Effect of a Small Amount of Hydrogen Chloride on High Temperature Oxidation of Chromium

Abstract

High temperature oxidation behavior of Cr was examined under a N₂-50%O₂ atmosphere including 1%HCl by volume. At 973-1073 K, mass gains of Cr in the atmosphere were larger than those in 100%O₂. Temperature dependence of the mass gain of Cr after oxidation in an 1%HCl atmosphere was very peculiar. At the temperatures lower than 1073 K, the mass gains in 1%HCl increased with a rise in oxidation temperature. But at higher temperatures than 1123 K, the mass gains were relatively small and became close to the values in 100%O₂. In addition, temperature dependence of corrosion loss of the specimen in 1%HCl was almost the same as that of mass gain in 1%HCl. It was also found by XRD and EDX analyses that scales formed on Cr in 1%HCl consisted of Cr₂O₃ containing some chromium chloride. These oxidation behaviors of Cr in 1%HCl were investigated thermodynamically, and it was proposed that the mechanism of the accelerated oxidation induced by HCl was explained by chlorination reaction of Cr and oxidation reaction of chromium chlorides inside the scale.