PREPARATION AND CORROSION OF MULLITE THIN FILM ON BETA-SiAlON CERAMICS

A mullite film was formed on beta-SiAlON (Si6-zAlzOzN8-z, z = 3) ceramics by the reaction of Al2O3 films with silica formed on oxidation to improve the high-temperature water vapour corrosion resistance. Sintered beta-SiAlON was fabricated by hot pressing of beta-sialon (z = 3) powder without additives at 1900 C and at 24 MPa for 4 h in N2. The Al2O3 film was deposited on polished beta-SiAlON ceramics by dip coating Al2O3 precursor sols prepared from an alkoxide solution and aluminium sol. The Al2O3-coated sample was heated in Ar/O2 (95/5 vol%) at 1300 C for 2 h, resulting in the formation of mullite by the reaction with silica produced from sialon. The resulting mullite-coated sample was corroded in H2O/Ar/O2 (90/8/2 vol%) at 1200 C for 2-100 h. The corroded samples were characterised by XRD and SEM-EDS to evaluate the corrosion resistance of mullite-coated sialons.