Sep 2007, Volume 1 Issue 3

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  • HU Kai, YANG Xianjin, CAI Yanli, CUI Zhenduo, WEI Qiang
    A hydroxyapatite (HA)/collagen (COL) composite coating on NiTi shape memory alloy (SMA) was prepared by electrochemical deposition (ELD) in modified simulated body fluid (MSBF). To draw comparisons of physical characteristics and bioactivity of the composite coating, the HA/COL composite coating was also prepared by chemically biomimetic growth (BG) and the ELD coating was re-soaked in MSBF again for further biomimetic growth (called EBG method in this paper). It was indicated that the c-axis of HA crystals was oriented parallel to the longitudinal direction of the COL fibril in BG and EBG coating, which could not found in ELD coating. The EBG method could induce a denser, thicker and better crystallized HA/COL coating. The cell culture test indicated that the BG coating presented better cell biocompatibility.
  • BAI Lun, XU Jianmei, SUN Qilong, DI Chuanxia, ZUO Baoqi, GUAN Guoping, WU Zhenyu
    In order to obtain porous silk fibroin films (PSFFs) fit for the repair of different tissues and organs and design the configuration of the PSFFs more rationally, a model of the oxygen diffusing system of the capillary was built, and also the equations of the model were solved. Moreover, the relationships between the distribution of the oxygen concentration and each affecting factors were discussed, a method was developed to estimate the density of the capillaries in the tissue, and hereby discussed the characteristics of the oxygen diffusion in the tissues around the open capillaries.
  • KONG Xiangdong, QIU Min, XIE Ruisheng, SUN Xiaodan
    In this paper, a novel method was developed to prepare mineralized fibroin fiber. We used fibroin gel to control the biomineralization of calcium phosphate and obtained one kind of mineralized fibroin fiber with the length of 1 2 mm. It has the potential to be used to enhance the strength of tissue engineering scaffold. Scanning electron microscopy (SEM) results showed that hydroxyapatite (HA) was mainly deposited on the surface of mineralized fiber. Fourier transform infrared spectroscopy (FTIR) results displayed the red shifts of absorption bands of amide II and amide III (9 and 5 cm-1, respectively), which were related to the strong chemical interaction between HA and fibroin. It was also found that HA was at low content (12.5%) and the ability of gelled fibroin to induce mineralization decreased greatly because of the formation of ?-structures in gelled fibroin molecules, which showed the importance of molecular structure in the regulation of the biomineralization process.
  • WU Qisheng, CHENG Futao, WEI Wuji
    In this study, polymethylmethacrylate (PMMA) bone cement (BC) was modified with ultra-fine glass fibers (UFGF) and nano-hydroxapatite (nano-HAP) synthesized by hydrothermal method. The results show that when the contents of both UFGF and nano-HAP powders are about 5%, the ultimate tensile strength (UTS), ultimate impact toughness (UIT), tensile strain (TS), and elastic modulus (EM) have been promoted a lot. The interface bond was improved by silicane treatment. Pre-grinding mixture of PMMA, UFGF, and nano-HAP can largely improve the mechanical property of PMMA. The PMMA modified with UFGF and HAP has better bioactivity than that modified with pure UFGF when they share the same content. Nano-HAP powder and modified PMMA were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR).
  • QI Yumin, CUI Chunxiang, LIU Shuangjin, WANG Huifen, HE Yun
    A potassium titanate biological thin film/titanium alloy biological composite was fabricated by way of bionic chemistry. The biocompatibility in vitro of Ti-15Mo-3Nb and the potassium titanate biological thin film/titanium alloy was studied using simulated body fluid cultivation, kinetic clotting of blood and osteoblast cell cultivation experiments in vitro. By comparing the biological properties of both materials, the following conclusions can be obtained: (1) The deposition of a calcium phosphate layer was not found on the surface of Ti-15Mo-3Nb, so it was bioinert. Because the network of potassium titanate biological thin film could induce the deposition of a calcium phosphate layer, this showed that it had excellent bioactivity. (2) According to the values of kinetic clotting, the blood coagulation time of the potassium titanate biological thin film was more than that of Ti-15Mo-3Nb. It was obvious that the potassium titanate biological thin film possessed good hemocompatibility. (3) The cell compatibility of both materials was very good. However, the growth trend and multiplication of osteoblast cells on the surface of potassium titanate biological thin film was better, which made for the concrescence of wounds during the earlier period. As a result, the potassium titanate biological thin film/titanium alloy showed better biocompatibility and bioactivity.
  • REN Yongjuan, SUN Xiaodan, CUI Fuzhai, KONG Xiangdong
    In the present study, the effects of pH and initial Ca2+-H2PO4- (Ca-P) concentration on fibroin mineralization were studied. The crystal growth of calcium phosphates was regulated by regenerated silk fibroin for 8 h (at pH 4.0, 7.0 and 10.0, respectively). Meanwhile, different concentrations of Ca2+ were employed at a certain pH value, keeping the initial Ca-P molar ratio constant at 1.67, i.e., the stoichiometry of hydroxyapatite [Ca10(PO4)6(OH)2, HAP]. The products were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The results demonstrated that, compared to pH 4.0 and 10.0, pH 7.0 promoted the transformation of brushite (CaHPO4°2H2O, DCPD) to HAP. In the composites of mineralized fibroin, DCPD is the main inorganic phase at both relatively low and high pH, while HAP is the main inorganic phase at pH 7.0. Additionally, the initial Ca-P concentration does not affect the kind of inorganic phase in the synthesized mineralized fibroin, but induce to different contents of inorganic mineral and different morphology of DCPD at pH 4.0 and pH 10.0.
  • LIU Shuxia, HE Junhui
    The structure of hair was replicated via a solgel process using human hair as a template. When using silicate and tetraethoxysilane (TEOS) as the precursor, the cell structure of the hair cuticle was not well replicated. When using Ti(OnBu)4 as the precursor, however, titania microtubes were obtained, with nanopores in their walls and nanoporous platelets on their outer surfaces, which were derived from cuticle cells on the hair surfaces. The nanopores in the microtubes acted as an effective nanoreactor for in situ synthesis of Au nanoparticles. The microchannels, nanopores and noble metal nanoparticles may provide a unique combination that would be attractive in applications such as catalysis, adsorption, and separation.
  • GAO Jinqiang, WU Chuansong, LIU Xizhang, XIA Dianxiu
    A low-cost visual sensing system is developed to realize weld seam tracking in gas metal arc welding (GMAW). The system consists of a commercial CCD camera, narrow-band composite filter lens, an image capturing card, an industrial computer, a welding control unit, a GMAW power source, and a worktable. Images of root gap and its vicinity are captured in the GMAW welding process by the system. The captured images are processed by an algorithm on the basis of the analysis of gray characteristics of the root gap to get the offsetting information between torch and root gap centerline. The offsetting information is then used to realize weld seam tracking in the GMAW process. Welding seam tracking experiment is conducted by a simple proportional (P) controller. The results show that tracking error is basically less than ±0.5 mm.
  • ZHU Guohui, S. V. Subramanian
    High Mn is added in line pipe steels to strengthen them. Also, Mn lowers the phase transformation temperature, which is an advantage because it lowers the rolling temperature for grain size control. However, Mn retards the kinetics of precipitation of NbC in thermo-mechanical processing in Nb microalloying steels. In high-grade line pipe steels, the control of strain accumulation behavior is the key to the control of grain size. Strain accumulation can only be obtained when static recrystallization between passes could be suppressed. The effect of NbC precipitates on suppressing recrystallization has been widely investigated, mostly focusing on the Zener pinning of NbC on grain boundaries. However, it is applicable in large strain and long inter-pass time. In short inter-pass time, such as strip mill rolling, recrystallization behavior is controlled by the complicated interaction of precipitation with recovery and recrystallization. In this paper, the effect of Mn on strain accumulation during multi-pass strip mill rolling based on the interaction of precipitates with the activation energy of grain boundary migration and recovery, and the thermodynamics and kinetics of recrystallization are discussed systematically.
  • ZHOU Jicheng, YAN Qinyun, JIANG Qinming, YANG Dan, HUANG Yun
    The thermal shock experiment of Au-Al bonding has been carried out. The mechanical characteristics, structure morphology and electrical characteristics degradation mechanism have also been researched. No cracks were observed in the bonding interface, and the bonding joints also showed good mechanical characteristics with pull stress of 3.0 to 12.0 g. Due to high temperature, the Au-Al intermetallic compound Au5Al2 with high resistibility was formed, which ultimately led to electrical failure. For the samples that were fabricated on the basis of the present technique, the bonding reliability has been evaluated. It has been found that the lifespan rule obeys the Weibull distribution, and at a high temperature of 150?C under 95% confidence level, the estimated results are η = 547 h, m = 3.83. In a room temperature environment, the Au-Al bonding samples  lifespan has also been predicted on the basis of the rule of reliability evaluation. The result shows that the lifespan is about 20 years, while the reliability degree is 90%.
  • MIAO Chunyan, L? Gang, YAO Youwei, TANG Guoyi, WENG Duan
    The shape-stabilized phase change materials (PCMs) composed of paraffin wax and silica were prepared in O/W emulsion with cetyl trimethylamine bromide as emulsifier and n-pentanol as assist emulsifier. The paraffin wax (with melting temperature of 29vH, crystallizing temperature of 26vH and latent heat of 142 J/g) served as latent heat storage material and the silica as supporting material, which prevented the leakage of the melted paraffin wax. Silica supporting material was formed in situ via hydrolysis and condensation from low-cost sodium silicate solution with chlorhydric acid and ammonium bicarbonate as neutralizing agent. The thermogravimetry (TG) curves show that the composite has a thermal stability superior to that of paraffin wax and that the content of paraffin wax in the composite is 65wt%. The maximum latent heat and its relevant melting point of composite are 95 J/g and 30vH, respectively.
  • ZHANG Long, CUI Zhenduo, WEI Qiang, YANG Xianjin
    This paper studied Ti-HA composites with low volume fractions of hydroxyapatite (HA), which are usually used as internal layers of functionally graded materials to withstand heavy load. Optical microscopy (OM), X-ray diffractometry (XRD), and scanning electron microscopy (SEM) were used to analyze the microstructure of cold-pressed composites after sintering at 1,100vH. Quantitative analysis of volume fractions and mean particle volumes of the ceramic phase was adopted to further discuss the reaction between Ti and HA. CaO and TixPy were produced in the Ti-HA reaction. With the increase of HA volume fraction, the Ti-HA reaction could be divided into three stages including stable initiation, stimulating term and re-stabilization according to the quantitative characteristics of the ceramic phase.
  • LIU Yong, SHEN Hui, DENG Youjun
    The absorption coefficients of N719 or N3 dyes at the longer wavelength region (>600 nm) are not enough to catch photons efficiently, but the solar spectrum has a large photon flux in the wavelength region between 500 and 1,000 nm, so it is desirable to enhance the absorption of light by the dye-sensitized solar cells (DSSC) to achieve higher efficiencies. To solve this problem, an improved structure of DSSC for enhancing light absorption is introduced in this paper, and I-V characteristics of DSSC are measured to illustrate the enhancement of the light absorption and efficiency. As a result, the improved DSSC exhibits higher light absorption and solar-to-electric conversion efficiency than traditional DSSC.
  • ZHANG Yinhong, HE Yunqiu
    A nano-scaled graphite oxide (GO) was prepared with a micro-layer structure for intercalation. Graphite-intercalated SnO2 was obtained at temperatures lower than 100vH. The morphology, microstructure, crystalline phases and thermal property of this intercalative composite were studied by atomic force microscopy (AFM), field-emission scanning electron microscopy (FE-SEM), X-ray diffractometry (XRD) and differential scanning calorimetrythermogravimetry (DSC-TG) doped with a proper amount of graphite-intercalated composites (GITs), GIT-SnO2 composite was obtained after heat treatment. This combined gas sensor reveals low resistance and high sensitivity to butane between 200vH and 300vH.
  • NI Jie, LI Zhengcao, ZHANG Zhengjun
    In this paper, we report a simple approach to synthesize silicon carbide (SiC) nanowires by solid phase source chemical vapor deposition (CVD) at relatively low temperatures. 3C-SiC nanowires covered by an amorphous shell were obtained on a thin film which was first deposited on silicon substrates, and the nanowires are 20–80 nm in diameter and several μm in length, with a growth direction of [200]. The growth of the nanowires agrees well on vapor-liquid-solid (VLS) process and the film deposited on the substrates plays an important role in the formation of nanowires.
  • LI Bin, ZHANG Changrui, HU Haifeng, QI Gongjin
    Liquid carbosilane was synthesized and analyzed by infrared (IR) and H-NMR (nuclear magnetic resonance) spectroscopy. Silicon carbide (SiC) powders were prepared by chemical vapor deposition (CVD) at 850ºC and 900ºC from liquid carbosilanes. The product powders were characterized by IR spectroscopy, X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Results show that liquid carbosilane synthesized was the mixture of several oligomers that had a Si-C backbone. The powders prepared at 850ºC contain some organic segments, and those prepared at 900ºC are pure nanosized SiC powders, which are partly crystallized, the size of which is about 50–70 nm.
  • REN Xin, HUANG Xinmin, ZHANG Huhai, HE Meiqing
    Cu nanotubes and nanowires were fabricated by electroless deposition using porous aluminum oxide membrane as template in coating bath at room temperature. The images of Cu nanotubes and nanowires are obtained by transmission electron microscopy (TEM). X-ray diffractometry (XRD) is employed to study the morphology. Results indicate that the success of fabrication depends on the reducing process of pore treatment. The outer diameter of Cu nanotubes can be controlled by adjusting the aperture of anodic alumina membranes (AAM) template, and the thickness of the tube wall can be controlled by deposition time. The morphology of Cu nanotubes and nanowires are polycrystalline.
  • DENG Xiangyun, LI Dejun, WANG Xiaohui, LI Longtu
    The density of states and band structure of 20 nm barium titanate (BaTiO3, BT) ceramics are investigated by first-principles calculation. The full potential linearized augmented plane wave (FLAPW) method is used and the exchange correlation effects are treated by the generalized gradient approximation (GGA). The results show that there is substantial hybridization between the Ti 3d and O 2p states in 20 nm BT ceramics and the interaction between barium and oxygen is typically ionic.
  • DENG Xiangyun, LI Dejun, WANG Xiaohui, LI Longtu
    Dense nanocrystalline BaTiO3 (BT) ceramics with 50 nm average grain size obtained by spark plasma sintering were investigated. The dielectric data showed a ferro para phase transition with a maximum permittivity of 1,602 at 120ºC and at 1 kHz. The polarization reversal characteristics were measured, and the typical piezoelectric hysteresis loop was recorded. The asymmetry of permanent polarization and coercive field in polarization-electric field curves were obtained and attributed to the existence of an internal electric field. The present results provide experimental evidence, indicating that if a critical grain size exists for ferroelectricity, then it is less than 50 nm for polycrystalline BT ceramics.
  • LIU Hong, PU Zhaohui, XIAO Dingquan, ZHU Jianguo, ZHU Xiaohong
    Lanthanum-doped lead titanate [(Pb0.9,La0.1)TiO3, PLT10] ferroelectric thin films were grown on Si(100) and Pt/Ti/SiO2/Si(100) substrates by radio frequency (RF) magnetron sputtering. The crystalline properties of PLT10 films were studied by X-ray diffractometry (XRD). Photolithographic technique was applied to fabricate the interdigital electrodes on PLT10 thin films on Si(100) substrates. The dielectric properties of PLT10 thin films with different electrodes were measured. At room temperature and 1 kHz testing frequency, the dielectric constant of the PLT10 thin film with interdigital electrodes is 386. The dielectric constant of the PLT10 thin film fabricated under the same technological conditions with parallel plate electrodes structure is 365, while the dielectric constant and loss of the PLT10 thin film with interdigital electrodes are decreased faster than those of the film with parallel plate electrodes with increasing frequency. This is because more influences of interface state are introduced due to the interdigital electrode configuration.
  • MA Hongyan, QIN Zuolu, TONG Zhangfa, QIU Shuheng, ZHANG Beili, LEE I-S
    The prismatic layer is obviously different from the parallel layer in seawater-cultured pearls. X-ray diffraction (XRD), optical microscopy (OM) and micro-infrared (IR) spectroscopy have been applied to characterize the crystallized layers of high- and low-quality seawater-cultured pearls produced in South China. The result shows that the prismatic layer is not only composed of calcite as reported in previous researches. Three types of prisms were found in seawater-cultured pearls: calcite prism, aragonite prism and calcite and aragonite prism. Therefore, we have a new understanding of the biomineralization of the prismatic layer in seawater-cultured pearls. The result makes us review the traditional viewpoint that the increased content of aragonite improves the quality of pearls. We discovered that some seawater prismatic pearls almost completely composed of aragonite have the worst quality. We thought that the thickness and the spatial distribution of prisms are the main factors that can affect the quality of seawater-cultured pearls.