TiO₂ coatings on silicon carbide and carbon fibre substrates by electrophoretic deposition

Abstract

Electrophoretic deposition (EPD) has been used to obtain TiO₂ coatings on three dimensional (3-D) SiC fibre (Nicalon ®-type) and carbon fibre substrates. Colloidal suspensions of commercially available TiO₂ nanoparticles in acetylaceton with addition of iodine were used. The EPD parameters, i.e., deposition time and voltage, were optimised for each fibre type. Strongly adhered TiO₂ deposits with high particle packing density were obtained. Scanning electron microscopy observations revealed high penetration of the titania nanoparticles into the fibre preforms. The TiO₂ deposits were sintered at 800°C for 1 h in order to produce relatively dense and uniform TiO₂ coatings covering completely the SiC or carbon fibres. For the carbon fibre/TiO₂ system, an effort was made to produce a 3-D titania matrix composite by further infiltration of the porous fibrous preform with TiO₂ by slurry dipping and subsequent pressureless sintering. The 3-D carbon fibre reinforced TiO₂ matrix composites fabricated contained residual porosity, indicating further infiltration and densification steps are required to produce dense composites of adequate structural integrity. For SiC fibre fabrics, oxidation tests in air established the effectiveness of the TiO₂ coating as oxidation protective barrier at 1000°C. After 120 h the increase of weight due to oxidation of coated fibres was more than twice lower than that of the uncoated fibres. TiO₂ coated SiC fibre preforms are attractive materials for manufacturing hot gas filters and as reinforcing elements for ceramic matrix composites.