During oxidation process, several type of defects are formed on the surface of the silicon crystal which was damaged mechanically before oxidation. As the size of abrasive particle increases, multiple dislocation loops are produced favorably over oxidation-induced stacking faults, which are dominantly produced when ground with finer abrasive particle. These defects are not related with the crystal growth process like Czochralski or directional solidification. During directional solidification process, twins and stacking faults are the two major defects observed in the bulk of the silicon crystal. On the other hand, slip dislocations produced by the thermal stress are not observed. Thus, not only in single crystalline silicon crystal but also in multi-crystalline silicon, extrinsic gettering process with programmed production of surface defects might be highly applicable to silicon wafers for purification.
We prepared orthorhombic LiMnO2 by emulsion drying method. The thermo-gravimetric measurement and X-ray diffraction studies indicated that the orthorhombic LiMnO2 phase was formed above 800oC by oxygen evaporation process from LiMn2O4 and Li2MnO3. In this process, we could control the ordering of LiMnO2 with heating rate. It was observed that electrochemical properties depended on the ordering of this material; the ordered one exhibited good capacity retention, whereas the disordered one suffered capacity fading upon cycling, especially in the 3 V region. Transmission electron microscopic (TEM) study showed that this difference is related with difference in the stress relieving effects in the samples.
Semiconductor carbon nanotube was grown on oxided silicon wafer with atmosphere pressure chemical vapor deposition (APCVD) method and investigated the electrical property after thermal oxidation at 300oC in air. The electrical property was measured at room temperature in air after thermal oxidation at 300oC for various times in air. Semiconductor carbon nanotube was steadily changed to metallic carbon nanotube as increasing of thermal oxidation times at 300oC in air. Some removed area of carbon nanotube surface was shown with transmission electron microscopy (TEM) after thermal oxidation for 6 hours at 300oC in air.
In this study a new growing method of silicon nitride whiskers in the inside of large pores made intentionally during the sintering was conducted. Pore size, pore vol%, and nitrogen pressure were used as experimental variables. Silicon nitride whiskers were well grown in the inside of pores with low pore vol% range from 14 to 27 but not grown with high pore vol% such as 39 and 50. On the other hand, pore size and nitrogen pressure did not have any influence on the whisker growth. Therefore the most important factor to grow silicon nitride whisker in the inside of large pores during sintering was to make pores isolated or closed.
The electrical arc furnace (EAF) classified as a special waste contains many flux components producing melts during a sintering process, so it decreases the sintering temperature and improves the mechanical properties of specimens. Increasing dust content in a clay-dust system brick, however, may cause the fraction defective higher due to the excessive liquid produced. To control the liquid behavior produced during sintering process for the clay-dust system specimens, the Al2O3 was added and the physical properties were analyzed. The microstructure for the clay-dust system body sintered with Al2O3 became homogeneous and the overall size of pores decreased. Adding Al2O3 to clay-dust system body increased the mechanical properties and the temperature of maximum strength increased as much as 50oC, and the apparent density increased and the absorption decreased. The mullite (3Al2O3?SiO2) was produced during sintering process by reaction of Al2O3 and SiO2 which could participate to liquid-producing-process and the viscosity of melts increased which was proved by measuring a critical viscosity temperature (Tcv) therefore, the refractoriness of specimens were improved to lower the fraction defective.
Silicon boride (SiB6) is very promising for use as thermoelectric materials at high temperature because of its high melting point and relatively large Seebeck coefficient. In the present work, spark plasma sintering (SPS) was applied for preparing dense SiB6 ceramics, and their thermoelectric properties were investigated, together with their microstructural evaluation. The SPS process was found to be effective in densifying a SiB6 ceramic, typically 99 % of the theoretical density at low temperature of 1500oC. In comparison with SiB6 specimen prepared by hot-pressing, the SPS-processed specimen exhibited the significantly improved Seebeck coefficient, resulting in the higher power factor.
Commercial hydroxyapatite (HA) powders were calcined at the temperature range of 1000~1350oC in air, for 2 h, and the calcined powders were immersed in simulated body fluid (SBF) of pH 7.4 at 37oC for 3 or 7 days. Thermal decomposition and their related dissolution behaviors of hydroxyapatite were investigated by XRD, FT-IR, and TEM. At the temperature of 1200oC, HA gradually releases its OH- ions and transforms to OHAP((oxyhydroxyapatite, (Ca10(PO4)6Ox(OH)2 - 2x)). HA thermally decomposes to a-TCP (a-tricalcium phosphate) and TTCP (tetracalcium phosphate) phase at 1350oC. It was found that the surface dissolution of the hydroxyapatite powders was accelerated by non-stoichiometric composition and decomposed to a-TCP and TTCP.
The layered structure of organic-inorganic perovskite hybrids, (CnH2n + 1NH3)2CuCl4 (n = 6, 8, 10, 12) have synthesized. In (CnH2n + 1NH3)2CuCl4 compounds, the long-chain protonated alkylammonium ions as tilted bilayer type are inserted into perovskite-type layers of corner sharing CuCl6 octahedron. Three solid phases have been characterized in the perovskite layered compound (CnH2n + 1NH3)2CuCl4 using HT-XRD and DSC. The (CnH2n + 1NH3)2CuCl4 compounds shows solid-solid phase transitions with stepwise increasing of the layer distance. Three different structures are explained by the conformational change of the long-chain protonated alkylammonium ions.