International Journal of Minerals, Metallurgy and Materials

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Value enhancement of olivine process dust through air classification

2012, 19(3): 185-191. doi: 10.1007/s12613-012-0536-z

中文摘要(192) PDF(8) SpringerLink

摘要:
As a result of the production of dry olivine sand products at A/S Olivin's production plant at Åheim in western Norway, an annual quantity of some 20000-30000 t of process dust is produced. The bulk of this material is currently being sold as a slag conditioner at a relatively low price; hence, alternative uses of the process dust are now being sought. Information regarding the chemical composition of the material as a function of particle size facilitates product modifications through exclusion or mixing of individual size fractions. This paper demonstrates how such information can be obtained from air classification experiments when these are combined with chemical analysis of the produced size fractions. The classification and subsequent analysis of the olivine process dust revealed that the finer size fractions had high loss on ignition (LOI) values and were relatively low in MgO when compared with the bulk analysis. Removal of the finer fractions resulted in a remaining coarse product of significantly higher quality. The coarse material could be used as a raw material for further processing; it could be recycled or it could constitute a new product in itself.

Physical chemistry mechanisms of CDR system in sulphide mineral flotation

To-hyon Pak, Ti-chang Sun, Jue Kou, Chol-Ryong Huang

2012, 19(3): 192-198. doi: 10.1007/s12613-012-0537-y

中文摘要(238) PDF(8) SpringerLink

摘要:
The flotation tests, zeta potential measurements, and Fourier transform infrared spectroscopy (FTIR) analysis on galena, sphalerite, and pyrite were studied in a collecting-depressing-reactivating (CDR) system. In this system, sulphide minerals were first collected and activated by the collector, and then depressed strongly by Ca(OH)₂ in a strong alkaline solution. Finally, they were reactivated by H₂SO₄. The flotation tests of pure minerals showed that in the Ca(OH)₂ depressing process sulphide minerals had similar flotation characteristics because they had already been influenced by the collector. Hence, the flotability differences between them were reduced. However, in the H₂SO₄ reactivating process considerable differences in the flotability between galena and sphalerite/pyrite were produced. That is to say, galena was relatively easy to be reactivated by H₂SO₄, but sphalerite and pyrite were not reactivated at pH > 11. The zeta potentials of sulfide minerals measured by the Zeta Plus presented irreversible characteristics on the change of pH values. The results of the FTIR spectra analysis indicated that the collectors already adsorbed on the mineral surface were removed partially by Ca(OH)₂.

Application of response surface methodology in optimizaing the sulfation-roasting-leaching process of nickel laterite

Xue-yi Guo, Dong Li, Zhan Wu, Qing-hua Tian

2012, 19(3): 199-204. doi: 10.1007/s12613-012-0538-x

中文摘要(354) PDF(16) SpringerLink

摘要:
Nickel was recovered from nickel laterite using a sulfation-roasting-leaching process and the effects of operation parameters including acid addition, roasting temperature, and roasting time on nickel extraction and iron dissolution were investigated using response surface methodology (RSM). Two second-order polynomial models of high significance were presented to show the relationship between the responses and the variables. The analysis of variance (ANOVA) showed high coefficients of determination (R²) of 0.894 and 0.980 for the two models, respectively. Optimum areas of ≥ 80% Ni extraction and ≤ 5% Fe dissolution were obtained by the overlaid contours. Verification experiments in the optimum areas were conducted and the results indicate a close agreement with the predicted values obtained from the models.

Preparation of titanium dioxide from titania-rich slag by molten NaOH method

Yan-fang Han, Ti-chang Sun, Jie Li, Tao Qi, Li-na Wang, Jing-kui Qu

2012, 19(3): 205-211. doi: 10.1007/s12613-012-0539-9

中文摘要(311) PDF(20) SpringerLink

摘要:
Preparing titanium dioxide from titania-rich slag (TiO₂ 73wt%) by molten NaOH method has been developed. The effects of temperature and reaction time on the titanium conversion were investigated. The results showed that temperature had significant influence on the titanium conversion as well as the structure of the product. About 92% of titanium in the titania-rich slag could be converted after reacting with NaOH at 500℃ for 1 h. Metatitanic acid was formed through the steps of washing treatment, acid dissolution, and hydrolysis. Well-dispersed spherical titanium dioxide particles with an average size of 0.1-0.4 μm can be obtained by calcination of metatitanic acid. In addition, the content of titanium dioxide in the product is up to 98.6wt%, which can be used as pigments after further treatment of coating and crushing.

Electro-deoxidation of V₂O₃ in molten CaCl₂-NaCl-CaO

Shu-lan Wang, Shi-chao Li, Long-fei Wan, Chuan-hua Wang

2012, 19(3): 212-216. doi: 10.1007/s12613-012-0540-3

中文摘要(243) PDF(10) SpringerLink

摘要:
The electro-deoxidation of V₂O₃ precursors was studied. Experiments were carried out with a two-terminal electrochemical cell, which was comprised of a molten electrolyte of CaCl₂ and NaCl with additions of CaO, a cathode of compact V₂O₃, and a graphite anode under the potential of 3.0 V at 1173 K. The phase constitution and composition as well as the morphology of the samples were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). 3 g of V₂O₃ could be converted to vanadium metal powder within the processing time of 8 h. The kinetic pathway was investigated by analyzing the product phase in samples prepared at different reduction stages. CaO added in the reduction path of V₂O₃ formed the intermediate product CaV₂O₄.

Ore-blending optimization model for sintering process based on characteristics of iron ores

Sheng-li Wu, Dauter Oliveira, Yu-ming Dai, Jian Xu

2012, 19(3): 217-224. doi: 10.1007/s12613-012-0541-2

中文摘要(415) PDF(34) SpringerLink

摘要:
An ore-blending optimization model for the sintering process is an intelligent system that includes iron ore characteristics, expert knowledge and material balance. In the present work, 14 indices are proposed to represent chemical composition, granulating properties and high temperature properties of iron ores. After the relationships between iron ore characteristics and sintering performance are established, the "two-step" method and the simplex method are introduced to build the model by distinguishing the calculation of optimized blending proportion of iron ores from that of other sintering materials in order to improve calculation efficiency. The ore-blending optimization model, programmed by Access and Visual Basic, is applied to practical production in steel mills and the results prove that the present model can take advantage of the available iron ore resource with stable sinter yield and quality performance but at a lower cost.

Influence of chemical liquids on the fatigue crack growth of the AZ31 magnesium alloy

Zhang-zhong Wang, Xian-cong He, Yun-qiang Bai, Zhi-xin Ba, Yu-ming Dai, Heng-zhi Zhou

2012, 19(3): 225-230. doi: 10.1007/s12613-012-0542-1

中文摘要(262) PDF(9) SpringerLink

摘要:
The fatigue crack growth behavior of an AZ31 magnesium alloy was investigated by comparing the effect of zirconate and phosphate chemical liquids. The morphology, components, and phase compositions of the chemical depositions at the fatigue crack tip were analyzed by employing scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD), respectively. For samples with and without the chemical liquids, their stress-intensity factor values at the fatigue crack tip were compared by using a stress-strain gauge. The results demonstrated that a zirconate film (Zr_xO_y·Zn_xO_y) and a phosphate film (Zn₃(PO₄)₂·4H₂O and MgZnP₂O₇) could be formed on the fatigue crack-surface at the fatigue crack tip. The stress distribution was changed because of the chemical depositions and the causticity of the chemical liquids. This could decrease the stress-intensity factor value and thus effectively cause fatigue crack closure, which reduces the fatigue crack growth rate. Moreover, it was found that the fatigue crack closure effect of zirconates was more positive than that of phosphates.

Effects of the types of overlap on the mechanical properties of FSSW welded AZ series magnesium alloy joints

Dan Wang, Jun Shen, Lin-zhi Wang

2012, 19(3): 231-235. doi: 10.1007/s12613-012-0543-0

中文摘要(329) PDF(7) SpringerLink

摘要:
The effects of the types of overlap on the mechanical properties of the friction stir spot welding (FSSW) welded AZ series magnesium alloy joints were investigated by microstructural observations, microhardness tests, and tensile tests. The results show that the microstructure of the stir zone adjacent to the periphery of the rotating pin is mainly composed of the upper sheet. The average distance D between the longitudinal segment of the curved interface and the keyhole periphery, the tensile shear force, and the microhardness of the stir zone of the FSSW welded AZ61 alloy joint are the highest in all samples. During FSSW of AZ31 and AZ61 dissimilar magnesium alloys, the irregular deformation of the longitudinal segment of the curved interface appears, while the microhardness of the stir zone is higher when AZ61 alloy is the upper sheet. Moreover, the microhardness of the stir zone increases initially and then decreases sharply in the longitudinal test position.

Nd₂Fe₁₇ nanograins effect on the coercivity of HDDR NdFeB magnets with low boron content

Ai-zhi Sun, Shen Wu, Wen-huan Xu, Jin Wang, Qian Zhang, Fu-qiang Zhai, Alex A. Volinsky

2012, 19(3): 236-239. doi: 10.1007/s12613-012-0544-z

中文摘要(304) PDF(19) SpringerLink

摘要:
Relationships between the coercivity of hydrogenation disproportionation desorption recombination (HDDR) Nd_12.5Fe_81.5-xCo₆B_x bonded magnets and boron content were investigated. Nd₂Fe₁₇ phase with planar magnetic anisotropy is present in the microstructure when x=4at%-5.88at%, which does not reduce the coercivity of the bonded magnets. High-resolution transmission electron microscopy (TEM) images show that Nd₂Fe₁₇ phase exists in the form of nanocrystals in the Nd₂Fe₁₄B matrix. There is an exchange-coupling interaction between the two phases so that the coercivity of HDDR Nd_12.5Fe_81.5-xCo₆B_x bonded magnets is hardly reduced with a decrease in boron content.

Enhanced thermoelectric properties of Co_1-x-yNi_x+ySb_3-xSn_x materials

Hong-quan Liu, Sheng-nan Zhang, Tie-jun Zhu, Xin-bing Zhao, Yi-jie Gu, Hong-zhi Cui

2012, 19(3): 240-244. doi: 10.1007/s12613-012-0545-y

中文摘要(235) PDF(7) SpringerLink

摘要:
Co_1-x-yNi_x+ySb_3-xSn_x polycrystals were fabricated by vacuum melting combined with hot-press sintering. The effect of alloying on the thermoelectric properties of unfilled skutterudite Co_1-x-yNi_x+ySb_3-xSn_x was investigated. A leap of electrical conductivity from the Co_0.93Ni_0.07Sb_2.93Sn_0.07 sample to the Co_0.88Ni_0.12Sb_2.88Sn_0.12 sample occurs during the measurement of electrical conductivity, indicating the adjustment of band structure by proper alloying. The results show that alloying enhances the power factor of the materials. On the basis of alloying, the thermoelectric properties of Co_0.88Ni_0.12Sb_2.88Sn_0.12 are improved by Ni-doping. The thermal conductivities of Ni-doping samples have no reduction, but their power factors have obvious enhancement. The power factor of Co_0.81Ni_0.19Sb_2.88Sn_0.12 reaches 3.0 mW·m^-1·K^-2 by Ni doping. The dimensionless thermoelectric figure of merit reaches 0.55 at 773 K for the unfilled Co_0.81Ni_0.19Sb_2.88Sn_0.12.

Microwave sintering of Ca_0.6La_0.2667TiO₃ microwave dielectric ceramics

Jia-mao Li, Tai Qiu

2012, 19(3): 245-251. doi: 10.1007/s12613-012-0546-x

中文摘要(313) PDF(14) SpringerLink

摘要:
Ca_0.6La_0.2667TiO₃ ceramics were prepared by conventional and microwave sintering techniques and their sinterability, microstructure, and microwave dielectric properties were investigated in detail for comparison. Densified Ca_0.6La_0.2667TiO₃ ceramics were obtained by microwave sintering at 1350℃ for 30 min and by conventional sintering at 1450℃ for 4 h. An unusual phenomenon was found that some larger grains (grain size range:8-10 μm) inclined to assemble in one area but some smaller ones (grain size range:2-4 μm) inclined to gather in another area in the microwave sintered ceramics. The microwave dielectric properties of Ca_0.6La_0.2667TiO₃ ceramics prepared by microwave sintering at 1350℃ were as follows:dielectric constant (ɛ_r)=119.6, quality factor (Qf)=17858.5 GHz, and temperature coefficient of resonant frequency (τ_f)=155.5 ppm/℃. In contrast, the microwave dielectric properties of the ceramics prepared by conventional sintering at 1450℃ were ɛ_r=117.4, Qf=13375 GHz, and τ_f=217.2 ppm/℃.

Effect of silica forms in rice husk ash on the properties of concrete

Le Anh-tuan Bui, Chun-tsun Chen, Chao-lung Hwang, Wei-sheng Wu

2012, 19(3): 252-258. doi: 10.1007/s12613-012-0547-9

中文摘要(314) PDF(16) SpringerLink

摘要:
The strength and durability properties of concrete with or without three types of rice husk ash (RHA), namely, amorphous, partial crystalline, and crystalline RHA, were investigates. The three types of RHA were added into concrete at a 20% replacement level. Consequently, the pozzolanic reactivity of amorphous RHA was higher than that of partial crystalline and crystalline RHA. Concrete added with amorphous RHA showed excellent characteristics in its mechanical and durability properties. The results showed that the higher the amount of crystalline silica in RHA, the lower the concrete resistivity value became. When compared with each other, concretes with 20% of the cement replaced with these types of RHA achieved similar ultrasonic pulse velocity values, but all were lower than that of the control concrete. The incorporation of these kinds of RHA significantly reduced chloride penetration. The results not only encourage the use of amorphous materials, they also support the application of crystalline or partial crystalline RHA as mineral and pozzolanic admixtures for cement.

Hydrothermal growth of Ni-based coatings on copper substrates

Fang Liu, Yong Zhang

2012, 19(3): 259-265. doi: 10.1007/s12613-012-0548-8

中文摘要(272) PDF(7) SpringerLink

摘要:
Ni-based coatings were deposited on copper substrates by a hydrothermal approach. The results showed that a Ni-based cellular microstructure was bridged by "fiber-like" products. A high microhardness of Hv 856 was achieved after 400℃ heat treatment, which is nine times that of copper substrates (Hv 95). Nucleation, growth, and fusion of Ni atoms along the linear direction, induced by a linear-type citrate-metal structural "molecule template", led to in-situ growth of Ni-based fibers between cellular microspheres. After 400℃ heat treatment, the precipitation of NiP and Ni₃P hard phases contributed to the high microhardness of Ni-based coatings.

Synthesis of NiCr₂O₄ spinel coatings with high emissivity by plasma spraying

Zhen-qi Zhu, Xu-dong Cheng, Wei-ping Ye, Jie Min

2012, 19(3): 266-270. doi: 10.1007/s12613-012-0549-7

中文摘要(414) PDF(12) SpringerLink

摘要:
Air plasma spraying (APS) was used to produce high emissivity coatings with a NiCr₂O₄ spinel structure. The relationship between the emissivity and the crystal structure was investigated. X-ray diffraction (XRD) analyses show that NiCr₂O₄ spinel has been fabricated with the space group Fd3m. Scanning electron microscope (SEM) photographs show that the coating consists of a laminated structure with homogeneous grains and high porosity because of the unique feature of plasma spraying. The emissivity measurement and Fourier transformation infrared radiation (FT-IR) spectra show that NiCr₂O₄ has a high emissivity of about 0.91 because of its special spinel structure. APS is a suitable method to produce high emissivity coatings.

Photoluminescence and cathodoluminescence properties of CaLaGa₃O₇:Eu³⁺ phosphors

Wen-yu Zhao, Sheng-li An, Bin Fan, Song-bo Li, Ya-tang Dai

2012, 19(3): 271-277. doi: 10.1007/s12613-012-0550-1

中文摘要(357) PDF(9) SpringerLink

摘要:
The CaLaGa₃O₇:Eu³⁺ phosphor was prepared by a chemical co-precipitation method. Field emission scanning electron microscopy (FE-SEM), laser particle size analysis, X-ray diffraction (XRD), photoluminescence (PL), and cathodoluminescence (CL) spectra were utilized to characterize the synthesized phosphor. The results revealed that the phosphor was composed of microspheres with a slight agglomerate phenomenon and was spherically shaped. The average grain size was about 1.0 μm. Eu³⁺ ions, as luminescent centers, substituted La³⁺ ions into the single crystal lattice of CaLaGa₃O₇ with the sites of C_s. Although the CL spectrum was greatly different from the PL spectrum, it had the strongest red emission corresponding to the ⁵D₀ →⁷F₂ transition of Eu³⁺. Under the excitation of UV light (287 nm) and electron beams (1.0-7.0 kV), the chromaticity coordinates of the phosphor were found to be in the nearly red and orange light regions, respectively.

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