Oxidation kinetics of silicon carbide‐containing refractory diborides, I: Revised model

Abstract

AbstractThe original model by Parthasarathy et al. for oxidation of MeB₂–SiC ultra‐high temperature ceramics (UHTCs) has been further expanded to include oxidation by water vapor and oxygen/water vapor mixtures. The revised model offers a more representative analysis of the composition of the glass phase and a thermodynamically consistent formulation for the processes governing the formation of the internal depletion zone. A key feature of the revised model is that it explicitly incorporates the out‐diffusion of CO(g) through the scale as a rate‐controlling parameter that defines the formation of internal depletion zone. In its present form, the expanded model explains some of the experimentally observed phenomena of oxidation of MeB₂–SiC UHTCs, such as the formation of MeO₂/B₂O₃ scale with embedded partially oxidized SiC at lower temperatures and limited growth of ZrO₂/borosilicate layer compared with the SiC‐depleted layer and the outer borosilicate layer in static oxidation at high temperatures. Application of the revised model to the experimental data from literature on oxidation of ZrB₂–SiC materials in air and water vapor is demonstrated and discussed.