Active Oxidation of SiC‐Based Ceramics in Ar–2% Cl 2 ‐O 2 Gas Mixtures at 1000°C

The corrosion in Ar–2% CI 2 gas mixtures of four low‐cost SiC‐based materials suitable for use in high‐temperature heat exchangers has been invesigated. The oxygen potential was controlled by addition of O 2 or H 2 at 1000°C. Little attack was observed in the reducing environment composed of Ar–2% Cl 2 –1% H 2 or the oxidizing environment composed of Ar–2% Cl 2 –20% O 2 but all of the materials were subject to active corrosion at intermediate oxygen potentials. Selective attack of the free silicon phase was obsrved for the siliconized silicon carbide materials. The severity of the active oxidation and the oxygen potentital at which the corrosion changed from active to passive were affected by the nature of the sintering aids used in the materials