The Corrosion of metals in an oxidizing‐chloridizing environment at high temperature

Abstract

AbstractAn investigation has been undertaken into the behaviour of metals which form the basis of high‐temperature alloys in an argon −5.5% oxygen −0.96% hydrogen chloride −0.86% sulphur dioxide gas mixture at 900°C. The intention has been to ascertain the reaction products, with particular emphasis on the formation of volatile species which can cause considerable degradation of commercial alloys in this environment. From consideration of the thermodynamics of the gas system, the potentials of the reactive species can be determined and correlated with the possible reaction products. In this gas mixture, the oxides of nickel, iron, cobalt, chromium, molybdenum and tungsten are the stable phases with respect to the corresponding metals. Indeed, on exposure of the metals to the environment, the appropriate oxide scales are developed. However, the reactions are complicated by formation of volatile corrosion products, particularly for nickel, cobalt and molybdenum. Although a Cr2O3 scale is established on chromium, there is evidence for penetration of chlorine‐containing species to the scale/alloy interface. The oxide scale on tungsten is not very protective and thickens rapidly while that on molybdenum is volatile, resulting in rapid consumption of the specimen.