Simultaneous Carbonization and Ceramic Coating of Carbon Fibers

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Silica film was deposited on carbon fiber precursors (CFPs) by oxidation of tetraethylorthosilicate (TEOS) in a low-temperature plasma CVD reactor. When the contact between CFPs and plasma gas was assured, the surface of CFPs was covered with thin silica film homogeneously. Then the CFPs were carbonized at 1000ﾟC in argon atmosphere and silica coated carbon fibers were formed. By the subsequent heat treatment at 1500ﾟC,silica film was reduced to silicon carbide film by carbothermal reaction. However, the tensile strength of the fibers obtained was decreased after the reaction.Carbon fibers were then directly coated with SiC film by thermally-activated CVD in hydrogen using triisopropylsilane. The film morphology was strongly affected by reaction conditions. The tensile strength of fibers was decreased in the early stage of the coating reaction. SiC films protected the fibers from the oxidation and obstructed the diffusion of surrounding molten aluminum into fibers at 1000ﾟC.Carbon fibers were also coated with polycarbosilane which was cured at 200ﾟC and pyrolyzed at 800-1000ﾟC.Amorphous SiC films were successfully formed on the carbon fibers. These coating methods demonstrated the possibility for simultaneous processing of carbonization and ceramic coating of CFPs.