International Journal of Minerals, Metallurgy and Materials

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Kinetics of thermal decomposition of hydrated minerals associated with hematite ore in a fluidized bed reactor

P. C. Beuria, S. K. Biswal, B. K. Mishra, G. G. Roy

2017, 24(3): 229-239. doi: 10.1007/s12613-017-1400-y

中文摘要(541) PDF(17) SpringerLink

摘要:
The kinetics of removal of loss on ignition (LOI) by thermal decomposition of hydrated minerals present in natural iron ores (i.e., kaolinite, gibbsite, and goethite) was investigated in a laboratory-scale vertical fluidized bed reactor (FBR) using isothermal methods of kinetic analysis. Experiments in the FBR in batch processes were carried out at different temperatures (300 to 1200℃) and residence time (1 to 30 min) for four different iron ore samples with various LOIs (2.34wt% to 9.83wt%). The operating velocity was maintained in the range from 1.2 to 1.4 times the minimum fluidization velocity (U_mf). We observed that, below a certain critical temperature, the FBR did not effectively reduce the LOI to a desired level even with increased residence time. The results of this study indicate that the LOI level could be reduced by 90% within 1 min of residence time at 1100℃. The kinetics for low-LOI samples (<6wt%) indicates two different reaction mechanisms in two temperature regimes. At lower temperatures (300 to 700℃), the kinetics is characterized by a lower activation energy (diffusion-controlled physical moisture removal), followed by a higher activation energy (chemically controlled removal of LOI). In the case of high-LOI samples, three different kinetics mechanisms prevail at different temperature regimes. At temperature up to 450℃, diffusion kinetics prevails (removal of physical moisture); at temperature from 450 to 650℃, chemical kinetics dominates during removal of matrix moisture. At temperatures greater than 650℃, nucleation and growth begins to influence the rate of removal of LOI.

研究论文

Isothermal reduction kinetics of Panzhihua ilmenite concentrate under 30vol% CO-70vol% N₂ atmosphere

Ying-yi Zhang, Wei Lü, Xue-wei Lü, Sheng-ping Li, Chen-guang Bai, Bing Song, Ke-xi Han

2017, 24(3): 240-248. doi: 10.1007/s12613-017-1401-x

中文摘要(514) PDF(9) SpringerLink

摘要:
The reduction of ilmenite concentrate in 30vol% CO-70vol% N₂ atmosphere was characterized by thermogravimetric and differential thermogravimetric (TG-DTG) analysis methods at temperatures from 1073 to 1223 K. The isothermal reduction results show that the reduction process comprised two stages; the corresponding apparent activation energy was obtained by the iso-conversional and model-fitting methods. For the first stage, the effect of temperature on the conversion degree was not obvious, the phase boundary chemical reaction was the controlling step, with an apparent activation energy of 15.55-40.71 kJ·mol^-1. For the second stage, when the temperatures was greater than 1123 K, the reaction rate and the conversion degree increased sharply with increasing temperature, and random nucleation and subsequent growth were the controlling steps, with an apparent activation energy ranging from 182.33 to 195.95 kJ·mol^-1. For the whole reduction process, the average activation energy and pre-exponential factor were 98.94-118.33 kJ·mol^-1 and 1.820-1.816 min^-1, respectively.

研究论文

Efficient and selective recovery of Ni, Cu, and Co from low-nickel matte via a hydrometallurgical process

Guang-ju Chen, Jian-ming Gao, Mei Zhang, Min Guo

2017, 24(3): 249-256. doi: 10.1007/s12613-017-1402-9

中文摘要(579) PDF(23) SpringerLink

摘要:
Low-nickel matte was intensively characterized, and Ni, Cu, and Co were determined to exist mainly as (Fe,Ni)₉S₈ and FeNi₃, Cu₅FeS₄, and (Fe,Ni)₉S₈ and Fe₃O₄ (in isomorphic form), respectively. The efficient and selective extraction of Ni, Cu, and Co from the low-nickel matte in an (NH₄)₂S₂O₈/NH₃·H₂O solution system was studied. The effects of (NH₄)₂S₂O₈ and NH₃·H₂O concentrations, leaching time, and leaching temperature on the metal extraction efficiency were systematically investigated. During the oxidative ammonia leaching process, the metal extraction efficiencies of Ni 81.07%, Cu 93.81%, and Co 71.74% were obtained under the optimal conditions. The relatively low leaching efficiency of Ni was mainly ascribed to NiFe alloy deactivation in ammonia solution. By introducing an acid pre-leaching process into the oxidative ammonia leaching process, we achieved the high extraction efficiencies of 98.03%, 99.13%, and 85.60% for the valuable metals Ni, Cu, and Co, respectively, from the low-nickel matte.

研究论文

Reconstruction of three-dimensional grain structure in polycrystalline iron via an interactive segmentation method

Min-nan Feng, Yu-cong Wang, Hao Wang, Guo-quan Liu, Wei-hua Xue

2017, 24(3): 257-263. doi: 10.1007/s12613-017-1403-8

中文摘要(592) PDF(14) SpringerLink

摘要:
Using a total of 297 segmented sections, we reconstructed the three-dimensional (3D) structure of pure iron and obtained the largest dataset of 16254 3D complete grains reported to date. The mean values of equivalent sphere radius and face number of pure iron were observed to be consistent with those of Monte Carlo simulated grains, phase-field simulated grains, Ti-alloy grains, and Ni-based super alloy grains. In this work, by finding a balance between automatic methods and manual refinement, we developed an interactive segmentation method to segment serial sections accurately in the reconstruction of the 3D microstructure; this approach can save time as well as substantially eliminate errors. The segmentation process comprises four operations:image preprocessing, breakpoint detection based on mathematical morphology analysis, optimized automatic connection of the breakpoints, and manual refinement by artificial evaluation.

研究论文

Effects of ausforming strain on bainite transformation in nanostructured bainite steel

Hong-liang Fan, Ai-min Zhao, Qing-chun Li, Hui Guo, Jian-guo He

2017, 24(3): 264-270. doi: 10.1007/s12613-017-1404-7

中文摘要(609) PDF(13) SpringerLink

摘要:
The effects of ausforming strain on bainite transformation in high-carbon low-alloy nanobainite steel were investigated using a Gleeble 3500 thermomechanical simulator machine. The bainite transformation speed at 300℃ was found to be accelerated by ausforming at 300, 600, and 700℃ under applied strains ranging from 10% to 50% followed by isothermal transformation at 300℃. The ausformed bainite volume fraction varied with the ausforming strain because of the mechanical stabilization of the deformed austenite. Ausforming at low temperatures not only enhanced the bainite ferrite volume fraction but also refined the microstructure substantially. Although the amount of bainite ferrite might have been reduced with increasing strain, the microstructures were refined by ausforming.

研究论文

Microstructure evolution and mechanical properties of a large-sized ingot of Mg-9Gd-3Y-1.5Zn-0.5Zr (wt%) alloy after a lower-temperature homogenization treatment

Zhi-yong Xue, Yue-juan Ren, Wen-bo Luo, Yu Ren, Ping Xu, Chao Xu

2017, 24(3): 271-279. doi: 10.1007/s12613-017-1405-6

中文摘要(491) PDF(8) SpringerLink

摘要:
In this paper, a large-sized ingot of Mg-9Gd-3Y-1.5Zn-0.5Zr (wt%) alloy with a diameter of 600 mm was successfully prepared by the semi-continuous casting method. The alloy was subsequently annealed at a relatively low temperature of 430℃ for 12 h as a homogenization treatment. The microstructure and room-temperature mechanical properties of the alloy were investigated systematically. The results show that the as-cast alloy contained a mass of discontinuous lamellar-shaped 18R long-period stacking ordered (LPSO) phases with a composition of Mg₁₀ZnY and an α-Mg matrix, along with net-shaped Mg₅(Y,Gd) eutectic compounds at the grain boundaries. Most of the eutectic compounds dissolved after the homogenization treatment. Moreover, the amount and dimensions of the lamellar-shaped LPSO phase obviously increased after the homogenization treatment. The structure of the phase transformed into 14H-type LPSO with composition Mg₁₂Zn(Y,Gd). The mechanical properties of the heat-treated large-sized alloy ingot are uniform. The ultimate tensile strength (UTS) and tensile yield strength (TYS) of the alloy reached 207.2 MPa and 134.8 MPa, respectively, and the elongation was 3.4%. The high performances of the large-sized alloy ingot after the homogenization treatment is attributed to the strengthening of the α-Mg solid solution and to the plentiful LPSO phase distributed over the α-Mg matrix.

研究论文

Microwave sintering effects on the microstructure and mechanical properties of Ti-51at%Ni shape memory alloys

Mustafa K. Ibrahim, E. Hamzah, Safaa N. Saud, E. N. E. Abu Bakar, A. Bahador

2017, 24(3): 280-288. doi: 10.1007/s12613-017-1406-5

中文摘要(635) PDF(16) SpringerLink

摘要:
Ti-51at%Ni shape memory alloys (SMAs) were successfully produced via a powder metallurgy and microwave sintering technique. The influence of sintering parameters on porosity reduction, microstructure, phase transformation temperatures, and mechanical properties were investigated by optical microscopy, field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), compression tests, and microhardness tests. Varying the microwave temperature and holding time was found to strongly affect the density of porosity, presence of precipitates, transformation temperatures, and mechanical properties. The lowest density and smallest pore size were observed in the Ti-51at%Ni samples sintered at 900℃ for 5 min or at 900℃ for 30 min. The predominant martensite phases of β2 and β19' were observed in the microstructure of Ti-51at%Ni, and their existence varied in accordance with the sintering temperature and the holding time. In the DSC thermograms, multi-transformation peaks were observed during heating, whereas a single peak was observed during cooling; these peaks correspond to the presence of the β2, R, and β19' phases. The maximum strength and strain among the Ti-51at%Ni SMAs were 1376 MPa and 29%, respectively, for the sample sintered at 900℃ for 30 min because of this sample's minimal porosity.

研究论文

Oxidation and interdiffusion behavior of a germanium-modified silicide coating on an Nb-Si-based alloy

Jin-long Li, Wan Wang, Chun-gen Zhou

2017, 24(3): 289-296. doi: 10.1007/s12613-017-1407-4

中文摘要(586) PDF(7) SpringerLink

摘要:
To investigate the interdiffusion behavior of Ge-modified silicide coatings on an Nb-Si-based alloy substrate, the coating was oxidized at 1250℃ for 5, 10, 20, 50, or 100 h. The interfacial diffusion between the (Nb,X)(Si,Ge)₂ (X=Ti, Cr, Hf) coating and the Nb-Si based alloy was also examined. The transitional layer is composed of (Ti,Nb)₅(Si,Ge)₄ and a small amount of (Nb,X)₅(Si,Ge)₃. With increasing oxidation time, the thickness of the transitional layer increases because of the diffusion of Si from the outer layer to the substrate, which obeys a parabolic rate law. The parabolic growth rate constant of the transitional layer under oxidation conditions is 2.018 μm·h^-1/2. Moreover, the interdiffusion coefficients of Si in the transitional layer were determined from the interdiffusion fluxes calculated directly from experimental concentration profiles.

研究论文

Improvement in the mechanical properties of Al/SiC nanocomposites fabricated by severe plastic deformation and friction stir processing

M. Sarkari Khorrami, M. Kazeminezhad, Y. Miyashita, A. H. Kokabi

2017, 24(3): 297-308. doi: 10.1007/s12613-017-1408-3

中文摘要(536) PDF(13) SpringerLink

摘要:
Severely deformed aluminum sheets were processed by friction stir processing (FSP) with SiC nanoparticles under different conditions to improve the mechanical properties of both the stir zone and the heat affected zone (HAZ). In the case of using a simple probe and the same rotational direction (RD) of the FSP tool between passes, at least three FSP passes were required to obtain the appropriate distribution of nanoparticles. However, after three FSP passes, fracture occurred outward from the stir zone during transverse tensile tests; thus, the strength of the specimen was significantly lower than that of the severely deformed base material because of the softening phenomenon in the HAZ. To improve the mechanical properties of the HAZ, we investigated the possibility of achieving an appropriate distribution of nanoparticles using fewer FSP passes. The results indicated that using the threaded probe and changing the RD of the FSP tool between the passes effectively shattered the clusters of nanoparticles and led to an acceptable distribution of SiC nanoparticles after two FSP passes. In these cases, fracture occurred at the HAZ with higher strength compared to the specimen processed using three FSP passes with the same RD between the passes and with the simple probe. The fracture behaviors of the processed specimens are discussed in detail.

研究论文

Microstructure and properties of mullite-based porous ceramics produced from coal fly ash with added Al₂O₃

Jian-bin Zhu, Hong Yan

2017, 24(3): 309-315. doi: 10.1007/s12613-017-1409-2

中文摘要(716) PDF(30) SpringerLink

摘要:
Using coal fly ash slurry samples supplemented with different amounts of Al₂O₃, we fabricated mullite-based porous ceramics via a dipping-polymer-replica approach, which is a popular method suitable for industrial application. The microstructure, phase composition, and compressive strength of the sintered samples were investigated. Mullite was identified in all of the prepared materials by X-ray diffraction analysis. The microstructure and compressive strength were strongly influenced by the content of Al₂O₃. As the Al/Si mole ratio in the starting materials was increased from 0.84 to 2.40, the amount of amorphous phases in the sintered microstructure decreased and the compressive strength of the sintered samples increased. A further increase in the Al₂O₃ content resulted in a decrease in the compressive strength of the sintered samples. The mullite-based porous ceramic with an Al/Si molar ratio of 2.40 exhibited the highest compressive strength and the greatest shrinkage among the investigated samples prepared using coal fly ash as the main starting material.

研究论文

Effect of Fe₂O₃ on the crystallization behavior of glass-ceramics produced from naturally cooled yellow phosphorus furnace slag

Hong-pan Liu, Xiao-feng Huang, Li-ping Ma, Dan-li Chen, Zhi-biao Shang, Ming Jiang

2017, 24(3): 316-323. doi: 10.1007/s12613-017-1410-9

中文摘要(561) PDF(14) SpringerLink

摘要:
CaO-Al₂O₃-SiO₂ (CAS) glass-ceramics were prepared via a melting method using naturally cooled yellow phosphorus furnace slag as the main raw material. The effects of the addition of Fe₂O₃ on the crystallization behavior and properties of the prepared glass-ceramics were studied by differential thermal analysis, X-ray diffraction, and scanning electron microscopy. The crystallization activation energy was calculated using the modified Johnson-Mehl-Avrami equation. The results show that the intrinsic nucleating agent in the yellow phosphorus furnace slag could effectively promote the crystallization of CAS. The crystallization activation energy first increased and then decreased with increasing amount of added Fe₂O₃. At 4wt% of added Fe₂O₃, the crystallization activation energy reached a maximum of 676.374 kJ·mol^-1. The type of the main crystalline phase did not change with the amount of added Fe₂O₃. The primary and secondary crystalline phases were identified as wollastonite (CaSiO₃) and hedenbergite (CaFe(Si₂O₆)), respectively.

研究论文

Reaction mechanism for in-situ β-SiAlON formation in Fe₃Si-Si₃N₄-Al₂O₃ composites

Hai-xia Qin, Yong Li, Li-xiong Bai, Meng-long Long, Wen-dong Xue, Jun-hong Chen

2017, 24(3): 324-331. doi: 10.1007/s12613-017-1411-8

中文摘要(532) PDF(8) SpringerLink

摘要:
In this work, Fe₃Si-Si₃N₄-Al₂O₃ composites were prepared at 1300℃ in an N₂ atmosphere using fused corundum and tabular alumina particles, Al₂O₃ fine powder, and ferrosilicon nitride (Fe₃Si-Si₃N₄) as raw materials and thermosetting phenolic resin as a binder. The effect of ferrosilicon nitride with different concentrations (0wt%, 5wt%, 10wt%, 15wt%, 20wt%, and 25wt%) on the properties of Fe₃Si-Si₃N₄-Al₂O₃ composites was investigated. The results show that the apparent porosity varies between 10.3% and 17.3%, the bulk density varies from 2.94 g/cm³ and 3.30 g/cm³, and the cold crushing strength ranges from 67 MPa to 93 MPa. Under the experimental conditions, ferrosilicon nitride, whose content decreases substantially, is unstable; part of the ferrosilicon nitride is converted into Fe₂C, whereas the remainder is retained, eventually forming the ferrosilicon alloy. Thermodynamic assessment of the Si₅AlON₇ indicated that the ferrosilicon alloy accelerated the reactions between Si₃N₄ and α-Al₂O₃ fine powder and that Si in the ferrosilicon alloy was nitrided directly, forming β-SiAlON simultaneously. In addition, fused corundum did not react directly with Si₃N₄ because of its low reactivity.

研究论文

A new synthetic route to MgO-MgAl₂O₄-ZrO₂ highly dispersed composite material through formation of Mg₅Al_2.4Zr_1.7O₁₂ metastable phase:synthesis and physical properties

Peng Jiang, Guo-xiang Yin, Ming-wei Yan, Jia-lin Sun, Bin Li, Yong Li

2017, 24(3): 332-341. doi: 10.1007/s12613-017-1412-7

中文摘要(540) PDF(7) SpringerLink

摘要:
Mg₅Al_2.4Zr_1.7O₁₂ metastable phase was successfully synthesized from analytical-grade MgO, α-Al₂O₃, MgAl₂O₄, and ZrO₂ under an N₂ atmosphere. The sintering temperature was varied from 1650 to 1780℃, and the highest amount of Mg₅Al_2.4Zr_1.7O₁₂ appeared in the composite material when the sintering temperature was 1760℃. According to our research of the formation mechanism of Mg₅Al_2.4Zr_1.7O₁₂, the formation and growth of MgAl₂O₄ dominated when the temperature was not higher than 1650℃. When the temperature was higher than 1650℃, MgO and ZrO₂ tended to diffuse into MgAl₂O₄ and the Mg₅Al_2.4Zr_1.7O₁₂ solid solution was formed. When the temperature reached 1760℃, the formation of Mg₅Al_2.4Zr_1.7O₁₂ was completed. The effect of MgAl₂O₄ spinel crystals was also studied, and their introduction into the composite material promoted the formation and growth of Mg₅Al_2.4Zr_1.7O₁₂. A highly dispersed MgO-MgAl₂O₄-ZrO₂ composite material was prepared through the decomposition of the Mg₅Al_2.4Zr_1.7O₁₂ metastable phase. The as-prepared composite material showed improved overall physical properties because of the good dispersion of MgO, MgAl₂O₄, and ZrO₂ phases.

研究论文

Electrochemical performance of a nickel-rich LiNi_0.6Co_0.2Mn_0.2O₂ cathode material for lithium-ion batteries under different cut-off voltages

Kai-lin Cheng, Dao-bin Mu, Bo-rong Wu, Lei Wang, Ying Jiang, Rui Wang

2017, 24(3): 342-351. doi: 10.1007/s12613-017-1413-6

中文摘要(921) PDF(27) SpringerLink

摘要:
A spherical-like Ni_0.6Co_0.2Mn_0.2(OH)₂ precursor was tuned homogeneously to synthesize LiNi_0.6Co_0.2Mn_0.2O₂ as a cathode material for lithium-ion batteries. The effects of calcination temperature on the crystal structure, morphology, and the electrochemical performance of the as-prepared LiNi_0.6Co_0.2Mn_0.2O₂ were investigated in detail. The as-prepared material was characterized by X-ray diffraction, scanning electron microscopy, laser particle size analysis, charge-discharge tests, and cyclic voltammetry measurements. The results show that the spherical-like LiNi_0.6Co_0.2Mn_0.2O₂ material obtained by calcination at 900℃ displayed the most significant layered structure among samples calcined at various temperatures, with a particle size of approximately 10 μm. It delivered an initial discharge capacity of 189.2 mAh·g^-1 at 0.2C with a capacity retention of 94.0% after 100 cycles between 2.7 and 4.3 V. The as-prepared cathode material also exhibited good rate performance, with a discharge capacity of 119.6 mAh·g^-1 at 5C. Furthermore, within the cut-off voltage ranges from 2.7 to 4.3, 4.4, and 4.5 V, the initial discharge capacities of the calcined samples were 170.7, 180.9, and 192.8 mAh·g^-1, respectively, at a rate of 1C. The corresponding retentions were 86.8%, 80.3%, and 74.4% after 200 cycles, respectively.

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2017年第24卷第3期