Oxidation of monolithic TiB₂ and of Al₂O₃-TiB₂ composite

In view of the susceptibility of TiB₂ to oxidation, the thermal stability of monolithic TiB₂ and Al₂O₃-TiB₂ composite was investigated. The temperature at which TiB₂ ceramic starts to oxidize is about 400°C, oxidation kinetic being controlled by diffusion up to T≈900°C and in the first stage of the oxidation at 1000 and 1100°C (up to 800 and 500 min, respectively), and by a linear law at higher temperatures and longer periods. Weight gains of Al₂O₃-TiB₂ composite can be detected only at temperatures above ≈700°C and the rate-governing step of the oxidation reaction is characterized by a one-dimensional diffusion mechanism at T=700 and 800°C and by two-dimensional diffusion at higher temperatures. The composition and morphology of the oxidized surfaces were analysed.