Sol-Gel Coatings on Continuous Ceramic Fibers

Equipment that coats continuous ceramic fibers and fiber tows has been built and tested. Fibers and tows could be cleaned, coated, and heat-treated without contamination from contact with coated parts and without bending. The equipment was used to coat AVCO SiC SCS-0 fibers with alumina, using an aluminum isopropoxide-derived sol Fibers were continuously coated at 95 cm/s to 0.5 cm/s at temperatures between 100° and 1300°C. Sol concentrations with alumina yields between 8 g/l and 118 g/l were used. Coating thickness increased directly with sol concentration, but thickness was relatively insensitive to temperature and coating rate. Thickness could be calculated from sol concentration assuming a 15–μm thick sol layer wetted the SCS-0 fibers. The coating thickness was not uniform at sol concentrations of 8 g/l and at high coating rates when 188 g/l sol concentrations were used. Multifilament tows of Du Pont fibers FP and PRD-166 were also coated with alumina sol. The outside of the tow bundle was coated, but filament surfaces inside the bundle may not have been coated; if the coating was present it was less than 50–nm thick. Extensive bridging of coating between filaments was observed, and filaments in the tow were often cemented together.