Started in 1985 Semimonthly
ISSN 1005-0302
CN 21-1315/TG
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      10 November 2015, Volume 31 Issue 11 Previous Issue    Next Issue
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    Orginal Article
    Correct Interpretation of Creep Rates: A Case Study of Cu
    W. Blum, J. Dvořák, P. Král, P. Eisenlohr, V. Sklenička
    J. Mater. Sci. Technol., 2015, 31 (11): 1065-1068.  DOI: 10.1016/j.jmst.2015.09.012
    Abstract   HTML   PDF

    Traditionally the deformation resistance in creep is characterized by the minimum creep rate ε?min and its sensitivity to stress (stress exponent n) and temperature (activation energy Q). Various values of constant n have been reported in the literature and interpreted in terms of specific mechanisms. The present case study of coarse-grained Cu at 573 K yields a stress exponent n = 9 for ε?min in tension and a relatively low activation energy. The evolution of the deformation resistance with strain at constant tensile creep load and comparison with creep in compression without fracture indicates that the tensile ε?min result from transition from uniform deformation to strain localization during fracture. This is confirmed by the results of creep in compression where fracture is suppressed. Both the tensile ε?min and the compressive creep rate at strains around 0.3 can be described using existing equations for quasi-stationary deformation containing the subgrain boundary misorientation θ as structure parameter. While in the latter case constant θ leads to monotonic increase of n with stress, the tensile nine-power-law results from variable θ, and has no simple meaning. The result of this case study means that uncritical interpretation of minimum tensile creep rates as stationary ones bears a high risk of systematic errors in the determination of creep parameters and identification of creep mechanisms.

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    Synthesis and Characterization of ZnO Nanowires and ZnO-CuO Nanoflakes from Sputter-Deposited Brass (Cu0.65-Zn0.35) Film and Their Application in Gas Sensing
    Bhagaban Behera, Sudhir Chandra
    J. Mater. Sci. Technol., 2015, 31 (11): 1069-1078.  DOI: 10.1016/j.jmst.2015.09.009
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    A novel method was presented for synthesis of ZnO and ZnO-CuO composites in the form of nanowires, nanorods and nanoflakes on oxidized silicon substrates. Further, the use of the synthesized nanostructures for gas sensing was demonstrated. Pure brass (Cu0.65-Zn0.35) films were deposited on oxidized Si substrate by radio frequency (RF) diode sputtering. Subsequently, these films having thickness in the range of 100-200 nm were oxidized in different oxidizing ambient in the temperature range of 300-550 °C. The effect of temperature, time and oxidizing ambient on the growth of nanostructures was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and photoluminescence (PL) techniques. The nanostructures surface was analyzed by X-ray photoelectron spectroscopy (XPS). The synthesized nanowires had diameter in the range of 60-100 nm and length up to 50 µm. Based on these observations, the growth mechanism has been suggested. For the nanorods, the diameter was observed to be ~150 nm. Samples having dense nanowires, nanorods and nanoflakes were used as a gas sensing material. The performance of the sensor was investigated for different nanostructured materials for various volatile organic compounds (VOCs). It was observed that ZnO-CuO nanoflakes were more sensitive to VOC sensing compared to ZnO nanowires and nanorods.

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    Structure and Properties of Nanostructured Vacuum-Deposited Foils of Invar Fe-(35-38 wt%)Ni Alloys
    V.M. Nadutov, A.I. Ustinov, S.A. Demchenkov, Ye.O. Svystunov, V.S. Skorodzievski
    J. Mater. Sci. Technol., 2015, 31 (11): 1079-1086.  DOI: 10.1016/j.jmst.2015.09.011
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    The process of electron beam vacuum deposition of the Fe-(35-38 wt%)Ni alloys at substrate temperatures Ts from 300 to700 °C were used to produce vacuum-deposited foils with the FCC structure, differing by the size of characteristic microstructural elements (grains and subgrains). It was shown that refinement of foil microstructural elements to nanoscale is accompanied by their microhardness increase up to 4-5 GPa. The change of the thermal expansion coefficient (TEC) of the nanostructured (NS) foil of the Fe-35.1Ni alloy within the temperature range from -50 to 150 °C has some deviation from that observed for cast Invar alloy of the same composition. It has been found that the main factors affecting the peculiarities of thermal expansion of the NS foil can be related to the presence of small fraction of BCC-phase in them, high level of crystalline lattice microstrains and inhomogeneous magnetic order in FCC-phase. It was shown that as a result of additional thermal treatment of NS foils their invar properties become similar to that observed for cast Invar alloy but mechanical properties remain on the same level.

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    On-Chip Fabrication of Carbon Nanoparticle-Chitosan Composite Membrane
    Weiping Ding, Cheng Liang, Sijie Sun, Liqun He, Dayong Gao
    J. Mater. Sci. Technol., 2015, 31 (11): 1087-1093.  DOI: 10.1016/j.jmst.2015.09.004
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    The on-chip fabrication of a carbon nanoparticle-chitosan composite membrane (i.e. a sorbent membrane or a mixed matrix membrane) using laminar flow-based interfacial deprotonation technology was presented in this paper. In addition, the effects of carbon nanoparticles and reactant flow rates on membrane formation were investigated. Finally, the permeability and adsorption capacities of the membrane were discussed. During fabrication, an acidic chitosan solution and a basic buffer solution that contained carbon nanoparticles were introduced into a microchannel. At the flow interface, a freestanding composite membrane with embedded carbon nanoparticles was formed due to the deprotonation of the chitosan molecules. The membrane growth gradually stopped with time from upstream to downstream and the thickness of the membrane increased rapidly and then slowly along the reactant flow direction. The formation of the membrane was divided into two stages. The average growth rate in the first stage was significantly larger than the average growth rate in the second stage. Carbon nanoparticles in the basic solution acted as nucleating agents and made the membrane formation much easier. As the flow rate of the chitosan solution increased, the averaged membrane thickness and the membrane hydraulic permeability initially increased and then decreased. Because of the addition of carbon nanoparticles, the formed membrane had adsorption abilities. The carbon nanoparticle-chitosan composite membrane that was fabricated in this study could be employed for simultaneous adsorption and dialysis in microdevices in the future.
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    Generation Mechanism of Inhomogeneous Minority Carrier Lifetime Distribution in High Quality mc-Si Wafers and the Impacts on Electrical Performance of Wafers and Solar Cells
    Xianxin Liu, Genghua Yan, Ruijiang Hong
    J. Mater. Sci. Technol., 2015, 31 (11): 1094-1100.  DOI: 10.1016/j.jmst.2015.07.015
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    To find out the causation of inhomogeneous minority carrier lifetime distribution in high quality multicrystalline silicon (mc-Si) wafers, impurities and lattice defects were systematically studied by means of Fourier transform infrared (FTIR) spectroscopy and metallography. Inhomogeneously distributed oxygen impurity and dislocations were demonstrated to be key leading factors, and the restriction mechanism was discussed. Scattering process caused by ionized impurities and dislocations decreased carrier mobility, while carrier concentration was not significantly affected. Measurements showed that resistivity was higher and more dispersive in low lifetime area. Solar cells were fabricated with these wafers. Cells' efficiency of inhomogeneous ones exhibited averagely 0.27% lower than the regular ones in absolute terms. Recombination centers and leakage loss induced by dislocations and impurities led to the reduction in shunt resistors and open-circuit voltage, and then affected the performance of cells.
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    SnO2-Decorated Graphene/Polyaniline Nanocomposite for a High-Performance Supercapacitor Electrode
    Guo Chen, Qiu-Feng Lü, Hai-Bo Zhao
    J. Mater. Sci. Technol., 2015, 31 (11): 1101-1107.  DOI: 10.1016/j.jmst.2015.09.013
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    An SnO2-decorated graphene/polyaniline (GSP) nanocomposite with homogeneous structure was prepared and adopted to achieve high electrochemical performance for supercapacitor electrode.Graphene sheets were decorated with tin dioxide (SnO2) particles, which effectively hinder the restacking of graphene nanosheets, and then were used as substrates for an in-situ polymerization of aniline monomers.The GSP nanocomposite was characterized by field emission scanning electron microscopy, X-ray diffraction, Fourier transform infrared, UV-Visible and X-ray photoelectron spectroscopy.The results revealed that polyaniline nanorods were orderly and vertically aligned on the SnO2-decorated graphene nanosheets via π-π stacking effect between basal planes of graphene nanosheets and phenyl group of polyaniline.The GSP nanocomposite exhibited an excellent specific capacitance of 429 F g-1 at a current density of 1 A g-1, excellent cycling stability and rate capability, which suggested a promising application for supercapacitor.

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    Structural, Optical and Electrical Properties of Ga Doped ZnO/Cu grid/Ga Doped ZnO Transparent Electrodes
    Cholho Jang, Qingjun Jiang, Jianguo Lu, Zhizhen Ye
    J. Mater. Sci. Technol., 2015, 31 (11): 1108-1110.  DOI: 10.1016/j.jmst.2015.07.018
    Abstract   HTML   PDF
    Ga doped ZnO (GZO)/Cu grid/GZO transparent conductive electrode (TCE) structures were fabricated at room temperature (RT) by using electron beam evaporation (EBE) for the Cu grids and RF magnetron sputtering for the GZO layers.In this work, we investigated the electrical and optical characteristics of GZO/Cu grid/GZO multilayer electrode for thin film solar cells by using evaporated Cu grid and sputtered GZO thin films to enhance the optical transparency without significantly affecting their conductivity.The optical transmittance and sheet resistance of GZO/Cu grid/GZO multilayer are higher than those of GZO/Cu film/GZO multilayer independent of Cu grid separation distance and increase with increasing Cu grid separation distances.The calculation of both transmittance and sheet resistance of GZO/Cu grid/GZO multilayer was based on Cu filling factor correlated with the geometry of Cu grid.The calculated values for the transmittance and sheet resistance of the GZO/Cu grid/GZO multilayer were similar to the experimentally observed ones.The highest figure of merit ΦTC is 5.18 × 10-3 Ω-1 for the GZO/Cu grid/GZO multilayer with Cu grid separation distance of 1 mm was obtained, in this case, the transmittance and resistivity were 82.72% and 2.17 × 10-4 Ω cm, respectively.The transmittance and resistivity are acceptable for practical thin film solar cell applications.
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    Tuning the Microstructural and Magnetic Properties of ZnO Nanopowders through the Simultaneous Doping of Mn and Ni for Biomedical Applications
    K.Karthika, K.Ravichandran
    J. Mater. Sci. Technol., 2015, 31 (11): 1111-1117.  DOI: 10.1016/j.jmst.2015.09.001
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    Undoped and Mn+Ni doped ZnO nanopowders were synthesized using a simple soft chemical route by varying the Ni doping level (1, 3, 5 and 7 at.%) and keeping the Mn doping level (10 at.%) constant.X-ray diffraction studies reveal that the incorporated Ni2+ ions form a secondary phase of cubic NiO beyond the Ni doping level of 3 at.%, which is also confirmed by Fourier transform infrared spectroscopy.The band gap of the nanopowders increases (from 3.32 to 3.44 eV) up to 3 at.% of Ni doping and decreases with further doping.ZnO:Mn:Ni nanopowders with 3 at.% of Ni concentration exhibit good antibacterial efficiency.The variation in the size of the nanoparticles, as observed from the TEM images and hydroxyl radicals as evidenced from the photoluminescence results, clearly substantiate the discussion on the antibacterial efficiency of the synthesized nanopowders.Magnetic properties of the synthesized nanopowders were studied using a vibrating sample magnetometer, and the results showed that the doping of Mn and Ni largely influences the magnetic properties of ZnO nanopowders.

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    Effect of Rare Earth and Transition Metal Elements on the Glass Forming Ability of Mechanical Alloyed Al-TM-RE Based Amorphous Alloys
    Ram S. Maurya, Tapas Laha
    J. Mater. Sci. Technol., 2015, 31 (11): 1118-1124.  DOI: 10.1016/j.jmst.2015.09.007
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    The present work aims to compare the amorphous phase forming ability of ternary and quaternary Al based alloys (Al86Ni8Y6, Al86Ni6Y6Co2, Al86Ni8La6 and Al86Ni8Y4.5La1.5) synthesized via mechanical alloying by varying the composition, i.e. fully or partially replacing rare earth (RE) and transition metal (TM) elements based on similar atomic radii and coordination number. X-ray diffraction and high resolution transmission electron microscopy study revealed that the amorphization process occurred through formation of various intermetallic phases and nanocrystalline FCC Al. Fully amorphous phase was obtained for the alloys not containing lanthanum, whereas the other alloys containing La showed partial amorphization with reappearance of intermetallic phases attributed to mechanical crystallization. Differential scanning calorimetry study confirmed better thermal stability with wider transformation temperature for the alloys without La.
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    Characterisation, Luminescence and Antibacterial Properties of Stable AgNPs Synthesised from AgCl by Precipitation Method
    Arockiasamy Ajaypraveenkumar, Johnson Henry, Kannusamy Mohanraj, Ganesan Sivakumar, Sankaran Umamaheswari
    J. Mater. Sci. Technol., 2015, 31 (11): 1125-1132.  DOI: 10.1016/j.jmst.2015.08.005
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    Silver nanoparticles (AgNPs) were synthesised using equimolar concentrations of reducing agent vitamin C and AgCl precursor by simple precipitation method. The synthesised AgNPs were characterised by X-ray diffraction (XRD), UV-Visible, photoluminescence and field emission scanning electron microscopy (FESEM) analysis. The formation of AgNPs was confirmed by the typical surface plasmon resonance band at 426 nm. The presence of elemental silver and pure crystalline face centre cubic (fcc) structure was confirmed by energy dispersive X-ray analysis and XRD analysis, respectively. The FESEM images showed the formation of spherical AgNPs for lower concentrations (0.1 and 0.3 mol/L) while spike and flower shaped particles were formed for higher concentration. Photoluminescence characteristic band was observed with no shift at 390 nm indicating the stable nature of AgNPs. The antibacterial property of the AgNPs was tested against gram negative bacteria Pseudomonas aeruginosa by using Cissus quadrangular as a control and the result showed that vitamin C reduced AgNPs have good antibacterial activity.
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    Growth of SiC as Binder to Adhere Diamond Particle and Tribological Properties of Diamond Particles Coated SiC
    Shengjie Yu, Zhaofeng Chen, Yang Wang, Shuwei Hu, Ruiying Luo, Sheng Cui
    J. Mater. Sci. Technol., 2015, 31 (11): 1133-1138.  DOI: 10.1016/j.jmst.2015.07.009
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    The purpose of this work was to grow SiC as binder to adhere diamond particles to graphite substrate by low pressure chemical vapor deposition (LPCVD) at 1100 °C and 100 Pa using methyltrichlorosilane (MTS: CH3SiCl3) as precursor. The composite coatings on graphite substrates were analyzed by various techniques. Results show that a dense SiC coating with a cloud-cluster shape was formed both on the diamond particles and the substrate after deposition. The thermal stress (290.6MPa) strengthened the interfacial bonding between the diamond particle and the SiC coating, which is advantageous for the purpose of adhering diamond particles to graphite substrate. The applied load of sliding wear test was found to affect not only the friction coefficient, but also the wear surface morphology. With increasing loads, the asperity penetration was high and the friction coefficient decreased.
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    Fabrication of the Superhydrophobic Surface on Magnesium Alloy and Its Corrosion Resistance
    Fen Zhang, Changlei Zhang, Liang Song, Rongchang Zeng, Shuoqi Li, Hongzhi Cui
    J. Mater. Sci. Technol., 2015, 31 (11): 1139-1143.  DOI: 10.1016/j.jmst.2015.09.003
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    The superhydrophobic surface was fabricated on the AZ31 alloy by the combination of the hydrothermal treatment method and post modification with stearic acid. The superhydrophobic surface showed a static water contact angle of 157.6°. The characteristics of the coatings were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The corrosion resistance of the superhydrophobic coatings was investigated by potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS). The results revealed that the superhydrophobic coatings, characterized by petal-like structure significantly improved the corrosion resistance of the AZ31 alloy.
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    Crack Initiation Mechanism of Z3CN20.09M Duplex Stainless Steel during Corrosion Fatigue in Water and Air at 290?°C
    H.C. Wu, B. Yang, Y.Z. Shi, Q. Gao, Y.Q. Wang
    J. Mater. Sci. Technol., 2015, 31 (11): 1144-1150.  DOI: 10.1016/j.jmst.2015.09.002
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    The crack initiation mechanism of a Z3CN20.09M duplex stainless steel (DSS) during corrosion fatigue (CF) in water and air at 290?°C was investigated by using a CF cracking machine and a scanning electron microscopy (SEM). The cracks were initiated successively at the persistent slip bands (PSBs), phase boundaries (PBs) and pitting corrosion points (PCPs) of the specimens when they were tested in water at 290?°C, while in air at 290?°C the cracks were only initiated at the PSBs and PBs. And the cracks were found mainly to initiate at the PSBs and PBs when the specimens were tested in water and air at 290?°C, respectively. The results also reveal that the cracks were likely to be initiated at the first 20% of fatigue life of the specimens tested in water at 290?°C. However, the cracks were not found until 50% of fatigue life when tested in air at 290?°C. Moreover, the crack numbers of the specimens tested in water at 290?°C were much more than those tested in air at 290?°C.
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    Healing Process of Casting Pores in a Ni-based Superalloy by Hot Isostatic Pressing
    X.G. Zheng, Y.-N. Shi, L.H. Lou
    J. Mater. Sci. Technol., 2015, 31 (11): 1151-1157.  DOI: 10.1016/j.jmst.2015.07.004
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    Hot isostatic pressing (HIP) with a pressure of 180?MPa at a temperature of 1170?°C was introduced to an investment cast Ni-based superalloy (M91) turbocharger blade to explore the healing process of casting pores generated during investment casting. Optical micrograph and scanning electron microscopy (SEM) observations indicate that eutectic pores are the main cast defects in the as-cast blade before HIP. These pores normally locate at the solidification front of γ/γ′ eutectic with a size of a few micrometers to a few tens of micrometers. After HIP for 4?h, most of the pores were closed. Based on phase characteristics, these pores were healed by the formation of γ matrix with finer and irregular-shaped γ′ precipitates. Healing interface can be easily distinguished by SEM. Line scan by using energy dispersive X-ray spectroscopy (EDS) reveals a much higher Ti and Al concentration in the healing interface. It is proposed that solute diffusion toward the casting pores during HIP results in the formation of γ, and the much higher concentration of γ′-forming elements Al and Ti near the healing interface contributes to the precipitation of γ′ in the healed region in the succeeding cooling process after HIP.
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    Crystallization Behavior of Nd2O3 Doped Na2O-CaO-SiO2 Laser Glass-ceramics
    Shuming Wang, Fenghua Kuang, Dazhan Zhang, Xu Zhou, Minghui Tang
    J. Mater. Sci. Technol., 2015, 31 (11): 1158-1160.  DOI: 10.1016/j.jmst.2015.10.003
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    For the desirable laser optical property, transition metals or rare-earths are always doped into parent glasses as active ions, and this doping will affect the crystallization of the precursor glasses inevitably. In this work, crystallization behavior of NaO-CaO-SiO2 system glasses doped with Nd2O3 was investigated. The crystallization kinetic parameters including the crystallization apparent activation energy (E) and the Avrami parameter (n) were also measured. The results show that the NaO-CaO-SiO2 system glass-ceramics with the Na2Ca2Si3O9 crystal as primary phase can be highly crystalized as above 90%. The Nd2O3 doping has a significant influence on the crystallization apparent activation energy and the Avrami parameter, which affect the crystallization behavior and morphology of the transparent glass-ceramics of this system.
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CN: 21-1315/TG
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