DEPOSITION OF OXIDE COATINGS ON FIBER CLOTHS BY ELECTROSTATIC ATTRACTION

Electrostatic attraction has been used to deposit alumina and mullite coatings onto woven cloths of Nicalon fiber. This approach produced un iformly coated cloths while minimizing the dependence on the wetting r elationship between the fiber and the coating precursor. The use of lo w sol concentrations (less than or equal to 1 g/L) facilitated the rem oval of excess sol from the cloth. Water was used to further displace excess aqueous sol from the cloth to give minimal fiber-fiber bridging while maintaining uniform fiber coatings. The use of a polyelectrolyt e enabled multiple deposition of coatings onto the fibers in the cloth . Multiple coating steps resulted in completely coated fiber surfaces; coverage was limited to <50% with only a single coating step. Vacuum infiltration was necessary to remove entrapped air from the cloths dur ing coating. A discussion of wetting and infiltration of fiber cloths has been presented, which highlights issues that are critical for obta ining uniformly coated fibers and minimal fiber bridging in a woven-fi ber cloth or preform.