Oxidation kinetics of silicon carbide‐containing refractory diborides. III: Critical assessment of glass viscosity and inter‐diffusivity data for model parameters

Inter‐diffusion coefficient and viscosity of borosilicate glass are critical parameters in the recently proposed revised model of oxidation of MeB 2 ‒SiC ultra‐high temperature ceramic (UHTC) materials. Inter‐diffusion in the glass controls the mode and the kinetics of oxidation, including the development of the internal depletion zone. The viscosity of the glass controls the shearing of the external glass layer and the oxide scale on MeB 2 ‒SiC UHTC materials under conditions of high temperatures and high rates of air flow. In this work, the available literature data on these two related parameters have been critically reviewed and evaluated. The viscosity and inter‐diffusivity of borosilicate glass exhibit significant deviation from the “ideal” log‐linear behavior across the compositional and temperature domains relevant to oxidation of MeB 2 ‒SiC UHTC materials in service and/or testing. Based on the available data, an empirical thermodynamic model is proposed that allows for the calculation of the inter‐diffusion coefficient and viscosity of borosilicate glass across the entire composition and temperature range of interest for modeling of the oxidation kinetics of silicon carbide‐containing refractory diborides.