Oxidation of ZrB2 -based ceramics in dry air

The oxidation behaviour of three different ZrB2-based ceramics: a monolithic ZrB2 and two composites ZrB2-SiC, was studied during heating up to 1350°C and under isothermal conditions at 1120°C. Oxidation kinetics and microstructure of the oxidized surfaces indicate that monolithic ZrB2 has a low thermal stability. On the contrary, the introduction of SiC particles markedly improves the oxidation resistance due to the formation of an adherent and protective borosilicate glassy layer that coats the sample surface, limiting the inward diffusion of oxygen towards the reaction interface. The influence of the grain boundary phases on oxidation is discussed.