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To simulate the wear and corrosion behavior of high-strength EH47 hull steel in a complicated marine environment in which seawater, sea ice, and sea sand coexist, accelerated wear and corrosion tests were performed in a laboratory setting using a tribometer. The effect of large loads on the behavior of abrasion and corrosion in a 3.5wt% NaCl solution with ice and sand to simulate a marine environment were investigated. The experimental results showed that the coefficient of friction (COF) decreases with increasing working load; meanwhile, the loading force and sand on the disk strongly influence the COF. The mechanisms of friction and the coupling effect of abrasion and corrosion in the 3.5wt% NaCl solution with sand were the wear and corrosion mechanisms; furthermore, the wear mechanism exerted the predominant effect.
We successfully constructed TiO2-pillared multilayer graphene nanocomposites (T-MLGs) via a facile method as follows: dodecanediamine pre-pillaring, ion exchange (Ti4+ pillaring), and interlayer in-situ formation of TiO2 by hydrothermal method. TiO2 nanoparticles were distributed uniformly on the graphene interlayer. The special structure combined the advantages of graphene and TiO2 nanoparticles. As a result, T-MLGs with 64.3wt% TiO2 showed the optimum photodegradation rate and adsorption capabilities toward ciprofloxacin. The photodegradation rate of T-MLGs with 64.3wt% TiO2 was 78% under light-emitting diode light irradiation for 150 min. Meanwhile, the pseudo-first-order rate constant of T-MLGs with 64.3wt% TiO2 was 3.89 times than that of pristine TiO2. The composites also exhibited high stability and reusability after five consecutive photocatalytic tests. This work provides a facile method to synthesize semiconductor-pillared graphene nanocomposites by replacing TiO2 nanoparticles with other nanoparticles and a feasible means for sustainable utilization of photocatalysts in wastewater control.
The present work employed the X-ray diffraction, scanning electron microscopy, electron backscattered diffraction, and electron probe microanalysis techniques to identify the microstructural evolution and mechanical and abrasive behavior of high carbon steel during quenching-partitioning treatment with an aim to enhance the toughness and wear resistance of high carbon steel. Results showed that, with the increase in partitioning temperature from 250 to 400°C, the amount of retained austenite (RA) decreased resulting from the carbide precipitation effect after longer partitioning times. Moreover, the stability of RA generally increased because of the enhanced degree of carbon enrichment in RA. Given the factors affecting the toughness of high carbon steel, the stability of RA associated with size, carbon content, and morphology plays a significant role in determining the toughness of high carbon steel. The analysis of the wear resistance of samples with different mechanical properties shows that hardness is the primary factor affecting the wear resistance of high carbon steel, and the toughness is the secondary one.
A new concept for producing highly pure Ti metal powder from ilmenite (FeTiO3) is proposed in this article. Titanium nitride (TiN) or titanium oxycarbonitride (TiOxCyNz) could be synthesized in the first step via the simultaneous carbothermal reduction and nitridation (CTRN) of FeTiO3 to remove oxygen roughly. To separate oxygen completely, high-quality TiS2 samples were then synthesized from TiN and TiC using S2 gas, and the clean sulfides were finally reduced to α-Ti powders with spherical morphology using electrolysis in molten CaCl2. X-ray diffraction (XRD), scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray spectroscopy (EDS), and elemental LECO analysis were used to study the phases and microstructures of the sulfides and the electrochemically reduced powders. The Ti powder showed no carbon contamination and consisted of high-purity foil-like Ti sheets with very low oxygen, carbon, and nitrogen contents of less than 0.15wt% O, 0.02wt% C, and 0.003wt% N, respectively. The quality of the Ti powder was much higher than that of the powder obtained using the conventional OS process (proposed by K. Ono and R.O. Suzuki) starting directly from the oxides.
Hydrogen is a promising renewable energy source for fossil-free transportation and electrical energy generation. However, leaking hydrogen in high-temperature production processes can cause an explosion, which endangers production workers and surrounding areas. To detect leaks early, we used a sensor material based on a wide bandgap aluminum nitride (AlN) that can withstand a high-temperature environment. Three unique AlN morphologies (rod-like, nest-like, and hexagonal plate-like) were synthesized by a direct nitridation method at 1400°C using γ-AlOOH as a precursor. The gas-sensing performance shows that a hexagonal plate-like morphology exhibited p-type sensing behavior and showed good repeatability as well as the highest response (S = 58.7) toward a 750 ppm leak of H2 gas at high temperature (500°C) compared with the rod-like and nest-like morphologies. Furthermore, the hexagonal plate-like morphology showed fast response and recovery times of 40 and 82 s, respectively. The surface facet of the hexagonal morphology of AlN might be energetically favorable for gas adsorption–desorption for enhanced hydrogen detection.
Thermomechanical cyclic quenching and tempering (TMCT) can strengthen steels through a grain size reduction mechanism. The effect of TMCT on microstructure, mechanical, and electrochemical properties of AISI 1345 steel was investigated. Steel samples heated to 1050°C, rolled, quenched to room temperature, and subjected to various cyclic quenching and tempering heat treatments were named TMCT-1, TMCT-2, and TMCT-3 samples, respectively. Microstructure analysis revealed that microstructures of all the treated samples contained packets and blocks of well-refined lath-shaped martensite and retained austenite phases with varying grain sizes (2.8–7.9 μm). Among all the tested samples, TMCT-3 sample offered an optimum combination of properties by showing an improvement of 40% in tensile strength and reduced 34% elongation compared with the non-treated sample. Nanoindentation results were in good agreement with mechanical tests as the TMCT-3 sample exhibited a 51% improvement in indentation hardness with almost identical reduced elastic modulus compared with the non-treated sample. The electrochemical properties were analyzed in 0.1 M NaHCO3 solution by potentiodynamic polarization and electrochemical impedance spectroscopy. As a result of TMCT, the minimum corrosion rate was 0.272 mm/a, which was twenty times less than that of the non-treated sample. The impedance results showed the barrier film mechanism, which was confirmed by the polarization results as the current density decreased.
Tailings from the vanadium extraction process are discarded each year as waste, which contain approximately 30wt% of Fe. In our previous work, we extracted Fe and Mn from vanadium slag, and Fe and Mn existed in the form of FeCl2 and MnCl2 after chlorination by NH4Cl to achieve effective and green usage of waste containing Fe and Mn. In this work, square wave voltammetry (SWV) and cyclic voltammetry (CV) were applied to investigate the electrochemical behaviors of Fe2+ and Mn2+ in NaCl–KCl melt at 800°C. The reduction processes of Fe2+ and Mn2+ were found to involve one step. The diffusion coefficients of FeCl2 and MnCl2 in molten salt of eutectic mixtures NaCl–KCl molten salt were measured. The electrodeposition of Fe and Mn were performed using two electrodes at a constant cell voltage. The Mn/Fe mass ratio of the electrodeposited product in NaCl–KCl–2.13wt%FeCl2–1.07wt%MnCl2 was 0.0625 at 2.3 V. After the electrolysis of NaCl–KCl–2.13wt%FeCl2–1.07wt%MnCl2 melted at 2.3 V, the electrolysis was again started under 3.0 V and the Mn/Fe mass ratio of the electrodeposited product was 36.4. This process provides a novel method to effectively separate Fe and Mn from simulated chlorinated vanadium slag.
To further clarify the dewatering performance and torque evolution during the tailings thickening process, a self-made rake was connected to a rheometer to monitor the shear stress and torque. The dewatering performance of the total tailings was greatly improved to a solid mass fraction of 75.33% in 240 min. The dewatering process could be divided into three stages: the rapid torque growth period, damping torque growth period, and constant torque thickening zone. The machine restart was found to have a significant effect on the rake torque; it could result in rake blockage. Furthermore, the simultaneous evolution of the torque and solid mass fraction of thickened tailings was analyzed. A relationship between the torque and the solid mass fraction was established, which followed a power function. Both the experimental and theoretical results provide a reference for the deep cone thickener design and operation to enhance the dewatering performance.
Sm extraction from a LiCl–KCl melt was carried out by forming alloys on various electrodes, including Al, Ni, Cu, and liquid Zn, and the electrochemical behaviors of the resultant metal products were investigated using different electrochemical techniques. While Sm metal deposition via the conventional two-step reaction process was not noted on the inert electrode, underpotential deposition was observed on the reactive electrodes because of the latter’s depolarization effect. The depolarization effects of the reactive electrodes on Sm showed the order Zn > Al > Ni > Cu. Sm–M (M = Al, Ni, Cu, or Zn) alloys were deposited by galvanostatic and potentiostatic electrolysis. The products were fully characterized by XRD and SEM–EDS, and the stability of the obtained M-rich compounds was determined. Finally, the relationship between the electrode potential and type of Sm–M intermetallic compounds formed was assessed on the basis of the observed electrochemical properties and electrodeposits.
This study documents laboratory-scale observation of the interactions between the Ni-based superalloy FGH4096 and refractories. Three different crucibles were tested—MgO, Al2O3, and MgO–spinel. We studied the variations in the compositions of the inclusions and the alloy–crucible interface with the reaction time using scanning electron microscopy equipped with energy dispersive X-ray spectroscopy and X-ray diffraction. The results showed that the MgO and MgO–spinel crucibles form MgO-containing inclusions (Al–Mg oxides and Al–Mg–Ti oxides), whereas the inclusions formed when using the Al2O3 crucible are Al2O3 and Al–Ti oxides. We observed a new MgAl2O4 phase at the inner wall of the MgO crucible, with the alloy melted in the MgO crucible exhibiting fewer inclusions. No new phase occurred at the inner wall of the Al2O3 crucible. We discuss the mechanism of interaction between the refractories and the Ni-based superalloy. Physical erosion was found to predominate in the Al2O3 crucible, whereas dissolution and chemical reactions dominated in the MgO crucible. No reaction was observed between three crucibles and the Ti of the melt although the Ti content (3.8wt%) was higher than that of Al (2.1wt%).
We investigated erosion-corrosion (E-C) and its mitigation on the internal surface of the expansion segment of N80 steel tube in a loop system using array electrode technique, weight-loss measurement, computational-fluid-dynamics simulation, and surface characterization techniques. The results show that high E-C rates can occur at locations where there is a high flow velocity and/or a strong impact from sand particles, which results in different E-C rates at various locations. Consequently, it can be expected that localized corrosion often occurs in such segments. The E-C rate at each location in the expansion segment can be significantly mitigated with an imidazoline derivative inhibitor, as the resulting inhibitor layer significantly impedes the electrochemical reaction rate. However, we found that this inhibitor layer could not effectively reduce the difference in the erosion rates at different locations on the internal surface of the expansion segment. This means that localized corrosion can still occur at the expansion segment despite the presence of the inhibitor.
A type of polymer/ceramic coating was introduced on a magnesium-based nanocomposite, and the nanocomposite was evaluated for implant applications. The microstructure, corrosion, and bioactivity of the coated and uncoated samples were assessed. Mechanical alloying followed by sintering was applied to fabricate the Mg–3Zn–0.5Ag–15NiTi nanocomposite substrate. Moreover, different contents of poly(lactic-co-glycolic acid) (PLGA) coatings were studied, and 10wt% of PLGA content was selected. The scanning electron microscopy (SEM) images of the bulk nanocomposite showed an acceptable homogenous dispersion of the NiTi nanoparticles (NPs) in the Mg-based matrix. In the in vitro bioactivity evaluation, following the immersion of the uncoated and coated samples in a simulated body fluid (SBF) solution, the Ca/P atomic ratio demonstrated that the apatite formation amount on the coated sample was greater than that on the uncoated nanocomposite. Furthermore, assessing the corrosion resistance indicated that the coatings on the Mg-based substrate led to a corrosion current density (icorr) that was considerably lower than that of the substrate. Such a condition revealed that the coating would provide an obstacle for the corrosion. Based on this study, the PLGA/hardystonite (HT) composite-coated Mg–3Zn–0.5Ag–15NiTi nanocomposite may be suitably applied as an orthopedic implant biomaterial.
Cu–Nb microcomposite wire was successfully prepared by a groove rolling process. The effects of groove rolling on the diffraction peaks, microstructure, and properties of the Cu–Nb microcomposite were investigated and the microstructure evolutions and strengthening mechanism were discussed. The tensile strength of the Cu–Nb microcomposite wire with a diameter of 2.02 mm was greater than 1 GPa, and its conductivity reached 68% of the International Annealed Copper Standard, demonstrating the Cu–Nb microcomposite wire with high tensile strength and high conductivity after groove rolling. The results show that an appropriate groove rolling method can improve the performance of the Cu–Nb microcomposite wire.
Crystalline rare-earth (RE) carbonates having large particle size were prepared from the lixivium of weathered crust elution-deposited rare-earth ores using the precipitation method with ammonium bicarbonate as the precipitant. Their chemical composition was studied using elemental and thermogravimetric analyses (TGA), and their structure and morphology were characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results demonstrate that the crystalline rare-earth carbonate is a hydrated basic carbonate or oxycarbonate and not astable intermediate carbonate in the process of thermal decomposition. The particle size of crystalline rare-earth carbonates with large particle size is in the range of 50–200 μm. With an RE2O3 content of up to 95wt%, the quality of crystalline rare-earth carbonates is higher compared to the Chinese National Standard (GB/T 28882–2012). The quality of the product is superior to the Chinese National Standard.
A type of calcium coke was developed for use in the oxy-thermal process of calcium carbide production. The calcium coke was prepared by the co-pyrolysis of coking coal and calcium carbide slag, which is a solid waste generated from the chlor-alkali industry. The characteristics of the calcium cokes under different conditions were analyzed experimentally and theoretically. The results show that the thermal strength of calcium coke increased with the increase in the coking coal proportion, and the waterproof property of calcium coke also increased with increased carbonation time. The calcium coke can increase the contact area of calcium and carbon in the calcium carbide production process. Furthermore, the pore structure of the calcium coke can enhance the diffusion of gas inside the furnace, thus improving the efficiency of the oxy-thermal technology.
The research aims to provide an alternative to austempering treatment of ductile cast iron with a simple and cost-effective heat-treatment process. This goal was accomplished by applying a simple one-step spheroidization heat treatment to the as-cast ductile iron, which would normally possess a coarse pearlitic microstructure to a significant extent. Spheroidization experiments involving isothermal holding below the lower critical temperature (A1) were conducted followed by standard mechanical testing and microstructural characterization for an experimental ductile iron. After improving the spheroidization holding time at a given temperature, the work shows that the ductility and toughness of an as-cast ductile iron can be improved by 90% and 40%, respectively, at the cost of reducing the tensile strength by 8%. Controlled discretization of the continuous cementite network in pearlitic matrix of the ductile iron is deemed responsible for the improved properties. The work also shows that prolonged holding time during spheroidization heat treatment leads to degradation of mechanical properties due to the inhomogenous microstructure formation caused by heterogeneous decomposition and cementite clustering in the material. The main outcome of this work is the demonstration of ductile cast iron’s necking behavior due to spheroidization heat treatment.
At low basicity and low temperature, the dephosphorization behavior and phosphorus distribution ratio (LP) between slag and molten steel in the double slag and remaining slag process were studied with a 180 t basic oxygen furnace industrial experiment. The dephosphorization slags with different basicities were quantitatively analyzed. At the lower basicity range of 0.9–2.59, both LP and dephosphorization ratio were increased as the basicity of dephosphorization slag increased. Dephosphorization slag consisted of dark gray P-rich, light gray liquid slag, and white Fe-rich phases. With increasing basicity, not only did the morphologies of different phases in the dephosphorization slag change greatly, but the area fractions and P2O5 content of the P-rich phase also increased. The transfer route of P during dephosphorization can be deduced as hot metal → liquid slag phase + Fe-rich phase → P-rich phase.
Zinc acetate is used as a raw material to synthesize the desired ZnO in hot solvent by controlling the amount of citric acid (CA) added. Notably, the amount of CA added has a significant relationship with the control of the morphology of ZnO. Spherical ZnO wrapped in nanosheets is synthesized through the secondary crystallization of Zn2+. The optical properties of the ZnO sample are tested through the degradation of organic pollutants. Notably, the photocatalytic properties of ZnO vary with the different amounts of CA added. Exposure of the active crystal face increases the photocatalytic activity of ZnO. In addition, the number of defects on the surface of the ZnO sample increases because of its large specific surface area, thus changing the bandgap of ZnO. Therefore, the resulting sample can respond under visible light.
An improved method of (NH4)2SO4 roasting followed by water leaching to utilize zinc oxidized ores was studied. The operating parameters were obtained by investigating the effects of the molar ratio of (NH4)2SO4 to zinc, roasting temperature, and holding time on zinc extraction. The roasting process followed the chemical reaction control mechanism with the apparent activation energy value of 41.74 kJ·mol−1. The transformation of mineral phases in roasting was identified by X-ray diffraction analysis combined with thermogravimetry–differential thermal analysis curves. The water leaching conditions, including the leaching temperature, leaching time, stirring velocity, and liquid-to-solid ratio, were discussed, and the leaching kinetics was studied. The reaction rate was obtained under outer diffusion without product layer control; the values of the apparent activation energy for two stages were 4.12 and 8.19 kJ·mol−1. The maximum zinc extraction ratio reached 96% while the efficiency of iron extraction was approximately 32% under appropriate conditions. This work offers an effective method for the comprehensive use of zinc oxidized ores.
Rapid flocculation and settlement (FS) of mine tailings is significant for the improvement and development of the filling process, whereas the settlement velocity (SV) of tailings in FS has been recognized as a key parameter to evaluate the settlement effect. However, the influence of temperature on the SV and its mechanism have not been studied. FS experiments on tailings with various ambient temperatures were carried out. The SVs of tailings with a solid waste content of 10wt% and an anionic polyacrylamide content of 20 g·t−1 were measured at different temperatures. The SV presented an “N”-shaped variation curve as the temperature changed from 5 to 40°C. The mechanism of these results can be explained from the perspective of the electric double-layer repulsive force, molecular dynamics, and the polymer flocculation principle, as revealed from the scanning electron microscopy of floc particles. The findings will be beneficial in the design of tailings dewatering processes and save costs in the production of cemented paste backfill.
This study investigated the hot corrosion performance of a dissimilar weldment of Ni-based superalloy and stainless steel joined by CO2-laser welding and improved by high-velocity oxy-fuel (HVOF) coating in a Na2SO4−60wt%V2O5 environment at 900°C. A dissimilar butt joint of AISI 321 and alloy 825 was fabricated by CO2-laser welding with low heat input after obtaining the optimum welding parameters by bead-on-plate trials. The metallurgical and mechanical properties of the laser weldment were evaluated. The tensile test results indicated the occurrence of fracture in the base metal AISI 321 side. The HVOF process was employed to coat Ni−20wt%Cr on the weldment. To evaluate the surface morphology of the corrosion products formed on the uncoated and Ni−20wt%Cr-coated weldments, scanning electron microscopy (SEM) analysis was performed. Energy-dispersive spectroscopy (EDS) was used to determine the different elements present on the surface scales. The existence of oxide phases on the weldments was determined by X-ray diffraction (XRD). The cross sections of the weldments were characterized by SEM with EDS line mapping analysis. The results indicated that the Ni−20wt%Cr-coated weldment exhibited superior hot corrosion resistance due to the development of Cr2O3 and NiCr2O4 protective oxide scales.
Magnesium titanate was prepared directly through external coal reduction of seashore titanomagnetite concentrate and magnesium oxide (MgO). The effects of roasting temperature and the type and dosage of reductants on the purity of generated magnesium titanate particles were systematically investigated. Scanning electron microscopy and energy-dispersive spectroscopy analyses were performed to characterize the magnesium titanate particles and observe their purity under different conditions. Results showed that the roasting temperature remarkably influenced the purity of magnesium titanate. At 1200, 1300, and 1400°C, some magnesium ferrite and magnesium aluminate spinel were dissolved in magnesium titanate. However, as the roasting temperature increased to 1500°C, relatively pure magnesium titanate particles were generated because no magnesium ferrite was dissolved in them. The type and dosage of the reductants also remarkably affected the purity of magnesium titanate. The amount of fine metallic iron disseminated in the magnesium titanate particles obviously decreased when lignite was used as a reductant at a dosage of 70wt%. Thus, high-purity magnesium titanate particles formed. At a roasting temperature of 1500°C and with 70wt% lignite, the magnesium titanate product with a yield of 30.63% and an iron content of 3.01wt% was obtained through magnetic separation.
Duplex-structured TC21 alloy samples were first solution-treated at a higher temperature in the α + β region (940°C) with furnace cooling (FC), air cooling (AC), and water cooling (WC), followed by a second-stage solution treatment at a lower temperature in the α + β region (900°C), and then finally aged at 590°C. The effects of the morphology and quantity of α phases on the structure and properties of the TC21 alloy after the different heat treatments were analyzed. The in-situ tensile deformation process and crack propagation behavior were observed using scanning electron microscopy (SEM). The quantity of equiaxed α phases as well as the thickness of lamellar α phases reduced, the tensile strength increased firstly and then decreased, the elongation decreased with the increasing cooling rate after the first-stage solution treatment. The amount and size of lamellar α phases increased after the second-stage solution treatment because of sufficient diffusion of the alloying elements, thereby leading to increased tensile strength. The amount of dispersed α phases increased after the third-stage aging treatment owing to the increase in the nucleation rate, resulting in a noteworthy strengthening effect. After the third-stage aging treatment, the first-stage FC sample exhibited better mechanical properties because it contained more equiaxed α and βtrans phases than the first-stage AC and WC samples.
The influence of welding speed on the joint microstructures of an austenitic stainless steel (ASS) produced by friction stir welding (FSW) was investigated. The FSW process was conducted using a rotational speed of 400 r/min and welding speeds of 50 and 150 mm/min. The study was carried out using electron backscattered diffraction (EBSD) technique in different regions of the resultant stir zones (SZs). The results show that the texture of the advancing side (AS) was mainly composed of
This study used specularite, a high-gradient magnetic separation concentrate, as a raw material in reverse flotation. An iron concentrate with a grade of 65.1wt% and a recovery rate of 75.31% were obtained. A centrifugal concentrator served as the deep purification equipment for the preparation of iron oxide red pigments, and its optimal rotating drum speed, feed concentration, and other conditions were determined. Under optimal conditions, a high-purity iron oxide concentrate with a grade of 69.38wt% and a recovery rate of 80.89% were obtained and used as a raw material for preparing iron oxide red pigment. Calcining with sulfuric acid produced iron red pigments with different hues. Simultaneously, middlings with a grade of 60.20wt% and a recovery rate of 17.51% were obtained and could be used in blast furnace ironmaking. High-value utilization of specularite beneficiation products was thus achieved.
The microwave-assisted reduction behaviours of two low-grade iron ores having a similar Fe content of 49wt% but distinctly different mineralogical and liberation characteristics were studied. Their performances in terms of the iron grade and recovery as obtained from statistically designed microwave (MW) roasting followed by low-intensity magnetic separation (LIMS) experiments were compared. At respective optimum conditions, the titano-magnetite ore (O1) could yield an iron concentrate of 62.57% Fe grade and 60.01% Fe recovery, while the goethitic ore (O2) could be upgraded to a concentrate of 64.4% Fe grade and 33.3% Fe recovery. Compared with the goethitic ore, the titano-magnetite ore responded better to MW heating. The characterization studies of the feed and roasted products obtained at different power and time conditions using X-ray diffraction, optical microscopy, vibrating-sample magnetometry, and electron-probe microanalysis explain the sequential reduction in the iron oxide phases. Finally, taking advantage of the MW absorbing character of the titano-magnetite ore, a blend of the same with the goethite-rich ore at a weight ratio of 60:40 (O2 : O1) was subjected to MW roasting that resulted in a concentrate of 61.57% Fe grade with a Fe recovery of 64.47%.
The preparation of functional material titanium carbide by the carbothermal reduction of Ti-bearing blast furnace slag with microwave heating is an effective method for valuable metals recovery; it can alleviate the environmental pressure caused by slag stocking. The dynamic dielectric parameters of Ti-bearing blast furnace slag/pulverized coal mixture under high-temperature heating are measured by the cylindrical resonant cavity perturbation method. Combining the transient dipole and large π bond delocalization polarization phenomena, the interaction mechanism of the microwave macroscopic non-thermal effect on the titanium carbide synthesis reaction was revealed. The material thickness range during microwave heating was optimized by the joint analysis of penetration depth and reflection loss, which is of great significance to the design of the microwave reactor for the carbothermal reduction of Ti-bearing blast furnace slag.
This study introduced a novel fabrication of aluminum–carbon nanotube (CNT) composites by employing bulk acoustic waves and accumulative roll bonding (ARB). In this method, CNT particles were aligned using ultrasonic standing wave in an aqueous media, and the arrayed particles were precipitated on the aluminum plate substrate. Then, the plates rolled on each other through the ARB process with four passes. Optical and scanning electron micrographs demonstrated the effective aligning of CNTs on the aluminum substrate with a negligible deviation of arrayed CNTs through the ARB process. The X-ray diffraction pattern of the developed composites showed no peaks for carbon and aluminum carbide. In addition, tensile tests showed that the longitudinal strength of the specimens processed with aligned CNTs was significantly greater than that of the specimens with common randomly dispersed particles. The proposed technique is beneficial for the fabrication of Al–CNT composites with directional mechanical strength.
The effect of three heat processes with different calcium contents on the evolution of inclusions during the ladle furnace refining process of AISI 321 stainless steel was investigated. The size, morphology, and composition of the inclusions were analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. After the addition of aluminum and titanium, the primary oxide in the AISI 321 stainless steel was an Al2O3–MgO–TiOx complex oxide, in which the mass ratio of Al2O3/MgO was highly consistent with spinel (MgO·Al2O3). After calcium treatment, the calcium content in the oxide increased significantly. Thermodynamic calculations show that when the Ti content was 0.2wt%, the Al and Ca contents were less than 0.10wt% and 0.0005wt%, respectively, which was beneficial for the formation of liquid inclusions in molten steel. Moreover, the modification mechanism of calcium on TiN-wrapped oxides in combination with temperature changes was discussed.
The specific distribution characteristics of inclusions along with the sliver defect were analyzed in detail to explain the formation mechanism of the sliver defect on the automobile exposed panel surface. A quantitative electrolysis method was used to compare and evaluate the three-dimensional morphology, size, composition, quantity, and distribution of inclusions in the defect and non-defect zone of automobile exposed panel. The Al2O3 inclusions were observed to be aggregated or chain-like shape along with the sliver defect of about 3–10 μm. The aggregation sections of the Al2O3 inclusions are distributed discretely along the rolling direction, with a spacing of 3–7 mm, a length of 6–7 mm, and a width of about 3 mm. The inclusion area part is 0.04%–0.16% with an average value of 0.08%, the inclusion number density is 40 mm−2 and the inclusion average spacing is 25.13 μm. The inclusion spacing is approximately 40–160 μm, with an average value of 68.76 μm in chain-like inclusion parts. The average area fraction and number density of inclusions in the non-defect region were reduced to about 0.002% and 1–2 mm−2, respectively, with the inclusion spacing of 400 μm and the size of Al2O3 being 1–3 μm.
The dilatometric curves of B1500HS high-strength steel at different heating rates were measured by a Gleeble-3800 thermal simulator and analyzed to investigate the effect of heating rate on austenitization. Results show that the value of starting temperature and ending temperature of austenite transformation increase with the rise of heating rates, whereas the temperature interval of austenite formation decreases. The kinetic equation of austenite transformation was solved using the Johnson–Mehl–Avrami model, and the related parameters of the equation were analyzed by the Kissinger method. For those calculations, the activation energy of austenite transformation is 1.01 × 106 J/mol, and the values of kinetic parameters n and ln k0 are 0.63 and 103.03, respectively. The relationship between the volume fraction of austenite and the heating time at different heating rates could be predicted using the kinetic equation. The predicted and experimental results were compared to verify the accuracy of the kinetic equation. The microstructure etched by different corrosive solutions was analyzed, and the reliability of kinetic equation was further verified from the microscopic perspective.
NH4HCO3 conversion followed by HCl leaching was performed and proven to be effective in extracting Pb and Sr from zinc extracted residual. The mechanism and operating conditions of NH4HCO3 conversion, including molar ratio of NH4HCO3 to zinc extracted residual, NH4HCO3 concentration, conversion temperature, conversion time, and stirring velocity, were discussed, and operating conditions were optimized by the orthogonal test. Experimental results indicate that NH4HCO3 conversion at temperatures ranging from 25 to 85°C follows the shrinking unreacted core model and is controlled by inner diffusion through the product layer. The extraction ratios of Pb and Sr under optimized conditions reached 85.15% and 87.08%, respectively. Moreover, the apparent activation energies of Pb and Sr were 13.85 and 13.67 kJ·mol−1, respectively.
For the purpose of exploring a potential process to produce FeMn, the effects of microwave heating on the carbothermal reduction characteristics of oxidized Mn ore was investigated. The microwave heating curve of the mixture of oxidized Mn ore and coke was analyzed in association with the characterization of dielectric properties. The comparative experiments were conducted on the carbothermal reductions through conventional and microwave heatings at temperatures ranging from 973 to 1373 K. The thermogravimetric analysis showed that carbothermal reactions under microwave heating proceeded to a greater extent and at a faster pace compared with those under conventional heating. The metal phases were observed in the microstructures only under microwave heating. The carbothermal reduction process under microwave heating was discussed. The electric and magnetic susceptibility differences were introduced into the thermodynamics analysis for the formation of metal Mn. The developed thermodynamics considered that microwave heating could make the reduction of MnO to Mn more accessible and increase the reduction extent.
This study was undertaken to investigate the tensile properties and hot tearing susceptibility of cast Al–Cu alloys containing excess Fe (up to 1.5wt%) and Si (up to 2.5wt%). According to the results, the optimum tensile properties and hot tearing resistance were achieved at Fe/Si mass ratio of 1, where the α-Fe phase was the dominant Fe compound. Increasing the Fe/Si mass ratio above unity increased the amounts of detrimental β-CuFe platelets in the microstructure, deteriorating the tensile properties and hot tearing resistance. Decreasing the mass ratio below unity increased the size and fraction of Si needles and micropores in the microstructure, also impairing the tensile properties and hot tearing resistance. The investigation of hot-torn surfaces revealed that the β-CuFe platelets disrupted the tear healing phenomenon by blocking interdendritic feeding channels, while the α-Fe intermetallics improved the hot tearing resistivity due to their compact morphology and high melting point.
The oxidation of oxygen ions and the generation of an anode effect at a low oxygen content of 150 mg/kg were discussed in this paper. Cyclic voltammetry and square-wave voltammetry tests were conducted to explore the anodic processes of LiF–NdF3 melt after a lengthy period of pre-electrolysis purification at 1000°C (during which the oxygen content reduced from 413 to 150 mg/kg). The oxidation process of oxygen ions was found to have two stages: oxidation product adsorption and CO/CO2 gas evolution. The adsorption stage was controlled by diffusion, whereas the gas evolution was controlled by the electrochemical reaction. In comparison with oxygen content of 413 mg/kg, the decrease in the amplitude of the current at low oxygen content of 150 mg/kg was much gentler during the forward scanning process when the anode effect occurred. Fluorine-ion oxidation peaks that occurred at about 4.2 V vs. Li/Li+ could be clearly observed in the reverse scanning processes, in which fluorine ions were oxidized and perfluorocarbons were produced, which resulted in an anode effect.
In last decade, the utilization of CO2 resources in steelmaking has achieved certain metallurgical effects and the technology is maturing. In this review, we summarized the basic reaction theory of CO2, the CO2 conversion, and the change of energy-consumption when CO2 was introduced in converter steelmaking process. In the CO2–O2 mixed injection (COMI) process, the CO2 conversion ratio can be obtained as high as 80% or more with a control of the CO2 ratio in mixture gas and the flow rate of CO2, and the energy is saving and even the energy consumption can be reduced by 145.65 MJ/t under certain operations. In addition, a complete route of CO2 disposal technology is proposed combining the comparatively mature technologies of CO2 capture, CO2 compression, and liquid CO2 storage to improve the technology of CO2 utilization. The results are expected to form a large-scale, highly efficient, and valuable method to dispose of CO2.
Compared with solid metals, liquid metals are considered more promising cathodes for molten slat/oxide electrolysis due to their fascinating advantages, which include strong depolarization effect, strong alloying effect, excellent selective separation, and low operating temperature. In this review, we briefly introduce the properties of the liquid metal cathodes and their selection rules, and then summarize development in liquid metal cathodes for molten salt electrolysis, specifically the extraction of Ti and separation of actinides and rare-earth metals in halide melts. We also review recent attractive progress in the preparation of liquid Ti alloys via molten oxide electrolysis by using liquid metal cathodes. Problems related to high-quality alloy production and large-scale applications are cited, and several research directions to further improve the quality of alloys are also discussed to realize the industrial applications of liquid metal cathodes.