modified diffusion equation considering slag viscosity was developed to study the dissolution mechanism of Al2O3 in slag. Diffusion coefficients of Al2O3 in slag were calculated as 2.8 ×10-10 to 4.1 ×10-10 m2/s. The dissolution rate of Al2O3 increased with higher temperature, CaO/Al2O3, and particle size. A new model was shown to be vAl2O3 = 0.16 × R01.58 × x3.52 × (T-Tmp)1.11 to predict the dissolution rate and the total dissolution time of Al2O3 inclusions with various sizes.
Rechargeable aqueous magnesium-ion batteries (MIBs) show great promise for low-cost, high-safety, and high-performance energy storage applications. Although manganese dioxide (MnO2) is considered as a potential electrode material for aqueous MIBs, the low electrical conductivity and unsatisfactory cycling performance greatly hinder the practical application of MnO2 electrode. To overcome these problems, herein, a novel Mg-intercalation engineering approach for MnO2 electrode to be used in aqueous MIBs is presented, wherein the structural regulation and electrochemical performance of the Mg-intercalation MnO2 (denoted as MMO) electrode are thoroughly investigated by Density functional theory (DFT) calculations and in-situ Raman investigation. The results demonstrate that the Mg intercalation is essential to adjusting the charge/ion state and electronic band gap of MMO electrode, as well as the highly reversible phase transition of the MMO electrode during the charging–discharging process. Because of these remarkable characteristics, the MMO electrode can be capable of delivering a significant specific capacity of ~419.8 mAh g-1, while exhibiting a good cycling capability over 1000 cycles in 1 M aqueous MgCl2 electrolyte. On the basis of such MMO electrode, we have successfully developed a soft-packaging aqueous MIB with excellent electrochemical properties, revealing its huge application potential as the efficient energy storage devices.
Bi0.5(Na0.68K0.22Li0.10)0.5Ti1-xCoxO3 lead-free perovskite ceramics (BNKLT-xCo, x = 0, 0.005, 0.010, 0.015 and 0.020) were fabricated via the solid-state combustion technique. A small-amount of Co2+ ion substitution into Ti-sites led to modification of the phase formation, microstructure, electrical and magnetic properties of BNKLT ceramics. Coexisting rhombohedral and tetragonal phases were observed in all samples using the XRD technique. The Rietveld refinement revealed that the rhombohedral phase increased from 39 to 88 % when x increased from 0 to 0.020. The average grain size increased when x increased. With increasing x, more oxygen vacancies were generated, leading to asymmetry in the S-E loops. For the composition of x = 0.010, a high dielectric constant (m) of 5384 and a large strain (Smax) of 0.23 % with d33* (Smax/Emax) of 460 pm/V were achieved. The BNKLT-0Co ceramic showed diamagnetic behavior but all of the BNKLT-xCo ceramics exhibited paramagnetic behavior, measured at 50 K.
The recovery of vanadium (V) from stone coal by bioleaching is a promising method. The bioleaching experiments and the biosorption experiments were carried out, aiming to explore the adsorption characteristics of Bacillus mucilaginosus (B. mucilaginosus) on the surface of vanadium-bearing stone coal, and the related mechanisms have been investigated. After bioleaching at 30°C for 28 days, the cumulative leaching rate of V reached 60.2%. The biosorption of B. mucilaginosus on stone coal was affected by many factors. When the leaching system pH=5.0, strong electrostatic attraction between bacteria and stone coal promoted biosorption. Bacteria in the logarithmic growth phase had mature and excellent biosorption properties. The initial bacterial concentration of 3.5×108 cfu/mL was conducive to adhesion, with 38.9% adsorption rate and 3.6×107 cfu/g adsorption quantity. The adsorption of B. mucilaginosus on the stone coal conformed to the Freundlich model and the pseudo-second-order kinetic model. Bacterial surface carried functional groups (-CH2, -CH3, -NH2, et al.), which were highly correlated with the adsorption behavior. In addition, biosorption changed the surface properties of stone coal, resulting in the isoelectric point (IEP) approaching the bacteria. The results of our study could provide an effective reference for the adsorption laws of bacteria on minerals.
Copper nanowires (CuNWs) are promising electrode materials, especially for being used in flexible and transparent electrodes, due to their advantages of earth-abundant, low-cost, high conductivity and flexibility. However, the poor stability of CuNWs against oxidation and chemical corrosion seriously hinders their practical applications. Herein, we propose a facile strategy to improve the chemical stability of CuNWs by in situ coating of carbon protective layer on top of them through hydrothermal carbonization method. The influential factors on the growth of carbon film including the concentration of the glucose precursor (carbon source), hydrothermal temperature and time are systematically studied. By tailoring these factors, carbon layers with thickness of 3-8 nm can be uniformly grown on CuNWs with appropriate glucose concentration around 80 mg mL-1, hydrothermal temperature of 160-170 ℃, and hydrothermal time of 1-3 h. The as-prepared carbon-coated CuNWs show excellent resistance against corrosion and oxidation and are of great potential to be used broadly in various optoelectronic devices.
Li addition is verified to be an effective method to increase the room temperature ductility and formability of Mg alloys. In the present study, the microstructure, texture and tensile properties of extruded Mg–1Zn–xLi (wt%, x=0, 1, 3, 5) alloy sheets were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), and electron backscatter diffraction (EBSD). It is found that Li addition resulted in the grain coarsening and the development of new transverse direction (TD)–tilting and 〈10–10〉 parallel to extrusion direction textures, which was related to the improved dynamic recrystallization and the increased prismatic slip during extrusion. The Mg–1Zn–5Li sheet showed the weakest texture, which contained both basal and TD–tilting oriented grains. No additional phase was formed with Li addition. Tensile properties showed that the yield strength of Mg–1Zn–xLi sheets gradually decreased with increasing Li content, which was mainly related to grain coarsening and texture weakening. In addition, the ductility of the Mg–1Zn–xLi sheet was remarkably enhanced by Li addition. The elongation of the Mg–1Zn–5Li sheet was 30.3% along the transverse direction, which was three times than that of Mg–1Zn sheet. Microstructural analysis implied that this significant ductility enhancement was associated with the improvement activation of prismatic and basal slips during the tensile tests. This study may provide insights into the development of high-ductility, low-density Mg–Zn–Li based alloys.
Al-Mg alloys are an important class of non-heat treatable alloys in which Mg solute and grain size play essential role in their mechanical properties and plastic deformation behaviors. In this work, a novel cyclical continuous expanded extrusion and drawing (CCEED) process was proposed and implemented on an Al-3Mg alloy to introduce large plastic deformation. The results showed that the continuous expanded extrusion mainly improved the ductility, while the cold drawing enhanced the strength of the alloy. With the increased processing CCEED passes, the multi-pass cross shear deformation mechanism progressively improved the homogeneity of the hardness distributions and refined grain size. The grain size of the processed Al-3Mg alloy rods was refined by continuous dynamic recrystallization. And the microstructural evolution was basically influenced by the special thermomechanical deformation conditions during the CCEED process.
Hexavalent chromium (Cr(VI)) compound is useful to various industries but is toxic and carcinogenic. In this research work, we fabricate an amperometric sensor for the determination of Cr(VI), using a titanium dioxide (TiO2)-reduced graphene oxide (rGO) composite as the sensing element. The composite was synthesized following sol-gel chemistry, yielding TiO2 nanoparticles of ~50 nm in size, immobilized on chemically exfoliated rGO sheets. The composite was employed in a 3-electrode electrochemical cell and operated in an amperometric mode, exhibiting good responses to the 50 to 500 ppb Cr(VI). Our best result from pH 3 Mcilvane’s buffer solution reveals the sensitivity of 9.12x10-4 ppb-1 and a detection limit of 6 ppb with no signal interference from 200 ppm Ca(II), 150 ppm Mg(II), and 50 ppb Pb(II). The excellent results of the TiO2-rGO sensor can be attributed to synergic effects between TiO2 and rGO, resulting from the presence of n-p heterojunctions and the formation of the TiO2 nanoparticles on rGO.
The thermal conductivity of diamond particles reinforced copper matrix composite as an attractive thermal management material is significantly lowered by the non-wetting heterointerface. The paper investigates the heat transport behavior between a 200 nm Cu layer and a single-crystalline diamond substrate inserted by a chromium (Cr) interlayer having a series of thicknesses from 150 nm down to 5 nm. The purpose is to detect the impact of the modifying interlayer thickness on the interfacial thermal conductance (h) between Cu and diamond. The time-domain thermoreﬂectance measurements suggest that the introduction of Cr interlayer dramatically improves the h between Cu and diamond owing to the enhanced interfacial adhesion and bridged dissimilar phonon states between Cu and diamond. The h value exhibits a decreasing trend as the Cr interlayer becomes thicker because of the increase in thermal resistance of Cr interlayer. The high h values are observed for the Cr interlayer thicknesses below 21 nm since phononic transport channel dominates the thermal conduction in the ultrathin Cr layer. The findings provide a way to tune the thermal conduction across the metal/nonmetal heterogeneous interface, which plays a pivotal role in designing materials and devices for thermal management applications.
The chemical composition of vanadium slag significantly affects its element distribution and phase composition, which affect the subsequent calcification roasting process and vanadium recovery. In this work, seven kinds of vanadium slags derived from different regions in China were used as the raw materials to study the effects of different components on the vanadium slag’s micromorphology, phase composition, calcification roasting, and leaching rate of major elements using SEM, XRD, and ICP-AES. The results showed that the spinel phase was wrapped with silicate phase in all vanadium slag samples. The main elements in the spinel phase were Cr, V, and Ti from the interior to the exterior. The size of spinel phase in low chromium vanadium slag was larger than other vanadium slags with higher chromium contents. The spinel phase of high-calcium and high-phosphorus vanadium slag was more dispersed. The strongest diffraction peak of vanadium spinel phase in vanadium slag migrated to a higher diffraction angle, and (Fe0.6Cr0.4)2O3 was formed after calcification roasting as the chromium content increased. A large amount of Ca2SiO4 was produced because excess Ca reacted with Si in high-calcium and high-phosphorus vanadium slag. The vanadium leaching rates reached 88% in some vanadium slags. The chromium leaching rates were less than 5% in all vanadium slags. The silicon leaching rate in high-calcium and high-phosphorus vanadium slag was much higher than other slags. The leaching rates of manganese were higher than 10%, and the leaching rate of iron and titanium were negligible.
Nanomaterials have been widely applied to many fields because of their excellent photocatalytic performance. The performance is closely related to the catalytic kinetics, but it is not completely clear that the influencing regularities of shape and particle size on the photocatalytic kinetics of nanomaterials and the photocatalytic kinetic mechanism. In this paper, nano-CeO2 with different shapes and particle sizes were prepared, the kinetic parameters of adsorption and photocatalytic degradation were determined, and the effects of shape and particle size on the kinetics of adsorption and photocatalysis and photocatalytic mechanism were discussed. The results show that the shape and particle size have significant influences. With the decreases of diameter, the performances of adsorption and photocatalysis of nano-CeO2 are improved; and these performances of spherical nano-CeO2 are greater than those of linear nano-CeO2. The shape and particle size have no effects on the kinetic order and mechanism of the whole photocatalytic process. Then a generalized mechanism of photocatalytic kinetics of nanomaterials was proposed and the mechanism rate equation was derived. Finally, the conclusion can be drawn: the desorption of photodegradation products is the control step of photocatalytic kinetics, and the kinetic order of photocatalytic degradation reaction is 1. The mechanism is universal and all nanomaterials have the same photocatalytic kinetic mechanism and order.
ZrC and ZrB2 are both typical ultra-high temperature ceramics, which can be used in hyperthermal environment. In this study, a method for preparing ultrafine ZrC-ZrB2 composite powder is provided, by using the raw materials of nano ZrO2, carbon black, B4C, and metallic Ca. It is worth pointing out that ZrC-ZrB2 composite powder with any proportion of ZrC to ZrB2 could be synthesized by this method. Firstly, a mixture of ZrC and C is prepared by carbothermal reduction of ZrO2. By adjusting the addition amount of B4C, ZrC is boronized by B4C to generate ZrC-ZrB2 composite powder with different compositions. Using this method, five composition powders with different molar ratios (100ZrC, 75ZrC-25ZrB2, 50ZrC-50ZrB2, 25ZrC-75ZrB2, and 100ZrB2) are prepared. When the temperature of boronization and decarburization process is 1473 K, the particle size of product is only tens of nanometres. Finally, the oxidation characteristics of different composite powders are investigated through oxidation experiments. The oxidation resistance of ZrC-ZrB2 composite powder continues to increase as the content of ZrB2 increased.
The low cell voltage during electrolytic Mn from the MnCl2 system can effectively reduce the power consumption. In this work, the Ti/ Sn-Ru-Co-Zr modified anodes were obtained by using thermal decomposition oxidation. The physical parameters of coatings were observed by SEM. Based on the electrochemical performance and SEM/XRD of the coatings, the influences of Zr on electrode performance were studied and analyzed. When the mole ratio of Sn-Ru-Co-Zr = 6:1:0.8:0.3, the cracks on the surface of coatings were the smallest, and the compactness was the best due to the excellent filling effect of ZrO2 nanoparticles. Moreover, the electrode prepared under this condition had the lowest mass transfer resistance and high chloride evolution activity in the 1M NH4Cl + 1.5M HCl system. The service life of 3102 h was achieved according to the empirical formula of accelerated-life-test of the new type anode.
The effect of CaCO3, Na2CO3 and CaF2 on the reduction roasting-magnetic separation of high-phosphorus iron ore containing phosphorus as Fe3PO7 and apatite was investigated. The result shows that Na2CO3 had the best effect on iron recovery and dephosphorization, followed by CaCO3, while CaF2 had almost no influence. The mechanism of CaCO3, Na2CO3 and CaF2 was studied by XRD and SEM-EDS. It turns out that Fe3PO7 was reduced to elemental phosphorus and formed iron phosphorus alloy with metallic iron without additives. The addition of CaCO3 reacted with Fe3PO7 to generate massive Ca3(PO4)2 and promoted the reduction of iron oxides, however, the growth of iron particles was inhibited. After adding Na2CO3, the phosphorus in Fe3PO7 was transferred to nepheline and Na2CO3 improved the reduction of iron oxides and the growth of iron particles, therefore, the recovery of iron and the separation of iron and phosphorus achieved the best. CaF2 reacted with Fe3PO7 to form fine Ca3(PO4)2 particles scattered around the iron particles, which made the separation of iron and phosphorus difficult.
The effects of trace yttrium (Y) element on the microstructure, mechanical properties, and corrosion resistance of Mg-2Zn-0.3Ca-0.1Mn-xY (x=0, 0.1, 0.2, 0.3) biological magnesium alloys are investigated. Results show that grain size decreases from 310μm to 144μm when the Y content increases from 0 wt.% to 0.3 wt.%. At the same time, the volume fraction of the second phase increases from 0.4% to 6.0%, the yield strength of the alloy continues to increase, and the ultimate tensile strength and elongation decrease initially and then increase. When the Y content element increases to 0.3 wt.%, Mg3Zn6Y phase begins to precipitate in the alloy; thus, the alloy exhibits the most excellent mechanical property. At this time, its ultimate tensile strength, yield strength, and elongation are 119MPa, 69MPa, and 9.1%, respectively. In addition, when the Y content is 0.3 wt.%, the alloy shows the best corrosion resistance in the simulated body fluid (SBF). This investigation has revealed that the improvement of mechanical properties and corrosion resistance is mainly attributed to the grain refinement and the precipitated Mg3Zn6Y phase.
TiAl alloy with high Nb content, nominally Ti-45Al-10Nb, was prepared by powder metallurgy, and the oxidation resistance at 850, 900, and 950℃ was investigated. The high-temperature oxidation-resistance mechanism and oxidation dynamics were discussed following the oxide skin morphology and microstructural evolution analysis. The oxide skin structures were similar for 850 and 900℃, with TiO2+Al2O3 mixture covering TiO2 with dispersed Nb2O5. At 950℃, the oxide skin was divided into four sublayers, from the outside to the parent metal: loose TiO2+Al2O3, dense Al2O3, dense TiO2+Nb2O5, and TiO2 matrix with dispersed Nb2O5. The Nb layer suppressed the outward diffusion of Ti atoms, hindering the growth of TiO2, and simultaneously promote the formation of a continuous Al2O3 protective layer, providing the alloy with long-term high-temperature oxidation resistance.
Reverse flotation desilication has been an indispensable step for obtaining high-grade fluorapatite. In this work, Dodecyl Trimethyl Ammonium Bromide (DTAB) was recommended as an efficient collector for the reverse flotation separation of quartz from fluorapatite. Its collectivity for quartz and selectivity for fluorapatite were also compared with the figures corresponding to the conventional collector dodecylamine hydrochloride (DAC) via micro-flotation experiments. The adsorption behaviors of both DTAB and DAC on minerals were systematically investigated with surface chemical analyses such as contact angle determination, zeta potential detection, and adsorption density measurement. It was revealed that compared to DAC, DTAB displayed similar and strong collectivity for quartz, while it showed a better selectivity (or worse collectivity) for fluorapatite, resulting in a high-efficiency for the separation of the two minerals. Surface chemical analyses showed that the adsorption ability of DTAB on quartz surface was as strong as DAC, while the adsorption amount of DTAB on fluorapatite surface was much lower than that of DAC, which associated to the flotation performance well. During the floatation separation of the actual ore, 8% fluorapatite with higher grade can be obtained by using DTAB in contrast to DAC. Therefore, DTAB is a promising collector to the high-efficiency purification and sustainable utilization of the valuable fluorapatite recourses.
Laser shock peening (LSP) is an attractive post-processing method to tailor surface microstructure and enhance mechanical performances of additive manufactured (AM) components. The effects of multiple LSP impacts on the microstructure and mechanical properties of Ti-6Al-4V part produced by electron beam melting (EBM), as a mature AM process, were studied in this work. Microstructure, surface topography, residual stress and tensile performance of EBM-manufactured Ti-6Al-4V specimens were systematically analyzed subjected to different LSP impacts. The distribution of porosities in EBM sample was assessed via X-ray computed tomography. The results show that EBM samples with two LSP impacts possess a lower porosity value of 0.05% compared to the value of 0.08% for untreated samples. The strength of EBM samples with two LSP impacts is remarkably raised by 12% as compared with the as-built samples. The grains of α phase is refined in near-surface layer and a dramatic increase in the depth and magnitude of compressive residual stress (CRS) is achieved in EBM sample with multiple LSP treatments. The grain refinement of α phase and CRS with larger depth are responsible for the strength enhancement of EBM samples with two LSP impacts.
With 3C industries developing rapidly, the demand for high-thermal-conductivity magnesium alloy with high mechanical performance is increasing rapidly. However, the thermal conductivities of most common Mg foundry alloys (such as Mg-9wt.%-1wt%Zn) are still relativity low. In the present study, we developed a high-thermal-conductivity Mg-4Al-4Zn-4RE-1Ca (wt.%, AZEX4441) alloy with good mechanical properties for ultrathin-walled cellphone components via high pressure die casting (HPDC). The HPDC AZEX4441 alloy exhibited a fine homogeneous microstructure (the average grain size is 2.8 μm) with granular Al11RE3, fibrous Al2REZn2, and networked Ca6Mg2Zn3 phases distributed at the grain boundaries. The room-temperature thermal conductivity of the HPDC AZEX4441 alloy was 94.4 W/(m·K), which was much higher than 53.7 W/(m·K) of the HPDC AZ91D alloy. The Al and Zn elements of the AZEX4441 alloy were largely consumed by the formation of Al11RE3 and Al2REZn2 as well as Ca2Mg6Zn3 phases due to the addition of RE and Ca. Therefore, the lattice distortion induced by solute atoms of the AZEX4441 alloy (0.171%) was much lower than that of AZ91D alloy (0.441%), which was responsible for the high thermal conductivity of the AZEX4441 alloy. Furthermore, the AZEX4441 alloy exhibited a high yield strength (YS) of ~185 MPa, ultimate tensile strength (UTS) of ~233 MPa, and elongation of ~4.2%, indicating comparable tensile properties to AZ91D alloy. The results will contribute to developing high-performance Mg alloys with a combination of high thermal conductivity, high strength, and good castability.
An excellent organolead halide perovskite film plays an important role for good-performance perovskite solar cells (PSCs), while there are many defects at perovskite crystals, which is bad for both the photovoltaic properties and the stability of solar cells. Therefore, a strategy of incorporating a complex of CdS and Cd(SCN2H4)2Cl2 into CH3NH3PbI3 active layer is proposed to solve this problem. This study systematically analyzes the effect of different doping concentration of CdS and Cd(SCN2H4)2Cl2 on the performance and stability of PSCs. Our results find that an appropriate incorporation concentration of CdS and Cd(SCN2H4)2Cl2 doped in CH3NH3PbI3 can improve the performance of the prepared solar cells, which is mainly due to that the CdS and Cd(SCN2H4)2Cl2 can effectively passivate the defects at perovskite crystals, thereby suppressing the charge recombination in PSCs and promoting the charge extraction at TiO2/perovskite interface. Furthermore, the stability of PSCs is also significantly improved due to the reduced perovskite crystal defects and enhanced compactness of the C:C:CH3NH3PbI3 composite film.
Since the physical and chemical properties of apatite and dolomite can be similar, the separation of these two minerals is difficult. Therefore, when performing this separation using the flotation method, it is necessary to search for selective depressants. An experimental research was performed on the separation behavior of apatite and dolomite using calcium lignosulfonate as a depressant, and the mechanism by which this occurs was analyzed. The results show that calcium lignosulfonate has a depressant effect on both apatite and dolomite, but the depressant effect on dolomite is stronger at the same dosage. Mechanism analysis shows that the adsorptive capacity of calcium lignosulfonate on dolomite is higher than that of apatite, which is due to the strong reaction between calcium lignosulfonate and the Ca sites on dolomite. In addition, there is a hydrogen bond between calcium lignosulfonate and dolomite, which further prevents the adsorption of sodium oleate to dolomite, thus greatly inhibiting the flotation of dolomite.
The oxidation behaviors of three austenitic cast steels with different morphology of primary carbides at 950°C in air was investigated using SEM, EDS, XRD and FIB/TEM. It was found that their oxidation kinetics followed a logarithmic law and the oxidation rate could be significantly decreased as long as a continuous silica layer formed at the scale/substrate interface. When the local Si concentration was inadequate, the internal oxidation beneath the oxide scale occurred. The spallation of oxides during cooling could be inhibited with the formation of internal oxidation, owing to the reduced mismatch stress between the oxide scale and the substrate. The "Chinese-script" primary Nb(C,N) was superior to the dispersed primary Nb(C,N) in suppressing the oxidation penetration in the interdendritic region by supplying a high density of Cr quick-diffusion channels. In addition, the innermost and the outermost oxidation layers were both found to be enriched with Cr, while the Cr evaporation in the outermost layer was significant when the water-vapor concentration in the environment was high enough. These findings further the understanding regarding the oxidation behavior of austenitic cast steels and will promote the alloy development for exhaust components.
Since ultraviolet (UV) light, as well as blue light, which was part of visible light, was harmful to skin, samarium-cerium compounds containing Sm2O2S were synthesized by co-precipitation method. This kind of compounds blocks not only UV light, but also blue light that is part of visible light. The minimum values of average transmittance (360–450 nm) and band gap of samarium-cerium compounds were 8.90% and 2.30 eV, respectively, which were less than 13.96% and 2.63 eV of CeO2. Elemental analysis (EA), X-ray diffraction (XRD), Fourier transformation infrared (FT-IR), and Raman spectra determined that the samples contained Ce4O7, Sm2O2S, Sm2O3, and Sm2O2SO4. The micro-structure of samples was analyzed by scanning and transmission electron microscopy (SEM, TEM). X-ray photoelectron spectrum (XPS) showed cerium had Ce3+ and Ce4+ valence states, and oxygen was divided into lattice oxygen and oxygen vacancy that was direct cause of the decrease of average transmittance and band gap.
This study investigates hydrochar combustion kinetics using a multi-Gaussian-distributed activation energy model (DAEM) to expand knowledge on combustion mechanisms. The results demonstrate that the kinetic parameters calculated by the multi-Gaussian-DAEM accurately represented the experimental conversion rate curves. Overall, the feedstock combustion could be divided into four stages: the decomposition of hemicellulose, cellulose, lignin, and char combustion. The hydrochar combustion could in turn be divided into three stages: the combustion of cellulose, lignin, and char. The mean activation energy ranges obtained for the cellulose, lignin, and char of the hydrochar were 273.7–292.8, 301.6–334.5, and 355.2–365.1 kJ/mol, respectively, with standard deviations of 2.1–23.1, 9.5–27.4, and 12.1–22.9 kJ/mol, respectively. The cellulose and lignin contents first increased and then decreased with increasing hydrothermal carbonization (HTC) temperature, while the mass fraction of char gradually increased.
Ni-based composite coatings incorporated with nano/micron SiC particles were fabricated via electrochemical co-deposition in Watts bath, followed by the evaluation of their mechanical and anti-corrosion properties. The micrographic observations suggest that the SiC particles with various sizes can be well incorporated to the Ni substrate. X-ray diffraction (XRD) patterns indicate that SiC particles with smaller sizes could weaken the preferential growth of Ni along (2 0 0) facet. In addition, it is found that the incorporated SiC particles with medium micron sizes (8 μm and 1.5 μm) could significantly enhance the micro-hardness of the Ni composite coatings. Nevertheless, electrochemical measurements demonstrate that micron-sized SiC particles would weaken the corrosion resistance of Ni composite coatings ascribed to the structure defects induced. In contrast, the combined incorporation of nanosized (50 nm) SiC particles with medium micron (1.5 μm) ones is capable of promoting the compactness of the composite coatings, which is beneficial to the long-term corrosion resistance with negligible micro-hardness loss.
The effect of Al2O3 on the viscosity and structure of CaO–SiO2–Cr2O3–Al2O3 slags is investigated to facilitate recycling of Cr in steelmaking slags. The slags exhibit good Newtonian behavior at high temperature. The viscosity of acidic slag first increases from 0.825 to 1.141 Pa·s as the Al2O3 content increases from 0 to 10wt% and then decreases to 1.071 Pa·s as the Al2O3 content increases further to 15wt%. The viscosity of basic slag first increases from 0.084 to 0.158 Pa·s as the Al2O3 content increases from 0 to 15wt% and then decreases to 0.135 Pa·s as the Al2O3 content increases further to 20wt%. Furthermore, Cr2O3-containing slag requires less Al2O3 to reach the maximum viscosity than Cr2O3-free slag; the Al2O3 contents at which the behavior changes are 10wt% and 15wt% for acidic and basic slags, respectively. The activation energy of the slags is consistent with the viscosity results. Raman spectra demonstrate that [AlO4] tetrahedra appear initially and are replaced by [AlO6] octahedra with further addition of Al2O3. The dissolved organic phosphorus content of the slag first increases and then decreases with increasing Al2O3 content, which is consistent with the viscosity and Raman results.
The study explores the excellent modification effect of Nb nanocatalyst prepared via surfactant assisted ball milling technique (SABM) on the hydrogen storage properties of MgH2. Optimal catalyst doping concentration was determined by comparing onset decomposition temperature, released hydrogen capacity and reaction rate for different MgH2+ywt% Nb (y = 0, 3, 5, 7, 9) composites. The MgH2+5wt% Nb composite started releasing hydrogen at 186.7℃ and a total of 7.0wt% hydrogen was released in the dehydrogenation process. In addition, 5wt% Nb doped MgH2 also managed to release 4.2wt% H2 within 14 minutes at 250℃ and had the ability to absorb 4.0wt% hydrogen in 30 minutes at 100℃. Cycling tests revealed that MgH2+5wt% Nb could retain 6.3 wt% H2 capacity (89.2%) after 20 cycles. Dehydrogenation and hydrogenation activation energy values were decreased from 140.51±4.74 kJ·mol-1 and 70.67±2.07 kJ·mol-1 to 90.04±2.83 kJ·mol-1 and 53.46±3.33 kJ·mol-1 after doping MgH2 with Nb, respectively. Microstructure analysis proved that homogeneously distributed NbH acted as active catalytic unit for improving the hydrogen storage performance of MgH2. These results indicate SABM can be considered as an option to develop other nanocatalysts for energy related areas.
The interfacial phenomena in mold have great impact on the smooth operation and the quality of the casting product. In this paper, the wetting behavior of CaO-Al2O3-based mold flux with different BaO and MgO contents was studied. The results show that the contact angle between molten flux and IF steel substrate increased from 62.4o to 74.5o with the increase of BaO content from 3wt% to 7wt%, while it decreased from 62.4o to 51.3o with the increase of MgO content from 3wt% to 7wt%. The interfacial tension also increased from 1630.3 to 1740.8 mN/m when the BaO content increased, but it reduced from 1630.3 to 1539.7 mN/m with the addition of MgO. The changes of contact angle and interfacial tension were mainly due to the fact that the bridging oxygen (O0) at the interface was broken into non-bridging oxygen (O-) and free oxygen (O2-) by MgO. However, more O- and O2- connected into O0 when BaO was added, since the charge compensation effect of BaO was so stronger that it offset the effect of providing O2−.
The effective recycling of waste printed circuit boards (WPCBs) can conserve resources and reduce environmental pollution. This study explores the pyrolysis and combustion characteristics of WPCBs in various atmospheres through thermogravimetric and Gaussian fitting analyses. Furthermore, this study analyses the pyrolysis products and combustion processes of WPCBs through thermogravimetric–Fourier transform infrared and thermogravimetric–mass spectrometry analytical techniques. Results show that the pyrolysis and combustion processes of WPCBs do not constitute a single reaction, but rather, they constitute an overlap of multiple reactions. The pyrolysis and combustion process of WPCBs is divided into multiple reactions by Gaussian peak fitting, and the kinetic parameters of each reaction are obtained by the Coats-Redfern method. In an argon atmosphere, pyrolysis consists of the overlap of the preliminary pyrolysis of epoxy resin, pyrolysis of small organic molecules, and pyrolysis of brominated flame retardants. The reaction mechanism functions are G(α)= (1-α)-1-1, G(α) = (1-α)-1-1 and G(α)= [-(1-α)]4 (α is the conversion rate of the reaction, G(α) is the mechanism function of the reaction). The combustion of WPCB in oxygen consists of the overlap of the epoxy resin and brominated flame retardant combustion reactions; the reaction mechanism functions are G(α)= ((1-α)-1/3-1)2 and G(α)= ((1-α)-1/3-1)2. This study provided the theoretical basis for pollution control, process optimization and reactor design of WPCBs pyrolysis.
The effect of Al content (0.035, 0.5, 1 and 2 wt%) on the composition change of steel and slag, as well as inclusion transformation of high manganese steel after equilibrated with CaO-SiO2-Al2O3-MgO slag was studied by method of slag/steel reaction. The experimental results show that, as the initial content of Al increased from 0.035% to 2%, Al gradually replaced Mn to react with SiO2 in slag to avoid the loss of Mn due to the reaction, which caused both Al2O3 in slag and Si in steel to increase, while SiO2 and MnO in slag to reduce. In addition, the type of inclusions also evolved as the initial Al content increased. The evolution route of inclusions was MnO→MnO-Al2O3-MgO→MgO→MnO-CaO-Al2O3-MgO and MnO-CaO-MgO. The shape of inclusions evolved from spherical to irregular, faceted, and finally transformed to spherical. The average size of inclusions presented a trend that was increasing first and then decreasing. The transformation mechanism of inclusions was explored. As the initial content of Al increased, Mg and Ca were reduced from top slag into molten steel in sequence, which consequently caused the transformation of inclusions.
Ni-rich layered material is a kind of high-capacity cathode to meet the requirement of electric vehicles. As for the typical LiNi0.8Co0.1Mn0.1O2 material, the particle formation is significant for electrochemical properties of the cathode. In this work, the structure, morphology and electrochemical performance of LiNi0.8Co0.1Mn0.1O2 secondary particles and single crystals are systematically studied. A lower Ni2+/Ni3+ ratio of 0.66 and a lower residual alkali content of 2280 ppm were achieved on the surface of single crystals. In addition, the single crystals showed a discharge capacity of 191.6 mAh/g at 0.2 C (~12 mAh/g lower than that of the secondary particles) and enhanced electrochemical stability, especially when cycled at 50 °C and in a wider electrochemical window (between 3.0 and 4.4 V vs. Li+/Li). The LiNi0.8Co0.1Mn0.1O2 secondary particles were suitable for applications requiring high specific capacity, whereas single crystals exhibited better stability, indicating that they are more suitable for use in long life requested devices.
Mg alloy casting parts commonly suffer from drawbacks of low surface properties, high susceptibility to corrosion, unsatisfactory absolute strength, and poor ductility, which seriously limit their wide application. Here, a surface nanocrystallization technique, i.e., ultrasonic surface rolling (USR), was applied on an as-cast AZ91 Mg alloy sheet to improve its corrosion resistance and mechanical properties. The USR produces double smooth surfaces with Ra=0.026 μm and gradient nanostructured surface layers on the sheet. Due to this special microstructure modification, the USR sheet exhibits 51% and 50% improvements in tensile yield strength and ultimate strength without visibly sacrificed ductility comparable to its untreated counterpart, as well as a 24% improvement in surface hardness. The USR sheet also shows good corrosion resistance in 3.5% NaCl aqueous solution. The corrosion current density of the USR sheet reduces by 63% after immersion for 1 h, and 25% after immersion for 24 h compared to that of the untreated counterpart. The enhanced strength and hardness are mainly related to the gradient nanostructure. The improved corrosion resistance is mainly ascribed to the decreased surface roughness, nanostructured surface, and residual compressive stress. The present results state that USR is an effective and attractive method to improve multiple properties of Mg alloy casting parts, and thus can be used as an additional and last working procedure to achieve high-performance Mg alloy casting parts.
Duplex stainless steels (DSSs) are suffering from various localized corrosion attacks such as pitting, selective dissolution, crevice corrosion during their service period. It is of great value to quantitatively analyze and grasp the micro-electrochemical corrosion behavior and related mechanism for DSSs on the micrometer or even smaller scales. In this work, scanning Kelvin probe force microscopy (SKPFM) and energy dispersive spectroscopy (EDS) measurements were performed to reveal the difference between the austenite phase and ferrite phase in microregion of DSS 2205. Then traditional electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) tests were employed for micro-electrochemical characterization of DSS 2205 with different proportion phases in Φ40 μm and Φ10 μm micro holes. Both of them can only be utilized for qualitative or semi-quantitative micro-electrochemical characterization of DSS 2205. Coulostatic perturbation method was employed for quantitative micro-electrochemical characterization of DSS 2205. What is more, the applicable conditions of coulostatic perturbation were analyzed in depth by establishing a detailed electrochemical interface circuit. A series of microregion coulostatic perturbations for DSS 2205 with different proportion phases in Φ10 μm micro holes showed that as the austenite proportion increases, the corresponding polarization resistance of microregion increases linearly.
An energy-efficient route was adopted to treat titanium-bearing blast furnace slag (TBBFS) in this study. Titanium, aluminum and magnesium were simultaneously extracted and silicon was separated by sulfuric acid curing in low temperature and low concentration sulfuric acid leaching. The process parameters of sulfuric acid curing TBBFS were systematically studied. Under the optimal conditions, the recovery of titanium, aluminum and magnesium reached 85.96%, 81.17% and 93.82%, respectively. The rapid leaching model was used to limit the dissolution and polymerization of silicon, and the dissolution of silicon was only 3.18%. The mechanism of sulfuric acid curing-leaching was investigated. During the curing process, the reaction occurred rapidly and released heat massively. Under the attack of hydrogen ions, the structure of TBBFS was destroyed, silicate was depolymerized to form filterable silica, and titanium, magnesium, aluminum, and calcium ions were replaced to form sulfates and enriched on the surface of silica particles. Titanium, aluminum, and magnesium were recovered in the leaching solution, and calcium sulfate and silica were enriched in the residue after leaching. This method could effectively avoid the formation of silica sol during the leaching process and accelerate the solid-liquid separation.
Many studies have investigated the selective laser melting (SLM) of AlSi10Mg and AlSi7Mg alloys, but there is still a lack of researches focused on Al-Si-Mg alloys specifically tailored for SLM. In this work, a novel high Mg-content AlSi8Mg3 alloy was specifically designed for SLM. The results showed that this new alloy exhibited excellent SLM processability with the lowest porosity of 0.07%. Massive lattice distortion led to a high Vickers hardness in samples fabricated at a high laser scanning speed due to the precipitation of Mg2Si nanoparticles from the α-Al matrix induced by high-intensity intrinsic heat treatment during SLM. The maximum microhardness and compressive yield strength of the alloy reached 211±4 HV and 526±12 MPa, respectively. After aging treatment at 150 ℃, the maximum microhardness and compressive yield strength of the samples were further improved to 221±4 HV and 577±5 MPa, respectively. These values are higher than those of most known aluminum alloys fabricated by SLM. This paper provides a new idea for optimizing the mechanical properties of Al-Si-Mg alloys fabricated using SLM.
The evolution of inclusions and the formation of acicular ferrite (AF) in Ca–Ti treated steel were systematically investigated after Mg and La addition. The inclusions in molten steel were Ca–Al–O, Ca–Al–Mg–O and La–Mg–Ca–Al–O after Ca, Mg and La addition, respectively. The type of oxide inclusions in final quenched samples was the same as that in molten steel. However, unlike these in molten steel, inclusions were Ca–Al–Ti–O + MnS, Ca–Mg–Al–Ti–O + MnS and La–Ca–Mg–Al–Ti–O + MnS in Mg-free, Mg-containing and La-containing samples, respectively. The inclusions distributed dispersedly in the La-containing sample. In addition, the average size of the inclusions in the La-containing sample was the smallest while the number density of inclusions was the highest. The size of effective inclusions (nucleus of AF formation) was mainly in the range of 1 to 3 μm. And the content of ferrite side plates (FSP) decreased, while the percentage of acicular ferrite (AF) increased by 16.2% due to the increase in the number of effective inclusions in the La-containing sample in this study.
The flotation kinetics of different size fractions of conventional and nanobubbles (NBs) flotation were compared to investigate the effect of NBs on flotation performance of various coal particle size. Six flotation kinetics models were selected to fit the flotation data and NBs were observed on the hydrophobic surface under hydrodynamic cavitation by atomic force microscope (AFM) scanning. The flotation results indicate that the best flotation performance of size fraction at -0.125+0.074 mm can be obtained either in conventional or NBs flotation, NBs increase the combustible recovery of almost all of the size fractions, but increase the product ash content of -0.25-0.074 mm and reduce the product ash content of -0.045 mm at the same time. The first-order models can both be used to fit the flotation data in conventional and NBs flotation, the classical first-order model is the most suitable one. NBs have an obvious enhancement of flotation rate on coarse size fraction (-0.5+0.25 mm) but decrease the flotation rate of the medium size (-0.25+0.074 mm), the improvement of flotation speed on fine coal particles (-0.074 mm) is probably the reason of the better flotation performance of raw sample flotation.
Nanobubbles play a potential role in the application of fine particles flotation. In this work, the identification of nanoentities was identified with contact mode atomic force microscope (AFM). Meanwhile, the influence of setpoint ratio and amplitude of cantilever and the responses of the formed surface nanobubbles to the fluctuations of pH, salt concentrations, and surfactant concentrations in the slurry, were studied respectively. Nanobubbles were found on highly oriented pyrolytic graphite (HOPG) surface as HOPG was immersed in deionized water in the ambient temperature. The coalescence of nanobubbles occurred under contact mode, which provides strong evidence supporting the gaseous nature of these nanostructures on HOPG. The measuring height of surface nanobubbles decreased with the setpoint ratio (Asetpoint/Afree). The change in concentrations of pH and MIBC shows a negligible influence on lateral size and height of the preexisting surface nanobubbles. The addition of LiCl results in a negligible change in lateral size but an obvious change in height of surface nanobubbles. The present results are expected to provide a valuable reference to understand the properties of surface nanobubbles and design nanobubbles-assisted flotation processes.
On the interface of the Cu-Al composite plate from horizontal continuous casting, the eutectic tissue layer thickness accounts for more than 90% of the total interface thickness, and the deformation in rolling forming plays an important role in the quality of the composite plate. The eutectic tissue material on the interface of the Cu-Al composite plate was prepared by changing the cooling rate of ingot solidification and the deformation in hot compression was investigated. The results show that deformation temperature is over 300 ℃, the softening effect of dynamic recrystallization of α-Al is greater than the hardening effect, and uniform plastic deformation of eutectic tissue is caused. The constitutive equation of flow stress in the eutectic tissue layer was established by Arrhenius hyperbolic-sine mathematics model, providing a reliable theoretical basis for the deformation of the Cu-Al composite plate.
Obtaining a uniform interface temperature field plays a crucial role in the interface bonding quality of bimetal compound rolls. Therefore, in this study, an improved electroslag remelting cladding (ESRC) process using external magnetic field is proposed to improve the uniformity of the interface temperature of compound rolls. The improved ESRC comprises a conventional ESRC circuit and an external coil circuit. A comprehensive 3D model, including multi-physics fields is solved to study the effect of external magnetic field on the multi-physics fields and interface temperature uniformity. The simulated results demonstrate that the non-uniform Joule heat and flow fields cause a non-uniform interface temperature in the conventional ESRC. As for the improved ESRC, the magnetic flux density (Bcoil) along the z-axis is produced by an anticlockwise current of the external coil. The rotating Lorentz force is generated from the interaction between the radial current and axial Bcoil. Therefore, the slag pool flows clockwise, which enhances circumferential effective thermal conductivity. As a result, the uniformity of the temperature field and interface temperature improve. In addition, the magnetic flux density and rotational speed of the simulated results are in good agreement with those of the experimental results, which verifies the accuracy of the improved ESRC model. Therefore, an improved ESRC is efficient for industrial production of the compound roll with a uniform interface bonding quality.
The effect of extrusion temperature and ratio on microstructure, hardness, compression, and corrosion behavior of Mg-5Zn-1.5Y alloy were analyzed. The microstructural observations revealed that the cast alloy consists of α-Mg grains, and Mg3Zn6Y and Mg3Zn3Y2 intermetallic compounds, mostly located on the α-Mg grain boundaries. Extruded alloy at higher temperatures showed coarser grain microstructures, whereas those extruded at higher ratios contained finer ones, although more DRXed grains with lower intermetallics were measured at both conditions. Combined conditions of the lower temperature (340°C) and higher ratio (1:11.5) provided higher compressive strengths. However, no significant hardness improvement was achieved. The extrusion process could decrease the corrosion rate of the cast alloy in simulated body fluid for over 80% due to primarily the refined microstructure. The extrusion temperature showed a more pronounced effect on corrosion resistance compared to the extrusion ratio, and the higher the extrusion temperature, the higher the corrosion resistance.
The limited wide applicability of commercial Mg alloys is mainly attributed to the poor corrosion resistance. Addition of alloying elements is the simplest and effective method to improve the corrosion properties. Based on the low-cost alloy composition design, the corrosion behavior of commercial Mg-3Al-Zn (AZ31) alloy bearing minor Ca or Sn element was characterized by scanning Kelvin probe force microscopy, hydrogen evolution, electrochemical measurements and corrosion morphology analysis. Results revealed that the potential difference of Al2Ca/α-Mg and Mg2Sn/α-Mg was ∼230±19 mV and ∼80±6 mV, much lower than that of Al8Mn5/α-Mg (∼430±31 mV) in AZ31 alloy, which illustrated that AZ31-0.2Sn alloy performed the best corrosion resistance, followed by AZ31-0.2Ca, while AZ31 alloy exihited the worst corrosion resistance. Moreover, Sn dissolved into matrix obviously increased the potential of α-Mg and participated in the formation of dense SnO2 film at the interface of matrix, while Ca element was enriched in the corrosion product layer, resulting in the corrosion product layer of AZ31-0.2Ca/Sn alloys more compact, stable and protective than AZ31 alloy. Therefore, AZ31 alloy bearing 0.2wt% Ca or Sn element exhibited excellent balanced properties, which is potential to be applied in commercial more comprehensively.
Nanosized WC/C catalyst was synthesized via a novel ultra-rapid confinement combustion synthesis method. Result showed that the amount of activated carbon (AC) played an important role in the morphology and structure controlling of both the precursor and the final powder. Due to the confinement of the pore structure and large specific surface area of AC, the WC particles synthesized inside the pores of AC had the size of 10-20 nm. When applied to oxygen reduction performance, the half-wave potential was -0.24 V and the electron transfer number was 3.45, which meant that the main reaction process is the transfer of four electrons. The detailed electrocatalytic performance and the underlying mechanism were investigated in this work. Our study provides a novel approach for the design of new composition and structure catalysts which has a certain significance for promoting the commercialization of fuel cells.
In order to study the effects of Nd addition on microstructure and mechanical properties of Mg-Gd-Zn-Zr alloys, the microstructure and mechanical properties of the as-cast Mg-12Gd-2Zn-xNd-0.4Zr (x = 0, 0.5, and 1 wt%) alloys were investigated by using optical microscope, scanning electron microscope, X-ray diffractometer, nano indentation tester, microhardness tester, and tensile testing machine. The results show that the microstructures mainly consist of α-Mg matrix, eutectic phase and stacking faults. The addition of Nd plays a significant role in grain refinement and uniform microstructure. The tensile yield strength and microhardness increase but the compression yield strength decreases with increasing Nd addition, leading to weakening tension-compression yield asymmetry in reverse of the Mg-12Gd-2Zn-xNd-0.4Zr alloys. The highest ultimate tensile strength (194 MPa) and ultimate compression strength (397 MPa) are obtained with 1 wt% Nd addition of the alloy.
Considering high novelty and potential on ultra–high (>80%) or full V–Ti–Magnetite ore under blast furnace smelting, we are conducting a series of works on physics character of high TiO2 bearing blast furnace slag (BFS) for slag optimization. This work discussed the density and surface tension of high TiO2 bearing BFS using the Archimedean principle and the maximum bubble pressure method, respectively. The influence of TiO2 content and MgO/CaO (mass ratio) on the density and surface tension of CaO–SiO2–TiO2–MgO–Al2O3 slags were investigated. Results indicated that the density of slags decreased as increasing TiO2 content from 20 to 30 wt%, but it increased slightly as increasing MgO/CaO from 0.32 to 0.73. In view of silicate network structure, the density and the degree of polymerization (DOP) of network structure have a consistent trend. The addition of TiO2 reduces (Q3)2/(Q2) ratio, decreases DOP, which leads to the decrease of slag density. The surface tension of CaO–SiO2–TiO2–MgO–Al2O3 slags decreased dramatically as increasing TiO2 content from 20 to 30 wt%. Conversely, it increased as increasing MgO/CaO from 0.32 to 0.73. Furthermore, the iso–surface tension lines were obtained under 1723K using the Tanaka developed model in view of Butler formula. It may be useful for slag optimization of ultra–high proportion (>80%) or even full V–Ti–Magnetite ore under BF smelting.
In the present research, the tri-metal Ti-Al-Nb composites were processed through three procedures: hot pressing, rolling, and hot pressing, followed by subsequent rolling. The fabricated composites were then subjected to annealing at 600, 625, and 650 ºC temperatures at different times. Microstructure observation at the interfaces reveals that the increase in plastic deformation strain significantly affects TiAl3 intermetallic layers’ evolution and accelerates the layers’ growth. On the contrary, the amount of applied strain does not significantly affect the evolution of the NbAl3 intermetallic layer thickness. It was also found that Al and Ti atoms’ diffusion has occurred throughout the TiAl3 layer, but only Al atoms diffuse through the NbAl3 layer. The slow growth rate of the NbAl3 intermetallic layer is due to the lack of diffusion of Nb atoms and the high activation energy of Al atoms’ reaction with Nb atoms.
The bobbin tool friction stir welding process was used to join 6 mm thick 5A06 aluminum alloy plates. Optical microscope was used to characterize the microstructure. The electron backscatter diffraction (EBSD) identified the effect of non-homogeneous microstructure on the tensile properties. It was observed that the grain size in the top of the stir zone (SZ) is smaller than that in the centre region. The lowest ratio of recrystallization and density of the geometrically-necessary dislocations (GNDs) in the SZ was found in the middle near the thermo-mechanically affected zone (TMAZ) being 22% and 1.15×10-13 m-2, respectively. The texture strength of the heat-affected zone (HAZ) is the largest, followed by that in the SZ, with the lowest being in the TMAZ. There were additional interfaces developed which contributed to the strengthening mechanism, and their effect on tensile strength was analysed. The tensile tests identified the weakest part in the joint at the interfaces, and the specific reduction value is about 93MPa.
This study aims to investigate the effects of heat treatments on microstructures of γ-TiAl alloys. Two Ti-47Al-2Cr-2Nb alloy ingots were manufactured by casting method and then heat treated in two types of heat treatments. Their microstructures were studied by both optical and scanning electron microscopies. The chemical compositions of two ingots were determined. The ingot with lower Al content only obtains lamellar structures while the one higher in Al content obtains nearly lamellar and duplex structures after heat treatment within 1270°C to 1185°C. A small amount of B2 phase is found to be precipitated in both as-cast and heat-treated microstructures. They are distributed at grain boundaries when holding at a higher temperature, such as 1260°C. However, B2 phase is precipitated at grain boundaries and in colony interiors simultaneously after heat treatments happened at 1185°C. Furthermore, the effects of heat treatments on grain refinement and other microstructural parameters are discussed.
The 8-Hydroxyquinoline (8-HQ) intercalated Layered Double Hydroxides (LDH) film as underlayer and sol-gel layer was combined for active corrosion protection of the AM60B magnesium alloy. The LDH, LDH/sol-gel, and LDH@HQ/sol-gel coatings were analyzed using the SEM, FESEM, EDX, XRD, AFM, and EIS methods. The SEM images showed that the surface was entirely coated by the LDH film composed of vertically-grown nanosheets. The same morphology was observed for the LDH/sol-gel and LDH@HQ/sol-gel coatings. Also, almost the same topography was observed for both composite coatings except that the LDH@HQ/sol-gel coating had relatively higher surface roughness. Although the LDH film had the same impedance behavior as the alloy sample in 3.5 wt. % NaCl solution, its corrosion resistance was much higher, which could be due to its barrier properties as well as to the trapping of the chloride ions. Similar to the LDH film, the corrosion resistance of the LDH/sol-gel composite diminished with increasing the exposure time. However, its values were much higher than that of the LDH film, which was mainly related to the sealing of the solution pathways. The LDH@HQ/sol-gel composite showed much better anti-corrosion properties than the LDH/sol-gel coating due to the adsorption of the 8-HQ on the damaged areas through the complexation.
Evolution laws of microstructures, mechanical properties and fractographs after different solution temperatures were investigated through various analyses methods. With the increasing solution temperatures, contents of primary α phase decreased, and contents of transformed β structures increased. Lamellar α grains dominated the characteristics of transformed β structures, and widths of secondary α lamellas increased monotonously. For as-forged alloy, large silicides with equiaxed and rod-like morphologies, and nano-scale silicides were found. Silicides with large sizes might be (Ti, Zr, Nb)5Si3 and (Ti, Zr, Nb)6Si3. Rod-like silicides with small sizes precipitated in retained β phase, exhibiting near 45° angles with α/β grain boundaries. Retained β phases in as-heat treated alloys were incontinuous. 980STA exhibited excellent combinations of room temperature (RT) and 650℃ mechanical properties. Characteristics of fracture surfaces largely depended on the evolutions of microstructures. Meanwhile, silicides promoted the formation of mico-voids.
In order to remove indoor formaldehyde (HCHO) efficiently and cheaply, two kinds of novel amino functionalized diatomite (DE) modified by 3-aminopropyltriethoxysilane (APTS) and glycine (GLY) (i.e. APTS/DE and GLY/DE) were successfully synthesized by wetting chemical method. First, the optimal preparation conditions of the two kinds of amino modified diatomite were determined, and then their microstructure and morphologies were characterized and analyzed. For comparation, a series of batch HCHO adsorption experiments of the two kinds of amino modified diatomite were conducted. According to the experimental results, the pseudo-second-order kinetic model and the Langmuir isotherm model could well describe the adsorption processes, and the maximum adsorption capacity of APTS/DE and GLY/DE prepared under the optimized conditions at 20 ℃ were 5.83 and 1.14 mg·g-1, respectively. In addition, the thermodynamic parameters indicated that the adsorption process is a spontaneous and exothermic process. Overall, the abundant amine groups grafting on the surface of diatomite was derived from Schiff base reaction, which is essential for high-efficient adsorption performance toward HCHO.
The effect of different cooling rates (2.7, 5.5, 17.1, and 57.5 °C/s) on the solidification parameters, microstructure, and mechanical properties of Al-15Mg2Si composites was studied. The results showed that, high cooling rate refined the Mg2Si particles and changed their morphology to the more compacted forms with less microcracking tendency The average radius and fraction of primary Mg2Si particles decreased from 20 µm and 13.5% to about 10 µm and 7.3%, respectively, as the cooling rate increased from 2.7 °C/s to 57.5 °C/s. Increasing the cooling rate also improved the distribution of microconstituents, decreased the size of grains, and reduced the volume fraction of micropores. The mechanical properties results revealed that augmenting the cooling rate from 2.7 °C/s to about 57.5 °C/s increased the hardness and quality index by 25% and 245%, respectively. High cooling rate also changed the fracture mechanism from brittle dominated to a high-energy ductile mode comprising of extensive dimpled zones.
Pure aluminum and boron carbide reinforced aluminum matrix composites with various content (1, 6, 15, 30 wt.%B4C) were fabricated using the powder metallurgy technique. The influence of boron carbide amount on the mechanical and tribological behavior of sintered Al-B4C was examined. The highest density (~2.54 g/cm3), lowest porosity (4%), maximum Vickers hardness (~75 HV), as well as, lowest weight loss (0.4 mg), and lowest specific wear rate (0.00042 mm3/Nm) under a 7 N load were obtained with Al-30B4C composites. Enhancement of 167% in hardness, a decrease of 75.8% in weight loss, and a decrease of 76.7% in specific wear rate under an applied load of 7 N were determined when compared with pure aluminum. Similarly, the SEM images of the worn surface revealed that the narrowest wear grove (0.85 mm) at a load of 7 N was detected at Al-B4C composite and the main wear mechanism was observed as an abrasive wear mechanism. According to the friction analysis, the coefficient of friction between surfaces increased with increasing boron carbide content and decreasing the applied load. In conclusion, boron carbide is an effective reinforcement material in terms of tribological and mechanical performance of Al-B4C composites.
For investigating the impact of an opening and joints with different inclination angles on the mechanical response behavior, the energy evolution characteristics and distribution law of granite specimens, uniaxial loading tests were performed on the parallel jointed rock samples with an opening. The results indicate that there is a trend of first decreasing and then increasing of the strength and deformation parameters with the increase of inclination angle, reaching the minimum values when the inclination angle was 45°. The evolution curves of the elastic strain energy and dissipated energy with strain of the samples show the characteristics of step-like gradual mutation. The peak total energy, elastic strain energy, dissipated energy, and total input energy during the failure of the samples showed significant nonlinear characteristics with increasing inclination angle. The opening and joints as well as the change of the inclination angle had significant influences on the proportion of the elastic strain energy of the samples prior to the peak, resulting in the difference of the distribution law of input energy. Moreover, the energy mechanism of the sample failure was discussed, and the energy release was the internal cause of the sudden destruction of the entire rock mass.
Interfacial bonding, microstructures and mechanical properties of an explosively-welded H68/AZ31B clad plate were systematically studied. It was found that the bonding interface demonstrated a “like-wavy” structure containing three typical zones/layers: 1) diffusion layer adjacent to the H68 brass plate; 2) solidification layer of melted metals at the interface; and 3) a layer at the side of AZ31B alloy which experienced severe deformation. Mixed copper, CuZn2 and α-Mg phases were observed in the melted-solidification layer. Regular polygonal grains with twins were found at the H68 alloy side while fine equiaxed grains due to the recrystallization were found at the AZ31B alloy side near the interface. Nanoindentation results revealed the formation of brittle intermetallic CuZn2 phases at the bonding interface. The interface was bonded well through metallurgical reactions owing to the diffusion of Cu, Zn and Mg atoms across the interface and the metallurgic reaction of partially melted H68 and AZ31B alloys.
Friction pull plug welding (FPPW) of 2219-T87 Tungsten Inert Gas (TIG) welded joint was studied. The microstructures, precipitate evolution, mechanical properties, and fracture morphologies of the joint were analyzed and discussed. Defect-free joints were obtained by using 7,000 r/min rotational speed, 12 mm axial feeding displacement and 20–22 kN axial force. It was found that, within the welding parameters as mentioned above, metallurgical bonding between the plug and plate can be achieved by the formation of recrystallized grains. According to the different microstructural features, the FPPW joint can be divided into different regions, including such as heat-affected zone (HAZ), thermo-mechanically affected zone (TMAZ), recrystallization zone, heat-affected zone in TIG weld (TIG-HAZ), and thermo-mechanically affected zone in TIG weld (TIG-TMAZ). In TIG-TMAZ, the grains were highly deformed and elongated owing to the shear and extrusion form the plug during FPPW process. The hardness distribution showed that TIG-TMAZ was the area with the lowest strength. The main reason of softening in TMAZ was identified as the dissolution of θ' and the coarsening of θ precipitate particles. In tensile test, the FPPW joint welded with 22 kN axial force showed the highest ultimate tensile strength of 237 MPa. The location of crack and facture was found in TIG-TMAZ. The fracture morphology of the tensile sample showed good plasticity and toughness.
Zn-38Al-3.5Cu-1.2Mg composite reinforced by nano SiCp was fabricated by stirring assisted ultrasonic vibration. In order to improve the abrasive resistance of the Zn-38Al-3.5Cu-1.2Mg/SiCp composite, several stabilization treatments with distinct solid solutions and aging temperatures were designed. The results indicate that the optimal stabilization treatment for the 38Al-3.5Cu-1.2Mg/SiCp composite involves a solution treatment at 380 °C for 6 h and aging at 170 °C for 48 h. The stabilization treatment leads to the formation of dispersive and homogeneous nano SiCp. During the friction wear condition, the nano SiCp limits the microstructure evolution from the hard α(Al, Zn) phase to the soft β(Al, Zn) phase. Besides, the increased amount of nano SiCp improves the grain dimension and contributes to abrasive resistance. Furthermore, the initiation and propagation of crack produced in the friction wear process are suppressed by the stabilization treatment, thereby improving the abrasive resistance of the Zn-38Al-3.5Cu-1.2Mg/SiCp composite.
Municipal solid waste incineration bottom ash (BA), fly ash (FA) and pickling sludge (PS), causing severe environmental pollution, were transformed into glass ceramic foams with the aid of CaCO3 as the pore-foaming agent by sintering in this paper. The effect of BA/FA ratio on the phase composition, pore morphology, pore size distribution, physical properties, glass structure unit of the samples was investigated, with results showing that with the increase of BA/FA ratio, the content of glass phase, Si-O-Si and Q3Si units decrease gradually. The glass transmission temperature of the mixture has also been reduced. These leads to the decrease of the glass viscosity, further causing bubble coalescence and uneven pore distribution. Glass ceramic foams with uniform spherical pores (average pore size of 106 μm) would be fabricated, when the content of BA, FA and PS were 35wt%, 45wt% and 20wt% respectively, contributing to the glass ceramic foams of high performance with bulk density of 1.76 g/cm3, porosity of 56.01% and compressive strength exceeding 16.23 MPa. This versatile and low-cost approach brings new insight of synergistically recycling solid wastes.
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.
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 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.
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.
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.
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.
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.
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.
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.
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 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.
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.
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.
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.
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.
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 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.
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.
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.
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.
Porous materials have many promising prospects in such fields as sound insulation, heat barrier, vibration attenuation, and catalysts, due to their special porous structures. Most of the industrial solid wastes such as tailings, coal gangue, and fly ash are rich in silicon. As far as this is concerned. In this regard, the high silicon content makes it a potential raw material for the synthesis of silicon-based multi-porous materials such as zeolites, mesoporous silica, glass ceramics, geopolymer foams, etc. In this mini review, the representative silicon-rich industrial solid wastes (SRISW) are selected as the objects, which focused on the processing and application of silicon porous materials from the aspects of physical and chemical properties of SRISW. The transformation methods of preparing porous materials from silicon rich industrial solid wastes are summarized, and their research status in micro-, meso-, and macro-scale porous materials are concluded, respectively. Also the possible problems existing in the application of silicon-rich industrial solid wastes, and in the preparation of functional porous materials are analyzed, and their developing orientation is prospected. This review should provide a typical reference for the recycling and utilization of industrial solid wastes to develop some sustainable “green materials”.
Current electronic technology based on silicon is approaching to its physical and scientific limits. When facing the compulsory choice of finding a practicable way of potential material alternatives for next generation electronics, carbon-based devices showing numerous superiorities (e.g., fast speed, low power consumption and simple process) combining with the unique nature of versatile allotropes of carbon element are unfolding the promise of upcoming electronics revolution. Now it is the time that carbon electronics are greatly advancing with not only developed preparation but also sophisticated design. In this perspective, the representatives with various dimensions, e.g., carbon nanotubes, graphene, bulk diamond, together with extraordinary performance are reviewed. Based on these members of carbon materials family, the associated state-of-the-art devices and composite hybrid all-carbon structures are also emphasized to embody their inherent dominances in the electronics field. Advances of commercial production with improved cost-efficiency and material quality as well as devices design are ongoingly accelerating to the bright future, and it is virtually even impossible to keep up with this burgeoning situation.
Applying an external field has been known to be a promising method to control the microstructure of materials, leading to their improved performance. In the present paper, the strengthening and toughening behaviors of some typical high-performance structural materials by coupling multi-physics fields, including electrostatic or electric-pulse, thermal, and stress fields, are reviewed in detail. In addition to the general observation that the plasticity of materials could be increased by multi external fields, their strengthening can also be achieved through controlling atomic diffusion or phase transformations. The paper is not limited to the strengthening and toughening mechanisms of the multi-field coupling effects on different types of structural materials, but is intended to provide a generic method to improve both the strength and ductility of the materials. Finally, future prospects about applications of multi external field have also been put forward based on the current works.
Diamond/metal composites are widely used in national defense technology and national production due to their outstanding properties of high thermal conductivity and low expansion. However, the difference of chemical properties leads to the interface incompatibility between diamond and metal, which has an important impact on the properties of the composites. Interfacial modification is an effective way to improve the interfacial bonding and reduce the interfacial thermal resistance. This paper reviews the experimental research on interface modification of diamond/metal composites and the application of material calculation simulation in diamond/metal composites. Combining computational simulation and experiment is an expected method to advance the research of diamond/metal composite interface modification.
Metal halide perovskite solar cells have caused great attention due to their high power conversion efficiency (PCE) and cost-effective solution-processable fabrication, but suffer from poor structure stability. Two-dimensional (2D) Ruddlesden-Popper (RP) metal halide perovskites could address the above issue and possess excellent stability because of the large organic spacer cation around the halide octahedron of perovskites. However, the crystallographic orientation of 2D crystals should be perpendicular to the bottom substrates for realizing fast charge transport and collection of the solar cells. It is still a great challenge to control the crystallographic orientation of the 2D RP perovskites prepared by the solution process. Herein, we reviewed the recent progress of the 2D RP perovskite films with the focus on the crystallographic orientation mechanism and orientation controlling methods. Furthermore, the current issues and prospects of the 2D RP perovskites in the photovoltaic field were also discussed, aiming to shed light on developing and widely applying them in the near future.
High hydrogen absorption and desorption rates are two of significant index parameters for the applications of hydrogen storage tanks. Analysis of the hydrogen absorption and desorption behaviours by the isothermal kinetic models is an efficient way to investigate the kinetic mechanism. Multitudinous kinetic models have been developed to describe the kinetic processes. However, these kinetic models were deduced based on some assumptions and only appropriate for the specific kinetic measurement methods and rate-controlling steps, which is sometimes confusing for application. The kinetic analysis procedures using those kinetic models, as well as the key kinetic parameters, are not clear for many researchers who do not become familiar with this field. These problems will prevent kinetic models and their analysis methods from revealing the kinetic mechanism of hydrogen storage alloys. Thus, this review mainly focuses on the summarisation of the kinetic models based on the different kinetic measurement methods and rate-controlling steps, and the introduction of the analysis procedures and the applications of kinetic models in metal hydrides.
Selective laser melting (SLM), an additive manufacturing (AM) process mostly applied in metal material field, can fabricate complex shaped metal objects with high precision. Nickel-based superalloy possesses excellent mechanical property at elevated temperature and plays an important role in aviation industry. This paper emphasizes the researches of SLM processed Inconel 718, Inconel 625, CM247LC and Hastelloy X which are typical alloys with different strengthening mechanism and operating temperature. The strengthening mechanism and phase change evolution of different Nickel-based superalloy under laser irradiation are discussed. The influence of laser parameter and heat-treatment process on mechanical properties of SLM Nickel-based superalloy are systematically introduced. Moreover, the attractive industrial applications of SLM Nickel-based superalloy and printed components are presented. At last, the development of Nickel-based superalloy materials for SLM technology is prospected.
Considering the valuable compositions and potential environmental hazardousness of titanium-bearing blast furnace slag (BFS), developing efficient and green approaches to utilization of BFS is highly desired for resource economization and environmental protection. In the past decades, many attempts have been adopted to efficiently reuse BFS, and significant advances in understanding the fundamental features and the development of efficient approaches have been made. In this review, we have provided a comprehensive overview of the latest progress on efficient utilization BFS, and discussed the mechanism and characteristics of various approaches, along with their application prospects. In particular, the approaches of extraction and enrichment of titanium-bearing phases from BFS are highlighted due to their high availability of titanium resources. This systemic and comprehensive review may benefit to design new and green utilization route with high efficiency and low cost.
Zeolite derived from coal-based solid wastes (coal gangue and coal fly ash) not only can cope with the environmental problems caused by coal-based solid wastes but also achieve their valuable utilization. In this paper, the physicochemical properties of coal gangue and coal fly ash were introduced. Then the mechanism and application characteristics of the pretreatment processes for zeolite synthesis from coal-based solid wastes were introduced as well. After that, the synthesis processes of coal-based solid waste zeolite and their merits and demerits were summarized in detail. Furthermore, the application characteristics of various coal-based solid waste zeolites and their common application fields were also illustrated. By the end of this review, we propose that alkaline fusion-assisted supercritical hydrothermal crystallization may be an efficient method for synthesizing coal-based solid waste zeolites. Besides, more attention should be paid to the recycling of alkaline waste liquid and the application of coal-based solid waste zeolites in the field of volatile organic compounds adsorption removal.