Oxidation of ZrB 2-SiC: Influence of SiC content on solid and liquid oxide phase formation

Abstract

The effect of SiC concentration on the liquid and solid oxide phases formed during oxidation of ZrB 2-SiC composites is investigated. Oxide-scale features called convection cells are formed from liquid and solid oxide reaction products upon oxidation of the ZrB 2-SiC composites. These convection cells form in the outermost borosilicate oxide film of the oxide scale formed on the ZrB 2-SiC during oxidation at high temperatures (≥1500°C). In this study, three ZrB 2-SiC composites with different amounts of SiC were tested at 1550°C for various durations of time to study the effect of the SiC concentration particularly on the formation of the convection cell features. A calculated ternary phase diagram of a ZrO 2-SiO 2-B 2O 3 (BSZ) system was used for interpretation of the results. The convection cells formed during oxidation were fewer and less uniformly distributed for composites with a higher SiC concentration. This is because the convection cells are formed from ZrO 2 precipitates from a BSZ oxide liquid that forms upon oxidation of the composite at 1550°C. Higher SiC-containing composites will have less dissolved ZrO 2 because they have less B 2O 3, which results in a smaller amount of precipitated ZrO 2 and consequently fewer convection cells. © 2009 The American Ceramic Society.