Mar 2007, Volume 1 Issue 1

  • Select all
  • ZHENG Qiang, ZUO Min, PENG Mao, SHEN Lie, FAN Yurun
    Rheological measurement has been a preferred approach in the characterization of the formation and evolution of microstructures for multi-component or multi-phase polymeric material systems owing to its sensitive response to changes of microstructures for heterogeneous polymers. In the present paper, based on applications of dynamic rheological measurements to multi-component polymer systems, some of the latest progress in studies on the correlations between the microstructure change and rheological response has been introduced as two aspects: relationships between viscoelastic behavior and microstructure of nano-composites and relationships between rheological behavior and liquid solid transition in isothermal crystallization of polyolefins. By means of rheological measurements, not only some valuable particulars responsible for the evolution of morphology and structure dealing with these polymer systems can be obtained, but also the corresponding results are in favor of designing and preparing novel polymer-based composites and functional materials.
  • FANG Qianfeng, WANG Xianping, CHENG Zhijun, ZHANG Guoguang
    La2Mo2O9-based oxide-ion conductors have attracted more and more attention since the high ionic conductivity was reported in 2000 by Lacorre et al. in this kind of material. In this paper the recent investigation on the novel La2Mo2O9-based oxide-ion conductors is reviewed. It is focused on the structure and phase transition, oxide-ion conductivity, mechanism of oxygen vacancy diffusion, chemical stability and thermal expansion coefficient in the pure and doped La2Mo2O9 samples. It is pointed out that the La2Mo2O9-based oxide-ion conductors could be possibly applied in the fields such as solid oxide fuel cells, oxygen sensors and oxygen permeable membranes.
  • Gall Floriane, LI Zhengcao, ZHANG Zhengjun
    When synthesizing tungsten oxide nanorods using thermal oxidation, the deposition conditions play an important role in the morphology and phase structure. The evaporation voltage greatly influences the average diameter of the nanorods. The evaporation time controls the deposit thickness, while the deposition temperature determines the phase structure.
  • MO Xiumei, CHEN Zonggang, Hans J. Weber
    Electrospun nanofibers could be used to mimic the nanofibrous structure of the extracellular matrix (ECM) in native tissue. In tissue engineering, the ECM could be used as tissue engineering scaffold to solve tissue engineering problems. In this paper, poly(L-lactid-co-ε-caprolactone) [P(LLA-CL)] nanofibers and collagen-chitosan complex nanofibers were fabricated by electrospinning. Results of the experiments showed that the mechanical properties of the collagenchitosan complex nanofibers varied with the collagen content in the complex. It was also found that the biodegradability of P(LLA-CL) nanofibers was faster than its membrane and that smooth muscle cells (SMC) grow faster on collagen nanofibers than on P(LLA-CL) nanofibers.
  • XU Guoxiang, WU Chuansong
    The weld pool geometry and its dimension in the globular-transfer mode during gas metal arc welding (GMAW) were numerically analyzed by using the thermal conduction model, which considered the influence of the deformation of weld pool surface on heat flow in the quasi-steady state. According to the features of the globular-transfer mode, the additional heat energy from molten metal droplets was treated as a plane or volumetric heat source term to correspond to different welding conditions. The weld pool surface profile was predicted while considering the effect of droplet impingement on the depression of the weld pool. The bead-on-plate GMAW experiments were performed under different welding conditions to validate the model of numerical analysis. It has been found that the predicted results agree well with the measured ones.
  • HU Qinghong, CAI Yurong, SHI Zhongli, YAN Weiqi, TANG Ruikang
    Spherical- or cylindrical-shaped nanosized calcium phosphate particles are considered as an integral part of biological hard tissues such as bone and tooth enamel. The size effects of these nanoparticles were evaluated by coculturing osteosarcoma (U2OS) cells on their films or in their aqueous suspensions. Experimental results demonstrated that these nanophase minerals could inhibit the proliferations of U2OS significantly. The effects were increased with decreasing particle sizes, and the 20-nm sized calcium phosphate, the basic building blocks during bone/enamel formations, was the most effective inhibitor. The particle size is believed to play an important role on cellular behaviors and this in vitro study suggested the potential of calcium phosphate nanoparticles for use in therapeutic replacement and reconstruction of bone merits after tumor extractions.
  • JIANG Haiyun, WANG Jigang, DUAN Zhichao, LI Fan
    Boron carbide (B4C) was selected as the additive for the modification of a phenol-formaldehyde (PF) resin, and the micro-structural evolution of the modified resin at high temperature was investigated. Results showed that the distribution of B4C particles became uniform at elevated temperatures. The primary oxidation of B4C started to occur at 450vH, and lots of B2O3 was formed above 650vH. By the modification reactions of B4C, the volatiles including CO was converted into amorphous carbon and remained in the resin matrix, which was responsible for maintaining the stability of the resin at high temperatures.
  • ZHANG Xuezhong, HUANG Yudong, WANG Tianyu, HU Lijiang
    Carbon fibres (CF) were modified with different oligomeric silsesquioxane (SSO) coatings to improve the interfacial property of carbon fibres/polyarylacetylene (CF/PAA). The interlaminar shear strength (ILSS) of CF/PAA was tested to determine the effect of the treatment. Atomic force microscopy (AFM) in force modulation mode was adopted to study the cross-section surface of unidirectional CF/PAA composites and the relative stiffness of various phases, including CF, interphase and resin. The probability histogram and line distribution of CF/PAA cross-section surface relative stiffness, obtained from the statistical analysis of relative stiffness image, were used to compare and study the interface characterizations of composites. The results show that the ILSS increases effectively and the effects on interfacial characterizations are distinguished from each other in accordance with the CF surface modified with different SSO coatings owing to the various structures. Cage oligomeric silsesquioxane, including large organic groups (methacryl isobutyl-POSS), has better treatment result. AFM observations lead to the conclusion that an interfacial transition layer with different morphology and stiffness appears in CF/PAA composites after being treated by the SSO coatings of different structures. It can be inferred that the appearance of the transition layer may contribute to the improvement of fibre/matrix adhesion.
  • SHEN Haijun, MU Xiancai
    The extended H?ckel method and the Green s function method were used to calculate the electronic structure and electrical transport of Au electrode-C60, 2C60 or 4C60 fullerene-Au electrode systems. Furthermore, their electronic structure and electrical transport characteristics were compared and analyzed. The results show that (i) owing to the contact with the Au electrodes, the C60, 2C60 and 4C60 molecules change in their electronic structures significantly, and their energy gaps between LUMO and HOMO are narrow; (ii) the bonding between C60, 2C60 or 4C60 fullerene and Au electrodes is partially covalent and partially electrovalent; and (iii) the conductance of the three fullerenes conforms to the order of C60>2C60>4C60.
  • ZHANG Maocai, GAO Xuexu, JIANG Honglin, ZHU Jie, ZHOU Shouzeng
    Fe83Ga17alloy ribbons with four thicknesses were prepared by the melt-spun method. The measured results show that magnetostriction is related to the thickness of the ribbons, and its maximum value, -2100 ppm,
  • ZHAO Yonglin, DU Piyi, WENG Wenjian, HAN Gaorong
    (Pbx,Sr1 x)0.85Bi0.1TiO3 thin films with the perovskite phase structure were prepared on an ITO glass substrate by sol-gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and an impedance analyzer were respectively used in order to characterize the phase status, morphology and dielectric properties of the thin films. The results show that during the formation process of (Pbx, Sr1 x)0.85KBi0.1TiO3 thin films, the nucleus of the perovskite phase are initially formed and then congregated. These aggregated nucleus are then transformed as the perovskite-phase crystalline in the thin film. Finally, the crystalline phase grows and separates gradually to form the perfect crystalline-phase structure. The content of the perovskite phase formed in the thin film under rapid thermal process (RTP) is more than that formed under traditional heat treatment with kinetic equilibrium. This is due to the high active decomposed ions that form the perovskite phase directly when heat-treated by RTP. The formation of the perovskite phase therefore overcomes a much lower barrier under RTP than that under traditional calcinations. The structure of the perovskite phase has a close relation to the ratio of Pb/Sr in the system because of the radius difference between Pb2+ and Sr2+. The transformation temperature between the cubic and the tetragonal structures of the perovskite phase increases with increasing Pb2+ content because the radius of Pb2+ is larger than that of Sr2+. It appears at room temperature when the content of Pb2+/Sr2+ is about 40/60 in the thin film. Meanwhile, the tetragonality of the perovskite phase is increased when Pb2+ ions increase due to its high polarization. The higher tunability of the (Pbx,Sr1 x)0.85Bi0.1TiO3 thin film is exhibited when the film composition is close to the transformation point between the paraelectric and ferroelectric phases. Pb2+ions show a dominant factor to affect the Curie point of the system and then changing tunability.
  • HONG Haoqun, JIA Demin, HE Hui
    In this paper, reactive organic montmorillonite (RMMT), prepared with compound alkylammoniums, were used in ternary-monomer solid phase graft copolymerization in order to enhance the melting intercalation of montmorillonite (MMT),
  • QIU Xunlin, XIA Zhongfu, WANG Feipeng
    The piezoelectricity of a pressure-treated cellular polypropylene (PP) (commercially available, trade name PQ50) film electret was studied by the measurement of direct- and inverse-piezoelectric d33 coefficient. The sample expanded with optimal parameters has a quasi-static piezoelectric d33 coefficient of more than 600 pC/N, which is about 40 times as high as that of polyvinylidene fluoride (PVDF). In addition, the hybrid multi-layer system, which properly combines single-layer cellular PP film electrets, shows a quasi-static piezoelectric sensitivity of as high as 2010 pC/N. This is around three times higher than that of well-known lead zirconate titanate (PZT) ceramics. The results are theoretically and technically helpful to promote the application of cellular PP film electrets.
  • FANG Yanli, WANG Huaming
    A wear-resistant alloy consisting of Cr13Ni5Si2 ternary silicide dendrites and the interdendritic nickel-base solid solution (γ ) was designed and fabricated by the laser melting/continuous deposition (LMCD) process. The wear resistance of Cr13Ni5Si2/γ alloy was evaluated on an MM-200 block-on-wheel dry sliding wear tester at room temperature. Results indicate that the Cr13Ni5Si2/γ alloy has excellent wear resistance and extremely low load-sensitivity of wear under dry sliding wear test conditions due to the high toughness and the high strength, as well as the transferred cover-layer on the worn surface of the alloy.
  • ZHANG Ming, AN Xuefeng, TANG Bangming, YI Xiaosu
    A 2/4 functional epoxy blend system (DGEBA/TGMDA) cured with 4,4´-diamino diphenyl sulphone (DDS) was used as the raw material in this research. Round disk compression mode DMA (dynamic mechanical analyzer) was employed to study the gelation at the different temperatures, and the relationship between gel-time (tgel) and temperature was obtained. The cure kinetics was studied by dynamic DSC (differential scanning calorimetry) analysis, and the parameters of the cure reaction were obtained to establish a phenomenological model. The relationship between glass transition temperature (Tg) and cure degree (α) was analyzed by an isothermal plus dynamic DSC method based on the DiBenedetto equation, which gave a mathematical description of Tg as a function of both time and temperature. Characteristic temperatures such as Tg0, gelTg and Tg" were also determined. The cure degree at gelation turned out to be 0.4539, while the temperature at which vitrification line and gel line transected was found to be 70.2?C. The time-temperature-transition (TTT) diagram was plotted based on the work above, which served as a tool for process optimization in the manufacture of advanced composites. A new cure procedure of this practical thermosetting system was extracted from the TTT diagram by prolonging the pre-gel time to restrict the diffusion ability and the flow ability of the solution. The final phase structure was proved by SEM to be ex-situ phase morphology compared with the traditional in-situ phase structure by exerting different cure procedures.
  • LAN Wei, PENG Xingping, LIU Xueqin, HE Zhiwei, WANG Yinyue
    Zinc oxide (ZnO) thin films were deposited on (100) Si substrates by sol-gel technique. Zinc acetate was used as the precursor material. The effect of different annealing atmospheres and annealing temperatures on composition, structural and optical properties of ZnO thin films was investigated by using Fourier transform infrared spectroscopy, X-ray diffraction, atomic force microscopy and photoluminescence (PL), respectively. At an annealing temperature of 400vH in N2 for 2 h, dried gel films were propitious to undergo structural relaxation and grow ZnO grains. ZnO thin film annealed at 400vH in N2 for 2 h exhibited the optimal structure and PL property, and the grain size and the lattice constants of the film were calculated (41.6 nm, α = 3.253 Åand c = 5.210 Å). Moreover, a green emission around 495 nm was observed in the PL spectra owing to the oxygen vacancies located at the surface of ZnO grains. With increasing annealing temperature, both the amount of the grown ZnO and the specific surface area of the grains decrease, which jointly weaken the green emission.
  • CAO Zhangyi, SUN Zhuo, GUO Pingsheng, CHEN Yiwei
    Carbon nanotube (CNT) films were grown on nickel foil substrates by thermal chemical vapor deposition (CVD) with acetylene and hydrogen as the precursors. The morphology and structure of CNTs depending on the acetylene flow rate wer
  • DUAN Yuexin, SHI Feng, LIANG Zhiyong, ZHANG Zuoguang
    The curing properties and rheological behavior of a bismaleimide resin system were studied with differential scanning calorimetry (DSC) analysis and viscometer measurements, respectively. A dual-Arrhenius viscosity model and an engineering viscosity model were established to predict the resin rheological behavior of this resin system. The two viscosity models were compared. The results show that the two models are both suitable for predicting the viscosity in the mold filling stage of resin transfer molding (RTM). However, the engineering model provides a more accurate prediction of the viscosity near the gel point. The effectiveness of the engineering viscosity model is verified both in isothermal and nonisothermal conditions. The limitation of the engineering model is that it cannot be used to predict the viscosity after cross-linking of the curing system. The engineering viscosity models can be used to predict the processing windows of different processing parameters of the RTM process, which is critical for the simulation and the optimization of composite manufacturing processes.
  • WANG Cong, WANG Cong, HAN Enhou, HAN Enhou, XU Yongbo, XU Yongbo
    Uni-axial tensile deformation of LA41 magnesium alloy has been carried out and the Portevin-Le Chatelier (PLC) effect, also known as serrated flow or plastic instability, is observed. This kind of alloy exhibits negative strain rate sensitivity (SRS) at room temperature, that is, SRS is negative at the strain rate range from 3.33?10-4 to 6.66?10-3 s-1 at ambient temperature. Both ultimate stress (?b) and 0.2% proof stress (?0.2) decrease when strain rate (ε°) increases, whilst critical strain (εc) of serrated flow is found to rise with enhancing ε°. A new explanation for this unusual phenomenon is presented. The model of dynamic strain aging (DSA) is established through diffusion of solute atoms to mobile dislocations, which are temporarily arrested at obstacles. Such interaction renders the movement of mobile dislocations more difficult so as to necessitate the required force to overcome the obstacles.
  • ZHENG Feihu, ZHANG Yewen, GONG Bin, CHEN Lingyan, XU Jiaqiang, WANG Chuanshan
    In this study, space charge was introduced into polymethyl methacrylate (PMMA) samples by electron beam. The effect of the electron beam on the conductivity and the permittivity of the PMMA sample were investigated, and the breakdown mechanism of the samples during charge detrapping was also studied. The experimental results clearly show that not only space charge injection but also space charge detrapping can lead to the breakdown of the samples. The dynamics of injected charges in the radiated PMMA samples and the mechanism of the breakdown resulting from the rapid discharge are discussed.
  • SUN Guoyuan, CHEN Guang, CHEN Guoliang
    A Zr56.2Ti13.8Nb5.0Cu6.9Ni5.6Be12.5 bulk metallic glass composite with enhanced plasticity by in situ formed bcc β-Zr solid solution was prepared by water quenching. The ductile β phase with a volume fraction of about 30% possesses a developed dendritic morphology. The composite exhibits a pure plastic strain of 10.2% combined with a large elastic strain limit of 2% and a high ultimate strength of 1778 MPa upon room-temperature compression. Microscopic observation shows numbers of wave-like shear bands distributed on the surface of the compressive samples.