In situ studies of oxidation of ZrB 2 and ZrB 2–SiC composites at high temperatures

Abstract

High temperature oxidation of ZrB 2 and the effect of SiC on controlling the oxidation of ZrB 2 in ZrB 2–SiC composites were studied in situ, in air, using X-ray diffraction. Oxidation was studied by quantitatively analyzing the crystalline phase changes in the samples, both non-isothermally, as a function of temperature, up to ∼1650 °C, as well as isothermally, as a function of time, at ∼1300 °C. During the non-isothermal studies, the formation and transformation of intermediate crystalline phases of ZrO 2 were also observed. The change in SiC content, during isothermal oxidation studies of ZrB 2–SiC composites, was similar in the examined temperature range, regardless of sample microstructure and composition. Higher SiC content, however, markedly retarded the oxidation rate of the ZrB 2 phase in the composites. A novel approach to quantify the extent of oxidation by estimating the thickness of the oxidation layer formed during oxidation of ZrB 2 and ZrB 2–SiC composites, based on fractional conversion of ZrB 2 to ZrO 2 in situ, is presented.