Started in 1985 Semimonthly
ISSN 1005-0302
CN 21-1315/TG
Impact factor:6.155

The journal has been awarded the excellent periodical in China, and its articles are covered by SCI, EI, CA, SA, JST, RJ, CSA, MA, EMA, AIA etc., PASCAL web. ISI web of Science,SCOPUS.

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      28 March 2008, Volume 24 Issue 02 Previous Issue    Next Issue
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    Research Articles
    Growth and characterization of high-quality LiAlO2 single crystal
    Taohua HUANG, Shengming ZHOU, Hao TENG, Hui LIN, Jun ZOU, Jianhua ZHOU, Jun WANG
    J. Mater. Sci. Technol., 2008, 24 (02): 145-148. 
    Abstract   HTML   PDF (1145KB)
    γ-LiAlO2 single crystal is a promising substrate for GaN heteroepitaxy. In this paper, we present the growth of large-sized LiAlO2 crystal by modified Czochralski method. The crystal quality was characterized by highresolution X-ray diffraction and chemical etching. The results show that the as-grown crystal has perfect quality with the full width at half maximum (FWHM) of 17.7–22.6 arcsec and etch pits density of (0.3–2.2)×104 cm-2 throughout the crystal boule. The bottom of the crystal boule shows the best quality. The optical transmission spectra from UV to IR exhibits that the crystal is transparent from 0.2 to 5.5 μm and becomes completely absorbing around 6.7 μm wavelength. The optical absorption edge in near UV region is about 191 nm.
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    A Group of Cu(Zr)-based BMGs with Critical Diameter in the Range of 12 to 18 mm
    Yong SHEN, Evan MA, Jian XU
    J. Mater. Sci. Technol., 2008, 24 (02): 149-152. 
    Abstract   HTML   PDF (4882KB)
    A group of Cu(Zr)-based bulk metallic glasses (BMGs) with critical diameter (Dc) in the 12 to 18 mm range have been obtained using copper mould casting. In the Cu-Zr-Y-Al quaternary system, a new record of Dc=14 mm was established for Cu-based compositions, and 16 mm for compositions based on equi-atomic CuZr. Additional partial substitution of Hf for Zr further elevated the Dc to 18 mm at Cu42Zr43Hf1.5Y3.5Al10.
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    Effect of Seed Sizes on Growth of Large Synthetic Diamond Crystals
    Chuanyi ZANG, Rui LI, Hongan MA, Shangsheng LI, Xiaopeng JIA
    J. Mater. Sci. Technol., 2008, 24 (02): 153-156. 
    Abstract   HTML   PDF (407KB)
    For the growth of large synthetic diamond crystals by temperature gradient method (TGM), the grit sizes of seed crystals have great effects on the growth rate and quality of large grown crystals. Because of the limited area of seed surfaces, the maximum diffusion flux of carbon source, which could be absorbed by the seed, is related to the seed size. And with increasing the seed sizes, the growth rates also increase markedly. However, the seed sizes should be lower than a certain value, which determines the crystal quality directly. For example, with NiMnCo alloy as the metal solvent, when the seed size increases from 0.5 to 1.8 mm, the growth rate increases greatly from about 1.1 to 3.2 mg/h; when the size is beyond 2.0 mm, more and more metal inclusions would be incorporated into the grown crystals, and the crystal quality is destroyed heavily. Finite element analysis (FEA) shows that, due to the special assembly of growth cell, the diffusion of carbon source in the metal solvent is very inhomogeneous, which could be substantiated directly by the appearances and shapes of large grown crystals and the remains of carbon source. And this inhomogeneous diffusion of carbon source would be very harmful to the growth of large diamond crystals, especially when large-size seed crystals are used.
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    Photovoltaic Properties of the Modified n-Si(111) Electrodes with Ethyl and Carboxyls
    Yuxue ZHAO, Yabo WEI, Wensheng YANG, Pudun ZHANG, Xin ZHOU, Qinghong XU
    J. Mater. Sci. Technol., 2008, 24 (02): 157-160. 
    Abstract   HTML   PDF (1071KB)
    n-Si(111) surface tailed -C2H5, -C2H4COOH, -C2H2COOH were prepared by the reactions among Si–H to ethyl-Grignard, methyl acrylate and ethyl propionate, and the carboxyls were formed under the existence of trifluoroacetic acid. The composite n-Si(111) electrodes were obtained by depositing Pt nanodots and the photovoltaic characteristics for these electrodes were studied in I-/I3- redox electrolyte. The j-U (photo current density-potential) behaviors of photo-voltage and photocurrent densities to the electrodes under solar illumination varied regularly with groups of -C2H2COOH>-C2H4COOH>-H>-C2H5. The photo-voltage and photocurrent density of the electrode tailed -C2H2COOH were -0.641 V and 5.25 mA/cm2, respectively, more negative than those of the non-conjugated modification.
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    Investigation of glass formability in Al-Co-Y ternary system
    Pan DONG, Jia ZHANG, Wanliang HOU, Xinchun CHANG, Jianqiang WANG, Mingxiu QUAN
    J. Mater. Sci. Technol., 2008, 24 (02): 161-164. 
    Abstract   HTML   PDF (1075KB)
    The glass formation was investigated in the melt-spun Al-rich Al-Co-Y alloys by the microstructure evolution. The best glass former Al88Co5Y7 with the thickness of 230 μm was found, and its glass forming ability (GFA) was higher than that of previously reported Al88Co4Y8 alloy. This result indicates that GFA is strongly sensitive to the alloy composition in the system. The phase selection method is an effective way to locate the optimum glass formation composition rather than Trg and △Tx parameters.
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    First-principles Study on the Ductility Effect of Zirconium and Its Distinct Behavior from Boron to Restrain Hydrogen-induced Embrittlement in Ni-Ni3Al Alloys
    Yuxi WU, Yuanming WANG
    J. Mater. Sci. Technol., 2008, 24 (02): 165-171. 
    Abstract   HTML   PDF (736KB)
    By studying a cluster model containing Ni region (phase), Ni3Al region (phase) and Ni/Ni3Al region (interface) with a first-principles method, the occupation behavior and the ductility effect of zirconium in a Ni-Ni3Al system were investigated. It is found that zirconium has a stronger segregation tendency to Ni region than to Ni3Al region. The bond order analyses based on Rice-Wang model and the maximum theoretical shear stress model, however, show that zirconium has different degrees of ductility effect in these three regions, which originates from its different ability to increase the Griffith work of interfacial cleavage 2γint and to decrease the maximum theoretical shear stress τmax. In addition, it is revealed in this paper that the distinct behavior of zirconium from boron to restrain hydrogen-induced embrittlement can be attributed to their different influences on the crystalline and electronic structures in Ni-Ni3Al alloys.
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    Effects of Power Density and Post Annealing Process on the Microstructure and Wettability of TiO2 Films Deposited by Mid-frequency Magnetron Reactive Sputtering
    Ying CUI, Hao DU, Jinquan XIAO, Lishi WEN
    J. Mater. Sci. Technol., 2008, 24 (02): 172-178. 
    Abstract   HTML   PDF (3923KB)

    The relationship of “preparation parameters-microstructures-wettability” of TiO2 films was reported. In this work, TiO2 films were deposited onto glass and silicon substrates by using mid-frequency dual magnetron sputtering technique at ambient temperature with various power densities and deposition time. After deposition, the films were heat treated at different annealing temperatures. X-ray diffraction (XRD), Raman spectroscopy, and field-emission scanning electron microscopy (FE-SEM) were utilized to characterize TiO2 films. The wettability of the films was evaluated by water contact angle measurement. The phase transition temperature of TiO2 films depended on the power density. It was demonstrated that wettability was strongly structure dependent and the film with the thickness of 610 nm (the power density was 2.22 W/cm2) showed the lowest contact angle (8°). It can be concluded that smaller crystallite size, the rutile phase with (110) face being parallel to the surface, and tensile stress favored the hydrophilicity of the TiO2 films.

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    Low Temperature DC Sputtering Deposition on Indium-Tin Oxide Film and Its Application to Inverted Top-emitting Organic Light-emitting Diodes
    Hui LIN, Junsheng YU, Shuangling LOU, Jun WANG, Yadong JIANG
    J. Mater. Sci. Technol., 2008, 24 (02): 179-182. 
    Abstract   HTML   PDF (615KB)
    Indium tin oxide (ITO) ultrathin films were prepared on glass substrate by DC (direct current) magnetron sputtering technique with the assistance of H2O vapor to avoid potential surface damage. The film properties were characterized by X-ray diffraction (XRD) technique, four-point probe method and spectrophotometer. The results show that the deposited ITO film with introduced H2O during sputtering process was almost amorphous. The average visible light transmission of 100 nm ITO film was around 85% and square resistivity was below 80 Ω/square. The film was used as the transparent anode to fabricate an inverted top-emitting organic light-emitting diodes (IT-OLEDs) with the structure of glass substrate/Alq3 (40 nm)/NPB (15 nm)/CuPc (x nm)/ITO anode (100 nm), where the film thickness of CuPc was optimized. It was found that the luminance of this IT-OLEDs was improved from 25 cd/m2 to more than 527 cd/m2 by increasing the thickness of CuPc, and luminance efficiency of 0.24 lm/W at 100 cd/m2 was obtained, which indicated that the optimized thickness of CuPc layer was around 15 nm.
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    Nucleation Thermodynamics inside Micro/nanocavity
    Qiuxiang LIU, Yanjuan ZHU, Guowei YANG, Qibin YANG
    J. Mater. Sci. Technol., 2008, 24 (02): 183-186. 
    Abstract   HTML   PDF (515KB)
    A thermodynamic approach at the nanometer scale was performed for the heterogeneous nucleation inside nanocavity, and an analytical expression of the critical energy of nucleation was evaluated considering a rough ball nucleus nucleating inside nanocavity. Compared with the case of the nucleation locating on planar or convex substrate, the critical energy of nucleation inside the concave substrate is the smallest. Based on the thermodynamic and kinetic analyses, at low supersaturation, the smaller the curvature radius of cavity and/or the smaller the contact angle, the smaller the critical energy of nucleation, and the larger the nucleation rate. At high supersaturation, the nucleation rate increases with increasing the contact angle and/or increasing the curvature radius of cavity. In this way, at the low supersaturation, the heterogeneous nucleation rate is larger than the homogeneous one, as the nucleation rate is mainly determined by the heterogeneous nucleation. At the high supersaturation, the heterogeneous nucleation rate is smaller than the homogeneous one, as the nucleation rate is mainly determined by the homogeneous nucleation.
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    Fluorescent Labeling of Nanometer Hydroxyapatite
    Yuan ZHANG, Yuan YUAN, Changsheng LIU
    J. Mater. Sci. Technol., 2008, 24 (02): 187-191. 
    Abstract   HTML   PDF (574KB)
    A novel surface treatment method using 3-aminopropyltriethoxysilane (AMPTES), was developed to immobilize the fluorescein molecule on nano-HAP (nanometer hydroxyapatite) powders. By pretreating the nano-HAP powders surface with AMPTES, fluorescein, chosen on the basis of the chemical structure of the nano- HAP powders, could be bound to the nano-HAP powders surface. The chemical compositions of nano-HAP before and after being labeled were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The morphology, phase composition, and the fluorescence characteristics of the nano-HAP powders with and without staining were also investigated. The FTIR and XPS results revealed that fluorescein had been successfully immobilized on the surface of AMPTES-bound nano-HAP powders via the acylamide bond formation between the -COOH of fluorescein and the -NH2 of AMPTES. The labeled nano-HAP powders possessed strong fluorescent intensity with a little deviation from the maximum emission wavelength of fluorescein. But the morphology and phase composition had no obvious alteration. Under fluorescence microscopy, the labeled nano-HAP powders, even after 24 h cell incubation, exhibited strong fluorescence.
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    Antibacterial Characterization of Silver Nanoparticles against E. Coli ATCC-15224
    M.Raffi, F.Hussain, T.M.Bhatti, J.I.Akhter, A.Hameed, M.M.Hasan
    J. Mater. Sci. Technol., 2008, 24 (02): 192-196. 
    Abstract   HTML   PDF (533KB)
    Silver nanoparticles of mean size 16 nm were synthesized by inert gas condensation (IGC) method. Crystalline structure, morphology and nanoparticles size estimation were conducted by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Antibacterial activity of these silver nanoparticles as a function of particles concentration against gram-negative bacterium Escherichia coli (E.coli) was carried out in liquid as well as solid growth media. Scanning electron microscopy (SEM) and TEM studies showed that silver nanoparticles after interaction with E.coli have adhered to and penetrated into the bacterial cells. Antibacterial properties of silver nanoparticles are attributed to their total surface area, as a larger surface to volume ratio of nanoparticles provides more efficient means for enhanced antibacterial activity.
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    Antibacterial Mechanism of Copper-bearing Antibacterial Stainless Steel against E.Coli
    Li NAN, Weichao YANG, Yongqian LIU, Hui XU, Ying LI, Manqi LÜ, Ke YANG
    J. Mater. Sci. Technol., 2008, 24 (02): 197-201. 
    Abstract   HTML   PDF (416KB)
    A preliminary study was made on the antibacterial mechanism of copper-bearing antibacterial stainless steels against E.coli through experiments of microbiology such as EDTA (ethylenediaminetetraacetic acid) complexing, DNA smearing and AFM (atomic force microscope) observation. It was measured that the antibacterial stainless steels showed excellent antibacterial functions with antibacterial rate to E.coli over 99.99%. The antibacterial rate was weak if the bacteria solution was complexed by EDTA, indicating that the copper ions play a dominant role in the antibacterial effect of the antibacterial stainless steels. The electrophoresis experiment did not show the phenomenon of DNA smearing for E.coli after contacting antibacterial stainless steels, which meant that DNA of E.coli was not obviously damaged. It was observed by AFM that the morphology of E.coli changed a lot after contacting antibacterial stainless steels, such as cell walls being seriously changed and lots of contents in the cells being leaked.
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    Effects of Austenite Stabilization on the Onset of Martensite Transformation in T91 Steel
    Baoqun NING, Yongchang LIU, Qingzhi SHI, Zhiming GAO, Liushuan YANG
    J. Mater. Sci. Technol., 2008, 24 (02): 202-206. 
    Abstract   HTML   PDF (1308KB)
    The influences of thermal stabilization of austenitic on the onset temperature for a martensite transformation in T91 ferritic heat-resistant steel were studied by high-resolution differential dilatometer. The phase transformation kinetic information was obtained by adopting lever rule from the recorded dilatometric curves. The results show that an inverse stabilization, featured by the damage of “the atmosphere of carbon atoms” and the increase of the starting temperature for martensite transformation takes place when the T91 ferritic steel is isothermally treated above the Ms point, and it becomes strong with increasing the holding time. While the continued temperature for martensite transformation decreases gradually when isothermally holding at a temperature below Ms point. The observed inverse stabilization behavior could be attributed to the relatively high temperature of Ms point in the explored T91 ferritic heat-resistant steel.
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    Dielectric Properties of Porous Reaction-boned Si3N4 Ceramics with Controlled Porosity and Pore Size
    Jie XU, Dongmei ZHU, Fa LUO, Wancheng ZHOU, Peng LI
    J. Mater. Sci. Technol., 2008, 24 (02): 207-210. 
    Abstract   HTML   PDF (396KB)
    This paper presents the microwave dielectric properties of reaction bonded porous silicon nitride ceramics with variant porosity and pore size, which were prepared by adding pore-forming agent grains into the silicon powders. The experimental results show that the dielectric constant and the dielectric loss of the samples reduce evidently with increasing porosity in the sample. When the porosity is constant, the dielectric constant and the dielectric loss of the ceramics decrease visibly as the pore size increases. Among all the obtained samples, the minimum dielectric constant is about 2.4.
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    Influences of Sintering Process of Sprayed Precursors on the Structure and Electrochemical Properties of LiMn2O4 Cathode Material
    Hui HUANG, Chen WANG, Lei ZHANG, Yongping GAN, Wenkui ZHANG
    J. Mater. Sci. Technol., 2008, 24 (02): 211-214. 
    Abstract   HTML   PDF (708KB)
    Well-defined spinel LiMn2O4 powders were synthesized via sintering a precursor, which was prepared by spraydrying method. The effects of sintering process on the structure and electrochemical properties of LiMn2O4 were discussed. It was found that a single sintering could not synthesize a pure LiMn2O4 compound, while two-step sintering procedure consisting of decomposing sprayed precursors at 350℃ and further sintering at an elevated temperature leads to the formation of a single-phased LiMn2O4 with homogeneous particle size distribution. As compared to that sintered in air, the two-step sintered LiMn2O4 in oxygen shows tighter structure and more uniform particle size, as well as better electrochemical properties. It delivers an initial discharge capacity of 131 mAh•g-1 (1/10C), and still has excellent cycling stability at higher rate (1/5C).
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    EIS Study on Pitting Corrosion of AA5083-H321 Aluminum-Magnesium Alloy in Stagnant 3.5% NaCl Solution
    K.Jafarzadeh, T.Shahrabi, M.G.Hosseini
    J. Mater. Sci. Technol., 2008, 24 (02): 215-219. 
    Abstract   HTML   PDF (3198KB)
    In this research, EIS (electrochemical impedance spectroscopy) technique was utilized to study the pitting corrosion behaviour of AA5083-H321 aluminum-magnesium alloy in 3.5% NaCl solution. Impedance spectra were obtained during 240 h of exposure of the sample to the test solution. The surface and cross-section of the samples were studied by scanning electron microscopy (SEM) and EDAX (energy dispersive analysis of X-ray) analysis. The results indicated that as the resistance of the passive layer on intermetallic particles is very small, this parameter on the sample surface layers is controlled by that of pure passive layer. However, the capacitors in the proposed equivalent circuit are replaced with the constant phase elements (CPE), due to non-uniformity and occurrence of pitting corrosion on the surface. The outward diffusion of Al+3 ions through the passive layer and the thickening of this layer cause the impedance decrease in the first 24 h and increase afterwards. The detachment of intermetallic particles from some of pits and the accumulation of the corrosion products inside some others are factors that prevents the continuation of cathodic reactions on the top of the intermetallic particles.
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    Characteristics of Laser Reflow Bumping of Sn3.5Ag and Sn3.5Ag0.5Cu Lead-Free Solder Balls
    Yanhong TIAN, Chunqing WANG, Yarong CHEN
    J. Mater. Sci. Technol., 2008, 24 (02): 220-226. 
    Abstract   HTML   PDF (2878KB)
    Lead-free Sn3.5Ag and Sn3.5Ag0.5Cu solder balls were reflowed by laser to form solder bumps. Shear test was performed on the solder bumps, and SEM/EDX (scanning electron microscopy/energy dispersive X-ray spectrometer) was used to analyze the formation of intermetallic compounds (IMCs) at interface region. A finite element modeling on the temperature gradient and distribution at the interface of solder bump during laser reflow process was conducted to elucidate the mechanism of the IMCs growth direction. The results show that the parameters window for laser reflow bumping of Sn3.5Ag0.5Cu was wider than that of Sn3.5Ag. The shear strength of Sn3.5Ag0.5Cu solder bump was comparable to that of Sn3.5Ag solder bump, and was not affected obviously by laser power and irradiation time when appropriate parameters were used. Both laser power and heating time had a significant effect on the formation of IMCs. A continuous AuSn4 intermetallic compound layer and some needle-like AuSn4 were observed at the interface of solder and Au/Ni/Cu metallization layer when the laser power is small. The formation of needle-like AuSn4 was due to temperature gradient at the interface, and the direction of temperature gradient was the preferred growth direction of AuSn4. With increasing the laser power and heating time, the needle-like AuSn4 IMCs dissolved into the bulk solder, and precipitated out once again during solidification along the grain boundary of the solder bump.
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    A Comparison between Direct and Indirect Laser Sintering of Metals
    Montasser M.Dewidar, Jae-Kyoo LIM, K.W.Dalgarno
    J. Mater. Sci. Technol., 2008, 24 (02): 227-232. 
    Abstract   HTML   PDF (2682KB)
    Layer manufacture technologies are gaining increasing attention in the manufacturing for the production of polymer mould tooling. Layer manufacture techniques can be used in this potential manufacturing area to produce tooling either indirectly or directly, and powder metal based layer manufacture systems are considered as an effective way of producing rapid tooling. Mechanical properties and accuracy are critical for tooling. This paper reports the results of an experimental study examining the potential of layer manufacturing processes to deliver production tooling for polymer manufacture. A comparison between indirectly selective laser sintering and directly selective laser sintering to provide the tooling was reported. Three main areas were addressed during the study: mechanical strength, accuracy, and build rate. Overviews of the results from the studies were presented.
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    Application of Vacuum Drying to Silica Sol Ceramic Mold
    Ming ZENG, Xinqiang YUAN, Baoluo SHEN, Yunqiu ZHENG
    J. Mater. Sci. Technol., 2008, 24 (02): 233-235. 
    Abstract   HTML   PDF (475KB)
    Silica sol ceramic mold was made at room temperature with JN-30 silica sol, silica powder and NH4Cl. It is found that the harden time of silica sol ceramic mold is only 0.5 to 1.5 h under the amount of NH4Cl solution of 7% to 8% with 15% concentration, and less surface cracks occur by using vacuum drying. The proper vacuum drying process parameters: vacuum drying temperature is 80 to 100℃, drying time is 5 h and vacuum is 0.06 to 0.07 MPa. The harden mechanics, vacuum drying mechanics and the reason of less surface cracks of silica sol ceramic mold by vacuum drying were also analyzed in this paper.
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    Effect of surface pretreatment on adhesive properties of aluminum alloys
    Jinsheng ZHANG, Xuhui ZHAO, Yu ZUO, Jinping XIONG, Xiaofeng ZHANG
    J. Mater. Sci. Technol., 2008, 24 (02): 236-240. 
    Abstract   HTML   PDF (606KB)
    The lap-shear strength and durability of adhesive bonded Al alloy joints with different pretreatments were studied by the lap-shear test and wedge test. The results indicate that the maximum lap-shear strength and durability of the bonding joints pretreated by different processes are influenced by the grade of abrasive papers and can be obviously improved by phosphoric acid anodizing. Alkali etching can obviously improve the durability of bonding joints although it slightly influences the maximum lap-shear strength. The process which is composed of grit-finishing, acetone degreasing, alkali etching and phosphoric acid anodizing, provides a better adhesive bonding property of Al alloy.
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    Elastic Properties of Potassium Halides under Pressure
    K.Haddadi, L.Louail, D.Maouche
    J. Mater. Sci. Technol., 2008, 24 (02): 241-244. 
    Abstract   HTML   PDF (5694KB)
    The moderate-pressure elastic properties of potassium halides KX (X=F, Cl, Br) was studied theoretically using the density functional theory (DFT) with normconserving pseudopotentials method. The phase transformation from the B1 phase (NaCl-type structure) to the denser B2 phase (CsCl-type structure) occurred at 7.7, 3.46 and 2.96 GPa for KF, KCl and KBr, respectively. The elastic stiffness coefficients and bulk modulus of these materials were calculated as function of hydrostatic pressure and compared with both the experimental and theoretical values.
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    Effect of Heat Treatment on the Microstructure of Multiphase NiAl-based Alloy
    Yi XIE, Lanzhang ZHOU, Jianting GUO, Hengqiang YE
    J. Mater. Sci. Technol., 2008, 24 (02): 245-250. 
    Abstract   HTML   PDF (814KB)
    The alloy Ni-Al26.6-Cr13.4-Co8.1-Ti4.3-W1.3-Mo0.9 (at. pct) was fabricated from superalloy K44 and Al element using vacuum induction and casting technique. Investigations to this alloy reveal that a new phase Cr3Ni2 possessing low melting point and poor ductility is formed, which is distributed as a network along NiAl matrix grain boundaries. Subsequent different solution and aging treatments are carried out and lead to microstructural changes to various extents. Rapid cooling after solution at 1250℃ for 20 h gives rise to macrocracks in the specimen while slow cooling after the same treatment results in the formation of spheric α-Cr solid solution and needle-like Ni3Al phase, which are embedded in NiAl matrix. It is comfirmed that aging treatments initiate lath-shaped Ni3Al phase and pearl-shaped α-Cr phase to precipitate from the NiAl matrix, which own orientation relationships with these precipitates.
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    Simulation of Microstructure Evolution of Ni75Al2.9V22.1 Alloy with Progressive Aging Mechanisms
    Yongsheng LI, Zheng CHEN, Qingbo LAI , Yongxin WANG
    J. Mater. Sci. Technol., 2008, 24 (02): 251-255. 
    Abstract   HTML   PDF (1060KB)
    The interrupted aging mechanisms were applied to Ni75Al2.9V22.1 alloy by using the microscopic phase-field simulation method. For the single phase region existing at high temperature, the low content alloy was used as the study object. With the progressive aging mechanisms, the metastable phase γ' of high temperature can be obtained from the low temperature two phase regions, and the quantity of γ' phase reduces with increasing temperature. The θ single phase morphology at high temperature regions will turn to be the γ'+θ two phase morphology at low temperature with the interrupted aging method. Despite of the different precipitation paths of γ' phase, the precipitation mechanisms are the same for the low temperature aging and high temperature interrupted aging.
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    Effects of Guiding Angle on Plastic Metal Flow and Defects in Extrusion of Aluminum Alloy
    Shijian YUAN, Feng LI, Zhubin HE
    J. Mater. Sci. Technol., 2008, 24 (02): 256-260. 
    Abstract   HTML   PDF (1872KB)
    To reduce defects, such as the shrinkage cavity and the surface cracks caused by non-homogeneous metal flow in extrusion process, an extrusion method was proposed by using a die with the guiding angle. Numerical simulation and experiment were conducted to investigate the metal flow in this extrusion process. It is shown that the stress state at the bottom of the die is changed. The tendency to generate the dead zone is decreased by employing the guiding angle at the die entrance. The shrinkage cavity is reduced because the non-homogeneous metal flow at the final stage of extrusion is improved. The axial stress is decreased greatly so that the surface cracks caused by additional stress are avoided.
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    Analysis of Microstructure of Silicon Carbide Fiber by Raman Spectroscopy
    Baohong JIN, Nanlin SHI
    J. Mater. Sci. Technol., 2008, 24 (02): 261-164. 
    Abstract   HTML   PDF (949KB)
    The SiC fiber was prepared by chemical vapour depostion, which consists of tungsten core, SiC layer and carbon coating. The microstructure of the fiber was investigated using Raman spectroscopy, illustrating SiC variation in different region of the fiber. The result shows that the SiC layer can be subdivided into two parts in the morphologies of SiC grains; their sizes increase and their orientations become order with increasing distance from the fiber center. It is demonstrated that the mount of free carbon in the fiber is responsible for the variation of SiC grains in sizes and morphologies. The analysis of Raman spectra shows that the predominant β-SiC has extensive stacking faults within the crystallites and mixes other polytypes and amorphous SiC into the structure in the fiber.
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    Study on the Electromagnetic Interference of CFRC Composites by Reflectivity
    Kezhi LI, Chuang WANG, Hejun LI, Gengsheng JIAO, Jian WEI
    J. Mater. Sci. Technol., 2008, 24 (02): 265-271. 
    Abstract   HTML   PDF (1901KB)
    The influence of dispersion of carbon fibers in carbon-fiber-reinforced cement-based composites (CFRC) on the mechanical properties of the composites was discussed. The microstructure of the fracture surface of the CFRC samples was observed with a scanning electron microscope (SEM). The electromagnetic interference (EMI) was evaluated indirectly by reflectivity in the Naval Research Laboratory (NRL) testing system. The reflectivity of the electromagnetic radiation by the composites was measured in the frequency range of 8.0–8.2 GHz for different carbon fiber contents of 0.2%, 0.4%, 0.6%, 0.8%, and 1.0% (in wt pct), respectively. The results showed that the reflectivity decreased with the growing fiber content till the percentage of 0.6%. The minimum reflectivity was -23 dB, far less than ¡10 dB, and the composites were strong wave absorbers. After this percentage, the curve increased abruptly as the fiber content proceeded. The electromagnetic waves were gradually reflected. When the fiber content reached 1.0% finally, the maximum reflectivity -7.5 dB appeared and there was stronger reflection. The shielding mechanism includes mainly reflection, absorption, and multiple reflections.
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    Toughening of Epoxy Resin with Solid Amine Terminated Poly (ethylene glycol) Benzoate and Effect of Red Mud Waste Particles
    B.C.Samanta, T.Maity, S.Dalai, A.K.Banthia
    J. Mater. Sci. Technol., 2008, 24 (02): 272-278. 
    Abstract   HTML   PDF (2737KB)
    An investigation was carried out to modify the toughness of triethylene tetramine cured DGEBA (diglycidyl ether of bisphenol-A) resin using solid amine terminated poly (ethylene glycol) benzoate (ATPEGB) as modifier with and without red mud waste particles. The solid ATPEGB modifier synthesized from the acid catalyzed esterification reaction of poly (ethylene glycol) (PEG) and 4-amino benzoic acid was characterized by Fourier transform infrared spectroscopy (FT-IR) and 1H-NMR (nuclear magnetic resonance) spectroscopies, viscosity measurements, and solubility parameter calculation. The unfilled and red mud waste filled modified epoxy networks were evaluated with impact, adhesive, tensile, flexural and thermal properties by differential scanning calorimetry (DSC), thermogravimetric (TG) and dynamic mechanical analysis (DMA). The effect of modifier concentration and red mud waste particles on toughening behavior was also investigated. The optimum properties were obtained at 12.5 phr (parts per hundred parts of resin) concentration of the modifier. The ATPEGB modified cured epoxy was thermally stable up to 315℃. The morphology on fracture surfaces of cured epoxy was also analyzed by scanning electron microscopy (SEM).
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    Preparation and Crystallization of Carbon Nanotube/maleic Anhydride-grafted Polypropylene Composites
    Xiaohua CHEN, Jing HU, Lingping ZHOU, Wenhua LI, Zi YANG, Yanguo WANG
    J. Mater. Sci. Technol., 2008, 24 (02): 279-284. 
    Abstract   HTML   PDF (4496KB)
    Carbon nanotube (CNT)/maleic acid anhydride (MAH)-grafted polypropylene (PP) composites were prepared by in situ grafting method. Infrared spectroscopy showed that the CNTs were linked to PP by MAH grafting. The microstructures and calorimetry analysis indicated that the crystallization behaviors of the filled and unfilled PP were quite different. The addition of CNTs dramatically reduced the spherulite size, increased crystallization rate and improved the thermal stability of PP. These results confirmed the expected nucleant effect of CNT on the crystallization of PP. Scanning and transmission electron microscopy showed that the CNTs were dispersed homogeneously, indicating that the original CNT bundles were separated into individual tubes by the grafting.
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    Effect of Additives on the Morphology of the Hydrated Product and Physical Properties of a Calcium Phosphate Cement
    Xiupeng WANG, Ji, ong YE, Yingjun WANG
    J. Mater. Sci. Technol., 2008, 24 (02): 285-288. 
    Abstract   HTML   PDF (449KB)
    The morphology of a hydrated calcium phosphate cement (CPC) doped with several normally used additives was investigated by scanning electron microscopy (SEM) and the compressive strength of the cement was determined in this study. The hydrated products of CPC without additives was rod-like hydroxyapatite (HA) grains with around 2-5 μm in length and 100 nm in width. The addition of Sr obviously decreased the crystal size of the rod-like grains. CPCs containing carbonate, collagen and gelatin showed flake-like crystal morphology. Crylic acid-containing CPC presented flocculus-like structure. And malic acid-containing CPC exhibited oriented flake-like structure. The X-ray diffraction (XRD) analysis showed that the additives used in this study did not alter the hydration products of the cement. The compressive strength tests indicated that the compressive strength of the cement with rod-like morphology HA crystals was much higher than that of the cement with flake-like morphology HA crystals, and the cement with oriented flake-like morphology HA crystals exhibited the poorest compressive strength.
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ISSN: 1005-0302
CN: 21-1315/TG
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