Materials Science Forum Vols. 510-511

Abstract: The nanostructural and optical features of hydrogenated nanocrystalline silicon (nc-Si:H) thin films, which were prepared by plasma enhanced chemical vapor deposition (PECVD), were investigated as a function of deposition conditions. It was found that the crystallite size varied with the relative fraction of Si-H3 bonds in the films, [ ] eger n n n H Si H Si int 3 1 3 / ] [ = = ∑ − − , which was sensitively related with the flow rate of SiH4 reaction gas. The silicon nanocrystallites in the films enlarged from ~2.0 to ~8.0 nm in their size with increasing gas flow rate, while the PL emission energy varied from 2.5 to 1.8 eV; the relative fractions of the Si-H3, Si-H2, and Si-H bonds in the amorphous matrix were also varied sensitively with the SiH4 flow rate. A model for the nanostructure of the nc-Si:H films was suggested to discribe the variations in the size and chemical bonds of the nanocrystallites as well as the amorphous matrix depending on the deposition conditions.

Abstract: Tension and compression fatigue property was investigated for lotus-type porous copper possessing cylindrical pores aligned in one direction. The cyclic stress was applied in the direction parallel and perpendicular to the longitudinal axis of the pores. It was found that the fatigue strength at finite life of lotus-type porous copper is lower than that of nonporous copper, and the strength in the direction parallel to the longitudinal axis of the pores is higher than that in the perpendicular direction.

Abstract: Based on the mechanism of high antibacterial performance of copper, an antibacterial stainless steel bearing1.5wt% copper was fabricated. Processing of vacuum arc melting, hot rolling, and a series of heat treatments were applied to prepare the specimens. The relationships among the microstructure, mechanical properties, and the regime of treatment were investigated. Furthermore, the antibacterial properties of the specimens were assessed. The results showed that fine and uniformed dispersion Cu-rich phase precipitated and accumulated along the grain boundaries of the matrix during the processing of aging, and a marked variation in tensile strength and yield strength was evaluated. In addition, antibacterial result showed that the as-received material has the ability to kill Staphylococcus and coliform bacteria in the excess of 99.99%, respectively.

Abstract: The bioactivity of Ti6Al4V induced by SSPB (supersonic particles bombarding) and alkali treatment was investigated in this work. More coarse surfaces were formed by SSPB and alkali treatment, which led to better bioactivity than that by only alkali treatment. Apatite began to appear on the surface of specimen only after 1 day of immersion in 1.5 SBF. As time passed, they gradually covered the whole surfaces. After 7 days of soaking in vitro, apatite formed and covered all the surfaces of the titanium alloys, and they packed very densely and uniformly. EDS and XRD results proved all the new-formed phases were composed of a carbonate containing hydroxyapatite with small crystallites and defective structure. As a result, SSPB treatment might be an effective way to enhance the bioactivity of titanium alloys for implantation.

Abstract: The compatibility efficiency on different compatibilizer for nano-hydroxyapatite (n-HA) reinforced polyamide 66 (PA66) and high density polyethylene (HDPE) blends at a composition of 40/42/18 as functionalized biomaterial was investigated by mechanical properties testing and scanning electron microscopy (SEM). The results showed that mechanical properties of compatibilized blends were much improved by the compatibilizers of maleic anhydride grafted polyethylene (PE-g-MAH) and ethylene/methacrylic acid ionomer-sodium ion (ION) compared with the uncompatibilized blends. Blends had peak mechanical values of different compatibilizer. Both PE-g and ION formed adhesion during melt mixing and stabilized the morphology and significantly reduced the size of dispersed PE phase. PE-g gave the blends with PE spheres ranging from 1 to 4µm and ION with well-dispersed spheres with an average diameter of 1µm. The more enlarged interphase of the blends containing ION reduced the lower interfacial energy to increase the miscibiliy of the blends. Consequently, ION had better contribution to rigidity properties than PE-g for n-HA/PA/PE blends.

Abstract: In this paper, the microwave absorption behaviors of zinc oxide whisker were studied. The morphological structure of zinc oxide whisker was observed through scanning electron microscope. The effect of the structure of zinc oxide whisker on the microwave absorption, such as length-diameter ratio, cross-section appearance, and doping was analyzed. The result shows that the more irregular the cross section of the needle of zinc oxide whisker is, the more prominent the microwave absorption appears. The less the length-diameter ratio of the needle of zinc oxide whisker is, the more obvious the microwave absorption of zinc oxide whisker becomes. The zinc oxide whisker, which had inlet ion, such as Al3+, Fe3+ , etc., in its crystal lattice has a better microwave absorption efficiency than the pure zinc oxide whisker. The further analysis found that electric conductive network can be formed easily because of the zinc oxide whisker, and the coating had the porous structure. When microwave reaches the coating of zinc oxide whisker, the polarization of zinc oxide whisker was resulted and the electromagnetic energy lost. Firstly, electric current was transmitted through the electric conductive network and the energy transformed to heat. Secondly, tips’ phenomenon has been observed, which lead to the energy lost. Finally, the microwave energy was lost because of the tunnel effect, which will bring about leakage current. Based on the three reasons above, microwave energy was absorbed by the coating containing the zinc oxide whisker.

Abstract: In this study, single phase aragonite PCC was synthesized by the solution process using Ca(OH)2 slurry and Na2CO3 solution as the main reactants. To begin with, the formation behavior of PCC polymorphs following changes in supersaturation was investigated, and the optimum synthetic condition of single-phase aragonite PCC was clarified after the role of NaOH in the reaction system was reviewed. In the results, it was considered that lower supersaturation was necessary to obtain a single phase aragonite; and, since the solubility of Ca(OH)2 was decreased with the addition of NaOH by a common ion effect, it is possible to perform a experiment at a lower Ca2+ concentration. In conclusion, in the case of the reaction of the 2.5M NaOH solution, single phase aragonite was obtained. Furthermore, NaOH solution was produced as a by-product in the solution process by reacting Ca(OH)2 slurry with Na2CO3. Thus, recycling of the NaOH solution was attempted in order to clear the environmental issue. It is difficult to recycle directly since the NaOH solution was diluted during the experiment. The optimum condition was investigated by control of experimental factors such as the concentration of Ca(OH)2, Na2CO3 and NaOH, and the reaction temperature, after which the NaOH solution was recycled without re-treatment. The formation characteristics of aragonite PCC, such as formation yield, particle morphology and aspect ratio, were investigated.

Abstract: The objective of this study is to synthesize the single phase aragonite precipitated calcium carbonate by the carbonation process in the Ca(OH)2-MgCl2-CO2 system. Many researchers reported the influence of Mg2+ ion on the synthetic properties. The inhibition of calcite nucleation and crystal growth, distortion of calcite lattice, and change of surface electrification were investigated. Variety of particle size and aspect ratio were observed according to changes in the concentration of Ca(OH)2 slurry, temperature, and CO2 gas flow rate. The nucleation rate increased when decreasing the temperature and increasing the CO2 gas flow rate. Particle size and aspect ratio increased at high temperature, low CO2 gas flow rate, and high concentration of Ca(OH)2 slurry, however small-sized aragonite was obtained at low temperature.

Abstract: The results obtained in this study confirm that the hydration of C4AF (C: CaO, A: Al2O3, F: F2O3) is retarded by the presence of silicate ions in the solution. In practical terms, C4AF has a low hydraulic reactivity in solution containing silicate ions. The silicate ions in the solution are adsorbed on the surface of the C4AF particles, and they form a silica layer on the surface. From the results of the calculation with the DX-Xα method, it is also believed that silicate ions adsorbed on the surface are very stable, and that there are strong interactions between silicate ions and the surface of C4AF.

Abstract: ZnO thin films were synthesized by metalorganic chemical vapor deposition on Al2O3 (0001) substrates particularly using isopropyl alcohol for oxygen precursor. Change in microstructure was investigated depending on the growth temperature and the O/Zn precursor ratio. Under an optimized condition, ZnO thin films having a very smooth surface and dense cross-sectional microstructure were obtained while possessing epitaxial crystalline alignment. However, the photoluminescent spectrum lacks the band-edge emission.