International Journal of Minerals, Metallurgy and Materials

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Formation and characterization of metallic iron grains in coal-based reduction of oolitic iron ore

Yong-sheng Sun, Yue-xin Han, Yan-feng Li, Yan-jun Li

2017, 24(2): 123-129. doi: 10.1007/s12613-017-1386-5

中文摘要(370) PDF(13) SpringerLink

摘要:
To reveal the formation and characteristics of metallic iron grains in coal-based reduction, oolitic iron ore was isothermally reduced in various reduction times at various reduction temperatures. The microstructure and size of the metallic iron phase were investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and a Bgrimm process mineralogy analyzer. In the results, the reduced Fe separates from the ore and forms metallic iron protuberances, and then the subsequent reduced Fe diffuses to the protuberances and grows into metallic iron grains. Most of the metallic iron grains exist in the quasi-spherical shape and inlaid in the slag matrix. The cumulative frequency of metallic iron grain size is markedly influenced by both reduction time and temperature. With increasing reduction temperature and time, the grain size of metallic iron obviously increases. According to the classical grain growth equation, the growth kinetic parameters, i.e., time exponent, growth activation energy, and pre-exponential constant, are estimated to be 1.3759 ±0.0374, 103.18 kJ·mol^-1, and 922.05, respectively. Using these calculated parameters, a growth model is established to describe the growth behavior of metallic iron grains.

研究论文

Dripping and evolution behavior of primary slag bearing TiO₂ through the coke packed bed in a blast-furnace hearth

Yan-xiang Liu, Jian-liang Zhang, Zhi-yu Wang, Ke-xin Jiao, Guo-hua Zhang, Kuo-chih Chou

2017, 24(2): 130-138. doi: 10.1007/s12613-017-1387-4

中文摘要(422) PDF(10) SpringerLink

摘要:
To investigate the flow of primary slag bearing TiO₂ in the cohesive zone of blast furnaces,experiments were carried out based on the laboratory-scale packed bed systems.It is concluded that the initial temperature of slag dripping increases with decreasing FeO content and increasing TiO₂ content.The slag holdup decreases when the FeO content is in the range of 5wt%-10wt%,whereas it increases when the FeO content exceeds 10wt%.Meanwhile,the slag holdup decreases when the TiO₂ content increases from 5wt% to 10wt% but increases when the TiO₂ content exceeds 10wt%.Moreover,slag/coke interface analysis shows that the reaction between FeO and TiO₂ occurs between the slag and the coke.The slag/coke interface is divided into three layers:slag layer,iron-rich layer,and coke layer.TiO₂ in the slag is reduced by carbon,and the generated Ti diffuses into iron.

研究论文

Effect of ultrasonic power introduced by a mold copper plate on the solidification process

Xiao-fang Shi, Li-zhong Chang, Jian-jun Wang

2017, 24(2): 139-146. doi: 10.1007/s12613-017-1388-3

中文摘要(426) PDF(11) SpringerLink

摘要:
An electroslag furnace with ultrasonic vibration introduced by a mold copper plate was designed. The effects of ultrasonic power on the element distribution and compactness in electroslag remelting (ESR) ingots were studied, and the mechanism of ultrasonic assistance was analyzed in cold experiments. In the results, silicon, manganese and chromium are uniformly distributed at an ultrasonic power of 300-750 W. The absence of ultrasonic or higher ultrasonic power is not conducive to the uniformity of alloying elements. Carbon demonstrates a highly uneven distribution at 300 W, gradually reaches the uniform distribution as the ultrasonic power further increases, and shows the poor distribution at 1000 W. The compactness of ESR ingots gradually increases with increasing ultrasonic power and reaches the uniform distribution at 500 W. A further increase in ultrasonic power does not improve the compactness. Introducing ultrasonic vibrations by a mold copper plate can improve the solidification quality; however, an appropriate ultrasonic power level should be determined.

研究论文

Deselenization and detellurization of precious-metal ore concentrates by swelling oxidizing roasting and successive alkaline leaching

Fu-yuan Zhang, Ya-jie Zheng, Guo-min Peng

2017, 24(2): 147-155. doi: 10.1007/s12613-017-1389-2

中文摘要(460) PDF(11) SpringerLink

摘要:

A new technique of swelling oxidizing roasting and alkaline leaching was proposed for deselenization and detellurization of precious-metal ore concentrates. Alkali-metal and alkaline-earth-metal chlorides and carbonates were preliminarily selected as swelling agents. The roasting removal rate and alkaline leaching rate of selenium and tellurium were investigated, and NaCl was selected as an appropriate swelling agent. Furthermore, the effects of various factors on the selenium gasification rate and leaching rate of selenium and tellurium were investigated. The results show that the selenium gasification rate reaches 88.41% after swelling oxidizing roasting for 2 h at 510℃ using an NaCl dosage coefficient of 100 and a sulfuric acid dosage coefficient of 1.3; the amorphous elemental tellurium is completely transformed into TeO₂. The roasted product is subjected to alkaline leaching using a 100 g/L NaOH solution, which results in a selenium leaching rate of 10.51%, a total selenium removal rate of 98.92%, and a tellurium leaching rate of 97.64%. In the alkaline leaching residue, the contents of selenium, tellurium, gold, platinum, and palladium are 0.7825%, 5.492%, 8.333%, 0.2587%, and 1.113%, respectively; the precious metals are enriched approximately sixfold.

研究论文

Synergistic effect of microwave irradiation and CaF₂ on vanadium leaching

Jing-peng Wang, Yi-min Zhang, Jing Huang, Tao Liu

2017, 24(2): 156-163. doi: 10.1007/s12613-017-1390-9

中文摘要(545) PDF(8) SpringerLink

摘要:
The effect and mechanism of microwave irradiation on vanadium leaching were studied via a comparison between microwave heating and conventional heating. The results show a synergistic effect of microwave irradiation and calcium fluoride (CaF₂) on the vanadium leaching efficiency. It is confirmed that the vanadium leaching process can be improved by microwave irradiation when CaF₂ is present. The leaching rate of vanadium under microwave irradiation is increased by 8%-15% when 5wt% CaF₂ is added; by contrast, in the absence of CaF₂, the leaching rate is almost unaffected compared to that by conventional heating. Morphological analysis reveals that the particles are gradually eroded by acid under microwave irradiation, whereas some of the fine particles in samples subjected to conventional heating are tightly covered by a flocculent silicate product. Moreover, a large amount of Al and V and a small amount of Si are dissolved from samples under microwave heating, as revealed by the elemental analysis of leachates. Fourier transform infrared spectroscopic analysis also indicates a higher mass transfer coefficient in the diffusion layer of the raw material by microwave irradiation. When CaF₂ is present, the reaction energy barrier is lowered and the leaching process is controlled by the tightly covered product layer, resulting in a prominent effect of microwave irradiation.

研究论文

Metallographic structure, mechanical properties, and process parameter optimization of 5A06 joints formed by ultrasonic-assisted refill friction stir spot welding

Xin-bo Liu, Feng-bin Qiao, Li-jie Guo, Xiong-er Qiu

2017, 24(2): 164-170. doi: 10.1007/s12613-017-1391-8

中文摘要(614) PDF(13) SpringerLink

摘要:
Novel hybrid refill friction stir spot welding (RFSSW) assisted with ultrasonic oscillation was introduced to 5A06 aluminum alloy joints. The metallographic structure and mechanical properties of 5A06 aluminum alloy RFSSW joints formed without ultrasonic assistance and with lateral and longitudinal ultrasonic assistance were compared, and the ultrasonic-assisted RFSSW process parameters were optimized. The results show that compared with lateral ultrasonic oscillation, longitudinal ultrasonic oscillation strengthens the horizontal bonding ligament in the joint and has a stronger effect on the joint's shear strength. By contrast, lateral ultrasonic oscillation strengthens the vertical bonding ligament and is more effective in increasing the joint's tensile strength. The maximum shear strength of ultrasonic-assisted RFSSW 5A06 aluminum alloy joints is as high as 8761 N, and the maximum tensile strength is 3679 N when the joints are formed at a tool rotating speed of 2000 r/min, a welding time of 3.5 s, a penetration depth of 0.2 mm, and an axial pressure of 11 kN.

研究论文

Microstructural characteristics and mechanical properties of bobbin-tool friction stir welded 2024-T3 aluminum alloy

Ji-hong Dong, Chong Gao, Yao Lu, Jian Han, Xiang-dong Jiao, Zhi-xiong Zhu

2017, 24(2): 171-178. doi: 10.1007/s12613-017-1392-7

中文摘要(444) PDF(17) SpringerLink

摘要:
Cold-rolled 2024-T3 sheet alloy was subjected to bobbin-tool friction stir welding (BTFSW). The microstructural characteristics and mechanical properties of the nugget zone in the as-welded state were investigated. The results show that the equiaxed grain size of BTFSW 2024-T3 alloy decreases from 7.6 to 2.8 μm as the welding speed is increased from 80 to 120 mm/min; in addition, fine grains are generated in the nugget zone and the size distribution is non-uniform. All Al₂CuMg (S') precipitates dissolve into the Al matrix, whereas Mn-rich phases confirmed as T phases (Al₂₀Cu₂Mn₃, Al₆Mn, or Al₃Mn) remain unchanged. The optimized parameters for BTFSW are verified as the rotation speed of 350 r/min and the travel speed of 100 mm/min. The variations in precipitation and dislocation play more important roles than grain size in the nugget zone with respect to influencing the mechanical properties during the BTFSW process. After the BTFSW process, the fracture mode of base material 2024-T3 alloy transforms from ductile rupture to ductile-brittle mixed fracture.

研究论文

Improved strength and ductility of high alloy containing Al-12Zn-3Mg-2.5Cu alloy by combining non-isothermal step rolling and cold rolling

V. V. Ravikumar, S. Kumaran

2017, 24(2): 179-185. doi: 10.1007/s12613-017-1393-6

中文摘要(477) PDF(11) SpringerLink

摘要:
Al-12Zn-3Mg-2.5Cu alloy was prepared using a liquid metallurgy route under the optimized conditions. A sample cut from the ingot was rolled non-isothermally from 400℃ to 100℃ in 100℃ steps, with 15% reduction in thickness; it was then cold rolled isothermally at room temperature for 85% reduction. The cold-rolled alloys were characterized by electron microscopy, hardness test, and tensile test to elucidate their structural evolution and evaluate their mechanical behavior. In the results, the cast alloy consists of α-aluminum and various intermetallic compounds. These compounds are segregated along the grain boundaries, which makes the alloy difficult to roll at room temperature. The combined effect of non-isothermal step rolling and cold rolling results in the nano/microsized compounds distributed uniformly in the matrix. The hardness is substantially increased after rolling. This increase in hardness is attributed to the ultra-fine grain size, fine-scale intermetallic compounds, and structural defects (e.g., dislocations, stacking faults, and sub-grains). The ultimate tensile strength of the rolled alloy is approximately 628 MPa with 7% ductility.

研究论文

Microstructure and physical properties of steel-ladle purging plug refractory materials

Bin Long, Gui-ying Xu, Buhr Andreas

2017, 24(2): 186-193. doi: 10.1007/s12613-017-1394-5

中文摘要(548) PDF(23) SpringerLink

摘要:
Three different castables were prepared as steel-ladle purging-plug refractory materials:corundum-based low-cement castable (C-LCC), corundum-spinel-based low-cement castable (C-S-LCC), and no-cement corundum-spinel castable (C-S-NCC) (hydratable alumina ρ-Al₂O₃ bonded). The properties of these castables were characterized with regard to water demand/flow ability, cold crushing strength (CCS), cold modulus of rupture (CMoR), permanent linear change (PLC), apparent porosity, and hot modulus of rupture (HMoR). The results show the CCS/CMoR and HMoR of C-LCC and C-S-LCC are greater than those of the castable C-S-NCC. According to the microstructure analysis, the sintering effect and the bonding type of the matrix material differ among the three castables. The calcium hexaluminate (CA₆) phase in the matrix of C-LCC enhances the cold and hot mechanical strengths. In the case of C-S-LCC, the CA₆ and 2CaO·2MgO·14Al₂O₃ (C₂M₂A₁₄) ternary phases generated from the matrix can greatly increase the cold and hot mechanical strengths. In the case of the no-cement castable, sintering becomes difficult, resulting in a lower mechanical strength.

研究论文

Synthesis of glass ceramics from kaolin and dolomite mixture

Mohamed Reda Boudchicha, Fausto Rubio, Slimane Achour

2017, 24(2): 194-201. doi: 10.1007/s12613-017-1395-4

中文摘要(729) PDF(20) SpringerLink

摘要:
Cordierite-and anorthite-based binary glass ceramics of the CaO-MgO-Al₂O₃-SiO₂ (CMAS) system were synthesized by mixing local and abundant raw minerals (kaolin and doloma by mass ratio of 82/18). A kinetics study reveals that the activation energy of crystallization (Ea) calculated by the methods of Kissinger and Marotta are 438 kJ·mol^-1 and 459 kJ·mol^-1, respectively. The Avrami parameter (n) is estimated to be approximately equal to 1, corresponding to the surface crystallization mechanism. X-ray diffraction (XRD) analysis shows that the anorthite and cordierite crystals are precipitated from the parent glass as major phases. Anorthite crystals first form at 850℃, whereas the µ-cordierite phase appears after heat treatment at 950℃. Thereafter, the cordierite allotropically transforms to α-cordierite at 1000℃. Complete densification is achieved at 950℃; however, the density slightly decreases at higher temperatures, reaching a stable value of 2.63 kg·m^-3 between 1000℃ and 1100℃. The highest Vickers hardness of 6 GPa is also obtained at 950℃. However, a substantial decrease in hardness is recorded at 1000℃; at higher sintering temperatures, it slightly increases with increasing temperature as the α-cordierite crystallizes.

研究论文

Synthesis of WC powder through microwave heating of WO₃-C mixture

Amir Karimzadeh Behnami, Arman Hoseinpur, Masoud Sakaki, Mohammad Sh. Bafghi, Kazumichi Yanagisawa

2017, 24(2): 202-207. doi: 10.1007/s12613-017-1396-3

中文摘要(412) PDF(9) SpringerLink

摘要:
A simple, easy, and low-cost process for the fabrication of tungsten carbide (WC) powder through microwave heating of WO₃-C mixtures was developed. Thermodynamic calculations and experimental investigations were carried out for WO₃-C and W-C systems, and a formation mechanism was proposed. In the results, for the synthesis of WC, the use of over stoichiometric amount of C together with a specially assembled experimental setup (which effectively retains heat in the system) is necessary. The WC powder is successfully obtained by heating WO₃:5C mixture for 900s in a domestic microwave oven.

研究论文

Modification and investigation of silica particles as a foam stabilizer

Qian Zhu, Hua-lei Zhou, Ying-xiao Song, Zhi-dong Chang, Wen-jun Li

2017, 24(2): 208-215. doi: 10.1007/s12613-017-1397-2

中文摘要(455) PDF(13) SpringerLink

摘要:
As a solid foam stabilizer, spherical silica particles with diameters ranging from 150 to 190 nm were prepared via an improved Stöber method and were subsequently modified using three different silane coupling agents to attain the optimum surface hydrophobicity of the particles. Fourier transform infrared (FTIR) spectra and the measured contact angles were used to characterize the surface properties of the prepared particles. The foam stability was investigated by the foam drainage half-life and the expansion viscoelastic modulus of the liquid film. The results demonstrate that all of the modified silica nanoparticles effectively improve the foam stability. The surface hydrophobicity of the modified particles is found to be a key factor influencing the foam stability. The optimum contact angle of the particles lies in the approximate range from 50° to 55°. The modifier molecular structure used can also influence the stabilizing foam property of the solid particles. The foam system stabilized by (CH₃)₂SiCl₂-modified silica particles exhibits the highest stability; its drainage half-life at maximum increases by 27% compared to that of the blank foam system and is substantially greater than those of the foam systems stabilized by KH570- and KH550-modified particles.

研究论文

Preparation and radar-absorbing properties of Al₂O₃/TiO₂/Fe₂O₃/Yb₂O₃ composite powder

Yi-fan Zhang, Zhen Ji, Ke Chen, Cheng-chang Jia, Shan-wu Yang, Meng-ya Wang

2017, 24(2): 216-221. doi: 10.1007/s12613-017-1398-1

中文摘要(452) PDF(8) SpringerLink

摘要:
Al₂O₃/TiO₂/Fe₂O₃/Yb₂O₃ composite powder was synthesized via the sol-gel method. The structure, morphology, and radar-absorption properties of the composite powder were characterized by transmission electron microscopy, X-ray diffraction analysis and RF impedance analysis. The results show that two types of particles exist in the composite powder. One is irregular flakes (100-200 nm) and the other is spherical Al₂O₃ particles (smaller than 80 nm). Electromagnetic wave attenuation is mostly achieved by dielectric loss. The maximum value of the dissipation factor reaches 0.76 (at 15.68 GHz) in the frequency range of 2-18 GHz. The electromagnetic absorption of waves covers 2-18 GHz with the matching thicknesses of 1.5-4.5 mm. The absorption peak shifts to the lower-frequency area with increasing matching thickness. The effective absorption band covers the frequency range of 2.16-9.76 GHz, and the maximum absorption peak reaches -20.18 dB with a matching thickness of 3.5 mm at a frequency of 3.52 GHz.

研究论文

High-temperature frictional wear behavior of MCrAlY-based coatings deposited by atmosphere plasma spraying

Chong Tao, Lei Wang, Xiu Song

2017, 24(2): 222-228. doi: 10.1007/s12613-017-1399-0

中文摘要(490) PDF(9) SpringerLink

摘要:
Al₂O₃-Cr₂O₃/NiCoCrAlYTa coatings were prepared via atmosphere plasma spraying (APS). The microstructure and phase composition of the coatings were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), laser confocal scanning microscopy (LSCM), and transmission electron microscopy (TEM). The dry frictional wear behavior of the coatings at 500℃ in static air was investigated and compared with that of 0Cr25Ni20 steel. The results show that the coatings comprise the slatted layers of oxide phases, unmelted particles, and pores. The hot abrasive resistance of the coatings is enhanced compared to that of 0Cr25Ni20, and their mass loss is approximately one-fifteenth that of 0Cr25Ni20 steel. The main wear failure mechanisms of the coatings are abrasive wear, fatigue wear, and adhesive wear.

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2017年第24卷第2期