Papers by Author: Tetunori Kajita

Abstract: The presence of pores in ceramics is directly related to the chosen forming process. So, in the starch consolidation method, the ceramics show, after burning, pores with morphology similar to that presented by this organic material. On the other hand, the increase in solid load leads up to alterations in dispersion viscosity, increasing the thermal stresses during drying and sintering processes. In order to verify the solid percentage influence in ceramic final properties, samples were prepared with silicon carbide in different compositions using or not starch as binder agent and pore forming element. The characterization of the ceramic pieces was performed by superficial roughness measurements, porosity besides by optical and scanning electron microscopy. The results showed ceramics with SiC and starch presented physical and microscopic properties slightly higher in relation to those with only ceramic powder in their composition. The presence of organic material, agglomerated and foam during the forming were essential for the final properties of the studied samples.

Abstract: The densification of carbon fiber substrates by chemical vapor deposition (CVD) is a process quite used since the fifties, for manufacturing carbon reinforced with carbon fiber composites (CRCF). The process is based in thermal decomposition of a gas which contains carbon in its molecules and the resulting pyrolytic carbon is continually deposited onto de carbon fiber substrate. For this experiment the substrate material was made of carbon fiber felt. The deposition was performed by isothermal process at atmospheric pressure and at temperature of 1050 oC. Methane (CH4) gas was used as carbon bearer and nitrogen (N2) as the carrier gas. Different volumetric ratio of N2 and CH4 (N2:CH4) were used in order to get an optimum densification of the substrate. Optical and electron scanning microscopy and density measurements were used to characterize the impregnated material. An increase in ratio of N2 and CH4 increase the overall deposition for the same time interval.