Preparation and corrosion of mullite thin film on β-sialon ceramics

Mullite film was formed on β-SiAlON (Si_6-zAl _zO_zN_8-z, z = 3) ceramics by reaction of Al ₂O₃ films with silica formed on oxidation to improve a high temperature water vapor corrosion resistance. Sintered β-SiAlON was fabricated by hot pressing of β-sialon (z = 3) powder without additive at 1900°C and at 24 MPa for 4 h in N₂. The Al₂O ₃ film was deposited on polished β-SiAlON ceramics by a dip coating process of Al₂O₃ precursor sols prepared from the alkoxide solution and aluminum 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 reaction with silica produced from sialon. The resulting mullite-coated sample was corroded in H ₂O/Ar/O₂ (90/8/2 vol.%) at 1200°C for 2-100 h. The corroded samples were characterized by XRD and SEM-EDS for the evaluation of the corrosion resistance of mullite-coated sialon.