International Journal of Minerals, Metallurgy and Materials

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Synthesis of a copper(Ⅱ) oxide-montmorillonite composite for lead removal

Davidson E. Egirani, Nanfe R. Poyi, Napoleon Wessey

2019, 26(7): 803-810. doi: 10.1007/s12613-019-1788-7

中文摘要(503) PDF(11) SpringerLink

摘要:
The synthesis of a copper(Ⅱ) oxide-montmorillonite composite and its application in the removal of lead(Ⅱ) ions in solution were investigated. The Acros Organics (ACOR) montmorillonite was activated using potassium hydroxide solution. The activated ACOR montmorillonite was titrated with copper(Ⅱ) nitrate solution to produce the copper(Ⅱ) oxide-montmorillonite composite. Adsorption experiments were conducted using batch-mode techniques under reducing conditions at ambient temperature. The reaction mechanism indicated a higher proton coefficient, greater intraparticle diffusion, and higher mass transfer rates compared with those achieved with bare montmorillonite. The intraparticle diffusion constant derived from the slope was 2.93-3 (mg·g^-1·min^-0.5), and the intercept C was 9.86, ≠ 0. In the presence of a CuO coating, the adsorption efficiency was 85.55% at pH 4 and 89.62% at pH 7. Therefore, the copper(Ⅱ) oxide-montmorillonite composite, as a novel adsorbent with a very high adsorption capacity, exhibited substantially enhanced adsorption of Pb²⁺ ions compared with bare montmorillonite.

研究论文

Combustion characteristics of unburned pulverized coal and its reaction kinetics with CO₂

Dong-wen Xiang, Feng-man Shen, Jia-long Yang, Xin Jiang, Hai-yan Zheng, Qiang-jian Gao, Jia-xin Li

2019, 26(7): 811-821. doi: 10.1007/s12613-019-1791-z

中文摘要(641) PDF(12) SpringerLink

摘要:
The combustion characteristics of two kinds of unburned pulverized coal (UPC) made from bituminous coal and anthracite were investigated by thermogravimetric analysis under air. The reaction kinetics mechanisms between UPC and CO₂ in an isothermal experiment in the temperature range 1000-1100℃ were investigated. The combustion performance of unburned pulverized coal made from bituminous coal (BUPC) was better than that of unburned pulverized coal made from anthracite (AUPC). The combustion characteristic indexes (S) of BUPC and AUPC are 0.47×10^-6 and 0.34×10^-6%2·min^-2·℃^-3, respectively, and the combustion reaction apparent activation energies are 91.94 and 102.63 kJ·mol^-1, respectively. The reaction mechanism of BUPC with CO₂ is random nucleation and growth, and the apparent activation energy is 96.24 kJ·mol^-1. By contrast, the reaction mechanism of AUPC with CO₂ follows the shrinkage spherical function model and the apparent activation energy is 133.55 kJ·mol^-1.

研究论文

Thermodynamic studies on gas-based reduction of vanadium titano-magnetite pellets

Jun-wei Chen, Yang Jiao, Xi-dong Wang

2019, 26(7): 822-830. doi: 10.1007/s12613-019-1795-8

中文摘要(548) PDF(22) SpringerLink

摘要:
Numerous studies have focused on the reduction thermodynamics of ordinary iron ore; by contrast, the literature contains few thermodynamic studies on the gas-based reduction of vanadium titano-magnetite (VTM) in mixed atmospheres of H₂, CO, H₂O, CO₂, and N₂. In this paper, thermodynamic studies on the reduction of oxidized VTM pellets were systematically conducted in an atmosphere of a C-H-O system as a reducing agent. The results indicate that VTM of an equivalent valence state is more difficult to reduce than ordinary iron ore. A reduction equilibrium diagram using the C-H-O system as a reducing agent was obtained; it clearly describes the reduction process. Experiments were performed to investigate the effects of the reduction temperature, the gas composition, and two types of iron ores on the reduction of oxidized VTM pellets. The results show that the final reduction degree increases with increasing reduction temperature, increasing molar ratio of H₂/(H₂ + CO), and decreasing H₂O, CO₂, and N₂ contents. In addition, the reduction processes under various conditions are discussed. All of the results of the reduction experiments are consistent with those of theoretical thermodynamic analysis. This study is expected to provide valuable thermodynamic theory on the industrial applications of VTM.

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Effect of NaCl on synthesis of ZrB₂ by a borothermal reduction reaction of ZrO₂

Yu Wang, Yue-dong Wu, Ke-han Wu, Shu-qiang Jiao, Kuo-chih Chou, Guo-hua Zhang

2019, 26(7): 831-838. doi: 10.1007/s12613-019-1794-9

中文摘要(577) PDF(13) SpringerLink

摘要:
ZrB₂ powders were synthesized via a borothermal reduction reaction of ZrO₂ with the assistance of NaCl under a flowing Ar atmosphere. The optimal temperature and reaction time were 1223 K and 3 h, respectively. Compared with the reactions conducted without the addition of NaCl, those performed with the addition of an appropriate amount of NaCl finished at substantially lower temperatures. However, the addition of too much NaCl suppressed this effect. With the assistance of NaCl, a special morphology of polyhedral ZrB₂ particles covered with ZrB₂ nanosheets was obtained. Moreover, the experimental results revealed that the special morphology was the result of the combined effects of B₂O₃ and NaCl. The formation of the special microstructure is explained on the basis of the "dissolution-recrystallization" mechanism.

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Chemical composition and structural identification of primary carbides in as-cast H13 steel

Ming-tao Mao, Han-jie Guo, Fei Wang, Xiao-lin Sun

2019, 26(7): 839-848. doi: 10.1007/s12613-019-1796-7

中文摘要(527) PDF(19) SpringerLink

摘要:
The aim of this study was to characterize the primary carbides formed in as-cast H13 steel. The composition, morphology, type, and size of primary carbides in as-cast H13 steel were investigated by optical microscope (OM), field emission scanning electron microscopy (FE-SEM), electron back-scattered diffraction (EBSD), and X-ray diffraction (XRD) analysis. The number of primary carbides was investigated by ASPEX automated inclusion analysis system. The results indicated that primary carbides in as-cast H13 steel are mainly composed of Cr, Mo, V, and Ti, and there exist four kinds of primary carbides in the interdendritic zones of H13 steel, which are stripy Mo-Cr-rich M₂C, eutectic Mo-Cr-rich M₂C, V-rich MC, and V-rich MC with Ti and N. Thermodynamic calculation indicated that M₂C precipitates in liquid phase at solid fractions larger than 0.99, while MC precipitates in liquid phase at solid fractions larger than 0.96. Statistical results indicated that the number of M₂C is much greater than the number of other kinds of primary carbides. Most primary carbides are blocky, with lengths of no more than 10 μm and a length/width ratio of no more than 3. The large primary carbides in as-cast H13 steel are mainly M₂C.

研究论文

Effects of postweld aging on the microstructure and properties of bobbin tool friction stir-welded 6082-T6 aluminum alloy

Yu-peng Li, Da-qian Sun, Wen-biao Gong, Liang Liu

2019, 26(7): 849-857. doi: 10.1007/s12613-019-1800-2

中文摘要(541) PDF(24) SpringerLink

摘要:
Samples of 6082-T6 aluminum alloy were subjected to bobbin tool friction stir welding (BT-FSW), and the joints were treated by postweld natural aging (PWNA) and postweld artificial aging (PWAA). The microstructure, microhardness, and tensile properties of the aged and as-welded specimens were investigated. Transmission electron microscopy (TEM) observations revealed that a large number of Guinier-Preston (GP) zones precipitated in the form of a network on the stir zone (SZ) after PWNA for 60 d, and a large number of β" phases precipitated in the matrix for after PWAA for 6 h. As the aging time increased, the microhardness of the SZ and the thermomechanically affected zone (TMAZ) increased significantly, and the hardness of the SZ after PWAA for 6 h was close to that of the base metal (BM). With increasing PWNA time, the strength and strain increased slightly. When the PWAA time increased, the strength clearly increased, with a maximum value of 279.9 MPa after 6 h, while the strain decreased.

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Effects of small additions of Zn on the microstructure, mechanical properties and corrosion resistance of WE43B Mg alloys

A. V. Koltygin, V. E. Bazhenov, R. S. Khasenova, A. A. Komissarov, A. I. Bazlov, V. A. Bautin

2019, 26(7): 858-868. doi: 10.1007/s12613-019-1801-1

中文摘要(649) PDF(17) SpringerLink

摘要:
Zn is a commonly used alloying element for Mg alloys owing to its beneficial effects on mechanical properties. To improve the mechanical and corrosion properties of WE43B Mg alloys, the effects of 0-0.7wt% Zn addition on the microstructure and properties of sample alloys were investigated. Addition of Zn to as-cast WE43B alloy promoted the formation of the Mg₁₂Nd phase; by contrast, after T6 heat treatment, the phase composition of WE43B alloys with and without Zn addition remained mostly the same. A long-period stacking ordered phase was predicted by CALPHAD calculation, but this phase was not observed in either the as-cast or heat-treated Zn-containing WE43B alloys. The optimum temperature and duration of T6 heat treatment were obtained using CALPHAD calculations and hardness measurements. Addition of Zn resulted in a slight reduction in the average grain size of the as-cast and T6 heat-treated WE43B alloys and endowed them with increased corrosion resistance with little effect on their mechanical properties.

研究论文

Effect of heat treatment on the microstructure and micromechanical properties of the rapidly solidified Mg_61.7Zn₃₄Gd_4.3 alloy containing icosahedral phase

Wen-bo Luo, Zhi-yong Xue, Wei-min Mao

2019, 26(7): 869-877. doi: 10.1007/s12613-019-1799-4

中文摘要(619) PDF(12) SpringerLink

摘要:
In this paper, the microstructure evolution of the rapidly solidified (RS) Mg_61.7Zn₃₄Gd_4.3 (at%, atomic ratio) alloy at high temperatures was investigated. The hardness and elastic modulus of the main precipitated phases were also analyzed and compared with those of the α-Mg matrix on the basis of nanoindentation tests. The results show that the RS alloy consists of either a petal-like icosahedral quasicrystal (IQC) phase (~20 μm) and block-shaped H1 phase (~15 μm) or IQC particles with an average grain size of~107 nm as well as a small proportion of amorphous phase, which mainly depends on the holding time at the liquid temperature and the thickness of the ribbons. The IQC phase gradually transforms at 400℃ to a short-rod-shaped μ-phase (Mg_28.6Zn_63.8Gd_7.7) with a hexagonal structure. The hardness of the IQC phase is higher than that of H1 phase, and both phases exhibit a higher hardness than the α-Mg matrix and the μ-phase. The elasticity of the H1 phase is superior to that of the α-Mg matrix. The IQC phase possesses a higher elastic modulus than H1 phase. The easily formed H1 phase exhibits the poorest plastic deformation capacity among these phases but a higher elastic modulus than the α-Mg matrix.

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Comparison of a commercial powder and a powder produced from Ti-6Al-4V chips and their effects on compacts sintered by the sinter-HIP method

Mustafa Ustundag, Remzi Varol

2019, 26(7): 878-888. doi: 10.1007/s12613-019-1787-8

中文摘要(647) PDF(20) SpringerLink

摘要:
The present paper is related to the conversion of Ti-6Al-4V chips into powder and investigates the usability of the produced powder in powder metallurgy applications. In this regard, a disc-milling process was applied to Ti-6Al-4V chips and the obtained powder was subsequently compacted. The compacted samples were sintered by the sinter hot isostatic pressing (sinter-HIP) method at 1200℃ under high vacuum, their mechanical properties and microstructure were investigated and compared with those of commercial powder compacts subjected to the same preparation processes. The results showed that the produced powder exhibits greater flowability and higher apparent density than the commercial powder. However, the sintered products prepared from the commercial powder exhibited a higher relative density, lower porosity, and, as a result, greater flexural strength compared with the sintered compacts prepared from the produced powder. In addition, transgranular fracture was greater in the sintered products of the commercial powder. The microstructural studies revealed that the sintered products made from both the commercial and the produced powders consisted of α-and β-phase but contained more α-phase. All of the examined properties were found to be substantially affected by the particle size of the powders.

研究论文

Microstructure and homogenization process of as-cast GH4169D alloy for novel turbine disk

Kai Chen, Shu-yuan Rui, Fa Wang, Jian-xin Dong, Zhi-hao Yao

2019, 26(7): 889-900. doi: 10.1007/s12613-019-1802-0

中文摘要(644) PDF(39) SpringerLink

摘要:
To investigate the microstructure, segregation, and suitable homogenization process of as-cast GH4169D alloy, the microstructure, elements segregation, and precipitates of cast GH4169D ingots prepared by vacuum induction melting (VIM) and vacuum arc remelting (VAR) were observed by optical microscopy (OM), scanning electron microscopy, and energy-dispersive X-ray spectroscopy (EDS). According to the residual segregation model and simulation results of DICTRA thermodynamic software, the homogenization temperature and time range were set as 1120-1170℃ and 5-20 h, respectively. The experimental results showed that microscopic dendrite and element segregation occurred in the interior of ingots and the main segregation elements were Nb and Ti. In addition, the precipitates were mainly distributed in interdendritic regions and were composed of NbC, Laves, γ', and δ phases. The homogenization process suggested that the interdendritic detrimental precipitated Laves phase can be eliminated or redissolved after homogenization at 1150℃ for 20 h, suggesting it was the most suitable homogenization treatment. Thermal compression test results showed that the GH4169D alloys after homogenization treatment had no cracks and dynamic recrystallization occurred, with recrystallization volume fraction increasing with temperature, indicating a good working plasticity at temperatures from 1050 to 1200℃.

研究论文

Effects of Ta on the solidification behavior and microstructure of a rhenium-containing hot corrosion resistant single crystal

Shi-hua Ma, Hong-quan Hao, Dong Wang, Lang-hong Lou, Jian Zhang

2019, 26(7): 901-907. doi: 10.1007/s12613-019-1817-6

中文摘要(567) PDF(21) SpringerLink

摘要:
The effects of Ta on the solidification microstructure of the Re-containing hot corrosion resistant Ni-base single crystal were investigated. Results showed that Ta addition significantly modified the solidification behavior and further influenced the as-cast microstructure. Ta addition changed the solidification characteristic temperatures and decreased the segregation of refractory elements (Re and W) as well as increased the solidification temperature range from 39.0 to 61.8℃ as Ta addition increased from 2wt% to 8wt%. The integration of these two factors increased the primary dendrite arm spacing and changed the morphology and size of γ' precipitates. With increasing Ta addition from 2wt% to 8wt%, the size of γ' precipitates in the dendrite core increased substantially from 0.24 to 0.40 μm, whereas the γ' precipitates in the interdendritic region decreased slightly from 0.56 to 0.47 μm. This paper then discussed the mechanism of these "Ta effects".

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Influence of nickel addition on the microstructure and mechanical properties of Al₂O₃-5vol%ZrO₂ ceramic composites prepared via precipitation method

Betül Kafkaslıoğlu Yıldız, Hüseyin Yılmaz, Yahya Kemal Tür

2019, 26(7): 908-914. doi: 10.1007/s12613-019-1792-y

中文摘要(560) PDF(10) SpringerLink

摘要:
The aim of this work was to investigate the microstructure and mechanical properties of 1vol%-Ni-added yttria-stabilized zirconia (YSZ) toughened alumina composites. First, Ni powders were heterogeneously precipitated in an alumina-zirconia powder mixture suspended in water; the prepared specimens were then pressureless sintered at 1550℃/2 h in a 90vol%Ar/10vol% H₂ atmosphere. The structure of phases and microstructure of the composites were characterized by X-ray diffraction and scanning electron microscopy, respectively. Mechanical characterization of the specimens was carried out through Vickers hardness, Vickers indentation toughness, and three-point flexural bending tests. The fine Ni particles were homogeneously dispersed throughout the alumina matrix because of the employed processing method. Furthermore, hardness and toughness values were found to increase by 8% and 50%, respectively, with Ni addition, whereas the relative densities and flexural strength values were found to remain unchanged.

研究论文

Effect of TiB₂ content on microstructure and properties of in situ Ti-TiB composites

Harshpreet Singh, Muhammad Hayat, Hongzhou Zhang, Raj Das, Peng Cao

2019, 26(7): 915-924. doi: 10.1007/s12613-019-1797-6

中文摘要(631) PDF(10) SpringerLink

摘要:
This study determined the optimal concentration of titanium diboride (TiB₂) particles for the development of in situ titanium-titanium boride (Ti-TiB) metal matrix composites (MMCs) prepared by a conventional powder metallurgy route to be used for industrial applications. The effect of concentration of TiB₂ particles was studied by reinforcing TiB₂ powder in different mass fractions (2wt%, 5wt%, 10wt%, and 20wt%) into pure Ti powder during the fabrication process. The MMCs were sintered at high temperatures under vacuum. The transmission electron microscopy (TEM) results revealed the formation of needle-shaped TiB whiskers, indicating that in situ reaction occurred during vacuum sintering of the powder compacts. All the composite samples had a high sintered density, and the hardness of the composites increased with an increase in the mass fraction of reinforcement. Mechanical and tribological properties such as flexural strength, impact, and wear properties were determined and found to be dependent on the mass fraction of the reinforcement. However, the mechanism for the in situ reaction needs further investigation by high-energy in situ X-ray diffraction techniques.

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2019年第26卷第7期