Materials Science Forum Vols. 510-511

Abstract: Fe/SiO2 nanocomposite powders were synthesized by the chemical vapor condensation(CVC) process. Phase and microstructures of the as-prepared powders were investigated with CVC experimental parameters by XRD, TEM and VSM. The analysis of XRD patterns revealed that the Fe/SiO2 powders could be produced above 700
. With increasing reaction temperature, the XRD peaks became clearer. The size of powders was about 50nm at 1100oC. The Fe/SiO2 powders showed an intricate long-stand structure attributed to their magnetic characteristics. TEM results revealed that the Fe powders were covered by SiO2 layer fully or partially depending on the experimental condition. The saturation magnetization and the coercive force of the as-sytheised powders were investigated with the decomposition temperature.

Abstract: Nano-scale SiC-based ceramic patterns on Si substrates were fabricated via imprint lithography technique by using viscous polyvinylsilane as a ceramic precursor and economic nano-scale master such as CD, followed by pyrolysis at 800oC under nitrogen atmosphere. The thickness of residual layers was controlled by varying the spin-coating conditions (solution concentration, spinning speed) and the patterning conditions (molding pressure). In addition, for the effective removal of the remaining residual layer, the etching kinetics of both polymeric and ceramic patterns was also comparatively studied by Ar or reactive ion etching process.

Abstract: Silver-containing porous frameworks have been extensively used in catalysis, electrochemistry, for heat dissipation and biofiltration. In this study, porous silver sponge was prepared by using a sacrificial macroporous carbon template. Aqueous AgNO3 was infiltrated into the carbon template and reduced to Ag by borohydride reduction reaction, followed by burning of the sacrificial template in air at 500~650°C. The products were characterized by SEM, XRD, and N2 adsorption-desorption isotherms. The Ag sponge exhibited a BET surface area of 12 m2/g.

Abstract: Microelectromechanical systems (MEMS) including microchemical devices have been widely concerned, in particular, when made of an extremely stable ceramic material for their use at harsh conditions. SiCBN preceramic polymer was derived from borazine (B3N3H6) modified allylhydridopolycarbosilane (AHPCS) via hydroboration of allyl groups with B-H groups at 0oC for 24 h by following the standard Schenk technique. The extent of polymer-to-ceramic conversion with an ultimate ceramic yield of 92 wt% was investigated by simultaneous TGA, 1H, 13C-NMR, IR, and XRD measurements. The polymer-derived SiCBN ceramic remained as an amorphous solid up to 1400oC. The ceramic product obtained after pyrolysis at 1000-1400oC exhibited excellent oxidation resistance in air. In addition, ceramic microstructures were fabricated by employing soft lithographic technique.

Abstract: Alumina ceramics as well as zirconia ceramics have been used to manufacture hip replacement components since the 1990’s. These materials have been used for the ceramic balls and cups in the replacements for the following reasons: in the case of alumina for its excellent wear behavior; and in the case of zirconia, for its good wear behavior but with greater fracture toughness than alumina. Nevertheless, since ceramics are brittle, the design of the components must consider ways to avoid detrimental stress concentrations. In this study the stress concentration on the rim of the ceramic cup is inspected by means of a two-dimensional axis symmetric finite element model. This model simulates contact between the components to obtain the stresses that are transferred from the ball to the cup. Different geometries of the cup’s edge are simulated to evaluate the incidence of the geometry over the stress pattern. Although this model concentrates on the contact between the ball and the cup, the loading is made from the stem to the ball, which means that the load is transferred from the stem to the ball and then to the cup. This approach may offer a more realistic output. The data from this study may be useful for hip replacement designers as well as for surgeons because it shows a direct relationship between the stress patterns and the geometrical parameters of the design.

Abstract: ZnO-TiO2 nanoparticles were synthesized by a reverse micelle and sol-gel process. The average particle size of the colloid was below 30 nm and well dispersed in the solution. ZnOTiO2 composite membranes were fabricated by using the dip-coating method on a porous alumina support. ZnO-TiO2 composite membranes showed a crack-free microstructure and narrow particle size distribution even after the heat treatment up to 600°C. The average particle size of the membrane was 30-40nm, and the pore size of ZnO-TiO2 composite membrane was below 10 nm.

Abstract: ZnO-SiO2 nanoparticles were synthesized using a reverse micelle technique combined with metal alkoxide hydrolysis and condensation. The size of the particles was controlled by manipulating the relative rates of the hydrolysis and condensation reaction of tetraethyl orthosilicate (TEOS) within the micro-emulsion. The average size of synthesized ZnO-SiO2 nanoparticles was in the range of 20-40 nm. The effects of synthesis parameters such as the molar ratio of water to precursor and the molar ratio of water to surfactant are discussed.

Abstract: The aim of this study is to clarify the alpha-case formation mechanisms for the economic net-shape forming of Ti and Ti alloys. The α-case formation reaction between Ti and Al2O3 mold was examined in a plasma arc melting furnace. The reaction products were characterized by using an electron probe micro-analyzer and transmission electron microscopy. The α-case generation between Ti and Al2O3 mold could not be explained by the conventional α-case formation mechanism, which is known to be formed by the interstitials, especially oxygen dissolved from mold materials. However, on the basis of our experimental results and thermodynamic consideration, it was confirmed that the α-case is formed not only by interstitial oxygen atoms but also by substitutional metal atoms dissolved from mold materials. Based on the α-case formation mechanism, α-case free net-shape forming of Ti and Ti alloys could be possible for biomedical applications.

Abstract: The purpose of this study is to develop a new system to control effective discharge of active substances such as agricultural chemicals. To synthesize a naturally dissolvable polymer; ε-caprolactone and diglycolide were copolymerized with ethylene glycol as an initiator to produce macrodiol. As macrodiol has hydroxyl groups in both ends, they are modified with methacryloyl chloride for photochemical networking. After standard macromonomer produced by this procedure was physically mixed with methylene blue, it was networked with ultra-violet rays to be filmed. This film is naturally dissolvable and hydrolytic. As a result of hydrolytic test with a crosslinked structure of 10 % methylene blue, it decreased by 9 % for seven weeks in 37 °C phosphate buffer solution (pH = 7). Thus, we verified that active substance can be discharged from a crosslinked structure for a long time at a constant rate under room temperature.