International Journal of Minerals, Metallurgy and Materials

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DDM regression analysis of the in-situ stress field in a non-linear fault zone

2012, 19(7): 567-573. doi: 10.1007/s12613-012-0597-z

中文摘要(223) PDF(10) SpringerLink

摘要:
A multivariable regression analysis of the in-situ stress field, which considers the non-linear deformation behavior of faults in practical projects, is presented based on a newly developed three-dimensional displacement discontinuity method (DDM) program. The Barton-Bandis model and the Kulhaway model are adopted as the normal and the tangential deformation model of faults, respectively, where the Mohr-Coulomb failure criterion is satisfied. In practical projects, the values of the mechanical parameters of rock and faults are restricted in a bounded range for in-situ test, and the optimal mechanical parameters are obtained from this range by a loop. Comparing with the traditional finite element method (FEM), the DDM regression results are more accurate.

Undersea safety mining of the large gold deposit in Xinli District of Sanshandao Gold Mine

Zhi-xiang Liu, Wen-gang Dang, Xian-qun He

2012, 19(7): 574-583. doi: 10.1007/s12613-012-0598-y

中文摘要(204) PDF(10) SpringerLink

摘要:
The exploration of undersea resources becomes popular as land resources decrease. Researches were conducted with emphasis on the safety and efficiency of undersea mining of the large gold deposit in Xinli District of Sanshandao Gold Mine. A series of tests for the physical and mechanical characteristics of rock mass were carried out, and the three-dimensional geo-stress distribution was tested in the mining area. Further, a similar experimental simulation platform, which revealed the mechanism of water inrush and ascertained the reasonable thickness of the safety isolate layer, was established for the undersea mining. Meanwhile, the feasibility of cancelling the ore pillars and the safety conditions was checked by numerical simulation. The simulation results show that it is safe to exploit the ore body below the -85 m level (presently, the exploitation level is below -160 m in Xinli District), and the ore pillars can be cancelled below the -560 m level. Furthermore, a novel backfill method was designed to reduce the rock strata disturbance and settlement, and the settlement of roof strata was monitored during the mining process. Engineering practice shows that the settlement of roof strata was small and that no disaster happened. This indicates that the undersea safety mining technology of the large gold deposit is achieved in Xinli District.

Computer modeling of high-pressure leaching process of nickel laterite by design of experiments and neural networks

Milovan Milivojevic, Srecko Stopic, Bernd Friedrich, Boban Stojanovic, Dragoljub Drndarevic

2012, 19(7): 584-594. doi: 10.1007/s12613-012-0599-x

中文摘要(376) PDF(14) SpringerLink

摘要:
Due to the complex chemical composition of nickel ores, the requests for the decrease of production costs, and the increase of nickel extraction in the existing depletion of high-grade sulfide ores around the world, computer modeling of nickel ore leaching process became a need and a challenge. In this paper, the design of experiments (DOE) theory was used to determine the optimal experimental design plan matrix based on the D optimality criterion. In the high-pressure sulfuric acid leaching (HPSAL) process for nickel laterite in "Rudjinci" ore in Serbia, the temperature, the sulfuric acid to ore ratio, the stirring speed, and the leaching time as the predictor variables, and the degree of nickel extraction as the response have been considered. To model the process, the multiple linear regression (MLR) and response surface method (RSM), together with the two-level and four-factor full factorial central composite design (CCD) plan, were used. The proposed regression models have not been proven adequate. Therefore, the artificial neural network (ANN) approach with the same experimental plan was used in order to reduce operational costs, give a better modeling accuracy, and provide a more successful process optimization. The model is based on the multi-layer neural networks with the back-propagation (BP) learning algorithm and the bipolar sigmoid activation function.

Extraction of vanadium from high calcium vanadium slag using direct roasting and soda leaching

Xin-sheng Li, Bing Xie

2012, 19(7): 595-601. doi: 10.1007/s12613-012-0600-8

中文摘要(414) PDF(15) SpringerLink

摘要:
The extraction of vanadium from high calcium vanadium slag was attempted by direct roasting and soda leaching. The oxidation process of the vanadium slag at different temperatures was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The effects of roasting temperature, roasting time, Na₂CO₃ concentration, leaching temperature, leaching time, and liquid to solid ratio on the extraction of vanadium were studied. The results showed that olivine phases and spinel phases in the vanadium slag were completely decomposed at 500 and 800℃, respectively. Vanadium-rich phases were formed at above 850℃. The leaching rate of vanadium reached above 90% under the optimum conditions:roasting temperature of 850℃, roasting time of 60 min, Na₂CO₃ concentration of 160 g/L, leaching temperature of 95℃, leaching time of 150 min, and liquid to solid ratio of 10:1 mL/g. The main impurities were Si and P in the leach liquor.

Influence of vanadium and chromium additions on the wear resistance of a gray cast iron

A. Hassani, A. Habibollahzadeh, S. Sadeghinejad

2012, 19(7): 602-607. doi: 10.1007/s12613-012-0601-7

中文摘要(313) PDF(11) SpringerLink

摘要:
A low-alloy gray cast iron containing hard carbide-forming elements, such as vanadium and chromium, was cast by sand mould casting. Its wear resistance was compared with that of an untreated gray cast iron. Three different loading conditions were tested under a constant speed. It was observed that this alloy could reduce the wear loss of standard gray cast iron by up to 89%, which was much greater than what was achieved in previous reports. Scanning electron microscopy (SEM) was used to determine the predominant wear mechanism of both the alloys. In a mild wear regime, the oxidative mechanism was predominant; however, in a severe wear regime, this mechanism was not predominant and the adhesive mechanism was involved. EDX analysis was conducted to evaluate the quantitative amounts of elements in the tribochemical films formed on the wear tracks.

Effect of inclusion size on the high cycle fatigue strength and failure mode of a high V alloyed powder metallurgy tool steel

Jun Yao, Xuan-hui Qu, Xin-bo He, Lin Zhang

2012, 19(7): 608-614. doi: 10.1007/s12613-012-0602-6

中文摘要(310) PDF(12) SpringerLink

摘要:
The fatigue strength of a high V alloyed powder metallurgy tool steel with two different inclusion size levels, tempered at different temperatures, was investigated by a series of high cycle fatigue tests. It was shown that brittle inclusions with large sizes above 30 μm prompted the occurrence of subsurface crack initiation and the reduction in fatigue strength. The fracture toughness and the stress amplitude both exerted a significant influence on the fish-eye size. A larger fish-eye area would form in the sample with a higher fracture toughness subjected to a lower stress amplitude. The stress intensity factor of the inclusion was found to lie above a typical value of the threshold stress intensity factor of 4 MPa·m^1/2. The fracture toughness of the sample with a hardness above HRC 56 could be estimated by the mean value of the stress intensity factor of the fish-eye. According to fractographic evaluation, the critical inclusion size can be calculated by linear fracture mechanics.

Rectifying control of wire diameter during dieless drawing by a deformation measuring method of interframe displacement

Yong He, Xue-feng Liu, Fang Qin, Jian-xin Xie

2012, 19(7): 615-621. doi: 10.1007/s12613-012-0603-5

中文摘要(265) PDF(9) SpringerLink

摘要:
A deformation measurement method of interframe displacement was proposed in this paper. By online monitoring the shape dimensions of both the deformation zone and its adjacent zone by machine vision, the initial and terminative positions of deformation were dynamically identified during dieless drawing, and the global monitoring and online closed-loop control of the deformation zone were achieved. The dieless drawing process was systematically carried out on NiTi shape memory alloy wires. It is shown that the deformation measurement method of interframe displacement can track the axial displacement of the wires, but this cannot be achieved by traditional machine vision. The initial and terminative positions of deformation can be accurately identified by this method. The proposed rectifying control technology can effectively decrease the wire diameter fluctuation during dieless drawing, that is, the standard deviation of the wire diameter fluctuation could be decreased from 0.30 to 0.08 mm after three passes of dieless drawing, indicating that the control system has a good rectifying ability.

Effect of 6H-SiC crystal growth shapes on thermo-elastic stress in the growing crystal

Yong-gui Shi, Pei-yun Dai, Jian-feng Yang, Zhi-hao Jin, Hu-lin Liu

2012, 19(7): 622-627. doi: 10.1007/s12613-012-0604-4

中文摘要(305) PDF(13) SpringerLink

摘要:
The effect of 6H-SiC crystal growth shapes on the thermo-elastic stress distribution in the growing crystal was systematically investigated by using a finite element method. The thermo-elastic stress distribution in the crystal with a flat growth shape was more homogeneous than that in the crystals with concave and convex growth shapes, and the value of thermo-elasticity in the crystal with a flat growth shape was also smaller than that in the two other types of crystals. The maximum values of thermo-elastic stress appeared at interfaces between the crystal and the graphite lid. If the lid was of the same properties as 6H-SiC, the thermo-elastic stress would decrease in two orders of magnitude. Thus, to grow 6H-SiC single crystals of high quality, a transition layer of SiC formed by deposition or reaction is suggested; meanwhile the thermal field in the growth chamber should be adjusted to maintain the crystals with flat growth shapes.

Structure of V₂O₅-P₂O₅-Sb₂O₃-Bi₂O₃ glass

Hong-yan Li, Zhi-liang Zhu, Feng-li Yang, Wei-dong Zhuang, Yun-sheng Hu, Xiao-fan Wen

2012, 19(7): 628-635. doi: 10.1007/s12613-012-0605-3

中文摘要(342) PDF(27) SpringerLink

摘要:
The structure of V₂O₅-P₂O₅-Sb₂O₃-Bi₂O₃ glass and its state of crystallization were studied by means of infrared spectroscopy and X-ray diffraction analysis. The results indicate that, in this glass, V and P exist mainly in the form of a single-stranded linear (VO₃)_n and an isolated (PO₄) tetrahedral with no double bond. Partial V and P are connected through O, forming an amorphous structure of layered vanadium phosphate. Trivalent Sb³⁺ and Bi³⁺ open the V=O bond and appear in interlayers, so a weak three-dimensional structure is connected successfully. Along with the substitution of Sb₂O₃ for partial V₂O₅ or that of P₂O₅ for partial V₂O₅, the network structure of the glass is reinforced, and the crystallization is reduced.

Effect of sintering temperature on the electrolysis of TiO₂

Ze-quan Li, Li-yue Ru, Cheng-guang Bai, Na Zhang, Hai-hua Wang

2012, 19(7): 636-641. doi: 10.1007/s12613-012-0606-2

中文摘要(291) PDF(7) SpringerLink

摘要:
The effects of sintering temperature on the microstructure and the conductivity of TiO₂ cathodes were studied by examining the phase composition, microstructure, and element contents of the sintered cathodes and the cathodic products using X-ray diffraction and scanning electronic microscopy-energy dispersive spectrometry. The oxygen vacancy, conductivity, average pore diameter, and specific surface area of the sintered cathodes were detected by X-ray photoelectron spectroscopy, four-point probe, and ASPA 2010. The results showed that TiO₂ phase transformations occurred, and oxygen vacancies formed with the increase of sintering temperature. The cathodic conductivity improved, but the average pore diameter and the effective response area of the TiO₂ cathode were reduced when the sintering temperature increased. These phenomena could weaken the contact between reaction ions and electrons and also had the same effect on the cathodes and the molten salt. Moreover, they were disadvantageous to ion migration, so a lower sintering temperature was favorable for the microstructure of electrolysis. Consequently, the cathodic conductivity may be improved, but the microstructure became compact with the increase of sintering temperature. The cathodic products at different temperatures indicated that the cathodic conductivity was more important for electrolysis.

Effect of hydrolysis conditions on hydrous TiO₂ polymorphs precipitated from a titanyl sulfate and sulfuric acid solution

Hao Song, Bin Liang, Li Lü, Pan Wu, Chun Li

2012, 19(7): 642-650. doi: 10.1007/s12613-012-0607-1

中文摘要(278) PDF(9) SpringerLink

摘要:
The relationship between hydrolysis conditions and hydrous titania polymorphs obtained in a titanyl sulfate and sulfuric acid solution was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). The results revealed that the feeding rate of the titanyl sulfate stock solution, the concentration of sulfuric acid, and the seed dosage of rutile crystal could significantly affect the hydrolysis rate, thus influencing the titania crystal phase. Hydrous TiO₂ in the form of rutile, anatase, or the mixture of both could be obtained in solutions of low titanium concentrations and 2.5wt% to 15wt% sulfuric acid at 100℃. When the hydrolysis rate of titanium expressed by TiO₂ was more than or equal to 0.04 g/(L·min), the hydrolysate was almost phase-pure anatase, while the main phase state was rutile when the hydrolysis rate was less than or equal to 0.01 g/(L·min). With the hydrolysis rate between 0.02 and 0.03 g/(L·min), the hydrolysate contained almost equal magnitude of rutile and anatase. It seems that although rutile phase is thermodynamically stable in very acidic solutions, anatase is a kinetically stable phase.

Production and characterization of ZnO nanoparticles and porous particles by ultrasonic spray pyrolysis using a zinc nitrate precursor

Burçak Ebin, Elif Arıg, Burak Özkal, Sebahattin Gürmen

2012, 19(7): 651-656. doi: 10.1007/s12613-012-0608-0

中文摘要(333) PDF(11) SpringerLink

摘要:
ZnO nanoparticles and porous particles were produced by an ultrasonic spray pyrolysis method using a zinc nitrate precursor at various temperatures under air atmosphere. The effects of reaction temperature on the size and morphology of ZnO particles were investigated. The samples were characterized by energy dispersive spectroscopy, X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. ZnO particles were obtained in a hexagonal crystal structure and the crystallite shapes changed from spherical to hexagonal by elevating the reaction temperature. The crystallite size grew by increasing the temperature, in spite of reducing the residence time in the heated zone. ZnO nanoparticles were obtained at the lowest reaction temperature and ZnO porous particles, formed by aggregation of ZnO nanoparticles due to effective sintering, were prepared at higher temperatures. The results showed that the properties of ZnO particles can be controlled by changing the reaction temperature in the ultrasonic spray pyrolysis method.

Microstructure and corrosion resistance of Fe/Mo composite amorphous coatings prepared by air plasma spraying

Chao-ping Jiang, Ya-zhe Xing, Feng-ying Zhang, Jian-min Hao

2012, 19(7): 657-662. doi: 10.1007/s12613-012-0609-z

中文摘要(337) PDF(10) SpringerLink

摘要:
Fe/Mo composite coatings were prepared by air plasma spraying (APS) using Fe-based and Mo-based amorphous and nanocrystalline mixed powders. Microstructural studies show that the composite coatings present a layered structure with low porosity due to adding the self-bonded Mo-based alloy. Corrosion behaviors of the composite coatings, the Fe-based coatings and the Mo-based coatings were investigated by electrochemical measurements and salt spray tests. Electrochemical results show that the composite coatings exhibit a lower polarization current density and higher corrosion potentials than the Fe-based coating when tested in 3.5wt% NaCl solutions, indicating superior corrosion resistance compared with the Fe-based coating. Also with the increase in addition of the Mo-based alloy, a raised corrosion resistance, inferred by an increase in corrosion potential and a decrease in polarization current density, can be found. The results of salt spray tests again show that the corrosion resistance is enhanced by adding the Mo-based alloy, which helps to reduce the porosity of the composite coatings and enhance the stability of the passive films.

Synthesis and luminescence properties of Ca₂SiO₄-based red phosphors with Sm³⁺ doping for white LEDs

Jin-jun Cai, Huan-huan Pan, Yi Wang

2012, 19(7): 663-667. doi: 10.1007/s12613-012-0610-6

中文摘要(268) PDF(8) SpringerLink

摘要:
Sm³⁺-activated Ca₂SiO₄ red phosphors were prepared by the conventional high-temperature solid-state reaction method, and the effects of sodium (Na⁺) and samarium (Sm³⁺) ions doping concentrations on their crystal structure and luminescent properties were investigated by X-ray diffraction (XRD) and fluorescent spectrofluorometer. XRD patterns demonstrate that a well-crystalline structure forms in the phosphors when they are treated by calcination at 1200℃ for 4 h, and the excitation spectra exhibit good absorption in the range between 350 and 420 nm. Under the irradiation of 405 nm near-ultraviolet (NUV) light, the spectra of the phosphors show a main emission peak at 601 nm attributed to the ⁴G_5/2→⁶H_7/2 transition of Sm³⁺ ions, and its intensity is greatly influenced by the concentrations of Sm³⁺ and Na₂CO₃. When the concentrations of Sm³⁺ ions and Na₂CO₃ are 2mol% and 6mol%, respectively, the optimal emission intensity can be obtained. From strong absorption in the near ultraviolet zone, the Na_0.06Sm_0.02Ca_1.92SiO₄ phosphor is a promising red-emitting phosphor for white light emitting diodes (W-LEDs).

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