Synthesis, Characterization, and Fabrication of Silicon Carbide Structural Ceramics

摘要

Five processes of SiC powder synthesis were investigated: chemical vapor decomposition, high-temperature rotary-furnace reactions, gel synthesis of precursors followed by carbothermic reduction, pyrolysis of polymeric precursors, and the Acheson process. Exploratory powder synthesis experiments were conducted on the gel process involving gelation of colloidal silica and petroleum pitch in toluene, or polymerization of methyltrimethoxysilane and resin in alcohol. The beta -SiC powders synthesized by these gel processes have specific surface areas (SSA) exceeding 20 m exp 2 /g and round or polyhedral particle shape. These materials have excellent pressure sintering capability. SiC powder made by the rotary-furnace process consists of fine beta -SiC particles with a round morphology and about 10 m exp 2 /g SSA. The rotary-furnace SiC powders with BN dopants were hot pressed to 95% dense. A commercial polycarbosilane prepared from dechlorination and polymerization reactions of vinyl and chloromethyl silanes was pyrolyzed and hot pressed without BN to 79% dense. In terms of pressureless sintering, the best result (96+% dense) is obtained with the Starck-SiC powder by doping with 0.8 wt % B and 2 wt % phenolic resin and sintering under argon in a graphite furnace for 2 h at 2050 exp 0 C. An SiC-TiC-BN composite was hot pressed to 97+% dense with an indentation toughness nearly double that of sintered beta -SiC. 10 figures, 6 tables. (ERA citation 08:010286)