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ISSN 1005-0302
CN 21-1315/TG
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      30 April 2012, Volume 28 Issue 4 Previous Issue    Next Issue
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    Nanomaterials and Nanotechnology
    Evaluation of Stored Energy from Microstructure of Multi-component Nanostructured Cu
    Feng Yan, Hongwang Zhang
    J. Mater. Sci. Technol., 2012, 28 (4): 289-293. 
    Abstract   HTML   PDF
    A polycrystalline Cu of 99.995% purity has been deformed by dynamic plastic deformation at liquid nitrogen temperature to a strain of 2.1 (LNT-DPD Cu). Three distinct regions that are dominated by dislocation slip, shear banding and nanotwinning, form a multi-component nanostructure. The microstructure of each region has been quantified by transmission electron microscopy assisted by Kikuchi line analysis. Based on the structural parameters the stored energy of each region was evaluated, and the total energy can be assumed to be a linear additivity of that in each region weighted by the respective volume fraction. A microstructure based evaluation of the stored energy of multi-component nanostructure has been proposed.
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    Carbon Xerogel-supported Iron as a Catalyst in Combustion Synthesis of Carbon Fibrous Nanostructures
    Wojciech Kicinski, Joanna Lasota
    J. Mater. Sci. Technol., 2012, 28 (4): 294-302. 
    Abstract   HTML   PDF
    The catalytically assisted self-propagating high-temperature synthesis of carbon fibrous nanostructures, where the iron-doped colloidal carbon xerogel is proposed as a catalyst system, was examined. The carbon xerogel was prepared through carbonization of an iron doped organic xerogel at temperatures ranging from 600 to 1050°C. The reaction between calcium carbide and hexachloroethane in the presence of sodium azide is exothermic enough to proceed at a high temperature, self-sustaining regime. The combustion reactions of those mixtures enriched with iron-doped carbon xerogels were conducted in a stainless steel reactor|calorimetric bomb under an initial pressure of 1 MPa of argon. Scanning electron microscopy analysis of the combustion products revealed low yield of various type of carbon fibers (presumably nanotubes), which grew via the tip-growth mechanism. The fibrous nanostructures were found in the vicinity of the spot of ignition, while in the outer and cooler area of the reactor, dusty products with soot-like morphology dominated. No significant correlation between the pyrolysis temperature of the carbon xerogel and the morphology of the obtained carbon fibrous nanostructures was observed.
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    Microforging Effect on the Microstructure and Magnetic Properties of FeSiB-based Nanoflakes
    Wooseung Kang
    J. Mater. Sci. Technol., 2012, 28 (4): 303-307. 
    Abstract   HTML   PDF
    The effect of microforging on the processing of nanocrystalline FeSiB alloy flakes was studied in terms of microstructure and magnetic properties. The flakes microforged from amorphous precursor showed submicron thicknesses with the crystal size of about 15 nm. The crystallite size during microforging was primarily determined by plastic deformation rather than fracturing and agglomeration. Unlike the general trend of coercivity reduction with annealing, the coercivity of the nanocrystalline flakes was slightly increased with increasing annealing temperature, which can be explained with the diffusion anisotropy of the magnetic moments resulting from the formation of Fe-atoms pairs. The magnetic remanence (Mr) of the planar nanocrystalline flakes was
    measured to be about 26% of the saturation magnetization (Ms), a significant increase from 2% of the initial amorphous precursor.
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    Fabrication of Submicron-Diameter and Taper Fibers Using Chemical Etching
    Hani J. Kbashi
    J. Mater. Sci. Technol., 2012, 28 (4): 308-312. 
    Abstract   HTML   PDF
    The thin, long length and high smoothness silica photonic nanowires and taper optical fiber were fabricated using a simple and low cost chemical etching method. A two-steps wet etch process were used consisting of etching with 30% HF acid to remove cladding and 24% HF acid to decrease fiber core diameter. An approach for on-line monitoring of etching using 1300 nm light power transmitted in the optical fiber was used to determine the diameter of the remaining core and showed a transition between two different operation regimes of nanofiber from the embedded regime, where the mode was isolated from the environment, to the evanescent regime. The data indicated that the diameter of the silica fiber decreased linearly for both 30% and 24% HF acid with 1.2 and 0.1 μm/min grad diameter, respectively at room temperature, and more than 70% of the mode intensity could propagate outside fiber when the  core diameter was less than 1 μm. The results of fiber taper showed that the fiber was tapered by a factor of 20 while retaining a thin core structure
    and leaving about more than 85% of core structure.
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    Influence of Co Content on Raman and Photoluminescence Spectra of Co Doped ZnO Nanowires
    Y.Q. Chang, P.W. Wang, S.L. Ni, Y. Long, X.D. Li
    J. Mater. Sci. Technol., 2012, 28 (4): 313-316. 
    Abstract   HTML   PDF
    Co doped ZnO nanowires with different Co contents have been fabricated by a chemical vapor deposition method. X-ray diffraction results show that all the samples are of single phase and crystallize in wurtzite ZnO structure. The lattice parameter a increases with increasing Co content, while the parameter c has no obvious change with increasing Co. Raman spectra show that the nonpolar E2(High) mode becomes broad and weak with the doping of Co, which indicates that the incorporation of Co causes structural disorder in the crystalline columnar ZnO lattice. The photoluminescence spectra exhibit that the position of the ultraviolet emission shifts to short wavelength and the intensity decreases with increasing Co. The green emission is affected by
    two contrary factors. It is increased by the introduced defects, but suppressed by the interaction between Co doping and native defects and the later affects it more significantly.
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    Effect of Oxygen Admittance Temperature on the Growth of ZnO Microcrystals by Thermal Evaporation Technique
    K.M.K. Srivatsa, Deepak Chhikara, M. Senthil Kumar
    J. Mater. Sci. Technol., 2012, 28 (4): 317-320. 
    Abstract   HTML   PDF
    Hexagonally well-faceted microcrystals of ZnO have been grown by thermal evaporation of Zn powder in oxygen ambient at 700 °C under atmospheric pressure. It has been observed that the properties (size and quality) of ZnO microcrystals have a strong dependence on the reactor temperature at which the oxygen gas is admitted into the growth zone. The microcrystals grown with oxygen admittance at 450 °C have a length of 1 ¹m and a diameter of 0.75 μm while that grown with oxygen admittance at 600 °C have a length of 1.5-2 μm and a diameter of 1 μm. Room temperature photoluminescence spectra show a ultraviolet (UV) emission peak at 385 nm with a green band emission at around 500 nm. The UV-to-green band emission ratio for the microcrystals grown with oxygen admittance at 450 °C is observed to be 1.25 and the ratio decreases to 0.45 for the sample grown with oxygen admittance at 600 °C.
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    Thin Film and Coatings
    Effects of Current Density on Microstructure of Titania Coatings by Micro-arc Oxidation
    Yue Yang, Hua Wu
    J. Mater. Sci. Technol., 2012, 28 (4): 321-324. 
    Abstract   HTML   PDF
    In the present study, titania coatings were prepared under different current density conditions in micro-arc oxidation (MAO) process on titanium alloy in NaAlO2 solution. The aim of this work was to study the effects of current density on the microstructure of titania coatings. The morphology and phase composition of the coatings were investigated by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and Raman spectra. The thickness and surface roughness of the coatings were characterized by confocal laser Scanning Microscopy (CLSM). The results showed that the coatings were composed of crystalline anatase and rutile phases of TiO2, and contain a network of evenly distributed small pores. It has also shown that an
    increase in current density leads to an increase in rutile content.
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    Properties of Resistivity, Reflection and Absorption Related to Structure of ITO Films
    Yipeng Chao, Wu Tang, Xuehui Wang
    J. Mater. Sci. Technol., 2012, 28 (4): 325-328. 
    Abstract   HTML   PDF
    Indium tin oxide (ITO) films were fabricated on polyethylene terephthalate (PET) substrate at room temperature using dc magnetron sputtering technique with different sputtering powers. The structural, electrical and optical properties were investigated by X-ray diffraction (XRD), Hall effect, reflection and transmission, respectively. XRD patterns show gradual enhancement of crystalline quality with increasing sputtering power. Significant improvement of Hall mobility due to the reduction of defects was observed though the carrier density varied slightly. Simultaneously, the mean transmission in visible light range decreased severely with increasing sputtering power. Slight move toward shorter-wavelength side of absorption peak was due to the variation of plasma wavelength. The reflection increase of near-infrared light originated from the decrease of resistivity. Finally, band gap was obtained using Tauc's relation and it was consistent with Burstein-Moss shift.
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    Effect of Al Doping on Structural, Electrical, Optical and Photoluminescence Properties of Nano-Structural ZnO Thin Films
    M. Mozibur Rahman, M.K.R. Khan, M. Rafiqul Islam, M.A. Halim, M. Shahjahan, M.A. Hakim, Dilip Kumar Saha, Jasim Uddin Khan
    J. Mater. Sci. Technol., 2012, 28 (4): 329-335. 
    Abstract   HTML   PDF
    The nano-structural Al-doped ZnO thin films of different morphologies deposited on glass substrate were successfully fabricated at substrate temperature of 350 °C by an inexpensive spray pyrolysis method. The structural, electrical, optical and photoluminescence properties were investigated. X-ray diffraction study revealed the crystalline wurtzite (hexagonal) structure of the films with nano-grains. Scanning electron microscopy (SEM) micrographs indicated the formation of a large variety of nano-structures during film growth. The spectral absorption of the films occurred at the absorption edge of ˜410 nm. In the present study, the optical band gap energy 3.28 eV of ZnO decreased gradually to 3.05 eV for 4 mol% of Al doping. The deep level activation energy decreased and carrier concentrations increased substantially with increasing doping. Exciting with the energy 3.543 eV (λ=350 nm), a narrow and a broad characteristic photoluminescence peaks that correspond to the near band edge (NBE) and deep level emissions (DLE), respectively emerged.
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    Iron and Steel
    Effect of Bainite Morphology on Mechanical Properties of the Mixed Bainite-martensite Microstructure in D6AC Steel
    Khodamorad Abbaszadeh, Hassan Saghafian, Shahram Kheirandish
    J. Mater. Sci. Technol., 2012, 28 (4): 336-342. 
    Abstract   HTML   PDF
    The effect of bainite morphology on mechanical properties of the mixed bainite-martensite microstructure in D6AC low alloy ultra-high strength steel has been studied in the present work. For this purpose, samples austenitized at 910 °C for 40 min were quenched in three different ways. Some of the samples were directly oil-quenched, some others were quenched in salt bath at 330 °C and the remaining samples were quenched in salt bath at 425 °C for various holding times. All samples were tempered at 200 °C for 2 h. Microstructures were examined by optical microscopy (OM) and scanning electron microscopy (SEM). Fracture surfaces also were studied by SEM. Results showed that the mixed microstructure containing martensite and 28 vol.% of
    the lower bainite exhibited higher yield and tensile strengths than the fully martensitic microstructure. This could be mainly attributed to the partitioning of the prior austenite grains by the lower bainite and enhancing the strength of lower bainite in the mixed microstructure by plastic constraint. Charpy V-notch (CVN) impact energy and ductility were improved by increasing the volume fraction of the lower bainite. This is not the case about the mixed microstructure containing the upper bainite and martensite. As a result, the tensile and CVN impact properties of mixed upper bainite-martensite microstructure are lower than those of the fully martensitic microstructure. Finally, fractography studies showed cleavage fracture at the surface of CVN impact specimens with martensitic and upper bainitic microstructures confirming the tendency to brittle behavior.
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    Influence of Heat Input on Martensite Formation and Impact Property of Ferritic-Austenitic Dissimilar Weld Metals
    M. Mukherjee, T.K. Pal
    J. Mater. Sci. Technol., 2012, 28 (4): 343-352. 
    Abstract   HTML   PDF
    The effect of heat input on martensite formation and impact properties of gas metal arc welded modified ferritic stainless steel (409M) sheets (as received) with thickness of 4 mm was described in detail in this work. The welded joints were prepared under three heat input conditions, i.e. 0.4, 0.5 and 0.6 kJ/mm using two different austenitic filler wires (308L and 316L) and shielding gas composition of Ar + 5% CO2. The welded joints were evaluated by  microstructure and charpy impact toughness. The dependence of weld metal microstructure on heat input and filler wires were determined by dilution calculation, Creq/Nieq ratio, stacking fault energy (SFE), optical microscopy (OM) and transmission electron microscopy (TEM). It was observed that the microstructure as well as impact property of weld metal was significantly affected by the heat input and filler wire. Weld metals prepared by high heat input exhibited higher amount of martensite laths and toughness compared with those prepared by medium and low heat inputs, which was true for both the filler wires. Furthermore, 308L weld metals in general provided higher amount of martensite laths and toughness than 316L weld metals.
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    Regular Papers
    Characterization of Different Surface States and Its Effects on the Oxidation Behaviours of Alloy 690TT
    Zhiming Zhang, Jianqiu Wang, En-Hou Han, Wei Ke
    J. Mater. Sci. Technol., 2012, 28 (4): 353-361. 
    Abstract   HTML   PDF
    Alloy 690TT samples with four kinds of surface states were prepared: 1) ground to 400 grit; 2) ground to 1500 grit; 3) mechanically polished (MP) and 4) electro-polished (EP). The surface morphologies and the surface skin layers0 microstructures of these samples were characterized systematically using  various methods and the effects of surface states on the oxidation behaviours of Alloy 690TT were also discussed. The results showed that surface roughness and micro-hardness decreased gradually from the ground to EP surfaces. The grains in the near-surface layers of the ground and MP surfaces had been refined and the residual strains were also very high. The dislocations on the ground surfaces were mainly parallel dislocation lines. The thickness  of the superficial cold-worked layers decreased gradually from the ground surfaces to polished surfaces. The oxide morphologies and oxidation rate depended greatly on the surface states of samples. Cold-working by grinding treatments could benefit the outward diffusion of metallic atoms and the nucleation of surface oxides and then accelerate the growth of surface oxide films.
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    Characterization of Gradual Porous Ceramic Structures Obtained by Powder Sedimentation
    Ioan Vida-Simiti, Nicolaie Jumate, Valentin Moldovan, Gyorgy Thalmaier, Niculina Sechel
    J. Mater. Sci. Technol., 2012, 28 (4): 362-366. 
    Abstract   HTML   PDF
    Asymmetric membranes present better separation and service characteristics than the symmetric ones. In our preliminary studies the possibility of obtaining sintered porous materials with gradual structure by sedimentation of metallic and ceramic powders was demonstrated. Zirconium silicate (ZrSiO4) particles were used for the manufacturing of the porous supports, and mullite powder was deposited by sedimentation in order to achieve
    the active layer with pores size gradient. The used powders and the obtained structures were characterized by laser scattering particle size analyzer, scanning electron microscopy and mercury porosimetry. The permeability and the filtration fineness of the structures were also determined. By using a thin active layer made of small particles deposited onto a macro-porous support, one can achieve membranes with high flow rates and filtration fineness in the microfiltration area.
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    Tribological Properties of A356.2/RHA Composites
    D. Siva Prasad, A. Rama Krishna
    J. Mater. Sci. Technol., 2012, 28 (4): 367-372. 
    Abstract   HTML   PDF
    Rice husk ash (RHA) is one of the industrial waste byproduct available abundantly in the world. In the present  work, an attempt is made to incorporate the RHA particles in the molten aluminum A356.2 alloy. The RHA particles were added into the matrix melt by creating a vortex with the help of a mechanical  stirrer and the melt temperature was maintained between 800 and 850 °C. Dry sliding wear experiments were performed in a pin on disc wear equipment against a chromium steel disc at 30 °C. Scanning electron microscopy is used to study the wear characteristics of the unreinforced Al alloy and the A356.2/RHA composites. From the experiments it is observed that the composites exhibit higher hardness and resistance to wear as compared to unreinforced Al alloy.
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    ZnCl2-assisted Synthesis of ZnSe Polycrystal
    Changyou Liu, Tao Wang, Gangqiang Zha, Zhi Gu, Wanqi Jie
    J. Mater. Sci. Technol., 2012, 28 (4): 373-378. 
    Abstract   HTML   PDF
    A chemical-assisted element direct-reaction method is developed to synthesize ZnSe compound semiconductor material at a relatively low temperature (~1000 °C). ZnSe polycrystal was obtained in the closed-tube systems with Zn-Se, Zn-Se-Zn(NH3)2Cl2, Zn-Se-NH4Cl and Zn-Se-ZnCl2. The as-synthesized samples were tested by X-ray diffraction (XRD), thermogravimetric analysis (TGA) and analyzed by thermodynamic numerical
    method. The results demonstrate that the synthesis efficiency is higher than 99.96% for Zn-Se-ZnCl2 system at around 1000 °C for 3 weeks. It also exhibits that not only temperature, but also low apparent ratio of volume and surface area of the source materials and higher ZnCl2 content are required to achieve high synthesis efficiency. A SeCl transporting reaction synthesis process is proposed based on the thermodynamic analysis.
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    Tunable Reactive Wetting of Sn on Microporous Cu Layer
    Qingquan Lai, Lei Zhang, Cai Chen, J.K. Shang
    J. Mater. Sci. Technol., 2012, 28 (4): 379-384. 
    Abstract   HTML   PDF
    Wetting of microporous Cu layer by liquid Sn resulted in contact angles from 0 to 33 deg., tunable by varying wetting temperature and porous microstructure. The wetting was dominated by the interfacial metallurgical reaction, which can lead to pore closure phenomenon, as the liquid infiltration facilitating the wetting process.
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ISSN: 1005-0302
CN: 21-1315/TG
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