International Journal of Minerals, Metallurgy and Materials

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First-principle study on the surface atomic relaxation properties of sphalerite

Jian Liu, Shu-ming Wen, Yong-jun Xian, Shao-jun Bai, Xiu-min Chen

2012, 19(9): 775-781. doi: 10.1007/s12613-012-0627-x

中文摘要(188) PDF(10) SpringerLink

摘要:
The surface properties of sphalerite (ZnS) were theoretically investigated using first principle calculations based on the density functional theory (DFT). DFT results indicate that both the (110) and the (220) surfaces of sphalerite undergo surface atom relaxation after geometry optimization, which results in a considerable distortion of the surface region. In the normal direction, i.e., perpendicular to the surface, S atoms in the first surface layer move outward from the bulk (d₁), whereas Zn atoms move toward the bulk (d₂), forming an S-enriched surface. The values of these displacements are 0.003 nm for d₁ and 0.021 nm for d₂ on the (110) surface, and 0.002 nm for d₁ and 0.011 nm for d₂ on the (220) surface. Such a relaxation process is visually interpreted through the qualitative analysis of molecular mechanics. X-ray photoelectron spectroscopic (XPS) analysis provides the evidence for the S-enriched surface. A polysulphide (S_n^2-) surface layer with a binding energy of 163.21 eV is formed on the surface of sphalerite after its grinding under ambient atmosphere. This S-enriched surface and the S_n^2- surface layer have important influence on the flotation properties of sphalerite.

Investigation on leaching of malachite by citric acid

M. A. Shabani, M. Irannajad, A. R. Azadmehr

2012, 19(9): 782-786. doi: 10.1007/s12613-012-0628-9

中文摘要(344) PDF(28) SpringerLink

摘要:
Leaching of an oxidized copper ore containing malachite, as a new approach, was investigated by an organic reagent, citric acid. Sulfuric acid is the most common reagent in the leaching of oxide copper ores, but it has several side effects such as severe adverse impact on the environment. In this investigation, the effects of particle size, acid concentration, leaching time, solid/liquid ratio, temperature, and stirring speed were optimized. According to the experimental results, malachite leaching by citric acid was technically feasible. Optimum leaching conditions were found as follows:the range of particle size, 105-150 µm; acid concentration, 0.2 M; leaching time, 30 min; solid/liquid ratio, 1:20 g/mL; temperature, 40℃; and stirring speed, 200 r/min. Under the optimum conditions, 91.61% of copper was extracted.

Numerical simulation of macrosegregation in steel ingots using a two-phase model

Wen-sheng Li, Hou-fa Shen, Bai-cheng Liu

2012, 19(9): 787-794. doi: 10.1007/s12613-012-0629-8

中文摘要(211) PDF(15) SpringerLink

摘要:
A two-phase model for the prediction of macrosegregation formed during solidification is presented. This model incorporates the descriptions of heat transfer, melt convection, solute transport, and solid movement on the system scale with microscopic relations for grain nucleation and growth. Then the model is used to simulate the solidification of a benchmark industrial 3.3-t steel ingot. Simulations are performed to investigate the effects of grain motion and pipe shrinkage formation on the final macrosegregation pattern. The model predictions are compared with experimental data and numerical results from literatures. It is demonstrated that the model is able to express the overall macrosegregation patterns in the ingot. Furthermore, the results show that it is essential to consider the motion of equiaxed grains and the formation of pipe shrinkage in modelling. Several issues for future model improvements are identified.

Effect of deep cryogenic treatment on the formation of nano-sized carbides and the wear behavior of D2 tool steel

Kamran Amini, Amin Akhbarizadeh, Sirus Javadpour

2012, 19(9): 795-799. doi: 10.1007/s12613-012-0630-2

中文摘要(223) PDF(13) SpringerLink

摘要:
The effect of deep cryogenic treatment on the microstructure, hardness, and wear behavior of D2 tool steel was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), hardness test, pin-on-disk wear test, and the reciprocating pin-on-flat wear test. The results show that deep cryogenic treatment eliminates retained austenite, makes a better carbide distribution, and increases the carbide content. Furthermore, some new nano-sized carbides form during the deep cryogenic treatment, thereby increasing the hardness and improving the wear behavior of the samples.

Influence of silane coupling agent on the conversion film forming of galvanized steel treated with cerium salt

Li-hua Gong, Rui-rui Tang, Yu-qiao Zhu, Dong-liang Chen

2012, 19(9): 800-804. doi: 10.1007/s12613-012-0631-1

中文摘要(187) PDF(11) SpringerLink

摘要:
The influence of silane coupling agent on the film forming of galvanized steel treated with cerium salt was studied by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), and the corrosion resistance of conversion films was analyzed by electro interstitial scanning (EIS). The results show that silane coupling agent KH-570 has significant influence on the compactness and homogeneity of cerium conversion films, and the process of film forming is promoted by increasing the content of tervalent and tetravalent cerium oxide. The impedance value of the cerium conversion film, especially modified with KH-570, is greater than that of the base metal, which reveals that it is necessary to add silane coupling agent to the film-forming solution in order to improve the corrosion resistance of the conversion film.

Effects of precipitates and inclusions on the fracture toughness of hot rolling X70 pipeline steel plates

Mai-wen Zhou, Hao Yu

2012, 19(9): 805-811. doi: 10.1007/s12613-012-0632-0

中文摘要(290) PDF(11) SpringerLink

摘要:
In order to investigate the fracture toughness, crack tip opening displacement (CTOD) experiments were conducted on two X70 pipeline steel plates with different rolling processes. After the experiments, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to observe the microstructure and fracture morphology. The effects of precipitates on the fracture toughness and the crack initiation mechanism induced by inclusions were analyzed. The CTOD result shows that the steel with a lower finishing cooling temperature has a higher fracture toughness. Inclusions with different shapes and two kinds of precipitates with different sizes were observed. It can be concluded that precipitates with different sizes have different effects and mechanisms on the fracture toughness. Distinguished from the earlier researches, inclusions enriched in silicon can be also served as the crack initiation.

Microstructural and mechanical characteristics of Al-alloyed ductile iron upon casting and annealing

N. Haghdadi, B. Bazaz, H. R. Erfanian-Naziftoosi, A. R. Kiani-Rashid

2012, 19(9): 812-820. doi: 10.1007/s12613-012-0633-z

中文摘要(205) PDF(11) SpringerLink

摘要:
Ductile iron containing 6.16wt% Al was developed to investigate the effects of aluminum on both its microstructure and hardness. It was found that aluminum not only increases the nodule count and pearlite content but also improves the hardness in both sand mold and metal mold castings. Annealing treatments were conducted to attain a homogenous microstructure and improve high-temperature serviceability. A ferrite/carbide or ferritic matrix was gained depending on the annealing temperature. It is also discovered that annealing has inverse influences on the hardness of the bulk alloy and the ferrite phase. Although it causes a small decrease in the bulk hardness of the specimens, it leads to an increase in the microhardness of the ferrite. Micro-segregation of the alloying elements was also investigated by means of electron probe micro-analysis for the specimens with different annealing durations and the as-cast specimen as well. An optimum annealing time was proposed to result in the least amount of micro-segregation of aluminum and silicon between graphite nodules.

A method to study interface diffusion of arsenic into a Nb-Ti microalloyed low carbon steel

Yuan-zhi Zhu, Jian-ping Xu

2012, 19(9): 821-826. doi: 10.1007/s12613-012-0634-y

中文摘要(152) PDF(9) SpringerLink

摘要:
A novel diffusion couple method was used to investigate the interface diffusion of arsenic into a Nb-Ti microalloyed low carbon steel and its effects on phase transformation at the interface. It is discovered that the content of arsenic has great effect on grain growth and phase transformation at high temperature. When the arsenic content is no more than 1wt%, there is no obvious grain growth and no obvious ferrite transitional region formed at the diffusion interface. However, when the arsenic content is no less than 5wt%, the grain grows very rapidly. In addition, the arsenic-enriched ferrite transitional layer forms at the diffusion interface in the hot-rolling process, which results from a slower diffusion rate of arsenic atoms than that of carbon in ferrite.

Effect of oxygen content and heat treatment on carbide precipitation behavior in PM Ni-base superalloys

Heng-san Liu, Lin Zhang, Xin-bo He, Xuan-hui Qu, Hong-min Zhu, Guo-qing Zhang

2012, 19(9): 827-835. doi: 10.1007/s12613-012-0635-x

中文摘要(195) PDF(13) SpringerLink

摘要:
The influence of oxygen content and heat treatment on the evolution of carbides in a powder metallurgy (PM) Ni-base superalloy was characterized. The results reveal that oxygen content has little influence on the precipitation of carbides inside the particles. However, under the consolidated state, stable Ti oxides on the particle surface act as nuclei for the precipitation of prior particle boundaries (PPB). Also, oxygen can diffuse internally along grain boundaries under compressive stress, which favors the precipitation of carbides inside the particles. Therefore, a higher amount of carbides will appear with more oxygen content in the case of consolidated alloys. It is also observed that PPB can be disrupted into discontinuous particles at 1200℃, but this carbide network is hard to be eliminated completely. The combined MC-M₂₃C₆ morphology approves the nucleation and growth mechanism of carbide evolution.

Effect of cross wedge rolling on the microstructure of GH4169 alloy

Ning Zhang, Bao-yu Wang, Jian-guo Lin

2012, 19(9): 836-842. doi: 10.1007/s12613-012-0636-9

中文摘要(226) PDF(10) SpringerLink

摘要:
The metal microstructure during the hot forming process has a significant effect on the mechanical properties of final products. To study the microstructural evolution of the cross wedge rolling (CWR) process, the microstructural model of GH4169 alloy was programmed into the user subroutine of DEFORM-3D by FORTRAN. Then, a coupled thermo-mechanical and microstructural simulation was performed under different conditions of CWR, such as area reduction, rolling temperature, and roll speed. Comparing experimental data with simulation results, the difference in average grain size is from 11.2% to 33.4% so it is verified that the microstructural model of GH4169 alloy is reliable and accurate. The fine grain of about 12-15 μm could be obtained by the CWR process, and the grain distribution is very homogeneous. For the symmetry plane, increasing the area reduction is helpful to refine the grain and the value should be around 61%. Moreover, when the rolling temperature changes from 1000 to 1100℃ and the roll speed from 6 to 10 r·min^-1, the grain size of the rolled piece decreases first and then increases. The temperature may be better to choose the value around 1050℃ and the speed less than 10 r·min^-1.

Influence of sintering temperature on the structure and piezoelectric properties of ZnO-modified (Li, Na, K)NbO₃ lead-free ceramics

Hai-tao Li, Bo-ping Zhang, Wei-gang Yang, Nan Ma

2012, 19(9): 843-848. doi: 10.1007/s12613-012-0637-8

中文摘要(215) PDF(29) SpringerLink

摘要:
ZnO-modified (Li, Na, K)NbO₃ lead-free ceramics with a nominal composition of Li_0.06(Na_0.535K_0.48)_0.94NbO₃+0.7mol% ZnO (LNKN-Z₇) was synthesized normally at 930-1000℃. The Zn ions incorporated into the A-site at a higher sintering temperature, which changed LNKN-Z₇ to soft piezoelectric ceramics with the mechanical quality factor decreasing from 228 to 192. A phase transition from tetragonal to orthorhombic symmetry was identified by XRD analysis, and the corresponding calculation of lattice parameters was conducted at 970-980℃. Because of such transitional behavior and fine microstructure, the optimized values of piezoelectric coefficient, planar electromechanical coupling coefficient, and relative dielectric constant were obtained.

Influence of yttrium on the structure and magnetostriction of Fe₈₃Ga₁₇ alloy

Xi-ming Xiao, Xue-xu Gao, Ji-heng Li, Jian-xin Xie

2012, 19(9): 849-855. doi: 10.1007/s12613-012-0638-7

中文摘要(202) PDF(7) SpringerLink

摘要:
Polycrystalline Fe₈₃Ga₁₇ alloy rods with various amounts of yttrium were prepared by high vacuum induction melting. It is found that yttrium addition has a significant effect on the structure and magnetostriction of Fe₈₃Ga₁₇ alloy. The small addition of yttrium alters the solidification character and the grain shape of Fe₈₃Ga₁₇ alloy, and as a result, columnar grains with the <100> preferential direction are produced. Yttrium addition improves the magnetostrictive performance of the as-cast Fe₈₃Ga₁₇ alloy. The magnetostriction values of the as-cast alloy with 0.32at% and 0.64at% yttrium addition go up to 119×10^-6 and 137×10^-6 under 15 MPa compressive stress, respectively. The energy dispersive spectroscopy (EDS) result shows that almost all of the yttrium atoms exist in the Y₂Fe_17-xGa_x phase. A small amount of this kind of secondary phase cannot obviously increase the saturate magnetic field.

Reaction mechanisms for 0.5Li₂MnO₃·0.5LiMn_0.5Ni_0.5O₂ precursor prepared by low-heating solid state reaction

Dong Li, Fang Lian, Xin-mei Hou, Kuo-chih Chou

2012, 19(9): 856-862. doi: 10.1007/s12613-012-0639-6

中文摘要(162) PDF(9) SpringerLink

摘要:
Lithium-excess manganese layered oxides, which are commonly described in chemical formula 0.5Li₂MnO₃·0.5LiMn_0.5Ni_0.5O₂, were prepared by low-heating solid state reaction. The reaction mechanisms of synthesizing precursors, the decomposition mechanism, and intermediate materials in calcination were investigated by means of Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The major diffraction patterns of 0.5Li₂MnO₃·0.5LiMn_0.5Ni_0.5O₂ powder calcinated at 720℃ for 15 h are indexed to the hexagonal structure with a space group of R3m, and the clear splits of doublets at (006)/(102) and (108)/(110) indicate that the sample adopts a well-layered structure. FESEM images show that the size of the agglomerated particles of the sample ranges from 100 to 300 nm.

SOFC composite electrolyte based on LSGM-8282 and zirconia or doped zirconia from zircon concentrate

Fitria Rahmawati, Bambang Prijamboedi, Syoni Soepriyanto, Ismunandar

2012, 19(9): 863-871. doi: 10.1007/s12613-012-0640-0

中文摘要(228) PDF(11) SpringerLink

摘要:
The aim of this research is to study zirconia-based electrolyte materials to increase the commercial value of zircon concentrate as a side product of tin mining industries. Synthesis of CaO-Y₂O₃-ZrO₂ (CYZ) and 8mol% Y₂O₃-ZrO₂ (8YSZ) was carried out by solid state reaction. The result shows that ZrO₂ presents in tetragonal phase. Doping of Y₂O₃ into ZrO₂ allows a phase transformation from tetragonal into cubic structure with small percentage of monoclinic phase. Meanwhile, doping of CaO-Y₂O₃ allows a phase transformation into a single cubic phase. These phase transformations enhance the ionic conductivity of the material. Introduction of 10wt% of LSGM-8282 into CYZ (CYZ-L90:10) allows further improvement of inter-grain contact shown by SEM morphological analysis and leads to the enhancement of ionic conductivity.

Thermal treatment and utilization of Al-rich waste in high calcium fly ash geopolymeric materials

Prinya Chindaprasirt, Ubolluk Rattanasak, Pimdao Vongvoradit, Supichart Jenjirapanya

2012, 19(9): 872-878. doi: 10.1007/s12613-012-0641-z

中文摘要(319) PDF(8) SpringerLink

摘要:
The Al-rich waste with aluminium and hydrocarbon as the major contaminant is generated at the wastewater treatment unit of a polymer processing plant. In this research, the heat treatment of this Al-rich waste and its use to adjust the silica/alumina ratio of the high calcium fly ash geopolymer were studied. To recycle the raw Al-rich waste, the waste was dried at 110℃ and calcined at 400 to 1000℃. Mineralogical analyses were conducted using X-ray diffraction (XRD) to study the phase change. The increase in calcination temperature to 600, 800, and 1000℃ resulted in the phase transformation. The more active alumina phase of active θ-Al₂O₃ was obtained with the increase in calcination temperature. The calcined Al-rich waste was then used as an additive to the fly ash geopolymer by mixing with high calcium fly ash, water glass, 10 M sodium hydroxide (NaOH), and sand. Test results indicated that the calcined Al-rich waste could be used as an aluminium source to adjust the silica/alumina ratio and the strength of geopolymeric materials. The fly ash geopolymer mortar with 2.5wt% of the Al-rich waste calcined at 1000℃ possessed the 7-d compressive strength of 34.2 MPa.

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2012年第19卷第9期