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      20 December 2018, Volume 34 Issue 12 Previous Issue    Next Issue
    Orginal Article
    Discoloration mechanism, structures and recent applications of thermochromic materials via different methods: A review
    Cheng Youliang, Zhang Xiaoqiang, Fang Changqing, Chen Jing, Wang Zhen
    J. Mater. Sci. Technol.. 2018, 34 (12): 2225-2234.   DOI: 10.1016/j.jmst.2018.05.016
    Abstract   HTML   PDF (2370KB)

    Thermochromic material is a kind of smart material whose color will vary as the result of the phase transition caused by the temperature change. The characteristics of thermochromic materials are the memory functions to the temperature, having great potential applications in aerospace, military, anti-counterfeiting technology, construction and other fields. In recent years, many kinds of thermochromic materials have been prepared by different methods and their discoloration mechanisms are various according to published literatures. In this paper, the classification, discoloration mechanism, preparation methods, application fields and development trend of thermochromic materials are reviewed.

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    A 12R long-period stacking-ordered structure in a Mg-Ni-Y alloy
    Liu Cheng, Zhu Yuman, Luo Qun, Liu Bin, Gu Qinfen, Li Qian
    J. Mater. Sci. Technol.. 2018, 34 (12): 2235-2239.   DOI: 10.1016/j.jmst.2018.06.015
    Abstract   HTML   PDF (2090KB)

    A hitherto unreported long-period stacking-ordered (LPSO) phase, designated 12R, was observed in a Mg80Ni5Y15 (at.%) alloy. Microstructure was investigated by electron diffraction and high-angle annular dark-field scanning transmission electron microscopy. Results show that the 12R has a trigonal lattice (a = b = 1.112 nm, c = 3.126 nm, α = β = 90°, and γ = 120°). Unit cell of the 12R is consisted of three ABCA-type building blocks and each building block contains dominant Ni6Y8-type building clusters. A sound structural model is proposed based on relative positions of Ni6Y8 clusters in neighboring building blocks.

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    Ultrasonic vibration assisted tungsten inert gas welding of dissimilar magnesium alloys
    Yang Fangzhou, Zhou Jie, Ding Rongrong
    J. Mater. Sci. Technol.. 2018, 34 (12): 2240-2245.   DOI: 10.1016/j.jmst.2018.06.009
    Abstract   HTML   PDF (3043KB)

    The effects of ultrasonic vibration assisted (UVA) treatment on the microstructures and mechanical properties of MB3/AZ31 dissimilar magnesium (Mg) alloy joints were studied by microstructural characterization, micro-hardness testing and tensile testing. Results indicate that the welding pores are eliminated and coarse α-Mg grains of fusion zone are refined to 26 μm, owing to the acoustic streaming effect and cavitation effect induced by the UVA treatment with an optimal ultrasonic power of 1.0 kW. In addition, Mg17Al12 precipitation phases are fine and uniformly distributed in the whole fusion zone of weldment. Micro-hardness of fusion zone of the Mg alloy joints increases to 53.5 HV after UVA process, and the maximum tensile strength with optimized UVA treatment increases to 263 MPa, which leads to fracture occurrence in the Mg alloy base plate. Eventually, it is experimentally demonstrated that robust MB3/AZ31 Mg alloy joints can be obtained by UVA process.

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    Microstructure evolution, mechanical properties and diffusion behaviour of Mg-6Zn-2Gd-0.5Zr alloy during homogenization
    Xiao Lei, Yang Guangyu, Liu Yang, Luo Shifeng, Jie Wanqi
    J. Mater. Sci. Technol.. 2018, 34 (12): 2246-2255.   DOI: 10.1016/j.jmst.2018.05.003
    Abstract   HTML   PDF (4942KB)

    The microstructure evolution and mechanical properties of Mg-6Zn-2Gd-0.5Zr alloy during homogenization treatment were investigated. The as-cast alloy was found to be composed of dendritic primary α-Mg matrix, α-Mg + W (Mg3Zn3Gd2) eutectic along grain boundaries, and icosahedral quasicrystalline I (Mg3Zn6Gd) phase within α-Mg matrix. During homogenization process, α-Mg + W (Mg3Zn3Gd2) eutectic and I phase gradually dissolved into α-Mg matrix, while some rod-like rare earth hydrides (GdH2) formed within α-Mg matrix. Both the tensile yield strength and the elongation showed a similar tendency as a function of homogenization temperature and holding time. The optimized homogenization parameter was determined to be 505 °C for 16 h according to the microstructure evolution. Furthermore, the diffusion kinetics equation of the solute elements derived from the Gauss model was established to predict the segregation ratio of Gd element as a function of holding time, which was proved to be effective to evaluate the homogenization effect of the experimental alloy.

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    Effect of rolling strain on microstructure and tensile properties of dual-phase Mg-8Li-3Al-2Zn-0.5Y alloy
    Liu Wencai, Feng Shi, Li Zhongquan, Zhao Jiong, Wu Guohua, Wang Xianfei, Xiao Lv, Ding Wenjiang
    J. Mater. Sci. Technol.. 2018, 34 (12): 2256-2262.   DOI: 10.1016/j.jmst.2018.05.002
    Abstract   HTML   PDF (3720KB)

    This study was conducted to discuss the effect of rolling strain on microstructure and tensile properties of dual-phase Mg-8Li-3Al-2Zn-0.5Y (wt%) alloy, which was prepared by casting, and then homogenized and rolled at 200?°C. The rolling process was conducted with 10% reduction per pass and five different accumulated strains, varying from 10% to 70%. The results indicate that the as-cast and as-rolled Mg-8Li-3Al-2Zn-0.5Y alloys are composed of α-Mg, β-Li, AlLi and Al2Y phases. After rolling process, anisotropic microstructure was observed. α-Mg phase got elongated in both rolling direction and transverse direction with the addition of rolling strain. Consequently, the strength of the alloy in both directions was notably improved whereas the elongation declined, mainly caused by strain hardening and dispersion strengthening. The tensile properties of the as-rolled alloys in the RD, no matter the YS, UTS or the elongation, are higher than those of the TD due to their larger deformation strain and significant anisotropy in the hcp α-Mg phase. In addition, the fracture and strengthening mechanism of the tested alloys were also investigated systematically.

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    Structural characterization and strengthening mechanism of forsterite nanostructured scaffolds synthesized by multistep sintering method
    Tavangarian Fariborz, Fahami Abbas, Li Guoqiang, Kazemi Mohammadhassan, Forghani Anoosha
    J. Mater. Sci. Technol.. 2018, 34 (12): 2263-2270.   DOI: 10.1016/j.jmst.2018.06.010
    Abstract   HTML   PDF (3618KB)

    In this study, highly porous forsterite scaffolds with interconnected porosities were synthesized using multi-step sintering (MSS) method. The starting powder was nanosized forsterite, which was synthesized from talc and magnesium carbonate powders. The phase composition, average particle size and morphology of the produced forsterite powder were characterized by X-ray diffraction technique (XRD) and transition electron microscopy (TEM). Forsterite scaffolds were produced by foamy method using polymeric sponges. MSS process including three steps was used to efficiently sinter the forsterite nanopowders without destroying the initial porous structure of polymeric sponges. The results showed that MSS technique is an efficient and appropriate procedure to produce highly porous forsterite scaffolds with pore size in the range of 100-300?μm. The compressive strength, compressive modulus and porosity of C12 specimen (sintered at 1650?°C for 1?h with subsequent annealing at 1000?°C for 1000?min) was 1.88?MPa, 29.2?MPa, and 72.4%, respectively, which is very close to that of cancellous bone. The approach studied in this research can be developed for other nanostructure ceramics to produce highly porous scaffolds with interconnected porosities for load bearing applications.

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    Initial formation of corrosion products on pure zinc in simulated body fluid
    Liu Lijun, Meng Yao, Dong Chaofang, an YuY, A. Volinsky Alex, Wang Lu-Ning
    J. Mater. Sci. Technol.. 2018, 34 (12): 2271-2282.   DOI: 10.1016/j.jmst.2018.05.005
    Abstract   HTML   PDF (5149KB)

    Zinc was recently suggested to be a potential candidate material for degradable coronary artery stent. The corrosion behavior of pure zinc exposed to r-SBF up to 336?h was investigated by electrochemical measurements and immersion tests. The morphology and chemical composites of the corrosion products were investigated by scanning electron microscope, grazing-incidence X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectrometer. The results demonstrate that the initial corrosion products on the pure zinc mainly consist of zinc oxide/hydroxide and zinc/calcium phosphate compounds. The pure Zn encounters uniform corrosion with an estimated corrosion rate of 0.02-0.07?mm?y-1 during the immersion, which suggests the suitability of pure Zn for biomedical applications.

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    Enhancement of shear stability of a Fe-based amorphous alloy using electrodeposited Ni layers
    Wang Y.C., Luo X.M., Chen L.J., Yang H.W., Zhang B., Zhang G.P.
    J. Mater. Sci. Technol.. 2018, 34 (12): 2283-2289.   DOI: 10.1016/j.jmst.2018.05.015
    Abstract   HTML   PDF (2435KB)

    Tensile and fracture behaviors of sandwich-structured composites consisting of a Fe-based amorphous layer with a constant thickness and ultrafine-grained Ni layers with different thicknesses were investigated. The results indicate that the initiation and the stable propagation of the shear band in the amorphous layer was dominated by the Ni layers due to their strong constraint role. The catastrophic fracture of the amorphous layer was postponed in the sandwich composites through properly increasing the constrained Ni layer thickness, which effectively decreased the shear stress on the shear fracture planes of the amorphous layer, and thus led to stable propagation of the primary SB characterized by the increase in the smooth region size of the shear band.

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    Fe-based metallic glass: An efficient and energy-saving electrode material for electrocatalytic degradation of water contaminants
    Qin Xindong, Li Zhengkun, Zhu Zhengwang, Fu Huameng, Li Hong, Wang Aimin, Zhang Hongwei, Zhang Haifeng
    J. Mater. Sci. Technol.. 2018, 34 (12): 2290-2296.   DOI: 10.1016/j.jmst.2018.04.012
    Abstract   HTML   PDF (2581KB)

    Excessive consumption of electrical energy has hampered the widespread application of electrochemical technology for degradation of various contaminants. In this paper, a Fe-based metallic glass (MG) was demonstrated as a new type of electrocatalyst to effectively and economically degrade an azo dye. In comparison to other typical electrodes, Fe-based MG electrodes exhibit a minimized degradation time, and the specific energy is 4-6 orders of magnitude lower than that of dimensionally stable anode (DSA), metal-like boron-doped diamond (BDD) and other electrodes. As sacrificial electrode materials, Fe-based MGs have less specific electrode mass consumption than iron electrodes. The use of Fe-based MGs will promote the practical application of electrochemical technology and the use of MGs as functional materials.

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    Evolution of secondary phase particles during deformation of Al-5Ti-1B master alloy and their effect on α-Al grain refinement
    Yu Hong, Wang Ning, Guan Renguo, Tie Di, Li Zheng, An Yanan, Zhang Yang
    J. Mater. Sci. Technol.. 2018, 34 (12): 2297-2306.   DOI: 10.1016/j.jmst.2018.04.018
    Abstract   HTML   PDF (6052KB)

    Addition of Al-5Ti-1B alloy to molten aluminum alloys can refine α-Al grains effectively and thereby improve their strength and toughness. TiAl3 and TiB2 in Al-5Ti-1B alloy are the main secondary-phase particles for refinement, while the understanding on the effect of their sizes on α-Al grain refinement continues to be fragmented. Therefore, Al-5Ti-1B alloys with various sizes and morphologies of the secondary-phase particles were prepared by equal channel angular pressing (ECAP). Evolution of the secondary-phase particles during ECAP process and their impact on α-Al grain refinement were studied by X-ray diffraction and scanning electron microscope (SEM). Results show that during the ECAP process, micro-cracks firstly appeared inside TiAl3 particles and then gradually expanded, which resulted in continuous refinement of TiAl3 particles. In addition, micro-distribution uniformity of TiB2 particles was improved due to the impingement of TiAl3 particles to TiB2 clusters during deformation. Excessively large sizes of TiAl3 particles would reduce the number of effective heterogeneous nucleus and thus resulted in poor grain refinement effectiveness. Moreover, excessively small TiAl3 particles would reduce inhibitory factors for grain growth Q and weaken grain refinement effectiveness. Therefore, an optimal size range of 18-22 μm for TiAl3 particles was suggested.

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    The Portevin-Le Châtelier effect of gradient nanostructured 5182 aluminum alloy by surface mechanical attrition treatment
    Meng Xiangchen, Liu Bei, Luo Lan, Ding Yan, Rao Xi-Xin, Hu Bin, Liu Yong, Lu Jian
    J. Mater. Sci. Technol.. 2018, 34 (12): 2307-2315.   DOI: 10.1016/j.jmst.2018.06.002
    Abstract   HTML   PDF (3974KB)

    Nanocrystalline surface layers and gradient nanostructure in 5182 aluminum alloy have been produced through surface mechanical attrition treatment (SMAT). The results indicate that the gradient nanostructure can not only improve the mechanical properties of 5182 Al alloy, but also has a certain effect on the Portevin-Le Chatelier (PLC) effect. The yield and ultimate tensile strength of 5182 Al alloy with SMAT are significantly improved combining with the decrease of fracture elongation compared with the as-received one. The PLC effect of 5182 Al alloy could be effectively postponed by the formation of gradient nanostructure after SMAT. It leads to the increase of critical strain of the PLC effect, more concentrated distribution of serrated strain, and increase of average stress amplitude in special strain range. The influence of grain size and gradient nanostructure on the PLC effect of 5182 Al alloy was also discussed in detail. Grain refinement could sharply increase the density of dislocations and hinder the movement of dislocations, which results in the decrease of moving speed of dislocations and the more concentrated distribution of solute atoms. The solute atoms would aggregate to form nano precipitates and further impede movement of dislocation. The stronger interaction between the dislocations and the nano precipitates is the main mechanism of postponed PLC effect.

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    Effects of Zr, Ti and Sc additions on the microstructure and mechanical properties of Al-0.4Cu-0.14Si-0.05Mg-0.2Fe alloys
    Feng Jian, Ye Bing, Zuo Lijie, Qi Ruijuan, Wang Qudong, Jiang Haiyan, Huang Rong, Ding Wenjiang, Yao Jie, Wang Chuntao
    J. Mater. Sci. Technol.. 2018, 34 (12): 2316-2324.   DOI: 10.1016/j.jmst.2018.05.011
    Abstract   HTML   PDF (5857KB)

    The evolution of microstructure and mechanical properties of Al-0.4Cu-0.14Si-0.05Mg-0.2Fe (wt.%) alloys, micro-alloyed with Zr, Ti and Sc, were investigated. The addition of 0.2%Zr to base alloy accelerates the precipitation of Si-rich nano-phase in α-Al matrix, which plays an important role in improving the mechanical properties of an alloy. The tensile strength increases from 102 MPa for the base alloy to 113 MPa for the Zr-modified alloy. Adding 0.2%Zr + 0.2%Ti to base alloy effectively refines α-Al grain size and accelerates the precipitation of Si and Cu elements, leading to heavy segregation at grain boundary. By further adding 0.2%Sc to Zr + Ti modified alloy, the segregation of Si and Cu elements is suppressed and more Si and Cu precipitates appeared in α-Al matrix. Accompanied with the formation of coherent Al3Sc phase, the tensile strength increases from 108 MPa for the Zr + Ti modified alloy to 152 MPa for the Sc-modified alloy. Due to excellent thermal stability of Al3Sc phase, the Sc-modified alloy exhibits obvious precipitation hardening behavior at 350 °C, and the tensile strength increases to 203 MPa after holding at 350 °C for 200 h.

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    Evolution of microstructure and phase composition of Ti-3Al-5Mo-4.5V alloy with varied β phase stability
    Xue Q., Ma Y.J., Lei J.F., Yang R., Wang C.
    J. Mater. Sci. Technol.. 2018, 34 (12): 2325-2330.   DOI: 10.1016/j.jmst.2018.04.002
    Abstract   HTML   PDF (3639KB)

    The microstructure evolution and phase composition of an α + β titanium alloy, Ti-3Al-5Mo-4.5V (wt.%), have been investigated. Electron probe micro analysis (EPMA) quantitative results manifest that the stability of β phase decreases with increasing quenching temperature, which is influenced by the significant variation of β-stabilizing elements concentration. Detailed microstructure analysis shows that the β → ω phase transformation does occur when quenching at 750 °C and 800 °C. The ω-reflections change from incommensurate ω-spots (750 °C) to ideal ω-spots (800 °C) as the β stability of the alloy decreases. Further the decrease of β phase stability encourages the formation of athermal α′′ martensite, which has the following orientation relationships: [111]β//[110]α′′, [100]β//[100]α′′ and [-110]β//[00-1]α′′ with respect to the β matrix.

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    Fabrication ofultrafine ZnFe2O4 nanoparticles for efficient photocatalytic reduction CO2 under visible light illumination
    Xiao Jun, Yang Weiyi, Gao Shuang, Sun Caixia, Li Qi
    J. Mater. Sci. Technol.. 2018, 34 (12): 2331-2336.   DOI: 10.1016/j.jmst.2018.06.001
    Abstract   HTML   PDF (1994KB)

    A one-pot, solvent-thermal process was used to create the ultrafine ZnFe2O4 nanoparticles photocatalyst. During the solvent-thermal process, the in situ self-forming NaCl not only served as a “cage” to confine the ion diffusion, but also acted as a microreactor for nanocrystallite growth. An average particle size of ~10 nm and a high-specific surface area of ~112.9 m2/g were observed for the ultrafine ZnFe2O4 nanoparticles Owing to the synergistic effect of ultrafine particle size, the full utilization of the visible light region and high conduction band (CB) position, ultrafine ZnFe2O4 photocatalyst displayed an efficient photocatalytic CO2 reduction under visible light illumination. Besides, the ultrafine ZnFe2O4 photocatalyst showed high production selectivity for CH3CHO and C2H5OH generation in aqueous CO2/NaHCO3 solution. This work may provide a new idea for the synthesis of new high-efficiency photocatalysts.

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    Catalytic reduction of low-concentration CO2 with water by Pt/Co@NC
    Wang Qianqian, Wang Wenzhong, Zhang Ling, Su Yang, Wang Kefu, Wu Huixia
    J. Mater. Sci. Technol.. 2018, 34 (12): 2337-2341.   DOI: 10.1016/j.jmst.2018.04.010
    Abstract   HTML   PDF (1834KB)

    The reduction of low-concentration carbon dioxide with water to organic fuels is still a huge challenge. In this study, we successfully designed the partially oxidized cobalt nanoparticles coated by the nitrogen-doped carbon layer (Co@NC) of 2-8?nm via a facile method and then interspersed with different amount of Pt nanoparticles. The Co@NC decorated with 1?wt% Pt exhibits the best ability for CO2 reduction to CH4 and a CH4 production rate of 14.4?μmol·g-1·h-1 is achieved. It is worth noting that the system is carried out under low-concentration CO2 (400?ppm) circumstance without any sacrificial agent, which could be meaningful to the design of catalysts for atmospheric CO2 reduction.

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    CuS nanoplatelets arrays grown on graphene nanosheets as advanced electrode materials for supercapacitor applications
    Li Xianfu, Zhou Kaixuan, Zhou Jianyu, Shen Jianfeng, Ye Mingxin
    J. Mater. Sci. Technol.. 2018, 34 (12): 2342-2349.   DOI: 10.1016/j.jmst.2018.06.013
    Abstract   HTML   PDF (4524KB)

    CuS nanoplatelets arrays grown on graphene nanosheets are successfully synthesized via a facile low-temperature solvothermal reaction with graphene oxide (GO), CH3CSNH2 and Cu(CH3COO)2·H2O as the reactants. CH3CSNH2 plays an important role in being the reducing agent for GO and the sulfur source of CuS. Supercapacitive performance of the graphene/CuS nanocomposite as active electrode materials has been evaluated by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy measurements. The results indicate that graphene/CuS electrode delivers a high capacitance of 497.8 F g-1 at a current density of 0.2 A g-1, which outperforms bare CuS electrode. This excellent performance is ascribed to the short diffusion path and large surface area of the unique hierarchical nanostructure with nanoflakes building blocks for bulk accessibility of faradaic reaction.

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    Hydrolytic dehydrogenation of ammonia borane catalyzed by poly(amidoamine) dendrimers-modified reduced graphene oxide nanosheets supported Ag0.3Co0.7 nanoparticles
    Ke Dandan, Wang Jin, Zhang Hongming, Li Yuan, Zhang Lu, Zhao Xin, Han Shumin
    J. Mater. Sci. Technol.. 2018, 34 (12): 2350-2358.   DOI: 10.1016/j.jmst.2018.06.003
    Abstract   HTML   PDF (2144KB)

    Poly(amidoamine) dendrimers-modified reduced graphene oxide nanosheets (PAMAM/rGO) composite was selected as a carrier of heterogeneous Ag0.3Co0.7 nanoparticles in order to obtain an excellent catalyst for ammonia borane (AB) hydrolysis. During the synthetic processes, GO could easily assembled with PAMAM by the electrostatic and hydrogen-bonding interactions. Structural characterization revealed that Ag0.3Co0.7 bimetallic nanoparticles with uniform size distribution of 5 nm are well dispersed on PAMAM/rGO composite architecture. Ag0.3Co0.7@PAMAM/rGO was found to be a highly active and reusable catalyst in hydrogen generation from the hydrolysis of AB with a turnover frequency value (TOF) of 19.79 molH2 min-1 molM-1 at 25.0 ± 0.1 °C and retained 75.4% of their initial activity with a complete release of hydrogen in five runs. The relatively high TOF value and low apparent activation energy (34.21 kJ mol-1) make these Ag0.3Co0.7@PAMAM/rGO NPs as a high-efficient catalyst for catalytic dehydrogenation of AB facilitating the development of practically applicable energy storage materials.

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    Antibacterial activity of Cu2O and Ag co-modified rice grains-like ZnO nanocomposites
    Hong Dunhua, Cao Guangzhong, Qu Junle, Deng Yuanming, Tang Jiaonin
    J. Mater. Sci. Technol.. 2018, 34 (12): 2359-2367.   DOI: 10.1016/j.jmst.2018.06.011
    Abstract   HTML   PDF (2881KB)

    In this work, a series of Cu2O-Ag/ZnO, Cu2O/ZnO and Ag/ZnO nanocomposites with various compositions were prepared via a hydrothermal method followed by chemical modification, and their antibacterial performance was investigated in detail. X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy results confirmed that 31?nm Cu2O and 30?nm Ag nanoparticles are well-dispersed on 202?nm ZnO grains to form a Cu2O/ZnO and Ag/ZnO heterojunction, respectively. The bi-heterojuction structure in the Cu2O-Ag/ZnO provided a synergistic effect on antibacterial activity, and the (Cu2O)0.04Ag0.06ZnO0.9 nanocomposites showed the highest antimicrobial activity of all samples with minimum inhibitory concentration and minimum bactericidal concentration against Escherichia coli and Staphylococcus aureus as low to 31.25?μg/mL, 250?μg/mL, 125?μg/mL and 500?μg/mL, respectively. This is the first report of the antibacterial activities of Cu2O and Ag co-modified ZnO nanocomposites.

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    Electrical properties of La2Mo1.98Nb0.02O8.99 oxide ionic conductors prepared by tape casting
    Liu Xiao, Xu Xiaomin, Du Huiling
    J. Mater. Sci. Technol.. 2018, 34 (12): 2368-2370.   DOI: 10.1016/j.jmst.2018.06.012
    Abstract   HTML   PDF (874KB)

    La2Mo2-xNbxO9-δ thick films have been successfully prepared by using a tape casting technique. Partial stabilization of the high temperature cubic phase is revealed in Nb doped La2Mo2O9 (LMO) films. The sintering temperature is decreased to 925?°C as compared with that of 1150?°C in bulk ceramics. The grain exhibits an oxide ionic conductivity of 0.014?S?cm-1 at 603?°C for La2Mo1.98Nb0.02O8.99, which is 39% higher than pure LMO. Additionally, the Nb doped LMO films present low grain boundary resistance showing the potential application as solid electrolytes.

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    High energy-storage properties of Bi0.5Na0.5TiO3-BaTiO3-SrTi0.875Nb0.1O3 lead-free relaxor ferroelectrics
    Shi Jing, Liu Xiao, Tian Wenchao
    J. Mater. Sci. Technol.. 2018, 34 (12): 2371-2374.   DOI: 10.1016/j.jmst.2018.06.008
    Abstract   HTML   PDF (1443KB)

    New lead-free ferroelectric (0.94-x)Bi0.5Na0.5TiO3-0.06BaTiO3-xSrTi0.875Nb0.1O3 (BNBT-STN, x = 0 and 0.2) are synthesized by using a solid state reaction process. In this work, an obvious evolution of dielectric relaxation behavior and slim P-E hysteresis loops with high Pmax and low Pr is observed for BNBT-0.2STN, indicating the dominant of ergodic relaxor phase with dynamic polar nano-regions (PNRs). A relatively large recoverable energy density (Wrec = 1.17 J/cm3) with high energy efficiency (η = 91%) is obtained. Furthermore, it shows small variation (9%) in the temperature range of 30-150 °C and fatigue-free behavior, which can be attributed to the absence of ferroelectric domain in the relaxor phase. The achievement of these characteristics provides that tailoring by B-site vacancies is a potential route when designing a new energy-storage system for BNT-based relaxor ferroelectric materials.

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    Cell-protecting regeneration from anode carbon deposition using in situ produced oxygen and steam: A combined experimental and theoretical study
    Han Zongying, Yang Zhibin, Han Minfang
    J. Mater. Sci. Technol.. 2018, 34 (12): 2375-2383.   DOI: 10.1016/j.jmst.2018.04.011
    Abstract   HTML   PDF (3096KB)

    Carbon deposition is a primary concern during the operation of solid oxide fuel cells (SOFCs) fueled with hydrocarbon fuels, leading to cell degradation and even cell damage. Carbon elimination is expected to be a promising approach to prolong cell life. This work reports on a combined experimental and theoretical investigation of cell regeneration from anode carbon deposition of tubular SOFCs fabricated by phase-inversion and co-sintering techniques. The as-prepared cell exhibits a maximum power density of 0.20?W?cm-2 at 800?°C fueling with wet CH4, but fails to stable operation due to severe carbon deposition. Based on thermodynamic predictions, a successive cell-protecting regeneration process is proposed to eliminate deposited carbon without oxidizing Ni catalysts, during which CH4 and H2 fuels are provided in circulation. Through a total of 35 cycling tests, cell performance can always successfully restore to the initial level. The possible carbon elimination mechanism is investigated in detail based on thermodynamic and first-principle calculations. The feasibility of carbon elimination using in situ produced oxygen or steam through electrochemical reaction has been revealed, providing a novel continuous operation mode for hydrocarbon-based SOFCs.

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    Nitrogen-doped hierarchical porous carbon materials derived from diethylenetriaminepentaacetic acid (DTPA) for supercapacitors
    Wu Tinghuan, Sun Lixian, Xu Fen, Cai Dan
    J. Mater. Sci. Technol.. 2018, 34 (12): 2384-2391.   DOI: 10.1016/j.jmst.2018.06.005
    Abstract   HTML   PDF (2634KB)

    Nitrogen-doped porous carbon materials (NPCs) have been successfully fabricated by a simple one-step pyrolysis of diethylenetriaminepentaacetic acid (DTPA) in the presence of KOH. The as-synthesized NPCs displayed a high specific surface area (3214?m2?g-1) and a well-defined porous structure when the annealing temperature reached 800?°C, which showed superior electrochemical performance as supercapacitor electrode materials. Electrochemical tests showed that the NPCs achieved an impressive specific capacitance of 323?F?g-1 at a current density of 0.5?A?g-1 in 6?M KOH aqueous solution and an outstanding cycle stability, negligible specific capacitance decay after 5000 cycles at 10?A?g-1. This strategy offered a new insight into the preparation of novel carbon materials for the advanced energy storage devices, such as supercapacitors, fuel cells and lithium ion batteries.

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    Effects of the annealing temperature on the structure and up-conversion photoluminescence of ZnO film
    Meng Xiaoqi, Zhao Changjiang, Xu Boxu, Wang Pei, Liu Juncheng
    J. Mater. Sci. Technol.. 2018, 34 (12): 2392-2397.   DOI: 10.1016/j.jmst.2018.05.018
    Abstract   HTML   PDF (1987KB)

    The up-conversion film is being tried to increase the photoelectric conversion efficiency of the silicon solar cell. To improve the efficiency of the photoluminescence film, the effects of the annealing temperature were investigated on the structure and photoluminescence of the ZnO up-conversion film, which was prepared using the sol-gel method and the spin-coating technique. The results show that the organic compounds and water in the ZnO film were completely eliminated when the annealing temperature reached 500?°C. The crystallinity of film is improved and the average grain size continuously increases as increasing the annealing temperature. The transmittance in the wavelength range of 400-2000?nm continuously increases as the annealing temperature increases from 500?°C to 700?°C, whilst it decreases first and then increases as the annealing temperature increases from 800?°C to 1000?°C. When the film is excited with a laser of 980?nm, there are two intense emission bands in the up-conversion emission spectra, 542-nm green light and 660-nm red light, corresponding to Ho3+: 5S2/5F4?→?5I8?and 5F5?→?5I8 transitions, respectively. In addition, the intensity of up-conversion luminescence for the film increases first and then decreases with the increase of the annealing temperature. When the annealing temperature is at 900?°C, the film consists of small round compact particles with a high degree of crystallization, reaching maximum up-conversion intensity of the film.

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    Growth behavior of CVD diamond films with enhanced electron field emission properties over a wide range of experimental parameters
    Jia Xinyi, Huang Nan, Guo Yuning, Liu Lusheng, Li Peng, Zhai Zhaofeng, Yang Bing, Yuan Ziyao, Shi Dan, Jiang Xin
    J. Mater. Sci. Technol.. 2018, 34 (12): 2398-2406.   DOI: 10.1016/j.jmst.2018.04.021
    Abstract   HTML   PDF (2922KB)

    In this study, diamond films were synthesized on silicon substrates by microwave plasma enhanced chemical vapor deposition (CVD) over a wide range of experimental parameters. The effects of the microwave power, CH4/H2 ratio and gas pressure on the morphology, growth rate, composition, and quality of diamond films were investigated by means of scanning electron microscope (SEM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). A rise of microwave power can lead to an increasing pyrolysis of hydrogen and methane, so that the microcrystalline diamond film could be synthesized at low CH4/H2 levels. Gas pressure has similar effect in changing the morphology of diamond films, and high gas pressure also results in dramatically increased grain size. However, diamond film is deteriorated at high CH4/H2 ratio due to the abundant graphite content including in the films. Under an extreme condition of high microwave power of 10 kW and high CH4 concentration, a hybrid film composed of diamond/graphite was successfully formed in the absence of N2 or Ar, which is different from other reports. This composite structure has an excellent measured sheet resistance of 10-100 Ω/Sqr. which allows it to be utilized as field electron emitter. The diamond/graphite hybrid nanostructure displays excellent electron field emission (EFE) properties with a low turn-on field of 2.17 V/μm and β = 3160, therefore it could be a promising alternative in field emission applications.

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    Thermal conductivity and mechanical properties of high density polyethylene composites filled with silicon carbide whiskers modified by cross-linked poly (vinyl alcohol)
    Fan Jiaming, Xu Shiai
    J. Mater. Sci. Technol.. 2018, 34 (12): 2407-2414.   DOI: 10.1016/j.jmst.2018.04.003
    Abstract   HTML   PDF (2898KB)

    A thin layer of poly (vinyl alcohol) (PVA) was coated on the surface of silicon carbide whiskers (SCWs) and crosslinked by glutaraldehyde, and then these modified whiskers (mSCWs) were incorporated into high density polyethylene (HDPE) to prepare HDPE/mSCW composites with a high thermal conductivity. The thermal conductivity, mechanical properties, heat resistance, thermal stability and morphology of HDPE/mSCW and HDPE/SCW composites were characterized and compared. The results reveal that the thermal conductivity of both HDPE/SCW and HDPE/mSCW composites increases with the increase of filler loading, and reaches a maximum of 1.48 and 1.69?W/(m?K) at 40?wt% filler loading, which is 251.2% and 300.75% higher than that of HDPE, respectively. Significantly, HDPE/mSCW composites have a higher thermal conductivity than their HDPE/SCW counterparts with the same filler loading. In addition, the heat resistance, Young’s modulus and yield strength of both HDPE/SCW and HDPE/mSCW composites are also improved compared with that of HDPE. mSCW can be homogenously dispersed in the HDPE matrix, which contributes to the formation of thermally conductive networks by the inter-connection of mSCWs.

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    Towards suppressing dielectric loss of GO/PVDF nanocomposites with TA-Fe coordination complexes as an interface layer
    Gong Ying, Zhou Wenying, Wang Zijun, Xu Li, Kou Yujia, Cai Huiwu, Liu Xiangrong, Chen Qingguo, Dang Zhi-Min
    J. Mater. Sci. Technol.. 2018, 34 (12): 2415-2423.   DOI: 10.1016/j.jmst.2018.06.007
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    In this work, graphene oxide (GO) nanosheets with surface modification by Tannic and Fe coordination complexes (TA-Fe) were incorporated into poly(vinylidene fluoride) (PVDF) to prepare high constant but low loss polymer nanocomposites, and the effect of TA-Fe interlayer on dielectric properties of the GO@TA-Fe/PVDF nanocomposites was investigated. The results indicate that the dosage, mixing ratio, and reaction time of TA-Fe complexes have obvious influences on the dielectric properties of the nanocomposites. Furthermore, the TA-Fe interlayer significantly influences the electrical properties of GO@TA-Fe nanoparticles and their PVDF composites, and the GO@TA-Fe/PVDF composites exhibit superior dielectric properties compared with raw GO/PVDF. Dielectric losses of the GO@TA-Fe/PVDF are significantly suppressed to a rather low level owing to the presence of TA-Fe layer, which serves as an interlayer between the GO sheets, thus preventing them from direct contacting with each other. Additionally, the dynamic dielectric relaxation of the GO/PVDF and GO@TA-Fe/PVDF nanocomposites was investigated in terms of temperature.

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    Synergistic effect of organic and inorganic nano fillers on the dielectric and mechanical properties of epoxy composites
    Khan Muhammad, A. Khurram Aqeel, Li Tiehu, Zhao Tingkai, Subhani T., Gul I.H., Ali Zafar, Patel Vivek
    J. Mater. Sci. Technol.. 2018, 34 (12): 2424-2430.   DOI: 10.1016/j.jmst.2018.06.014
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    Titanium oxide TiO2/epoxy and TiO2 with detonation nano-diamond (DND)/epoxy nanocomposites were prepared by using ultrasonication method. TiO2 and DND particles as reinforcement species and epoxy as matrix were used to produce nanocomposites. The addition of DND particles into TiO2/epoxy composite improved the dielectric and mechanical properties of nanocomposites in significant amount. The dielectric properties of TiO2-DND/epoxy nanocomposite demonstrated increase in permittivity and conductivity after addition of the DND particles. The maximum and minimum reflection losses of TiO2-DND/epoxy nanocomposite for 0.6 and 0.2 wt% DND loading were detected at -14.5 and -1.3 dB, respectively. The flexural and tensile strength of TiO2-DND/epoxy nanocomposites with the addition of 0.4 wt% DNDs were enhanced to 220% and 223%, respectively. Additionally, the energy to break and percent break strain were 3.9 J and 3.86, respectively for 0.4 wt% DND loading in TiO2-DND/epoxy nanocomposite. Therefore, the present work findings claim that DND particles are well suitable to enrich the dispersion of TiO2 nanoparticles in epoxy matrix, which develops a strong load transfer interface between the nanoparticles and epoxy matrix and consequently leads to superior properties.

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    Effect of the simultaneous application of a high static magnetic field and a low alternating current on grain structure and grain boundary of pure aluminum
    Li Chengshuai, Hu Shaodong, Ren Zhongming, Fautrelle Yves, Li Xi
    J. Mater. Sci. Technol.. 2018, 34 (12): 2431-2438.   DOI: 10.1016/j.jmst.2018.04.013
    Abstract   HTML   PDF (4309KB)

    Effect of the simultaneous application of a high static magnetic field and a low alternating electric current on the solidification structure of pure aluminum has been investigated. Results show that the refinement of the solidification structure is enhanced by the electric current under a certain magnetic field. However, when the magnetic field intensity exceeds a certain value, the refinement is impaired under a certain electric current. The observation by electron backscattered diffraction (EBSD) shows the complex fields have led to the increase of the low angle boundaries with the refinement. Moreover, the application of the static gradient magnetic field is capable of modifying the distribution of the refined grains. The above results may be attributed to the formation of the cavities during the electromagnetic vibration process and the high magnetic field.

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    Hot deformation characteristics and hot working window of as-cast large-tonnage GH3535 superalloy ingot
    Wang Yao, Wang Junsong, Dong Jiasheng, Li Aimin, Li Zhijun, Xie Guang, Loua Langhong
    J. Mater. Sci. Technol.. 2018, 34 (12): 2439-2446.   DOI: 10.1016/j.jmst.2018.04.001
    Abstract   HTML   PDF (3166KB)

    Deformation characteristics and range of optimized hot working parameters of a 6.5 tons GH3535 superalloy ingot with an average columnar grain size of over 1?mm in diameter were investigated. Axial compression experiments were performed in temperature range of 900-1240?°C and strain rate range of 0.001-30?s-1 at a total strain of 0.8. The hot deformation activation energy of the experimental GH3535 alloy is calculated to be 483.22?kJ/mol. Furthermore, the deformation constitutive equation is established by the peak stresses obtained from the stress-strain curves under various conditions. The hot working window of the alloy ingot at a strain of 0.8 can be preliminarily discussed based on the deformed microstructures and processing maps. The optimized hot working window was thus determined at the strain of 0.95 for 6.5 tons GH3535 alloy ingot by the supplementary compression tests. A large-size GH3535 superalloy ring with a dimension of Φ3010?mm?×?410?mm was ultimately manufactured.

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    Exopolysaccharide produced by Vibrio neocaledonicus sp. as a green corrosion inhibitor: Production and structural characterization
    Moradi Masoumeh, Song Zhenlun, Xiao Tao
    J. Mater. Sci. Technol.. 2018, 34 (12): 2447-2457.   DOI: 10.1016/j.jmst.2018.05.019
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    An exopolysaccharide substances produced by Vibrio neocaledonicus sp. was introduced as a novel green inhibitor against the corrosion of carbon steel in artificial seawater and acidic media. The produced extracellular polymeric substance (EPS) is heterogeneous with composition of polysaccharides, nucleic acids and protein and average molecular weight of 29,572 Da. Adsorption of EPS on the metal surfaces and formation of Fe-EPS complexes acted as a barrier to prevent the oxygen penetration and hindered anodic and cathodic reactions. The inhibitory effect increases with increasing EPS concentration and exposure time. The highest corrosion inhibitory effect (95.1%) was observed for 10 g/L of EPS after 5 days of exposure in seawater. This is the highest inhibitory effect ever been reported by EPSs. While, the optimum concentration of EPS with the highest inhibition efficiency in 1 N H2SO4 was 1000 ppm. The influence of different parameters, such as initial pH, growth phase, various nitrogen and carbon sources on the production of EPS and its corrosion inhibitory effect were also investigated. According to results, the optimum culture medium for EPS production is contained artificial seawater including 5% mannitol as carbon source and 0.1% (NH4)2SO4 as nitrogen source at pH = 8. This medium could produce 22.24 g/L EPS during 3 days’ incubation at 30 °C. The corrosion inhibitory efficiency of obtained EPS was 95.97%.

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    Introduction of porous structure: A feasible and promising method for improving thermoelectric performance of Bi2Te3 based bulks
    Hu Jie, Fan Xi’An, Jiang Chengpeng, Feng Bo, Xiang Qiusheng, Li Guangqiang, He Zhu, Li Yawei
    J. Mater. Sci. Technol.. 2018, 34 (12): 2458-2463.   DOI: 10.1016/j.jmst.2018.05.010
    Abstract   HTML   PDF (1841KB)

    The porous p-type Bi0.4Sb1.6Te3 bulks containing irregularly and randomly oriented pores were obtained by artificially controlling the relative density of sintered samples during resistance pressing sintering process. It is demonstrated that the thermoelectric performances are significantly affected by the porous structure, especially for the electrical and thermal conductivity due to the enhanced carrier scattering and phonon scattering. The increasing porosity resulted in the obvious decrease in electrical and thermal conductivity, and little change in Seebeck coefficients. It is encouraging that the reduction of thermal conductivity can compensate for the deterioration of electrical performance, leading to the enhancement in thermoelectric figure of merit (ZT). The maximum ZT value of 1.0 was obtained for the sample with a relative density of 90% at 333?K. Unfortunately, the increase in porosity also brought in obvious degradations in Vickers hardness from 51.71 to 27.74?HV. It is worth mentioning that although the Vickers hardness of the sample with a relative density of 90% decreased to 40.12?HV, it was still about twice as high as that of the zone melting sample (21.25?HV). To summarize, introducing pores structure into bulks properly not only enhances the ZT value of Bi2Te3 based alloys, but also reduces the use of raw materials and saves production cost.

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    Corrosion protection of waterborne epoxy coatings containing mussel-inspired adhesive polymers based on polyaspartamide derivatives on carbon steel
    Yang Mingliang, Wu Jianhua, Fang Daqing, Li Bo, Yang Yang
    J. Mater. Sci. Technol.. 2018, 34 (12): 2464-2471.   DOI: 10.1016/j.jmst.2018.05.009
    Abstract   HTML   PDF (2514KB)

    A novel mussel-inspired adhesive polymer (PHEA-DOPA) containing the 3,4-dihydroxyphenylalanine (DOPA) functional group based on polyaspartamide derivatives was synthesized. The corrosion protection of the waterborne epoxy coatings containing the adhesive polymers was investigated by electrochemical impedance spectroscopy (EIS). The results indicated that the PHEA-DOPA could improve the corrosion resistance of the waterborne epoxy coating. The corrosion products were also analyzed by Raman microspectroscopy (RM), indicating the formation of the insoluble DOPA-Fe complexes on the carbon steel surface. These complexes simultaneously acting as a passivating layer, can inhibit the process of corrosion at the metal-solution interface. The differential scanning calorimeter (DSC) measurement indicated that PHEA-DOPA can increase the crosslinking density of coating. The effect of O2 on the protective mechanism of the PHEA-DOPA coating in a 3.5% NaCl solution was also evaluated by EIS. The results indicated that the barrier effect was significantly improved under aerated conditions because DOPA was oxidized to DOPA-quinone (Dq) by O2, which triggered the reaction with Fe ions that were released from the surface of the carbon steel. This led to more compact coatings.

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    Significant effect of as-cast microstructure on texture evolution and magnetic properties of strip cast non-oriented silicon steel
    Jiao Haitao, Xu Yunbo, Qiu Wenzheng, Xu Haijie, Misra R.D.K., Du Yifeng, Li Jianping, Wang Guodong
    J. Mater. Sci. Technol.. 2018, 34 (12): 2472-2479.   DOI: 10.1016/j.jmst.2018.05.007
    Abstract   HTML   PDF (4581KB)

    In this study, two types of as-cast microstructure produced by strip casting were cold rolled and annealed to investigate the effect of initial microstructure on the textural evolution and magnetic properties of non-oriented silicon steel. The results indicated that the cold-rolled sheets of coarse-grained strip with pronounced {100} components exhibited stronger λ fiber (〈100〉//ND) and weaker γ fiber (〈111〉//ND) texture as composed to the fine-grained strip with strong Goss ({110}〈001〉) texture. After annealing, the former was dominated by η fiber (〈001〉//RD) texture with a peak at {110}〈001〉 orientation, while the latter consisted of strong {111}〈112〉 and relatively weak {110}〈001〉 texture. In addition, a number of precipitates of size ~30-150?nm restricted the grain growth during annealing, resulting in recrystallization of grain size of ~46?μm in the coarse-grained specimen and ~41?μm in the fine-grained specimen. Ultimately, higher magnetic induction (~1.72?T) and lower core loss (~4.04?W/kg) were obtained in the final annealed sheets of coarse-grained strip with strong {100} texture.

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    Microbial corrosion resistance of a novel Cu-bearing pipeline steel
    Shi Xianbo, Yan Wei, Xu Dake, Yan Maocheng, Yang Chunguang, Shan Yiyin, Yang Ke
    J. Mater. Sci. Technol.. 2018, 34 (12): 2480-2491.   DOI: 10.1016/j.jmst.2018.05.020
    Abstract   HTML   PDF (6264KB)

    Microbiologically influenced corrosion (MIC) is becoming a serious problem for buried pipelines. Developing environmentally friendly strategies for MIC control is increasingly urgent in oil/gas pipeline industry. Copper (Cu) in steels can not only provide aging precipitation strengthening, but also kill bacterium, offering a special biofunction to steels. Based on the chemical composition of traditional X80 pipeline steel, two Cu-bearing pipeline steels (1% Cu and 2% Cu) were fabricated in this study. The microstructure, mechanical properties and antibacterial property against sulphate-reducing bacteria (SRB) and Pseudomonas aeruginosa (P. aeruginosa) were studied. It was found that the novel pipeline steel alloyed by 1%Cu exhibited acicular ferrite microstructure with nano-sized Cu-rich precipitates distribution in the matrix, resulting in better mechanical properties than the traditional X80 steel, and showed good MIC resistance as well. The pitting corrosion resistance of 1% Cu steel in as-aged condition was significantly better than that of X80 steel. A possible antibacterial mechanism of the Cu-bearing pipeline steel was proposed.

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    6.5 wt% Si high silicon steel sheets prepared by composite electrodeposition in magnetic field
    Peng Minghu, Zhong Yunbo, Zheng Tianxiang, Fan Lijun, Zhou Junfeng, Ren Weili, Ren Zhongming
    J. Mater. Sci. Technol.. 2018, 34 (12): 2492-2497.   DOI: 10.1016/j.jmst.2018.06.004
    Abstract   HTML   PDF (2447KB)

    A new preparation method of near-net-shape 6.5?wt% Si high silicon steel sheets was proposed by combining composite electrodeposition (CED) and diffusion annealing under magnetic field. The obtained sheets were characterized by scanning electron microscopy, energy dispersive spectrometry, analytical balance and a silicon steel material measurement system. The results show that the surface morphology, the elemental distribution, the cathode current efficiency and the silicon content of coatings were obviously influenced by the micro and macro magnetohydrodynamics (MHD) flows under magnetic field. With the effect of magnetic field, the silicon particles content of coatings showed an increasing trend and the diffusion process showed that an approximately uniform 6.5?wt% silicon steel sheet has been successfully obtained. The magnetism measurement showed that the high silicon steel sheet has the lower iron loss, and the iron loss further decreased under magnetic field. The new method proposed in this article, which is more environmentally friendly and low energy consumption, is feasible to prepare high silicon steel sheets.

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    Enhanced localized and uniform corrosion resistances of bulk nanocrystalline 304 stainless steel in high-concentration hydrochloric acid solutions at room temperature
    Wang S.G., Sun M., Xu Y.H., Long K., Zhang Z.D.
    J. Mater. Sci. Technol.. 2018, 34 (12): 2498-2506.   DOI: 10.1016/j.jmst.2018.06.006
    Abstract   HTML   PDF (2402KB)

    The localized and uniform corrosion resistances of bulk nanocrystalline 304 stainless steel (NC-304SS) produced by severe rolling technique, and its conventional polycrystalline 304 stainless steel (CC-304SS) counterpart, were investigated in high-concentration hydrochloric acid solutions at room temperature. NC-304SS can scarcely suffer from localized corrosion in 4 mol/L and 5 mol/L HCl solutions during 5-day immersion tests, and in 1-3 mol/L HCl solutions during thirty-five-day immersion tests. The corrosion rate of NC-304SS was also less than that of CC-304SS during these immersion tests. The improved localized and uniform corrosion resistances of NC-304SS were explained in terms of the adsorption and chemical activity of Cl- on NC-304SS and CC-304SS characterized by X-ray photoelectron spectroscopy, and the valence electron configurations of NC-304SS and CC-304SS were characterized by ultra-violet photoelectron spectroscopy rather than conventional electrochemical results.

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    Mechanical properties and deformation mechanisms of Ti-3Al-5Mo-4.5 V alloy with varied β phase stability
    Xue Q., Ma Y.J., Lei J.F., Yang R., Wang C.
    J. Mater. Sci. Technol.. 2018, 34 (12): 2507-2514.   DOI: 10.1016/j.jmst.2018.04.004
    Abstract   HTML   PDF (2366KB)

    Evolution of deformation mechanisms and mechanical properties of Ti-3Al-5Mo-4.5 V alloy with different β phase stability have been systematically investigated. β phase stability alteration is achieved through quenching temperature variation from dual α + β field (700 °C) to single β field (880 °C). Tensile tests at ambient temperature show that apparent yield strength of the alloy experiences an abrupt decrease followed by a significant increase from 700 °C to 880 °C. Work hardening behavior is characterized by transition from the initial two-regime feature to the three-stage outlook. Concurrently, the maximum working hardening rate drops from 14000 MPa to 3000 MPa, which is concurrent with the shrinking volume fraction of primary α phase. Detailed discussion about the relationship between deformation mechanisms and β phase stability has been outlined.

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    Facile synthesis and superior photocatalytic and electrocatalytic performances of porous B-doped g-C3N4 nanosheets
    Yan Qian, Huang Gui-Fang, Li Dong-Feng, Zhang Ming, Pan An-Lian, Huang Wei-Qing
    J. Mater. Sci. Technol.. 2018, 34 (12): 2515-2520.   DOI: 10.1016/j.jmst.2017.06.018
    Abstract   HTML   PDF (1344KB)

    As a low-cost visible-light-driven metal-free catalyst, graphitic carbon nitride (g-C3N4) has attracted increasing attention due to its wide applications for solar energy conversion, environmental purification, and organic photosynthesis. In particular, the catalytic performance of g-C3N4 can be easily modulated by modifying morphology, doping, and copolymerization. Simultaneous optimization, however, has little been achieved. Herein, a facile one-pot strategy is developed to synthesize porous B-doped g-C3N4 nanosheets by using H3BO3 and urea as the precursor during thermal polymerization. The resultant B-doped g-C3N4 nanosheets retain the original framework of bulk g-C3N4, while induce prominently enhanced visible light harvesting and narrowing band gap by 0.32 eV compared to pure g-C3N4. Moreover, the adsorption capacity and photodegradation kinetics of methylene blue (MB) under visible light irradiation over B-doped g-C3N4 nanosheets can be improved by 20.5 and 17 times, respectively. The synthesized porous B-doped g-C3N4 nanosheets also exhibit higher activities than pure g-C3N4 as bifunctional electrocatalyst for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The enhanced catalyst performance of porous B-doped g-C3N4 nanosheets stems from the strong synergistic effect originating from the larger exposed active sites generated by the exfoliation of g-C3N4 into nanosheets and the porous structure, as well as the better conductivity owing to B-doping. This work provides a simple, effective, and robust method for the synthesis of g-C3N4-based nanomaterial with superior properties to meet the needs of various applications.

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    One-Pot Room-Temperature Synthesis of Mg Containing MCM-41 Mesoporous Silica for Aldol Reactions
    Fujita Shin-Ichiro, Segawa Shinji, Kawashima Kazuki, Nie Xuejing, Erata Tomoki, Arai Masahiko
    J. Mater. Sci. Technol.. 2018, 34 (12): 2521-2528.   DOI: 10.1016/j.jmst.2016.08.025
    Abstract   HTML   PDF (1681KB)

    One-pot synthesis of Mg containing MCM-41 (Mg-MCM-41) materials was respectively carried out by a room temperature (RT) method and a hydrothermal (HT) method for aldol condensation of 4-nitrobenzaldehyde and acetone and self-condensation of acetone. The RT method can prepare MCM-41 materials containing large amounts of Mg while maintaining the structural characteristics of MCM-41 even at very low Si/Mg ratios (large Mg loadings), but the HT method cannot. The RT method can also give more active catalysts than the HT method, because the catalysts prepared by the RT method are more basic than those prepared by the HT one. The characterization indicates that Mg atoms in the Mg-MCM-41 prepared by the RT method exist as MgO disperses well on the wall surface of pores, while those in Mg-MCM-41 prepared by the HT method are included in the bulk with a smectite-like structure.

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