International Journal of Minerals, Metallurgy and Materials

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Effects of bioleaching on the mechanical and chemical properties of waste rocks

Sheng-hua Yin, Ai-xiang Wu, Shao-yong Wang, Chun-ming Ai

2012, 19(1): 1-8. doi: 10.1007/s12613-012-0507-4

中文摘要(291) PDF(10) SpringerLink

摘要:
Bioleaching processes cause dramatic changes in the mechanical and chemical properties of waste rocks, and play an important role in metal recovery and dump stability. This study focused on the characteristics of waste rocks subjected to bioleaching. A series of experiments were conducted to investigate the evolution of rock properties during the bioleaching process. Mechanical behaviors of the leached waste rocks, such as failure patterns, normal stress, shear strength, and cohesion were determined through mechanical tests. The results of SEM imaging show considerable differences in the surface morphology of leached rocks located at different parts of the dump. The mineralogical content of the leached rocks reflects the extent of dissolution and precipitation during bioleaching. The dump porosity and rock size change under the effect of dissolution, precipitation, and clay transportation. The particle size of the leached rocks decreased due to the loss of rock integrity and the conversion of dry precipitation into fine particles.

Extraction behaviours of titanium and other impurities in the decomposition process of ilmenite by highly concentrated KOH solution

Yu-min Liu, Hua Lü, Tao Qi, Yi Zhang

2012, 19(1): 9-14. doi: 10.1007/s12613-012-0508-3

中文摘要(328) PDF(18) SpringerLink

摘要:
To effectively utilize ilmenite and recycle KOH solution, the extraction behaviours of titanium and other associated impurities in the decomposition process of ilmenite by highly concentrated KOH solution were studied. Experiments on the extraction behaviours of titanium as well as other associated impurities of ilmenite such as iron, silicon, calcium, and aluminium were carried out. The effects of various parameters, including reaction temperature, KOH concentration, reaction time, alkali-to-ore mass ratio, and particle size on the extraction rate of titanium and other impurities were examined. When the finely ground ore (58-75 μm) reacted with KOH solution (80wt%) in an alkali-to-ore mass ratio of 7:1 at 260℃ for 60 min, almost complete extraction of titanium was achieved, while the extraction rate of aluminium was 78% and that of other impurities was less than 22%. Moreover, high purity (98.2wt%) TiO₂ with the anatase structure could be gained in the purification process.

Improvement of tundish shape and optimization of flow control devices for sequence casting heavy steel ingots

Guang-hua Wen, Yong-feng Huang, Ping Tang, Ming-mei Zhu

2012, 19(1): 15-20. doi: 10.1007/s12613-012-0509-2

中文摘要(292) PDF(14) SpringerLink

摘要:
The metallurgical effect of a round tundish used to cast heavy steel ingots in machine works at present was evaluated through water modeling experiments. The flow control devices of the improved oval tundish, which was used instead of the round tundish, had been optimized. The results show that the residence time of the round tundish is short, its inclusion removal efficiency is too low, and it has more dead zones and an unreasonable flow field. Compared with the round tundish, the improved oval tundish with the optimized weir and dam has a better effect:its minimum residence time is prolonged by 38.1 s, the average residence time is prolonged by 233.4 s, its dead volume fraction decreases from 26% to 15%, and the ratio of plug volume fraction to dead volume fraction increases from 0.54 to 1.27. The inclusion removal efficiency also increases by 17.5%.

Formation of internal cracks during soft reduction in rectangular bloom continuous casting

Xiao-bin Li, Hua Ding, Zheng-you Tang, Ji-cheng He

2012, 19(1): 21-29. doi: 10.1007/s12613-012-0510-9

中文摘要(246) PDF(9) SpringerLink

摘要:
To investigate the formation of internal cracks in GCr15 bearing steels during the soft reduction process in rectangular bloom continuous casting, fully coupled thermomechanical finite element models were developed using the commercial software MSC.MARC, and microstructures and fractographs were also observed. With the finite element models, the contours of temperature, equivalent plastic strain, and equivalent von Mises stress were simulated. It is observed that the fracture surfaces of internal cracks are covered by cleavage or quasi-cleavage facets. The region of internal cracks in the intergranular brittle fracture mode is in the mushy zone between the zero ductility temperature (ZDT) and the zero strength temperature (ZST). The simulated equivalent plastic strain in the crack region is 2.34%-2.45%, which is larger than the critical strain (0.4%-1.5%), and the equivalent von Mises stress is 1.84-5.05 MPa, which is within the range of critical stress (3.9-7.2 MPa), thus resulting in the occurrence of internal cracks. Reducing the soft reduction amount from 3 to 2 mm can lower the stress under the critical value.

Effect of deep cryogenic treatment on the properties of 80CrMo12 5 tool steel

Kamran Amini, Said Nategh, Ali Shafyei, Ahmad Rezaeian

2012, 19(1): 30-37. doi: 10.1007/s12613-012-0511-8

中文摘要(378) PDF(19) SpringerLink

摘要:

The effect of deep cryogenic treatment on the mechanical properties of 80CrMo12 5 tool steel was investigated. Moreover, the effects of stabilization (holding at room temperature for some periods before deep cryogenic treatment) and tempering before deep cryogenic treatment were studied. The results show that deep cryogenic treatment can eliminate the retained austenite, making a better carbide distribution and a higher carbide amount. As a result, a remarkable improvement in wear resistance of cryogenically treated specimens is observed. Moreover, the ultimate tensile strength increases, and the toughness of the sample decreases. It is also found that both stabilization and tempering before deep cryogenic treatment decrease the wear resistance, hardness, and carbides homogeneity compared to the deep cryogenically treated samples. It is concluded that deep cryogenic treatment should be performed without any delay on samples after quenching to reach the highest wear resistance and hardness.

Electrochemical and analytical characterization of three corrosion inhibitors of steel in simulated concrete pore solutions

Jin-jie Shi, Wei Sun

2012, 19(1): 38-47. doi: 10.1007/s12613-012-0512-7

中文摘要(270) PDF(11) SpringerLink

摘要:
Corrosion inhibitors for steel, such as sodium phosphate (Na₃PO₄), sodium nitrite (NaNO₂), and benzotriazole (BTA), in simulated concrete pore solutions (saturated Ca(OH)₂) were investigated. Corrosion behaviors of steel in different solutions were studied by means of corrosion potential (E_corr), linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP). A field emission scanning electron microscope (FESEM) equipped with energy dispersive X-ray analysis (EDXA) was used for observing the microstructures and morphology of corrosion products of steel. The results indicate that, compared with the commonly used nitrite-based inhibitors, Na₃PO₄ is not a good inhibitor, while BTA may be a potentially effective inhibitor to prevent steel from corrosion in simulated concrete pore solutions.

Preparation of semi-solid aluminum alloy slurry poured through a water-cooled serpentine channel

Zheng-zhou Chen, Wei-min Mao, Zong-chuang Wu

2012, 19(1): 48-53. doi: 10.1007/s12613-012-0513-6

中文摘要(252) PDF(8) SpringerLink

摘要:
A water-cooled serpentine channel pouring process was invented to produce semi-solid A356 aluminum alloy slurry for rheocasting, and the effects of pouring temperature and circulating cooling water flux on the microstructure of the slurry were investigated. The results show that at the pouring temperature of 640-680℃ and the circulating cooling water flux of 0.9 m³/h, the semi-solid A356 aluminum alloy slurry with spherical primary α(Al) grains can be obtained, whose shape factors are between 0.78 and 0.86 and the grain diameter can reach 48-68 μm. When the pouring temperatures are at 660-680℃, only a very thin solidified shell remains inside the serpentine channel and can be removed easily. When the serpentine channel is cooled with circulating water, the microstructure of the semi-solid slurry can be improved, and the serpentine channel is quickly cooled to room temperature after the completion of one pouring. In terms of the productivity of the special equipment, the water-cooled serpentine channel is economical and efficient.

A generalized Norde plot for reverse biased Schottky contacts

Chin-Min Hsiung, Chuen-Shii Chou, Ting-Lung Chiang

2012, 19(1): 54-58. doi: 10.1007/s12613-012-0514-5

中文摘要(253) PDF(9) SpringerLink

摘要:
When a metal makes intimate contact with a semiconductor material, a Schottky barrier may be created. The Schottky contact has many important applications in the integrated circuit (IC) electronics field. The parameters of such contacts can be determined from their current-voltage (I-V) characteristics. The literature contains many proposals for extracting the contact parameters using graphical methods. However, such methods are generally applicable only to contacts with a forward bias, whereas many Schottky contacts actually operate under a reverse bias. Accordingly, the present study proposed a generalized reverse current-voltage (I-V) plot which enables the series resistance, barrier height, and ideality factor of a reverse biased Schottky contact to be extracted from a single set of I-V measurements. A theoretical derivation of the proposed approach was presented and a series of validation tests were then performed. The results show that the proposed method is capable of extracting reliable estimates of the contact parameters even in the presence of experimental noise.

Optimization of axial symmetrical FGM under the transient-state temperate field

Xiao-dan Zhang, Ya-li Hong, Ai-hua Li

2012, 19(1): 59-63. doi: 10.1007/s12613-012-0515-4

中文摘要(275) PDF(8) SpringerLink

摘要:
A numerical procedure for analyzing the temperature distribution in a hollow axisymmetric cylinder, made of functionally gradient material (FGM), was investigated. Based on the thermal elasticity theory and the arbitrary difference precise integration (ADPI) method, temperature distribution through the FGM cylinder in the ring section under a transient-state temperature field was developed and presented. A genetic algorithm (GA) was applied to the thermal stress optimal design of an FGM hollow cylinder, and as a result, the minimum thermal stress distribution in the FGM cylinder was obtained. A corresponding numerical procedure regarding to a ceramic-metal FGM cylinder was performed, and the computational results were discussed.

Growth kinetics of cubic carbide free layers in graded cemented carbides

Liu-yong Shi, Yi-min Liu, Ji-hua Huang, Shou-quan Zhang, Xing-ke Zhao

2012, 19(1): 64-71. doi: 10.1007/s12613-012-0516-3

中文摘要(245) PDF(7) SpringerLink

摘要:
In order to reveal the formation mechanism of cubic carbide free layers (CCFL), graded cemented carbides with CCFL in the surface zone were fabricated by a one-step sintering procedure in vacuum, and the analysis on microstructure and element distribution were performed by scanning electron microscopy (SEM) and electron probe micro-analyzer (EPMA), respectively. A new physical model and kinetic equation were established based on experimental results. Being different from previous models, this model suggests that nitrogen diffusion outward is only considered as an induction factor, and the diffusion of titanium through liquid phase plays a dominative role. The driving force of diffusion is expressed as the differential value between nitrogen partial pressure and nitrogen equilibrium pressure essentially. Simulation results by the kinetic equation are in good agreement with experimental values, and the effect of process parameters on the growth kinetics of CCFL can also be explained reasonably by the current model.

Effects of submicron diamonds on the growth of copper in Cu-diamond co-deposition

You-yang Wei, Wei-ping Li, Hui-cong Liu, Yong-zheng Liu, Li-qun Zhu

2012, 19(1): 72-76. doi: 10.1007/s12613-012-0517-2

中文摘要(258) PDF(8) SpringerLink

摘要:
Submicron diamonds were co-deposited on aluminum substrates with copper from the acid copper sulfate electrolyte by electrolyte-suspension co-deposition. After submicron diamonds were added to the electrolyte, the shape of copper grains transformed from oval or round to polyhedron, the growth mode of copper grains transformed from columnar growth to gradual change in size, and the preferred orientation of copper grains transformed from (220) to (200). Analyzing the variation of cathodic overpotential, it was found that the cathodic overpotential tended to remain unchanged when copper plane (220) grew in the process of electrodepositing pure copper, while it tended to decrease with time when copper plane (200) grew in the process of co-deposition. It was inferred that copper plane (200) was propitious to the deposition of submicron diamonds.

Effect of magnesium and nickel coatings on the wetting behavior of alumina toughened zirconia by molten Al-Mg alloy

H. Sharifi, A. R. Khavandi, M. Divandari, M. I. Hasbullah

2012, 19(1): 77-82. doi: 10.1007/s12613-012-0518-1

中文摘要(331) PDF(9) SpringerLink

摘要:
The wettability of alumina toughened zirconia (ZTA) by Al-Mg alloy was investigated using the sessile drop technique. The effects of nickel coating, magnesium content, nitrogen atmosphere, and processing temperature on the contact angle between the molten alloy and the substrate were determined. Likewise, the effect of these factors on the wetting properties was studied. The results showed that the nickel coating on the ceramic substrate caused a significant reduction in solid/liquid surface energy and the contact angle decreased obviously. The presence of magnesium in the molten aluminum alloy in nitrogen atmosphere reduced the contact angle effectively. The presence of magnesium in the alloy must be at a minimum amount of 2wt%-3wt%. Moreover, it was suggested that some chemical reactions in the Al-Mg-N system led to the production of Mg₃N₂ and AlN compositions. These compositions improved the wetting properties of the systems by reducing the surface energy of the molten. It was shown that increasing the temperature is also an effective factor for the enhancement of wetting properties.

Characterization of 17-4PH stainless steel powders produced by supersonic gas atomization

Xin-ming Zhao, Jun Xu, Xue-xin Zhu, Shao-ming Zhang, Wen-dong Zhao, Guo-liang Yuan

2012, 19(1): 83-88. doi: 10.1007/s12613-012-0519-0

中文摘要(213) PDF(10) SpringerLink

摘要:
17-4PH stainless steel powders were prepared using a supersonic nozzle in a close-coupled gas atomization system. The characteristics of powder particles were carried out by means of a laser particle size analyzer, scanning electron microscopy (SEM), and the X-ray diffraction (XRD) technique. The results show that the mass median particle diameter is about 19.15 μm. Three main types of surface microstructures are observed in the powders:well-developed dendrite, cellular, and cellular dendrite structure. The XRD measurements show that, as the particle size decreases, the amount of fcc phase gradually decreases and that of bcc phase increases. The cooling rate is inversely related to the particle size, i.e., it decreases with an increase in particle size.

Mechanical properties of Mn-doped ZnO nanowires studied by first-principles calculations

Zhan-jun Gao, You-song Gu, Xue-qiang Wang, Yue Zhang

2012, 19(1): 89-94. doi: 10.1007/s12613-012-0520-7

中文摘要(248) PDF(8) SpringerLink

摘要:
First-principles calculations were performed to investigate the mechanical properties of ZnO nanowires and to study the doping and size effects. A series of strains were applied to ZnO nanowires in the axial direction and the elastic moduli of ZnO nanowires were obtained from the energy versus strain curves. Pure and Mn-doped ZnO nanowires with three different diameters (1.14, 1.43, and 1.74 nm) were studied. It is found that the elastic moduli of the ZnO nanowires are 146.5, 146.6, and 143.9 GPa, respectively, which are slightly larger than that of the bulk (140.1 GPa), and they increase as the diameter decreases. The elastic moduli of the Mn-doped ZnO nanowires are 137.6, 141.8, and 141.0 GPa, which are slightly lower than those of the undoped ones by 6.1%, 3.3%, and 2.0%, respectively. The mechanisms of doping and size effect were discussed in terms of chemical bonding and geometry considerations.

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