International Journal of Minerals, Metallurgy and Materials

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Removal of zirconium from hydrous titanium dioxide

Xue-qin Ma, Ya-hui Liu, Jing-long Chu, Jie Li, Tian-yan Xue, Li-na Wang, Tao Qi

2013, 20(1): 1-8. doi: 10.1007/s12613-013-0686-7

中文摘要(257) PDF(14) SpringerLink

摘要:
A method was proposed for removing zirconium (Zr) from hydrous titanium dioxide (HTD) by the NaF solution. The effects of main parameters, i.e. pH values, NaF dosage, temperature and retention time, on the removal of zirconium were studied. The optimal conditions were found as the following: pH value, <5.5; molar ratio of NaF to TiO₂, 0.6; retention time, 80 min; and temperature, 80℃. The removal rate of Zr under the optimized conditions was above 87.7%. The adsorption energy of the preferential absorption of hydrofluoric acid for Zr(OH)₂SO₄(OH₂) on the (001) crystal surface of HTD was determined by theoretical calculation. The possible mechanism of the removal process was also discussed.

Role of trivalent antimony in the removal of As, Sb, and Bi impurities from copper electrolytes

Fa-xin Xiao, Dao Cao, Jian-wei Mao, Xiao-ni Shen, Feng-zhang Ren

2013, 20(1): 9-16. doi: 10.1007/s12613-013-0687-6

中文摘要(268) PDF(9) SpringerLink

摘要:
The role of trivalent antimony was investigated in removing As, Sb, and Bi impurities from a copper electrolyte. Purification experiments were carried out by adding a various concentrations of Sb(III) ions in a synthetic electrolyte containing 185 g/L sulfuric acid, 45 g/L Cu²⁺, 10 g/L As, and 0.5 g/L Bi under stirring at 65℃ for 2 h. The electrolyte was filtered, and the structure, morphology and composition of the precipitate were analyzed by means of chemical analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and IR spectroscopy. The precipitate is composed of irregular lumps which are agglomerated by fine dendritic and floccus particles, and it mainly consists of As, Sb, Bi, and O elements. Characteristic bands in the IR spectra of the precipitate are As-OX (X=As, Sb, Bi), Sb-OY (Y=Sb, Bi), O-As-O, As-OH, Sb-OH, and O-H. The precipitate is a mixture of microcrystalline SbAsO₄, (Sb,As)₂O₃, and amorphous phases. As, Sb, and Bi impurities are effectively removed from the copper electrolyte by Sb(III) ions attributing to these precipitates.

K₂CO₃ catalysis on the reactivity of top charged coke and stamp charged coke

Qing-hai Pang, Jian-liang Zhang, Cheng-lin Qi, Chao Ma, De-wen Kong, Rui Mao

2013, 20(1): 17-27. doi: 10.1007/s12613-013-0688-5

中文摘要(283) PDF(8) SpringerLink

摘要:
The catalysis of K₂CO₃ on the reactivity of top charged coke and stamp charged coke from Pansteel in China was studied. The coke reaction index of the stamp charged coke was 1%–2% higher than that of the top charged coke. Under the catalysis of K₂CO₃, the coke reaction index of both cokes approximately increased by 4%, 6%, 10% and 6% at 900, 1000, 1100 and 1200℃, respectively. The reactivity of the K-enriched stamp charged coke was 1%–2% higher than that of the K-enriched top charged coke below 1100℃. However, only negligible differences were found in the temperature zone between 1100 and 1200℃. Scanning electron microscopy images illustrated that pores in the top charged coke were smaller and equally distributed, while relatively more big pores exist non-homogenously in stamp charged coke. Due to the different processes in production, the stamp charged coke was more porous and most of the pores tended to be applanate. Cracks were observed in the microstructure of the stamp charged coke during the carbon solution reaction, implying the inferior quality of the stamp charged coke to the top charged coke at high temperature. Diffusion of K during the carbon solution reaction was studied by the energy dispersive spectrometry. It is found that K gradually spreads into the center of lumpy coke with the rising of temperature and is equally distributed on the edges of pores at 1200℃. Besides, oxidation reactions of functional groups become faster with the catalysis of K.content

Precipitation behavior of BN type inclusions in 42CrMo steel

Yu-nan Wang, Yan-ping Bao, Min Wang, Le-chen Zhang

2013, 20(1): 28-36. doi: 10.1007/s12613-013-0689-4

中文摘要(279) PDF(16) SpringerLink

摘要:
Automobile crankshaft steel 42CrMo, which requires excellent machinability and mechanical properties, cannot be manufactured by traditional methods. To achieve these qualities, the formation behavior of boron nitride (BN) inclusions in 42CrMo steel was studied in this article. First, the precipitation temperature and the amount of BN type inclusions with different contents of boron and nitrogen in molten steel were calculated thermodynamically by FactSage software. Then the morphology and the size of BN type inclusions as well as the influence of cooling methods on them were investigated by scanning electron microscopy. Furthermore, the effects of cooling rate and the contents of B and N in molten steel on the morphology, size, and distribution of BN type inclusions were studied quantitatively and detailedly by directional solidification experiments. It is found that different BN inclusions in molten steel can form by controlling the cooling rate and the contents of B and N, which is important for obtaining the excellent machinability of 42CrMo steel.

Application of multi-scale feature extraction to surface defect classification of hot-rolled steels

Ke Xu, Yong-hao Ai, Xiu-yong Wu

2013, 20(1): 37-41. doi: 10.1007/s12613-013-0690-y

中文摘要(318) PDF(15) SpringerLink

摘要:
Feature extraction is essential to the classification of surface defect images. The defects of hot-rolled steels distribute in different directions. Therefore, the methods of multi-scale geometric analysis (MGA) were employed to decompose the image into several directional subbands at several scales. Then, the statistical features of each subband were calculated to produce a high-dimensional feature vector, which was reduced to a lower-dimensional vector by graph embedding algorithms. Finally, support vector machine (SVM) was used for defect classification. The multi-scale feature extraction method was implemented via curvelet transform and kernel locality preserving projections (KLPP). Experiment results show that the proposed method is effective for classifying the surface defects of hot-rolled steels and the total classification rate is up to 97.33%.

Investigation on the dissolution of η phase in a cast Ni-based superalloy

M. R. Jahangiri, H. Arabi, S. M. A. Boutorabi

2013, 20(1): 42-48. doi: 10.1007/s12613-013-0691-x

中文摘要(332) PDF(18) SpringerLink

摘要:
The dissolution behavior of η phase has been investigated in a cast Ni-based superalloy. The results showed that the platelets and blocks of η phase were formed within the interdendritic regions of the microstructure. Applying standard solution annealing at 1150–1160℃ for a period of 4 h did not result in the complete dissolution of η phase. For the complete dissolution of η phase without residual incipient melting, a 2-step solution annealing has been recommended. After dissolution at high temperatures, the η phase transforms to two MC-type carbides: one is enriched in Ti, Nb, and Ta, and the other is of (Zr,Ti)C type.

Compressive deformation behavior of an indirect-extruded Mg-8Sn-1Al-1Zn alloy

Wei-li Cheng, Zhong-ping Que, Jin-shan Zhang, Chun-xiang Xu, Wei Liang, Bong Sun You, Sung Soo Park

2013, 20(1): 49-56. doi: 10.1007/s12613-013-0692-9

中文摘要(371) PDF(48) SpringerLink

摘要:
The medium and warm deformation behaviors of an indirect-extruded Mg-8Sn-1Al-1Zn alloy were investigated by compression tests at temperatures between 298 and 523 K and strain rates of 0.001–10 s⁻¹. It was found that the twinning-slip transition temperature was strain rate dependent, and all the true stress-true strain curves could be divided into two groups: concave and convex curves. Associated microstructural investigations indicated that the dynamic recrystallization (DRX) behavior of the alloy varied with deformation conditions. At high strain rate and low temperature, dynamically recrystallized grains preferentially nucleated and developed in the twinned regions, indicating that twinning-induced DRX was dominant. While, at low strain rate, DRX developed extensively at grain boundaries and twins, and the process of twinning contributed to both oriented nucleation and selective growth. For the studied alloy, cracks mainly initiated from the shear band and twinning lamellar over the ranges of temperature and strain rate currently applied.

Microstructure and mechanical properties of Ni-based composite coatings reinforced by in situ synthesized TiB₂ + TiC by laser cladding

Jun Li, Xuan-jun Zhang, Hui-ping Wang, Man-ping Li

2013, 20(1): 57-64. doi: 10.1007/s12613-013-0693-8

中文摘要(348) PDF(20) SpringerLink

摘要:
A Ni-based composite coating reinforced by in situ synthesized TiB₂ and TiC particles was fabricated on Ti6Al4V by laser cladding. An attempt was made to correlate the thermodynamic predictions and experimental observation. The microstructure and the microhardness profile across the coating were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and a hardness tester. It is found that the coating mainly consists of a large number of reinforcements (black blocky TiB₂, flower-like or equiaxial TiC, and fine acicular CrB) and the γ matrix. The hardness of TiB₂, TiC, and CrB reinforcements is much higher than that of the γ matrix. The dispersive distribution of such high hardness reinforcements causes the increase in hardness of the whole coating. The average value of the hardness is approximately Hv_0.2 700 in the coating. The hardness of the coating is obviously higher than that of the substrate due to the dispersion strengthening of reinforcements.

Magnetic properties of NdFeB-coated rubberwood composites

Jureeporn Noodam, Chitnarong Sirisathitkul, Nirundorn Matan, Watcharee Rattanasakulthong, Pongsakorn Jantaratana

2013, 20(1): 65-70. doi: 10.1007/s12613-013-0694-7

中文摘要(268) PDF(9) SpringerLink

摘要:
Magnetic properties of composites prepared by coating lacquer containing neodymium iron boron (Nd-Fe-B) powders on rubberwood were characterized by vibrating sample magnetometry (VSM), magnetic moment measurements, and attraction tests with an iron-core solenoid. The Nd-Fe-B powders were recycled from electronic wastes by the ball-milling technique. Varying the milling time from 20 to 300 min, the magnetic squareness and the coercive field of the Nd-Fe-B powders were at the minimum when the powders were milled for 130 min. It followed that the coercive field of the magnetic wood composites was increased with the milling time increasing from 130 to 300 min. For the magnetic wood composites using Nd-Fe-B obtained from the same milling time, the magnetic squareness and the coercive field were rather insensitive to the variation of Nd-Fe-B concentration in coating lacquer from 0.43 to 1.00 g/cm³. By contrast, the magnetization and magnetic moment were increased with the Nd-Fe-B concentration increasing. Furthermore, the electrical current in the solenoid required for the attraction of the magnetic wood composites was exponentially reduced with the increase in the amount of Nd-Fe-B used in the coating.

Preparation of sol-gel derived microcrystalline corundum abrasives with hexagonal platelets

Na Li, Yu-Mei Zhu, Kai Gao, Zhi-Hong Li

2013, 20(1): 71-75. doi: 10.1007/s12613-013-0695-6

中文摘要(335) PDF(9) SpringerLink

摘要:
The effects of different additives on the mechanical properties, microstructures, and wear behavior of corundum abrasives were investigated. When the number of additive phases increases, the sintering temperature and wear rate decrease, while the densification and mechanical properties increase. The additive SiO₂ is responsible for the development of equiaxed grains, whereas both CaO and MgO promote the development of platelike grains. By controlling the molar ratio of additives, it is possible to obtain different microstructures. With SiO₂-MgO-CaO (molar ratio, 2:1:1) as the additives and nano α-Al₂O₃ powders as the seed, microcrystalline corundum abrasives with hexagonal platelets were obtained using sol-gel process by sintering at 1300℃ for 0.5 h. The average diameter and thickness of hexagonal platelets are 1.38 μm and 360 nm respectively, the single-particle compressive strength is 26.44 N, and the wear rate is (3.06±0.21)×10⁻⁷ mm³/(N·m).

Carbothermal synthesis of Si₃N₄ powders using a combustion synthesis precursor

Ai-min Chu, Ming-li Qin, Bao-rui Jia, Hui-feng Lu, Xuan-hui Qu

2013, 20(1): 76-81. doi: 10.1007/s12613-013-0696-5

中文摘要(286) PDF(13) SpringerLink

摘要:
Si₃N₄ powders were synthesized by a carbothermal reduction method using a SiO₂ + C combustion synthesis precursor derived from a mixed solution consisting of silicic acid (Si source), polyacrylamide (additive), nitric acid (oxidizer), urea (fuel), and glucose (C source). Scanning electron microscopy (SEM) micrographs showed that the obtained precursor exhibited a uniform mixture of SiO₂ + C composed of porous blocky particles up to ~20 μm. The precursor was subsequently calcined under nitrogen at 1200–1550℃ for 2 h. X-ray diffraction (XRD) analysis revealed that the initial reduction reaction started at about 1300℃, and the complete transition of SiO₂ into Si₃N₄ was found at 1550℃. The Si₃N₄ powders, synthesized at 1550℃, exhibit a mixture phase of α- and β-Si₃N₄ and consist of mainly agglomerates of fine particles of 100–300 nm, needle-like crystals and whiskers with a diameter of about 100 nm and a length up to several micrometers, and a minor amount of irregular-shaped growths.

Injection molding and debinding of micro gears fabricated by micro powder injection molding

Xin-lei Ni, Hai-qing Yin, Lin Liu, Shan-jie Yi, Xuan-hui Qu

2013, 20(1): 82-87. doi: 10.1007/s12613-013-0697-4

中文摘要(235) PDF(11) SpringerLink

摘要:
Micro powder injection molding (μPIM) was investigated for possible mass production of micro-components at relatively low cost. However, scaling down to such a level produces challenges in injection molding and debinding. Micro gears were fabricated by μPIM from in-house feedstock. The effect of injection speed and injection pressure on the replication of the micro gear cavity was investigated. Solvent debinding and thermal debinding processes were discussed. The results show that micro gears can be successfully fabricated under the injection pressure of 70 MPa and the 60% injection speed. Either too low or too high injection speed can cause incomplete filling of micro gears. The same is the case with too low injection pressure. Too high injection pressure can bring cracks. Solvent debinding of micro gears was performed in a mixture of petroleum ether and ethanol. Subsequently, micro gears were successfully debound by a multistep heating schedule.

Effect of Na⁺ on xonotlite crystals in hydrothermal synthesis

Fei Liu, Xiao-dan Wang, Jian-xin Cao

2013, 20(1): 88-93. doi: 10.1007/s12613-013-0698-3

中文摘要(309) PDF(11) SpringerLink

摘要:
The effect of Na⁺ ion concentration on the crystalline phase composition and morphology of xonotlite crystals prepared in a CaO-SiO₂-H₂O system via hydrothermal synthesis was analyzed. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicate that Na⁺ ion concentration has a significant impact on the composition and morphology of crystalline phases in the products under the initial conditions of a molar ratio of CaO/SiO₂ of 1.0 and a reactant concentration of 0.05 mol·L⁻¹ at 225℃ for 15 h. The main crystalline phase in the products has a phase transition from xonotlite to pectolite, and the morphology changes from fibrous to broomlike shape with the Na⁺ ion concentration increasing. Therefore, the content of Na₂O in the raw material should be less than 5wt% for preparing pure xonotlite crystals via hydrothermal synthesis in a CaO-SiO₂-H₂O system.

Effect of cement types, mineral admixtures, and bottom ash on the curing sensitivity of concrete

Kinaanath Hussain, Pongsak Choktaweekarn, Warangkana Saengsoy, Theerati Srichan, Somnuk Tangtermsirikul

2013, 20(1): 94-105. doi: 10.1007/s12613-013-0699-2

中文摘要(264) PDF(14) SpringerLink

摘要:
The curing sensitivity of concrete with cement Types 1, 3, and 5 as well as multiple powders consisting of cement, fly ash, and limestone powder was studied. Bottom ash was also used in the study as an internal curing agent and a partial substitution of fine aggregate. The curing sensitivity index was calculated by considering the performances of compressive strength and carbonation depth. Specimens were subjected to two curing conditions: continuously water-cured and continuously air-cured. The results show that cement Type 3 has a lower curing sensitivity, while cement Type 5 increases the curing sensitivity. For the mixes without bottom ash, the use of fly ash increases the curing sensitivity, while limestone powder reduces the curing sensitivity of concrete. The use of bottom ash in concrete reduces the curing sensitivity, especially at a lower mass ratio of water to binder. Concrete with limestone powder, together with bottom ash, is least sensitive to curing. The curing sensitivity calculated from carbonation depth also has a similar tendency as that derived by considering compressive strength. From the test results of compressive strength and curing sensitivity, bottom ash has been proven to be an effective internal curing agent.

Energy consumption of electrooxidation systems with boron-doped diamond electrodes in the pulse current mode

Jun-jun Wei, Xu-hui Gao, Li-fu Hei, Jawaid Askari, Cheng-ming Li

2013, 20(1): 106-112. doi: 10.1007/s12613-013-0700-0

中文摘要(321) PDF(8) SpringerLink

摘要:
A pulse current technique was conducted in a boron-doped diamond (BDD) anode system for electrochemical wastewater treatment. Due to the strong generation and weak absorption of hydroxyl radicals on the diamond surface, the BDD electrode possesses a powerful capability of electrochemical oxidation of organic compounds, especially in the pulse current mode. The influences of pulse current parameters such as current density, pulse duty cycle, and frequency were investigated in terms of chemical oxygen demand (COD) removal, average current efficiency, and specific energy consumption. The results demonstrated that the relatively high COD removal and low specific energy consumption were obtained simultaneously only if the current density or pulse duty cycle was adjusted to a reasonable value. Increasing the frequency slightly enhanced the COD removal and average current efficiency. A pulse-BDD anode system showed a stronger energy saving ability than a constant-BDD anode system when the electrochemical oxidation of phenol of the two systems was compared. The results prove that the pulse current technique is more cost-effective and more suitable for a BDD anode system for real wastewater treatment. A kinetic analysis was presented to explain the above results.

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