Preprints of Annual Meeting of The Ceramic Society of Japan<br> Preprints of Fall Meeting of The Ceramic Society of Japan

Weight changes during high temperature oxidation of SiC in Ar-H₂O and Ar-H₂O-O₂ gas flows were less than those in dry Ar-O₂ gas flows. Oxidation of SiC was slower in case of flowing dry Ar-O₂ gas after heating SiC than in case of heating SiC after flowing dry Ar-O₂ gas. In dry Ar-O₂ gas flow, oxidation rate dropped suddenly. Evolution of CO₂ or SiO gas was detected at the initial stage of oxidation in dry Ar-O₂ gas flow, while less CO₂ or SiO gas evolution was detected after the sudden drop of oxidation rate. No marked change of CO₂ or SiO gas concentration was observed during oxidation of SiC in Ar-H₂O and Ar-H₂O-O₂ gas flows.

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The aqueous dispersion of Si3N4 powder with polyethylenimine as a dispersant was studied by zeta-potential, adsorption and viscosity measurements. The hydrolysis behavior of Si3N4 powder in the acidic and basic regions was evaluated by measuring suspension pH and zeta-potential as a function of stirring time. It is shown that in the absence of PEI, the Si3N4 suspensions at initial acidic pH show a continuous increase in the pH from the acidic pH ~ 4 to basic pH ~ 9.3 and a reversal of the zeta-potential sign from the higher positive value to the negative value, indicating that the strong hydrolysis occurs, but the presence of PEI suppresses this hydrolysis to some extent when the amount of PEI exceeds 0.5 dwb%. Though the adsorption of PEI significantly change the electrokinetic behavior of Si3N4 particles, resulting in the shift of the isoelectric point (IEP) from pH ~ 6 to pH 11, the dispersion of Si3N4 can not be predicted in terms of the zeta-potential curves. The stabilization of Si3N4 by PEI can be achieved in the basic region and even at the IEP, depending on the amount of PEI, but the stabilization can not be achieved in the acidic region despite higher positive zeta-potentials of > 40 mV. In addition, the initial ionization treatment of PEI has little effect on the dispersion of Si3N4. The mechanisms of the suppressed hydrolysis and stabilization of Si3N4 by PEI were discussed in detail.

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A planetary homogenizing was employed as a novel method to prepare Al2O3 slurries. The planetary-homogenized slurries showed very low viscosity, compared to the balled-milled slurries. Moreover, the viscosity of the planetary-homogenized slurries was stable for long time. The relative density of the green bodies prepared from the planetary-homogenized slurries was about 60 % or more and was independent of the slurry solid content. Linear shrinkage of the sintered bodies prepared from the planetary-homogenized slurries was very low and independent of the slurry solid content, as compared to that of the sintered bodies prepared from ball-milled slurries.

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We fabricated stripe micro-patterns from a few vol% solid loading suspension of SnO2 nano-powders by Micromolding in Capillary (MIMIC) method. We analyzed the dimensions of generated structures by SPM and SEM. The each constituent line was about 20 m in width and millimeter-scale in length, and their thickness was about 1 m, related to the solid loading of used suspensions. The result indicates that the MIMIC process enables us to fabricate thick and dense micro-scale patterns for cm scale area with reproducibility from suspensions of low solid loading.

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