Aqueous Sol-Gel Coating of Pitch-Based Graphite Fibers for Inclusion in Aluminum Matrix Composites

A coating on graphite is required to provide a wettable surface and prevent reaction between the graphite and the molten metal during the fabrication of high thermal conductivity metal matrix composites. An aqueous sol-gel procedure using zirconium acetate precursors to form continuous, crack-free, bridge-free zirconia coatings approximately 0.1 µm thick on graphite fibers 10 µm in diameter is described. Parameters were determined for dip-coating the fibers as a tow in an aqueous zirconium acetate solution and developing the coating structure by thermal desiccation, pyrolysis, and crystallization in a controlled environment.