Influence of steam flow rate on oxidation kinetics of silicon carbide at 1400–1600 °C

Being potential future materials for accident-tolerant fuel cladding, the oxidation behavior and kinetics of silicon carbide (SiC) under extreme conditions like severe accidents must be elucidated. In this study, oxidation tests of SiC at 1400–1600 °C for 1–5 h using a newly developed test facility using laser as a heat source, under two different flow rates of H₂O/Ar gas mixture have been conducted. The objective is to investigate the influence of steam flow rate on the formation of SiO₂ scale and its subsequent volatilization. Oxidation kinetics of SiC was evaluated via mass change of samples before and after the oxidation tests. Based on these mass changes, parabolic oxidation rates for SiO₂ formation and its subsequent linear volatilization rates were calculated. The Arrhenius dependence of the parabolic oxidation and linear volatilization rate constants were then plotted. Results of this study indicated that SiC exhibits excellent oxidation resistance at 1400–1600 °C in Ar/steam atmospheres. Steam flow rate has a significant influence on volatilization of SiO₂ but has minor effects over its formation. Oxidation of SiC in steam at high temperature may follow mass gain or mass loss regime, depending on the steam flow rate. Two oxidation patterns were suggested and discussed. In the first oxidation pattern, the SiO₂ formation is dominated by its volatilization. The second oxidation pattern (steady stage) is reached when the SiO₂ formation rate is equivalent to its volatilization rate. Time to reach this steady stage was defined, based on the parabolic oxidation rate and linear volatilization rate.