International Journal of Minerals, Metallurgy and Materials

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Pre-desilication and digestion of gibbsitic bauxite with lime in sodium aluminate liquor

Xiao-lin Pan, Hai-yan Yu, Kai-wei Dong, Gan-feng Tu, Shi-wen Bi

2012, 19(11): 973-977. doi: 10.1007/s12613-012-0657-4

中文摘要(304) PDF(24) SpringerLink

摘要:
The effect of lime on the pre-desilication and digestion of gibbsitic bauxite in synthetic sodium aluminate liquor at different temperatures was investigated. The bauxite is comprised of gibbsite, aluminogoethite, hematite, kaolin, quartz, and minor boehmite. Lime increases the desilication efficiency of the bauxite during the pre-desilication process by promoting the conversion of sodalite and cancrinite to hydrogarnet. Desilication reactions during the digestion process promoted by lime result in the loss of Al₂O₃ entering the red mud, but the amount of aluminogoethite-to-hematite conversion promoted by lime leads to the increase of aluminogoethitic Al₂O₃ entering the digested liquor. The alumina digestion rate at 245℃ is higher than that at 145℃ due to the more pronounced conversion of aluminogoethite to hematite. The soda consumption during the digestion process decreases due to lime addition, especially at higher temperatures.

Preparation of Cr₂O₃ precursors by hydrothermal reduction in the abundant Na₂CO₃ and Na₂CrO₄ solution

Guang-ye Wei, Jing-kui Qu, Yu-dong Zheng, Tao Qi, Qiang Guo

2012, 19(11): 978-985. doi: 10.1007/s12613-012-0658-3

中文摘要(186) PDF(12) SpringerLink

摘要:
Precursors of chromium oxide (p-Cr₂O₃) were prepared by reducing hexavalent chromium in the presence of sodium carbonate solution under hydrothermal conditions. Methanal was used as the reductant, and carbon dioxide was the acidulating agent. The influences of reaction temperature, initial pressure of carbon dioxide, isothermal time and methanal coefficient on Cr(VI) reduction were investigated. Experimental results showed that Cr(VI) was reduced to Cr(III) with a yield of 99%. Chemical titration, thermogravimetry (TG), X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM) were used to characterize the p-Cr₂O₃ and Cr₂O₃. The series of p-Cr₂O₃ were found to be multiphase even if they presented different colors, from gray green to lavender. After these p-Cr₂O₃ samples were calcined, the product of rhombohedral Cr₂O₃ with a purity of 99.5wt% was obtained.

Reduction mechanisms of pyrite cinder-carbon composite pellets

Zheng-jian Liu, Xiang-dong Xing, Jian-liang Zhang, Ming-ming Cao, Ke-xin Jiao, Shan Ren

2012, 19(11): 986-991. doi: 10.1007/s12613-012-0659-2

中文摘要(193) PDF(9) SpringerLink

摘要:
The non-isothermal reduction mechanisms of pyrite cinder-carbon composite pellets were studied at laboratory scale under argon (Ar) atmosphere. The composite pellets as well as the specimens of separate layers containing pyrite cinder and coal were tested. The degree of reduction was measured by mass loss. The microstructures of the reduced composite pellets were characterized by scanning electron microscopy (SEM). It is found that the reduction processes of the composite pellets may be divided into four stages:reduction via CO and H₂ from volatiles in coal at 673-973 K, reduction via H₂ and C produced by cracking of hydrocarbon at 973-1123 K, direct reduction by carbon via gaseous intermediates at 1123-1323 K, and direct reduction by carbon at above 1323 K. Corresponding to the four stages, the apparent activation energies (E) for the reduction of the composite pellets are 86.26, 78.54, 72.01, and 203.65 kJ·mol^-1, respectively.

Characterization of dolochar wastes generated by the sponge iron industry

Ranjan Kumar Dwari, Danda Srinivas Rao, Akhila Kumar Swar, Palli Sita Ram Reddy, Barada Kanta Mishra

2012, 19(11): 992-1003. doi: 10.1007/s12613-012-0660-9

中文摘要(300) PDF(19) SpringerLink

摘要:
Solid wastes generated by the metallurgical industry contribute significantly towards the enhancement of environmental pollution. The handling, utilization, and safe disposal of these solid wastes are major concerns for the world. Dolochar is such a solid waste generated by the sponge iron industry. Investigations were carried out on the physical, mineralogical, and chemical characteristics for the efficient utilization of dolochar. The detailed studies on physico-chemical properties and petrography were carried out by optical microscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Characterization studies revealed that the dolochar consists of quartz (free as well as locked), free lime, Fe particles, and Ca or Mg and/or Ca+Mg+Fe oxide phases. The washability data of -300 μm dolochar samples indicated that clean coal with 41wt% ash at 18% yield can be produced from dolochar with 78wt% ash. The studies further suggested that the liberation of the dolochar is hard to achieve for clear separation. The dolochar is observed to have high ash fusion temperature and the unburned carbon can be best utilized for power generation.

Effects of Ru on the microstructure and phase stability of a single crystal superalloy

Zhen-xue Shi, Jia-rong Li, Shi-zhong Liu

2012, 19(11): 1004-1009. doi: 10.1007/s12613-012-0661-8

中文摘要(206) PDF(13) SpringerLink

摘要:
Two experimental single crystal superalloys, the Ru-free alloy and the Ru-containing alloy with[001] orientation, were cast in a directionally solidified furnace, while other alloying element contents were kept unchanged. The effects of Ru on the microstructure and phase stability of the single crystal superalloy were investigated. γ' directional coarsening and rafting were observed in the Ru-free alloy and Ru-containing alloy after long-term aging at 1070℃ for 800 h. Needle-shaped σ topologically close packed (TCP) phases precipitated and grew along the fixed direction in both the alloys. The precipitating rate and volume fraction of TCP phases decreased significantly by adding Ru. The compositions of γ and γ' phases measured using an energy-dispersive X-ray spectroscope (EDS) in transmission electron microscopy (TEM) analysis showed that the addition of Ru lessened the partition ratio of TCP forming elements, Re, W and Mo, and decreased the saturation degrees of these elements in γ phase, which can enable the Ru-containing alloy to be more resistant to the formation of TCP phases. It is indicated that the addition of Ru to the Ni-based single crystal superalloy with high content of the refractory alloying element can enhance phase stability.

Structural characteristics and mechanism of hydrogen-induced disproportionation of the ZrCo alloy

Xiu-mei Guo, Shu-mao Wang, Xiao-peng Liu, Zhi-nian Li, Jian-hua Ye, Hui-ping Yuan, Li-jun Jiang

2012, 19(11): 1010-1015. doi: 10.1007/s12613-012-0662-7

中文摘要(183) PDF(8) SpringerLink

摘要:
The intermetallic compound ZrCo was prepared, and its hydrogen-induced disproportionation in hydrogen desorption processes was investigated. The hydrogenation-dehydrogenation thermodynamics of the ZrCo alloy was evaluated by pressure-composition isotherm measurements at different temperatures. The kinetic processes of hydrogen-induced disproportionation at different temperatures under certain pressures were detailedly studied. The disproportionation rate of the ZrCo alloy increased with the increases of temperature and initial hydrogen pressure under experimental conditions. However, the maximum attainable extent of disproportionation did not change much with an increase in temperature or initial hydrogen pressure. The crystallographic structure analysis of the ZrCo alloy combining with its corresponding dehydrogenation kinetic curves under the conditions of an initial hydrogen pressure of 0.2 MPa and a temperature of 723 K indicated that the basic process of disproportionation reactions was composed of four stages:rapid dehydrogenation of ZrCoH₃, equilibrium of dehydrogenation, simultaneity of dehydrogenation and disproportionation, and completion of disproportionation.

Microstructural evolution of a recycled aluminum alloy deformed by equal channel angular pressing process

Thabet Makhlouf, Atef Rebhi, Jean-Philippe Couzinié, Yannick Champion, Nabil Njah

2012, 19(11): 1016-1022. doi: 10.1007/s12613-012-0663-6

中文摘要(220) PDF(9) SpringerLink

摘要:
The microstructural evolution of a recycled aluminum alloy after equal channel angular pressing (ECAP) up to four passes was investigated using X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). Microhardness tests were performed to determine the associated changes in mechanical properties. An ultrafine-grained material has been obtained with a microstructure showing a mixture of highly strained crystallites. A high density of dislocations was achieved as a result of severe plastic deformation (SPD) through the die. Changes in mechanical behavior are also revealed after ECAP due to strain hardening. Thermal analysis and TEM micrographs obtained after annealing indicate the succession of the recovery, recrystallization, and grain growth phenomena. Moreover, the energy stored during ECAP may be related to the dislocation density introduced by SPD. We finally emphasize the role played by the precipitates in this alloy.

Effect of heating rate on the densification of NdFeB alloys sintered by an electric field

Gang Yang, Yi Yang, Dong Lu, Kun-lan Huang, Jun Wang

2012, 19(11): 1023-1028. doi: 10.1007/s12613-012-0664-5

中文摘要(191) PDF(10) SpringerLink

摘要:
This study introduces a novel method of electric field sintering for preparing NdFeB magnets. NdFeB alloy compacts were all sintered by electric fields for 8 min at 1000℃ with different preset heating rates. The characteristics of electric field sintering and the effects of heating rate on the sintering densification of NdFeB alloys were also studied. It is found that electric field sintering is a new non-pressure rapid sintering method for preparing NdFeB magnets with fine grains at a relatively lower sintering temperature and in a shorter sintering time. Using this method, the sintering temperature and process of the compacts can be controlled accurately. When the preset heating rate increasing from 5 to 2000℃/s the densification of NdFeB sintered compacts gradually improves. As the preset heating rate is 2000℃/s, Nd-rich phases are small, dispersed and uniformly distributed in the sintered compact, and the magnet has a better microstructure than that made by conventional vacuum sintering. Also, the maximum energy product of the sintered magnet reaches 95% of conventionally vacuum sintered magnets.

Effect of indium addition on the microstructural formation and soldered interfaces of Sn-2.5Bi-1Zn-0.3Ag lead-free solder

Ming-jie Dong, Zhi-ming Gao, Yong-chang Liu, Xun Wang, Li-ming Yu

2012, 19(11): 1029-1035. doi: 10.1007/s12613-012-0665-4

中文摘要(237) PDF(9) SpringerLink

摘要:
The microstructural formation and properties of Sn-2.5Bi-xIn-1Zn-0.3Ag (in wt%) alloys and the evolution of soldered interfaces on a Cu substrate were investigated. Apart from the relatively low melting point (about 195℃), which is close to that of conventional eutectic Sn-Pb solder, the investigated solder presents superior wettability, solderability, and ductility. The refined equiaxial grains enhance the mechanical properties, and the embedded bulk intermetallic compounds (IMCs) (Cu₆Sn₅ and Cu₅Zn₈) and granular Bi particles improve the joint reliability. The addition of In reduces the solubility of Zn in the β-Sn matrix and strongly influences the separation and growth behaviors of the IMCs. The soldered interface of Sn-2.5Bi-xIn-1Zn-0.3Ag/Cu consists of Cu-Zn and Cu-Sn IMC layers.

Potential red-emitting phosphor GdNbO₄:Eu³⁺,Bi³⁺ for near-UV white light emitting diodes

Ding-fei Zhang, An Tang, Liu Yang, Zeng-tao Zhu

2012, 19(11): 1036-1039. doi: 10.1007/s12613-012-0666-3

中文摘要(210) PDF(7) SpringerLink

摘要:
A red-emitting phosphor GdNbO₄:Eu³⁺,Bi³⁺ was prepared by a high temperature solid-state reaction technique. The phosphor was characterized by X-ray diffraction (XRD), particle size analyzer and fluorescence spectrometer. The single phase of GdNbO₄:Eu³⁺,Bi³⁺ was obtained at 1150℃ and the average particle diameter was about 2.30 μm. Excitation and emission spectra reveal that the phosphor can be efficiently excited by ultraviolet (UV) light (394 nm) and emit the strong red light of 612 nm due to the Eu³⁺ transition of ⁵D₀→⁷F₂. The optimum content of Eu³⁺ doped in the phosphor GdNbO₄:Eu³⁺ is 20mol%. The phosphor Gd_0.80NbO₄:0.20Eu³⁺,0.03Bi³⁺ shows much stronger photoluminescence intensity and better chromaticity coordinates (x=0.642, 0.352) than GdNbO₄:Eu³⁺. It is confirmed that Gd_0.80NbO₄:0.20Eu³⁺,0.03Bi³⁺ is a potential candidate for near-UV chip-based white light emitting diodes.

Corrosion properties in a simulated body fluid of Mg/β-TCP composites prepared by powder metallurgy

Yong Wang, Ze-hong Wu, Hong Zhou, Zhi-dong Liao, Heng-fei Zhang

2012, 19(11): 1040-1044. doi: 10.1007/s12613-012-0667-2

中文摘要(202) PDF(8) SpringerLink

摘要:
Magnesium matrix composites (MMC) reinforced with 5wt% tricalcium phosphate (TCP) particles were prepared by powder metallurgy. Pure magnesium (CP-Mg) was fabricated by the same procedure for comparison. Scanning electron microscopy and energy-dispersive X-ray spectroscopy analyses revealed that TCP particles were distributed homogeneously in the MMC. In order to investigate the corrosion properties, MMC samples were immersed in a simulated body fluid (SBF) at 310±0.5 K for 72 h. The mass loss of the samples in SBF and the pH values of the SBF were evaluated. Moreover, electrochemical measurements were conducted in the SBF. It was shown that the corrosion rate of the MMC decreased with the addition of TCP compared with CP-Mg. Hydroxyapatite was formed on the surface of MMC samples after immersion in the SBF for 72 h but not on the surface of CP-Mg.

Preparation of narrow band gap V₂O₅/TiO₂ composite films by micro-arc oxidation

Qiang Luo, Xin-wei Li, Qi-zhou Cai, Qing-song Yan, Zhen-hua Pan

2012, 19(11): 1045-1051. doi: 10.1007/s12613-012-0668-1

中文摘要(218) PDF(8) SpringerLink

摘要:
V₂O₅/TiO₂ composite films were prepared on pure titanium substrates via micro-arc oxidation (MAO) in electrolytes consisting of NaVO₃. Their morphology and elements were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis. Phase composition and valence states of species in the films were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS) were also employed to evaluate the photophysical property of the films. The V₂O₅/TiO₂ composite films show a sheet-like morphology. Not only V₂O₅ phase appears in the films when the NaVO₃ concentration of the electrolyte is higher than 6.10 g/L and is loaded at the surface of anatase, but also V⁴⁺ is incorporated into the crystal lattice of anatase. In comparison with pure TiO₂ films the V₂O₅/TiO₂ composite films exhibit significantly narrow band gap energy. The film prepared in an electrolyte consisting of NaVO₃ with a concentration of 8.54 g/L exhibits the narrowest band gap energy, which is approximately 1.89 eV. The V₂O₅/TiO₂ composite films also have the significantly enhanced visible light photocatalytic activity. The film prepared in an electrolyte consisting of NaVO₃ with a concentration of 8.54 g/L exhibits the best photocatalytic activity and about 93% of rhodamine is degraded after 14 h visible light radiation.

Effect of stearic acid on the morphological and structural evolution of mechanically milled Nb-based powder

De-zhi Zhang, Xuan-hui Qu, Ming-li Qin, Lin Zhang, Xin Lu

2012, 19(11): 1052-1057. doi: 10.1007/s12613-012-0669-0

中文摘要(185) PDF(7) SpringerLink

摘要:
Nb-based powder was fabricated via mechanical grinding. The influence of stearic acid on the grinding process was studied. The structural evolution and morphological evolution of the milled powder were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) analysis. It is indicated that an appropriate amount of stearic acid accelerates the particle refinement process and favors the production of superfine Nb-based particles with good dispersivity and high activity. However, an inappropriate amount of stearic acid has an adverse effect on the refinement process.

Synthesis of dandelion-like TiO₂ microspheres as anode materials for lithium ion batteries with enhanced rate capacity and cyclic performances

Jin Yi, Yan-lin Liu, Yuan Wang, Xiao-ping Li, She-jun Hu, Wei-shan Li

2012, 19(11): 1058-1062. doi: 10.1007/s12613-012-0670-7

中文摘要(196) PDF(9) SpringerLink

摘要:
Dandelion-like TiO₂ microspheres consisting of numerous rutile single-crystalline nanorods were synthesized for the first time by a hydrothermal method. Their crystal structure, morphology and electrochemical properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and galvanostatic charge and discharge tests. The results show that the synthesized TiO₂ microspheres exhibit good rate and cycle performances as anode materials of lithium ion batteries. It can be found that the dandelion-like structure provides a larger specific surface area and the single-crystalline nanorod provides a stable structure and fast pathways for electron and lithium ion transport, which contribute to the rate and cycle performances of the battery.

Preparation of spherical ultrafine copper powder via hydrogen reduction-densification of Mg(OH)₂-coated Cu₂O powder

Yue-jun Wang, Kang-gen Zhou

2012, 19(11): 1063-1068. doi: 10.1007/s12613-012-0671-6

中文摘要(251) PDF(8) SpringerLink

摘要:
A novel process was developed to produce spherical copper powder for multilayer ceramic capacitors (MLCC). Spherical ultrafine cuprous oxide (Cu₂O) powder was prepared by glucose reduction of Cu(OH)₂. The Cu₂O particles were coated by Mg(OH)₂ and reduced to metallic copper particles. At last, the copper particles were densified by high-temperature heat treatment. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), tap density, and thermogravimetry (TG). It is found that the shape and size distribution of the copper powder are determined by the Cu₂O powder and the copper particles do not agglomerate during high-temperature heat treatment because of the existence of Mg(OH)₂ coating. After densification at high temperature, the particle tap density increases from 3.30 to 4.18 g/cm³ and the initial oxidation temperature rises from 125 to 150℃.

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2012年第19卷第11期

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2012年第19卷第11期