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-degrees-C, oxidation kinetic being controlled by diffusion up to T almost-equal-to 900-degrees-C and in the first stage of the oxidation at 1000 and 1100-degrees-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 almost-equal-to 700-degrees-C and the rate-governing step of the oxidation reaction is characterized by a one-dimensional diffusion mechanism at T = 700 and 800-degrees-C and by two-dimensional diffusion at higher temperatures. The composition and morphology of the oxidized surfaces were analysed.