Showing papers in "Transactions of Nonferrous Metals Society of China in 2014"
TL;DR: In this article, an overview of the use of aluminium alloys in passenger cars is presented, and advances concerning multi-material light weight design are presented by examples for aluminium solutions in advanced "Multi-material” Super-Light-Car (SLC) concepts, which reaches significant mass reductions.
Abstract: Aspects of material selection and innovative concepts of car construction using aluminium as best suited light-weight materials were presented, and recent development in established and advanced use of aluminium in passenger cars was discussed that help to meet economic and environmental requirements. 5xxx and 6xxx aluminium alloys were presented that have been improved for the increasing demands regarding higher strength and better formability, resulting in a mass reduction and improved crashworthiness. Furthermore, advances concerning multi-material light weight design were presented by examples for aluminium solutions in advanced “Multi-material” Super-Light-Car (SLC) concepts, which reaches significant mass reductions.
515 citations
TL;DR: In this paper, the effects of homogenization, solution treatment, quenching and ageing treatments on the evolution of the microstructure and properties of some important medium to high-strength 7xxx alloys are described.
Abstract: The 7xxx series alloys are heat treatable wrought aluminium alloys based on the Al-Zn-Mg(-Cu) system. They are widely used in high-performance structural aerospace and transportation applications. Apart from compositional, casting and thermo-mechanical processing effects, the balance of properties is also significantly influenced by the way in which the materials are heat-treated. This paper describes the effects of homogenisation, solution treatment, quenching and ageing treatments on the evolution of the microstructure and properties of some important medium to high-strength 7xxx alloys. With a focus on recent work at Monash University, where the whole processing route from homogenisation to final ageing has been studied for thick plate products, it is reported how microstructural features such as dispersoids, coarse constituent particles, fine-scale precipitates, grain structure and grain boundary characteristics can be controlled by heat treatment to achieve improved microstructure–property combinations. In particular, the paper presents methods for dissolving unwanted coarse constituent particles by controlled high-temperature treatments, quench sensitivity evaluations based on a systematic study of continuous cooling precipitation behaviour, and ageing investigations of one-, two- and three-step ageing treatments using experimental and modelling approaches. In each case, the effects on both the microstructure and the resulting properties are discussed.
265 citations
TL;DR: In this paper, the authors tried to find the optimal level of machining parameters for multi-performance characteristics in turning of Al−SiC−Gr hybrid composites using grey-fuzzy algorithm.
Abstract: Metal matrix composites reinforced with graphite particles provide better machinability and tribological properties. The present study attempts to find the optimal level of machining parameters for multi-performance characteristics in turning of Al−SiC−Gr hybrid composites using grey-fuzzy algorithm. The hybrid composites with 5%, 7.5% and 10% combined equal mass fraction of SiC−Gr particles were used for the study and their corresponding tensile strength values are 170, 210, 204 MPa respectively. Al−10%(SiC−Gr) hybrid composite provides better machinability when compared with composites with 5% and 7.5% of SiC−Gr. Grey-fuzzy logic approach offers improved grey-fuzzy reasoning grade and has less uncertainties in the output when compared with grey relational technique. The confirmatory test reveals an increase in grey-fuzzy reasoning grade from 0.619 to 0.891, which substantiates the improvement in multi-performance characteristics at the optimal level of process parameters setting.
135 citations
TL;DR: Based on the characteristics of strata movement of solid backfilling mining technology, the surface subsidence prediction method based on the equivalent mining height theory was proposed, and the parameters selection guideline of this method was also described as discussed by the authors.
Abstract: Based on the characteristics of strata movement of solid backfilling mining technology, the surface subsidence prediction method based on the equivalent mining height theory was proposed, and the parameters selection guideline of this method was also described. While comparing the parameters of caving mining with equivalent height, the subsidence efficient can be calculated according to the mining height and bulk factor of sagging zone and fracture zone, the tangent of main influence angle of solid backfilling mining is reduced by 0.2–0.5 (while it cannot be less than 1.0). For sake of safety, offset of the inflection point is set to zero, and other parameters, such as horizontal movement coefficient and main propagation angle are equal to the corresponding parameters of caving mining with equivalent height. In the last part, a case study of solid backfilling mining subsidence prediction was described. The results show the applicability of this method and the difference of the maximum subsidence point between the prediction and the observation is less than 5%.
84 citations
TL;DR: In this paper, the effects of cooling rate on the solidification parameters and microstructure of Al-7Si-0.3Mg 0.15Fe alloy during solidification process were studied.
Abstract: The effects of cooling rate on the solidification parameters and microstructure of Al-7Si-0.3Mg-0.15Fe alloy during solidification process were studied. To obtain different cooling rates, the step casting with five different thicknesses was used and the cooling rates and solidification parameters were determined by computer-aided thermal analysis method. The results show that at higher cooling rates, the primary α(Al) dendrite nucleation temperature, eutectic reaction temperature and solidus temperature shift to lower temperatures. Besides, with increasing cooling rate from 0.19 °C/s up to 6.25 °C/s, the secondary dendritic arm spacing decreases from 68 μm to 20 μm, and the primary dendritic volume fraction declines by approximately 5%. In addition, it reduces the length of Fe-bearing phase from 28 μm to 18 μm with a better uniform distribution. It is also found that high cooling rates make for modifying eutectic silicon into fibrous branched morphology, and decreasing block or lamella shape eutectic silicon.
83 citations
TL;DR: In this paper, the authors presented the consolidated references on the machining of SMAs using EDM and WEDM and subsequently identified the research gaps, and also evolved the future research directions.
Abstract: Shape memory alloys (SMAs) are the developing advanced materials due to their versatile specific properties such as pseudoelasticity, shape memory effect (SME), biocompatibility, high specific strength, high corrosion resistance, high wear resistance and high anti-fatigue property. Therefore, the SMAs are used in many applications such as aerospace, medical and automobile. However, the conventional machining of SMAs causes serious tool wear, time consuming and less dimensional deformity due to severe strain hardening and pseudoelasticity. These materials can be machined using non-conventional methods such as laser machining, water jet machining (WJM) and electrochemical machining (ECM), but these processes are limited to complexity and mechanical properties of the component. Electrical discharge machining (EDM) and wire EDM (WEDM) show high capability to machine SMAs of complex shapes with precise dimensions. The aim of this work is to present the consolidated references on the machining of SMAs using EDM and WEDM and subsequently identify the research gaps. In support to these research gaps, this work has also evolved the future research directions.
82 citations
TL;DR: In this paper, the surface broken bonds of some typical sulfide, oxide and salt-type minerals, which may belong to cubic, tetragonal, hexagonal, or orthorhombic system, were calculated.
Abstract: The population of surface broken bonds of some typical sulfide, oxide and salt-type minerals which may belong to cubic, tetragonal, hexagonal, or orthorhombic system, were calculated. In terms of the calculation results, the cleavage natures of these minerals were analyzed, and the relationship between surface broken bonds density and surface energy was also established. The results show that the surface broken bonds properties could be used to predict the cleavage nature of most of minerals, and the predicted cleavage planes agree well with those reported in previous literature. Moreover, this work explored a rule that, surface broken bonds density is directly related to surface energy with determination coefficient ( R 2 ) of over 0.8, indicating that the former is a dominant factor to determine the latter. Therefore, anisotropic surface broken bonds density can be used to predict the stability of mineral surface and the reactivity of surface atoms.
82 citations
TL;DR: In this paper, the effect of friction on the open circuit potentials of AISI 316 stainless steel and Ti6Al4V alloys sliding against Al2O3 in artificial seawater using a pin-on-disk test rig was investigated.
Abstract: The corrosion and tribocorrosion behaviors of AISI 316 stainless steel and Ti6Al4V alloys sliding against Al2O3 in artificial seawater using a pin-on-disk test rig were investigated. And the synergistic effect between corrosion and wear was emphatically evaluated. The results show that the open circuit potentials of both alloys drop down to more negative value due to friction. The corrosion current densities obtained under tribocorrosion condition are much higher than those under corrosion-only condition. Friction obviously accelerates the corrosion of the alloys. The wear loss for both alloys is larger in seawater than that in pure water. Wear loss is obviously accelerated by corrosion. And AISI 316 stainless steel is less resistant to sliding damage than Ti6Al4V alloy. The synergistic effect between wear and corrosion is a significant factor for the materials loss in tribocorrosion. In this surface-on-surface contact geometry friction system, the material loss is large but the ratio of wear-accelerated-corrosion to the total wear loss is very low.
76 citations
TL;DR: In this paper, the development of fracture around pre-existing cylindrical cavities in brittle rocks was examined using physical models and acoustic emission technique, and it was shown that both tensile and compressive stresses play an important role in fracture evolution process around cavities.
Abstract: The development of fracture around pre-existing cylindrical cavities in brittle rocks was examined using physical models and acoustic emission technique. The experimental results indicate that when granite blocks containing one pre-existing cylindrical cavity are loaded in uniaxial compression condition, the profiles of cracks around the cavity can be characterized by tensile cracking (splitting parallel to the axial compression direction) at the roof−floor, compressive crack at two side walls, and remote or secondary cracks at the perimeter of the cavity. Moreover, fracture around cavity is size-dependent. In granite blocks containing pre-existing half-length cylindrical cavities, compressive stress concentration is found to initiate at the two sidewalls and induce shear crack propagation and coalescence. In granite blocks containing multiple parallel cylindrical cavities, the adjacent cylindrical cavities can influence each other and the eventual failure mode is determined by the interaction of tensile, compressive and shear stresses. Experimental results show that both tensile and compressive stresses play an important role in fracture evolution process around cavities in brittle rocks.
74 citations
TL;DR: In this paper, a multi-response optimization method using Taguchi design with utility concept has been proposed for simultaneous optimization of wire electric discharge machining (WEDM) characteristics of TiNi SMA.
Abstract: TiNi shape memory alloys (SMAs) have been normally used as the competent elements in large part of the industries due to outstanding properties, such as super elasticity and shape memory effects. However, traditional machining of SMAs is quite complex due to these properties. Hence, the wire electric discharge machining (WEDM) characteristics of TiNi SMA was studied. The experiments were planned as per L 27 orthogonal array to minimize the experiments, each experiment was performed under different conditions of pulse duration, pulse off time, servo voltage, flushing pressure and wire speed. A multi-response optimization method using Taguchi design with utility concept has been proposed for simultaneous optimization. The analysis of means (ANOM) and analysis of variance (ANOVA) on signal to noise (S/N) ratio were performed for determining the optimal parameter levels. Taguchi analysis reveals that a combination of 1 μs pulse duration, 3.8 μs pulse off time, 40 V servo voltage, 1.8×10 5 Pa flushing pressure and 8 m/min wire speed is beneficial for simultaneously maximizing the material removal rate (MRR) and minimizing the surface roughness. The optimization results of WEDM of TiNi SMA also indicate that pulse duration significantly affects the material removal rate and surface roughness. The discharged craters, micro cracks and recast layer were observed on the machined surface at large pulse duration.
69 citations
TL;DR: In this article, a regression model was developed to predict the wear rate of the prepared composite and validated by statistical software SYSTAT 12 and statistical tools such as analysis of variance (ANOVA) and student's t test.
Abstract: The dry sliding wear behavior of AA6061 matrix composite reinforced with aluminium nitride particles (AlN) produced by stir casting process was investigated. A regression model was developed to predict the wear rate of the prepared composite. A four-factor, five-level central composite rotatable design matrix was used to minimize the number of experimental runs. The factors considered in this study were sliding velocity, sliding distance, normal load and mass fraction of AlN reinforcement in the matrix. The developed regression model was validated by statistical software SYSTAT 12 and statistical tools such as analysis of variance (ANOVA) and student's t test. It was found that the developed regression model could be effectively used to predict the wear rate at 95% confidence level. The influence of these factors on wear rate of AA6061/AlNp composite was analyzed using the developed regression model and predicted trends were discussed with the aid of worn surface morphologies. The regression model indicated that the wear rate of cast AA6061/AlNp composite decreased with an increase in the mass fraction of AlN and increased with an increase of the sliding velocity, sliding distance and normal load acting on the composite specimen.
TL;DR: In this article, a series of experiments were performed by considering pulse-on time, pulse-off time, peak current and wire tension as input parameters and the surface roughness and cutting speed were considered responses.
Abstract: The experimental analysis presented aims at the selection of the most optimal machining parameter combination for wire electrical discharge machining (WEDM) of 5083 aluminum alloy. Based on the Taguchi experimental design (L9 orthogonal array) method, a series of experiments were performed by considering pulse-on time, pulse-off time, peak current and wire tension as input parameters. The surface roughness and cutting speed were considered responses. Based on the signal-to-noise (S/N) ratio, the influence of the input parameters on the responses was determined. The optimal machining parameters setting for the maximum cutting speed and minimum surface roughness were found using Taguchi methodology. Then, additive model was employed for prediction of all (3 4 ) possible machining combinations. Finally, a handy technology table has been reported using Pareto optimality approach.
TL;DR: In this article, the influence of friction stir welding processing parameters on dissimilar joints conducted between aluminium alloy (AA5754) and commercially pure copper (C11000) was studied.
Abstract: The influence of friction stir welding processing parameters on dissimilar joints conducted between aluminium alloy (AA5754) and commercially pure copper (C11000) was studied. The welds were produced by varying the rotational speed from 600 to 1200 r/min and the feed rate from 50 to 300 mm/min. The resulting microstructure and the corrosion properties of the welds produced were studied. It was found that the joint interfacial regions of the welds were characterized by interlayers of aluminium and copper. The corrosion tests revealed that the corrosion resistance of the welds was improved as the rotational speed was increased. The corrosion rates of the welds compared to the base metals were improved compared with Cu and decreased slightly compared with the aluminium alloy. The lowest corrosion rate was obtained at welds produced at rotational speed of 950 r/min and feed rate of 300 mm/min which corresponds to a weld produced at a low heat input.
TL;DR: In this paper, different friction stir welding operations were performed at different rotation and travel speeds, and defect-free weld was obtained with a rotation speed of 1000 r/min and travel speed of 40 mm/min.
Abstract: Dissimilar friction stir welding between AZ31-O Mg and 6061-T6 Al alloys was investigated. 3 mm thick plates of aluminum and magnesium were used. Friction stir welding operations were performed at different rotation and travel speeds. The rotation speeds varied from 600 to 1400 r/min, and the travel speed varied from 20 to 60 mm/min. Defect-free weld was obtained with a rotation speed of 1000 r/min and travel speed of 40 mm/min. Metallographic studies showed that the grain size in the stir zone is much finer than that in the base metals. Complex flow pattern was formed in the stir zone. Microhardness measurement revealed an uneven distribution in the stir zone. Tensile test results indicated that the tensile strength of the welded specimen is about 76% of AZ31 Mg alloy and 60% of the 6061 Al alloy in tensile strength. SEM fracture surface image of the welded specimen indicated that the welded specimen failed through brittle-mode fracture.
TL;DR: In this article, the effect of Morinda tinctoria (MT) leaves extract on the corrosion inhibition of Al in acid medium was studied and the inhibition studies were carried out on Al in 0.5 mol/L HCl with the extract of leaves of MT using mass loss and electrochemical techniques.
Abstract: The effect of Morinda tinctoria (MT) leaves extract on the corrosion inhibition of Al in acid medium was studied. The inhibition studies were carried out on Al in 0.5 mol/L HCl with the extract of leaves of MT using mass loss and electrochemical techniques. Parameters, such as concentration of the inhibitor, concentration of the acid, temperature and concentration of halide ions, were varied and optimized. Increase of the temperature and concentration of acid can decrease the performance of the inhibitor. Thermodynamic parameters show that the physisorption of the inhibitor molecules on Al surface obeys Langmuir isotherm.
TL;DR: In this paper, the molar ratios of Cu2+ to Ni2+ as 3:7, 4:6, 5:5, 6:4 and 7:3 were calculated by a microwave combustion method with the average crystallite sizes in the range of 21.56-33.25 nm.
Abstract: Cu-Ni alloy nanoparticles were prepared by a microwave combustion method with the molar ratios of Cu2+ to Ni2+ as 3:7, 4:6, 5:5, 6:4 and 7:3. The as-prepared samples were characterized by XRD, HR-SEM, EDX and VSM. XRD and EDX analyses suggest the formation of pure alloy powders. The average crystallite sizes were found to be in the range of 21.56–33.25 nm. HR-SEM images show the clustered/agglomerated particle-like morphology structure. VSM results reveal that for low Ni content (Cu5Ni5, Cu6Ni4 and Cu7Ni3), the system shows paramagnetic behaviors, whereas for high Ni content (Cu3Ni7 and Cu4Ni6), it becomes ferromagnetic.
TL;DR: In this paper, a new algorithm was proposed to extract large deformation mining subsidence using differential interferometric Synthetic Aperture Radar (D-InSAR) and probability integral method.
Abstract: Due to the difficulties in obtaining large deformation mining subsidence using differential Interferometric Synthetic Aperture Radar (D-InSAR) alone, a new algorithm was proposed to extract large deformation mining subsidence using D-InSAR technique and probability integral method. The details of the algorithm are as follows: the control points set, containing correct phase unwrapping points on the subsidence basin edge generated by D-InSAR and several observation points (near the maximum subsidence and inflection points), was established at first; genetic algorithm (GA) was then used to optimize the parameters of probability integral method; at last, the surface subsidence was deduced according to the optimum parameters. The results of the experiment in Huaibei mining area, China, show that the presented method can generate the correct mining subsidence basin with a few surface observations, and the relative error of maximum subsidence point is about 8.3%, which is much better than that of conventional D-InSAR (relative error is 68.0%).
TL;DR: In this article, the effect of heat treatment on microstructure and mechanical properties of the Ti-steel explosive-rolling clad plate was elaborated by optical microscopy (OM), scanning electron microscopy, X-ray diffraction (XRD), transmission electron microscope (TEM), micro-hardness test and shear test.
Abstract: The effect of heat treatment on microstructure and mechanical properties of the Ti–steel explosive-rolling clad plate was elaborated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), micro-hardness test and shear test. The composites were subjected to heat treatment at temperature of 650–950 °C for 60 min. The results show that the heat treatment process results in a great enhancement of diffusion and microstructural transformation. The shear strength decreases as the treatment temperature increases. Heated at 850 °C or below, their shear strength decreases slowly as a result of the formation of TiC in the diffusion interaction layer; while at the temperature of 850 °C or above, the shear strength decreases obviously, which is the consequence of a large amount of Ti–Fe intermetallics (Fe 2 Ti/FeTi) along with some TiC distributing continuously at diffusion reaction layer.
TL;DR: The archaeal and bacterial diversities were examined using a PCR-based cloning approach and Canonical correlation analysis suggested that microbial community structures had great association with pH and the concentration of Hg2+, Pb2+, Fe3+, Cl−, SO42− in water.
Abstract: To expand knowledge on microbial communities of various metal-rich levels of mine drainage environments in Anhui province, China, the archaeal and bacterial diversities were examined using a PCR-based cloning approach. Eight acid mine water samples were collected from five areas in Tongling. Phylogenetic analyses revealed that bacteria mainly fell into ten divisions, which were Betaproteobacteria, Gammaproteobacteria, Alphaproteobacteria, Deinococcus-Thermus, Nitrospira, Firmicutes, Actinobacteria, Deltaproteobacteria, Bacteroidetes, Chloroflexi. Archaea fell into three phylogenetic divisions, Thermoplasma, Ferroplasma and Thermogymnomonas. The unweighted pair group method with arithmetic mean (UPGMA) cluster analysis based on the microbial communities' compositions revealed that five samples shared similarity with the dominance of Meiothermus and Thermomonas. Two samples had the preponderant existence of Acidithiobacillus and Leptospirillum. The remaining sample owned higher microbial communities' diversity with the Shannon-Weaver H up to 2.91. Canonical correlation analysis (CCA) suggested that microbial community structures had great association with pH and the concentration of Hg2+, Pb2+, Fe3+, Cl−, SO42− in water.
TL;DR: In this paper, numerical and experimental studies based on particle image velocimetry (PIV) measurement were carried out for the flow field in a d50 mm hydrocyclone, and the results showed that air core generally forms after 0.7 s, the similar characteristics of air core can be observed.
Abstract: For the flow field in a d50 mm hydrocyclone, numerical studies based on computational fluid dynamics (CFD) simulation and experimental studies based on particle image velocimetry (PIV) measurement were carried out respectively. The results of two methods show that air core generally forms after 0.7 s, the similar characteristics of air core can be observed. Vortexes and axial velocity distributions obtained by numerical and experimental methods are also in good agreement. Studies of different parameters based on CFD simulation show that tangential velocity distribution inside the hydrocyclone can be regarded as a combined vortex. Axial and tangential velocities increase as the feed rate increases. The enlargement of cone angle and overflow outlet diameter can speed up the overflow discharge rate. The change of underflow outlet diameter has no significant effect on axial and tangential velocities.
TL;DR: In this paper, the growth of intermetallic compounds at the interface between solid Al and Fe and the effects of inter-metallic compound layers on the interfacial bonding of clad materials were investigated.
Abstract: The growth of intermetallic compounds at the interface between solid Al and Fe and the effects of intermetallic compound layers on the interfacial bonding of clad materials were investigated. The results showed that the interface between the solid Fe and Al formed by heat-treatment consisted of Fe 2 Al 5 and FeAl 3 intermetallic compound layers, which deteriorated the interfacial bonding strength. Fractures occurred in the intermetallic compound layer during the shear testing. The location of the fracture depended on the defects of microcracks or voids in the intermetallic compound layers. The microcracks in the intermetallic compound layer were caused by the mismatch of thermal expansion coefficients of materials during cooling, and the voids were consistent with the Kirkendall effect. The work will lay an important foundation for welding and joining of aluminum and steel, especially for fabrication of Al-Fe clad materials.
TL;DR: In this paper, the chemical composition, microstructure and micro-hardness of the as-deposited GSM were investigated, and the results showed that the TA2 part of exhibiting near-equiaxed grains was Widmanstatten α-laths micro-structure.
Abstract: TA2/TA15 graded structural material (GSM) was fabricated by the laser additive manufacturing (LAM) process. The chemical composition, microstructure and micro-hardness of the as-deposited GSM were investigated. The results show that the TA2 part of exhibiting near-equiaxed grains was Widmanstatten α-laths microstructure. The TA15 part containing large columnar grains was fine basket-weave microstructure. The graded zone was divided into four deposited layers with 3000 μm in thickness. As the distance from the TA2 part increases, the alloy element contents and the β phase volume fraction increase, the α phase volume fraction decreases and the microstructure shows the evolution from Widmanstatten α-laths to basket-weave α-laths gradually. The micro-hardness increases from the TA2 part to the TA15 part due to the solid solution strengthening and grain boundary strengthening.
TL;DR: In this article, a series of innovative green metallurgical processes using novel reaction media including the NaOH/KOH sub-molten salt media and NaOH-NaNO3 binary molten salt medium, for the extraction of vanadium and chromium from the vanadium slag have been developed.
Abstract: A series of innovative green metallurgical processes using novel reaction media including the NaOH/KOH sub-molten salt media and the NaOH-NaNO3 binary molten salt medium, for the extraction of vanadium and chromium from the vanadium slag have been developed. In comparison with the traditional sodium salt roasting technology, which operates at 850 degrees C, the operation temperatures of these new processes drop to 200-400 degrees C. Further, the extraction rates of vanadium and chromium utilizing the new approaches could reach 95% and 90%, respectively, significantly higher than those in the traditional roasting process, which are 75% and approximate zero, respectively. Besides, no hazardous gases and toxic tailings are discharged during the extraction process. Compared with the conventional roasting method, these new technologies show obvious advantages in terms of energy, environments, and the mineral resource utilization efficiency, providing an attractive alternative for the green technology upgrade of the vanadium production industries.
TL;DR: In this article, Gabonese manganese oxide ores from Gabon and Xiangxi were leached with waste tea as reductant in dilute sulfuric acid solution.
Abstract: Manganese oxide ores from Gabon and Xiangxi were leached with waste tea as reductant in dilute sulfuric acid solution. The effects of waste tea dosage, concentration of sulfuric acid, liquid-to-solid ratio, leaching temperature and reaction time on leaching process were explored. The leaching efficiency of Gabonese manganese oxide ore reached almost 100% under the optimal condition which was determined as follows: manganese oxide ore to waste tea mass ratio of 10:1, sulfuric acid concentration of 2.5 mol/L, liquid-to-solid ratio of 7.5:1, leaching temperature of 368 K, time of 8 h. The leaching efficiency of Xiangxi manganese oxide ore reached 99.8% under the optimal condition which was determined as follows: manganese oxide ore to waste tea mass ratio of 10:1, sulfuric acid concentration of 1.7 mol/L, liquid-to-solid ratio of 7.5:1, leaching temperature of 368 K, time of 8 h. The leaching process followed the internal diffusion controlled kinetic model, and the apparent activation energies of Gabonese manganese oxide ore and Xiangxi manganese oxide ore were calculated to be 38.2 kJ/mol and 20.4 kJ/mol, respectively. The morphological changes and mineralogical forms of the ore before and after the chemical treatment were discussed with the support of XRD analysis and SEM analysis.
TL;DR: In this article, the phase and microstructure of the reduction product were characterized by XRD, SEM and EDS methods, based on which the mechanism of the solid-state reduction was investigated.
Abstract: The solid-state reduction kinetics of pre-oxidized vanadium-titanium magnetite concentrate was studied. The phase and microstructure of the reduction product were characterized by XRD, SEM and EDS methods, based on which the mechanism of the solid-state reduction was investigated. The results showed that using coal as reductant at 950-1100 °C, the solid-state reduction of the pre-oxidized vanadium-titanium magnetite concentrate was controlled by interface chemical reaction and the apparent activation energy was 67.719 kJ/mol. The mineral phase transformation during the reduction process can be described as follows: pre-oxidized vanadium-titanium magnetite concentrate → ulvospinel → ilmenite → FeTi 2 O 5 → (Fe n Ti 1- n )Ti 2 O 5 . M 3 O 5 -type (M can be Fe, Ti, Mg, Mn, etc) solid solutions would be formed during the reduction process of the pre-oxidized vanadium-titanium magnetite concentrate at 1050 °C for 60 min. The poor reducibility of iron in M 3 O 5 solid solutions is the main reason to limit the reduction property of pre-oxidized vanadium-titanium magnetite concentrate.
TL;DR: In this article, the effects of size distribution (particle size and content of fine fraction (<10 μm)) on scheelite flotation were studied using flotation tests and theoretical calculations.
Abstract: Effects of size distribution (particle size and content of fine fraction (<10 μm)) on scheelite flotation were studied using flotation tests and theoretical calculations. The results show that particle size influences the scheelite recovery and the performance of combined reagents. The scheelite recovery is lowered by adding fine particles (<10 μm) into the pulp containing coarse particles. Extended DLVO (EDLVO) theory confirms that the fine fractions (<10 μm) could interface with the coarse fractions. The interaction energy and fluid forces are relative to the particle size, which might explain why the fine fractions influence the scheelite flotation. The highest recovery of scheelite using combined reagents as collector and optimum ratio of combined reagents were determined by scheelite particle size and reagent performance. However, the optimum adding order was only determined by reagent performance, which has nothing to do with particle size.
TL;DR: In this paper, the microstructure and mechanical characterization of dissimilar friction stir welded AA5083-H111 and AA6351-T6 aluminum alloys were studied.
Abstract: The microstructure and mechanical characterization of dissimilar friction stir welded AA5083-H111 and AA6351-T6 aluminum alloys were studied. Three different welding speeds (36, 63 and 90 mm/min) were used to weld the dissimilar alloys. The effect of welding speed on mechanical and metallurgical properties was analyzed. It is found that the welding speed of 63 mm/min produces better mechanical and metallurgical properties than other welding speeds. The weld zone is composed of three kinds of microstructures, namely unmixed region, mechanically mixed region and mixed flow region. The fracture mode was observed to be a ductile fibrous fracture.
TL;DR: In this paper, the photocatalytic activity of zinc oxides was investigated using X-ray diffraction (XRD) and photoelectron spectroscopy (XPS) patterns, showing that Nd atoms were successfully incorporated into the ZnO lattice.
Abstract: To improve the photocatalytic activity of zinc oxides, ZnO powders doped with different neodymium (Nd) concentrations were prepared via hydrothermal method. X-ray diffraction (XRD) together with X-ray photoelectron spectroscopy (XPS) patterns revealed that Nd atoms were successfully incorporated into the ZnO lattice. XRD pattern also showed some anisotropy of the powders. The photoluminescence (PL) spectrum demonstrated a strong and broad peak in the visible light region, and the intensity of visible light emission was enhanced by Nd-doping. The photocatalytic activity was evaluated by the degradation of methyl orange solution. It is shown that doping of Nd into ZnO induces an increase of the photocatalytic activity and it attains to optimum at 3% (mole fraction) doping concentration. The intense visible light emission and the enhanced photocatalytic activity were explained by the increase in electron hole pairs and induced defects like antisite oxygen OZn and interstitial oxygen Oi, due to the doping of Nd.
TL;DR: In this paper, the initial concentration of ferrous iron in the growth medium, pH, and temperature were examined in the laboratory to determine how they affect the precipitation of jarosite in the presence of acidithiobacillus ferrooxidans bacteria.
Abstract: The precipitation of jarosite adversely affects the bio-leaching of copper sulfides in the Sarcheshmeh heap bio-leaching process. The variables of the initial concentration of ferrous iron in the growth medium, pH, and temperature were examined in the laboratory to determine how they affect the precipitation of jarosite in the presence of Acidithiobacillus ferrooxidans bacteria. It was found that the maximum ferric precipitate occurred at a ferrous sulfate concentration of 50 g/L, a temperature of 32 °C, and an initial pH value of 2.2. The effects of the precipitation of ferric iron on the quantities of ions that are important for A. ferrooxidans bacteria in aqueous phase, i.e., ferric, sulfate, potassium, phosphate, and magnesium ions, also were assessed. The results showed relatively similar patterns for the ferric and potassium ions, and then reason might have been the co-precipitation of these ions as constituent elements of jarosite mineral. At pH values greater than 1.6, the solubility of phosphate ions decreased dramatically due to the co-precipitation of phosphate ions with the jarosite precipitate and due to the significant growth rate of A. ferrooxidans bacteria in this pH range. Due to the dissolution of a gangue constituent in the ore, the magnesium levels increased in the first few days of the bio-leaching process; thereafter, it decreased slightly.
TL;DR: In this paper, the authors showed that the distribution coefficient and removal efficiency of boron are greatly improved with the increase of CaO proportion in the slag, and the maximal value of L B reaches 1.57 with a slag composition of 60%CaO-40%SiO 2 (mass fraction).
Abstract: Boron removal from metallurgical grade silicon (MG-Si) using a calcium silicate slag was studied. The results show that it is impossible basically to remove boron using a pure SiO 2 refining. The oxidizing ability of CaO–SiO 2 slag for boron removal was characterized by establishing the thermodynamic relationship between the distribution coefficient of boron ( L B ) and the activities of SiO 2 and CaO. The experimental results show that the distribution coefficient and the removal efficiency of boron are greatly improved with the increase of CaO proportion in the slag. The maximal value of L B reaches 1.57 with a slag composition of 60%CaO-40%SiO 2 (mass fraction). The boron content in the refined silicon is reduced from 18×10 −6 to 1.8×10 −6 using slag refining at 1600 °C for 3 h with a CaO–SiO 2 /MG-Si ratio of 2.5, and the removal efficiency of boron reaches 90%.