International Journal of Minerals, Metallurgy and Materials

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A model to determine hole spacing in the rock fracture process by non-explosive expansion material

Shobeir Arshadnejad, Kamran Goshtasbi, Jamshid Aghazadeh

2011, 18(5): 509-514. doi: 10.1007/s12613-011-0470-5

中文摘要(296) PDF(13) SpringerLink

摘要:
The application of the non-explosive expansion material (NEEM) is widely used as the controlled fracture method in quarry mining, especially in hard rocks. The pressure of NEEM is an important parameter in causing rock fracture. An empirical model based on hole spacing was developed to determine the pressure of NEEM in the rock fracture process. Primarily, the empirical model was developed by the mathematical method, utilizing dimensional analysis. Then, the Phase2 code, which is based on the finite element method, was utilized to predict crack growth in rocks. The results of numerical analysis show slight deviations from the empirical model. Hence, the polynomial regression analysis was used to modify the model. Finally, the modified model shows a good agreement with the results gained from numerical modeling.

Effectiveness of sodium silicate as gangue depressants in iron ore slimes flotation

Danda Srinivas Rao, Tadiparthi Venkata VijayaKumar, Sripada Subba Rao, Swarna Prabhakar, Guntamadugu Bhaskar Raju

2011, 18(5): 515-522. doi: 10.1007/s12613-011-0471-4

中文摘要(384) PDF(16) SpringerLink

摘要:
The recovery of iron from the screw classifier overflow slimes by direct flotation was studied. The relative effectiveness of sodium silicates with different silica-to-soda mole ratios as depressants for silica and silicate bearing minerals was investigated. Silica-to-soda mole ratio and silicate dosage were found to have significant effect on the separation efficiency. The results show that an increase of Fe content in the concentrate is observed with concomitant reduction in SiO₂ and Al₂O₃ levels when a particular type of sodium silicate at a proper dosage is used. The concentrate of 58.89wt% Fe, 4.68wt% SiO₂, and 5.28wt% Al₂O₃ with the weight recovery of 38.74% and the metal recovery of 41.13% can be obtained from the iron ore slimes with 54.44wt% Fe, 6.72wt% SiO₂, and 6.80wt% Al₂O₃, when Na₂SiO₃ with a silica-to-soda mole ratio of 2.19 is used as a depressant at a feed rate of 0.2 kg/t.

Zinc bioleaching from an iron concentrate using Acidithiobacillus ferrooxidans strain from Hercules Mine of Coahuila, Mexico

Diola Marina Núñez-Ramírez, Aquiles Solís-Soto, Javier López-Miranda, Benito Pereyra-Alférez, Miriam Rutiaga-Quiñónes, Luis Medina-Torres, Hiram Medrano-Roldán

2011, 18(5): 523-526. doi: 10.1007/s12613-011-0472-3

中文摘要(312) PDF(9) SpringerLink

摘要:
The iron concentrate from Hercules Mine of Coahuila, Mexico, which mainly contained pyrite and pyrrhotite, was treated by the bioleaching process using native strain Acidithiobacillus ferrooxidans (A. ferrooxidans) to determine the ability of these bacteria on the leaching of zinc. The native bacteria were isolated from the iron concentrate of the mine. The bioleaching experiments were carried out in shake flasks to analyze the effects of pH values, pulp density, and the ferrous sulfate concentration on the bioleaching process. The results obtained by microbial kinetic analyses for the evaluation of some aspects of zinc leaching show that the native bacteria A. ferrooxidans, which is enriched with a 9K Silverman medium under the optimum conditions of pH 2.0, 20 g/L pulp density, and 40 g/L FeSO₄, increases the zinc extraction considerably observed by monitoring during15 d, i.e., the zinc concentration has a decrease of about 95% in the iron concentrate.

Inclusion variations and calcium treatment optimization in pipeline steel production

Jian-hua Liu, Hua-jie Wu, Yan-ping Bao, Min Wang

2011, 18(5): 527-534. doi: 10.1007/s12613-011-0473-2

中文摘要(341) PDF(22) SpringerLink

摘要:
SiCa line and SiCaBaFe alloy were injected into liquid pipeline steel at the end of LF refining as calcium treatment, and samples were taken from the ladles, mould, and slabs. Analysis of Ca content and inclusions shows that Ca content in steel decreases obviously in the following process after calcium treatment; the compositions, morphology, and sizes of inclusions also vary much in the production; primary inclusions in the ladles prior to calcium treatment are mainly Al₂O₃ inclusions, but they turn to fine irregular CaS-CaO-Al₂O₃ compound inclusions after the treatment, then become fine globular CaO-Al₂O₃ inclusions in the mould, and finally change to a few larger irregular CaS-CaO-Al₂O₃ complex inclusions in the slabs. Thermodynamic study reveals that inclusion variations are related with the preferential reactions among Ca, Al₂O₃, and S and the precipitation of S in CaO-Al₂O₃ inclusions with high sulfur capacity. New evaluation standards for calcium treatment in high-grade pipeline steel were put forward according to the inclusion variations and requirements of pipeline steel on inclusion controlling, and the calcium process was studied and optimized.

Numerical investigation of the effect of transitory strand opening on mixing in a multistrand tundish

Sabin Kumar Mishra, Pradeep Kumar Jha, Satish Chandra Sharma, Satish Kumar Ajmani

2011, 18(5): 535-542. doi: 10.1007/s12613-011-0474-1

中文摘要(312) PDF(17) SpringerLink

摘要:
In a multistrand, the outlet near the inlet produces short circuiting flow. This leads to the formation of dead zones inside the tundish, and consequently, the mean residence time decreases. In the present study, numerical investigation of mixing inside a delta shaped tundish with sloping boundaries was carried out by solving the Navier-Stokes equation and employing the standard turbulence model. To decrease the dead zone volume inside the tundish, the effect of closing the outlet near the inlet for a small amount of time and further opening it on the mixing behavior of the tundish was studied. The outlets near the inlet were closed for varying amount of time, and the transient analysis of fluid flow and the tracer dispersion study were carried out to find the mixing parameters of the tundish, namely, mean residence time and the ratio of mixed to dead volume of the tundish. An optimum closure time of the near outlet has been found, which yields best mixing inside the tundish. The numerical code was validated against the experimental observation by performing the tracer dispersion study inside a multistrand tundish and the reasonably good match between the experimental and numerical results in terms of residence time distribution (RTD) curves. The results obtained from the present study confirm the strong role of choosing the right time for opening and closing the outlets to get improved characteristics for the fluid flow and mixing behavior of the tundish. The educational version of computational fluid dynamics (CFD) software PHOENICS was used to solve the governing equations and interpret the results in different forms.

Effects of Si on the stability of retained austenite and temper embrittlement of ultrahigh strength steels

Li-jun Wang, Qing-wu Cai, Hui-bin Wu, Wei Yu

2011, 18(5): 543-550. doi: 10.1007/s12613-011-0475-0

中文摘要(366) PDF(21) SpringerLink

摘要:
Effects of silicon (Si) content on the stability of retained austenite and temper embrittlement of ultrahigh strength steels were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), and other experimental methods. The results show that Si can suppress temper embrittlement, improve temper resistance, and hinder the decomposition of retained austenite. Reversed austenite appears gradually with the increase of Si content during tempering. Si has a significant effect on enhancing carbon (C) partitioning and improving the stability of retained austenite. Si and C atoms are mutually exclusive in lath bainite, while they attract each other in austenite. ɛ-carbides are found in 1.8wt% Si steel tempered at 250℃, and they get coarsened obviously when tempered at 400℃, leading to temper embrittlement. Not ɛ-carbides but acicular or lath carbides lead to temper embrittlement in 0.4wt% Si steel, which can be inferred as cementites and composite compounds. Temper embrittlement is closely related to the decomposition of retained austenite and the formation of reversed austenite.

Effect of cooling parameters on the microstructure and properties of Mo-bearing and Cr-bearing steels

Xiang-dong Huo, Yu-qian Li, Yu-tao Zhao, Hai-wang Zhang, Zhao-hui Li

2011, 18(5): 551-556. doi: 10.1007/s12613-011-0476-z

中文摘要(175) PDF(10) SpringerLink

摘要:
To develop low-cost low carbon bainitic steel, Mo-bearing and Cr-bearing steels were melted in a vacuum induction furnace and were researched by thermal simulation and hot rolling at the laboratory. As the cooling rate increases from 0.2 to 50℃/s, the transformation temperatures of two steels lie between 650 and 400℃, and the final microstructures of them change from quasi-polygonal ferrite and granular bainite to lath bainite. Compared with cooling in air or by interrupted cooling, Mo-bearing and Cr-bearing steel plates cooled by sprayed water boast higher strength and superior toughness, for large-size islands are responsible for the poor mechanical properties. Compared to Mo, Cr is effective to isolate the bainitic reaction in low carbon steel, and the bainitic microstructure can also be obtained in Cr-bearing steel cooled at a wide range of cooling rate.

Effects of cold rolling on the microstructure and mechanical properties of Fe-Ni-Mn-Mo-Ti-Cr maraging steels

Abbas Mahmudi, Syamak Hossein Nedjad, Mir Masud Jabbari Behnam

2011, 18(5): 557-561. doi: 10.1007/s12613-011-0477-y

中文摘要(388) PDF(12) SpringerLink

摘要:
Effects of cold rolling on the microstructure and mechanical properties of Fe-Ni-Mn-Mo-Ti-Cr maraging steels were studied. To investigate the microstructure and mechanical properties, optical microscopy, scanning electron microscopy, X-ray diffraction, tensile test, and hardness test were used. The results show that the solution-annealing treatment in the cold-rolled steel redounds to the formation of submicrocrystalline Fe₂(Mo, Ti) Laves phase particles, which are stable at high temperatures. These secondary Laves phase particles prevent from recrystallization at high temperatures and correspond to semi-brittle fracture in the subsequent aging treatment.

Simulation of the continuous casting process in a mold of free-cutting steel 38MnVS based on a MiLE method

Yun-jin Xia, Fu-ming Wang, Jin-long Wang, Guo-zhong Li

2011, 18(5): 562-569. doi: 10.1007/s12613-011-0478-x

中文摘要(267) PDF(11) SpringerLink

摘要:
A new method called mixed Lagrangian and Eulerian (MiLE) method was used to simulate the continuous casting process in a mold of free-cutting steel 38MnVS. The simulation results are basically in agreement with experimental data in the literature, achieving the three-dimensional visualization of temperature distribution, melt flow, shell thickness, and stress distribution of blooms in a mold. It is shown that the flow velocity of steel melt becomes smaller gradually as the casting proceeds. When the flow reaches a certain depth, two types of flow patterns can be observed in the upper zone of the mold. The first flow pattern is to flow downwards, and the second one is to flow upwards to the meniscus. The corner temperature is higher, and the thickness is thinner than those in the mid-face. The effective stress in the corner area is much bigger than that in the mid-face, indicating that the corner area is the dangerous zone of cracking.

Kinetics of recrystallization for twin-roll casting AZ31 magnesium alloy during homogenization

Hu Zhao, Pei-jie Li, Liang-ju He

2011, 18(5): 570-575. doi: 10.1007/s12613-011-0479-9

中文摘要(391) PDF(11) SpringerLink

摘要:
The kinetics of recrystallization for twin-roll casting AZ31 magnesium alloy with different thicknesses during homogenization was analyzed. It is shown that fine grains are first formed at the boundaries of deformed bands in the twin-roll casting slab. The recrystallized grains with no strain are gradually substituted for the deformed microstructure of twin-roll casting AZ31 magnesium alloy. The incubation temperature and time for the recrystallization of a twin-roll casting AZ31 magnesium alloy strip with a thickness of 3 mm are lower and shorter than those of the 6-mm thick strip, respectively. The 3-mm thick twin-roll casting magnesium alloy has finer grains than the 6-mm thick strip. The activation energies of recrystallization for twin-roll casting AZ31 magnesium alloy slabs with the thickness of 3 and 6 mm are 88 and 69 kJ/mol, respectively. The kinetics curves of recrystallization for twin-roll casting AZ31 magnesium alloy were obtained.

Grain boundary characteristics and tensile properties of Ti14 alloy after semi-solid deformation

Yong-nan Chen, Jian-feng Wei, Yong-qing Zhao

2011, 18(5): 576-581. doi: 10.1007/s12613-011-0480-3

中文摘要(332) PDF(11) SpringerLink

摘要:
The microstructure and room-temperature tensile properties of Ti14, a new α+Ti₂Cu alloy, were investigated after conventional forging at 950℃ and semi-solid forging at 1000 and 1050℃, respectively. Results show that coarse grains and grain boundaries are obtained in the semi-solid alloys. The coarse grain boundaries are attributed to Ti₂Cu phase precipitations occurred on the grain boundaries during the solidification. It is found that more Ti₂Cu phase precipitates on the grain boundaries at a higher semi-solid forging temperature, which forms precipitated zones and coarsens the grain boundaries. Tensile tests exhibit high strength and low ductility for the semi-solid forged alloys, especially after forging at 1000℃. Fracture analysis reveals the evidence of ductile failure mechanisms for the conventional forged alloy and cleavage fracture mechanisms for the alloy after semi-solid forging at 1050℃.

Mechanical properties of directionally solidified lead-antimony alloys

Mevlüt Şahin, Hasan Kaya

2011, 18(5): 582-588. doi: 10.1007/s12613-011-0481-2

中文摘要(460) PDF(18) SpringerLink

摘要:
The Pb-17wt% Sb alloy was directionally solidified under two solidification conditions: with different temperature gradients (G=0.93–3.67 K/mm) at a constant growth rate (V=17.50 μm/s) and with different growth rates (V=8.3–497 μm/s) at a constant temperature gradient (G=3.67 K/mm) in a Bridgman furnace. Microstructure parameters, such as primary dendrite arm spacing (λ₁), secondary dendrite arm spacing (λ₂), and dendrite tip radius (R), were measured. The microhardness (Hv) and ultimate tensile strength (σ) of the directional solidification samples were also measured. The influences of solidification and microstructure parameters on Hv and σ were investigated. The results obtained in this work were compared with similar experimental researches in literatures. It is shown that the Hv and σ values increase with the increase of G and V, but decrease with the increase of λ₁, λ₂, and R.

Comparative study of oxidation ability between boron-doped diamond (BDD) and lead oxide (PbO₂) electrodes

Jun-jun Wei, Xiu-ping Zhu, Fan-xiu Lü, Jin-ren Ni

2011, 18(5): 589-593. doi: 10.1007/s12613-011-0482-1

中文摘要(263) PDF(14) SpringerLink

摘要:
The electrochemical oxidation capabilities of two high-performance electrodes, the boron-doped diamond film on Ti (Ti/BDD) and the lead oxide film on Ti (Ti/PbO₂), were discussed. Hydroxyl radicals (·HO) generated on the electrode surface were detected by using p-nitrosodimethylaniline (RNO) as the trapping reagent. Electrochemical oxidation measurements, including the chemical oxygen demand (COD) removal and the current efficiency (CE), were carried out via the degradation of p-nitrophenol (PNP) under the galvanostatic condition. The results indicate that an indirect reaction, which is attributed to free hydroxyl radicals with high activation, conducts on the Ti/BDD electrode, while the absorbed hydroxyl radicals generated at the Ti/PbO₂ surface results in low degradation efficiency. Due to quick mineralization which combusts PNP to CO₂ and H₂O absolutely by the active hydroxyl radical directly, the CE obtained on the Ti/BDD electrode is much higher than that on the Ti/PbO₂ electrode, notwithstanding the number of hydroxyl radicals produced on PbO₂ is higher than that on the BDD surface.

Synthesis and characterization of Pt-MoO_x-TiO₂ electrodes for direct ethanol fuel cells

Xiu-yu Wang, Jing-chang Zhang, Xu-dong Cao, Yuan-sheng Jiang, Hong Zhu

2011, 18(5): 594-599. doi: 10.1007/s12613-011-0483-0

中文摘要(290) PDF(15) SpringerLink

摘要:
To enhance the CO-tolerance performance of anode catalysts for direct ethanol fuel cells, carbon nanotubes were modified by titanium dioxide (donated as CNTs@TiO₂) and subsequently served as the support for the preparation of Pt/CNTs@TiO₂ and Pt-Mo/CNTs@TiO₂ electrocatalysts via a UV-photoreduction method. The physicochemical characterizations of the catalysts were carried out by using X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and infrared spectroscopy of adsorbed probe ammonia molecules. The electrocatalytic properties of the catalysts for methanol oxidation were investigated by the cyclic voltammetry technique. The results show that Pt-Mo/CNTs@TiO₂ electrode exhibits the highest performance in all the electrodes. It is explained that, the structure, the oxidation states, and the acid-base properties of the catalysts are influenced due to the strong interaction between Ti and Mo species by adding TiO₂ and MoO_x to the Pt-based catalysts.

Influence of Ag doping on the microstructure and electrical properties of ZnO-Bi₂O₃-based varistor ceramics

Long-Biao Zhu, Da-yang Chen, Xin-xin Wu, Qing-dong Zhong, Yu-fa Qi, Li-yi Shi

2011, 18(5): 600-605. doi: 10.1007/s12613-011-0484-z

中文摘要(271) PDF(18) SpringerLink

摘要:
Silver in the form of AgNO₃ was added to ZnO-based varistor ceramics prepared by the solid-state reaction method. The effects of AgNO₃ on both the microstructure and electrical properties of the varistors were studied in detail. The optimum addition amount of AgNO₃ in ZnO-based varistors was also determined. The mechanism for grain growth inhibition by silver doping was also proposed. The results indicate that the varistor threshold voltage increases substantially along with the AgNO₃ content increasing from 0 to 1.5mol%. Also, the introduction of AgNO₃ can depress the mean grain size of ZnO, which is mainly responsible for the threshold voltage. Furthermore, the addition of AgNO₃ results in a slight decrease of donor density and a more severe fall in the density of interface states, which cause a decline in barrier height and an increase in the depletion layer.

Synthesis, characterization, and theoretical study of N, S-codoped nano-TiO₂ with photocatalytic activities

Hong-tao Gao, Yuan-yuan Liu, Cui-hong Ding, Dong-mei Dai, Guang-jun Liu

2011, 18(5): 606-614. doi: 10.1007/s12613-011-0485-y

中文摘要(261) PDF(9) SpringerLink

摘要:
Nitrogen and sulfur doped titanium dioxide photocatalysts were prepared by the sol-gel method. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV-visible diffuse reflectance spectra (DRS). Photocatalytic activities of the samples were investigated on the degradation of methyl orange (MO). The effect of the dopants on the electronic structure of TiO₂ was studied by the first-principles calculations based on the density functional theory (DFT). The orbital hybridization resulted in energy gap narrowing and electronic delocalization in the crystal of doped TiO₂. Mobile electrons of varied energetic states could offer enhanced electron transfer, together with optical absorption improvement. The results show that the doping elements of N and S play a cooperative role in the modification of electronic structure, which enhances the photocatalytic performance. The experimentally observed absorption edges of N-doped TiO₂, S-doped TiO₂, and N, S-codoped TiO₂ are 420, 413, and 429 nm, respectively, which can be explained by the theoretical calculation results.

Electroless copper-phosphorus coatings with the addition of silicon carbide (SiC) particles

Soheila Faraji, Afidah Abdul Rahim, Norita Mohamed, Coswald Stephen Sipaut

2011, 18(5): 615-622. doi: 10.1007/s12613-011-0486-x

中文摘要(256) PDF(16) SpringerLink

摘要:
Cu-P-silicon carbide (SiC) composite coatings were deposited by means of electroless plating. The effects of pH values, temperature, and different concentrations of sodium hypophosphite (NaH₂PO₂·H₂O), nickel sulfate (NiSO₄·6H₂O), sodium citrate (C₆H₅Na₃O₇·2H₂O) and SiC on the deposition rate and coating compositions were evaluated, and the bath formulation for Cu-P-SiC composite coatings was optimised. The coating compositions were determined using energy-dispersive X-ray analysis (EDX). The corresponding optimal operating parameters for depositing Cu-P-SiC are as follows: pH 9; temperature, 90℃; NaH₂PO₂·H₂O concentration, 125 g/L; NiSO₄·6H₂O concentration, 3.125 g/L; SiC concentration, 5 g/L; and C₆H₅Na₃O₇·2H₂O concentration, 50 g/L. The surface morphology of the coatings analysed by scanning electron microscopy (SEM) shows that Cu particles are uniformly distributed. The hardness and wear resistance of Cu-P composite coatings are improved with the addition of SiC particles and increase with the increase of SiC content.

Thermal conductivity model of filled polymer composites

Ming-xia Shen, Yin-xin Cui, Jing He, Yao-ming Zhang

2011, 18(5): 623-631. doi: 10.1007/s12613-011-0487-9

中文摘要(369) PDF(19) SpringerLink

摘要:
Theoretical and empirical models for predicting the thermal conductivity of polymer composites were summarized since the 1920s. The effects of particle shape, filler amount, dispersion state of fillers, and interfacial thermal barrier on the thermal conductivity of filled polymer composites were investigated, and the agreement of experimental data with theoretical models in literatures was discussed. Silica with high thermal conductivity was chosen to mix with polyvinyl-acetate (EVA) copolymer to prepare SiO₂/EVA co-films. Experimental data of the co-films’ thermal conductivity were compared with some classical theoretical and empirical models. The results show that Agari’s model, the mixed model, and the percolation model can predict well the thermal conductivity of SiO₂/EVA co-films.

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2011年第18卷第5期