Formation of Condensed Chlorides During Mixed Oxidation–Chlorination of Iron at 1000 K

The mixed oxidation-chlorination of iron in gas mixtures of Ar, O₂, and Cl₂ at 1000 K has been investigated by thermogravimetric analysis and examination of the corrosion products by optical and scanning electron microscopy and X-ray diffraction analysis. Vapor phase transport of iron chlorides influences the rate of oxidation-chlorination when the concentration of chlorine in the gas mixture is low. When the concentration of chlorine in the gas mixture is high enough to support the formation of a liquid iron chloride deposit on the corroding surface, fluxing of the oxide scale can produce much faster corrosion than is observed in lower chlorine environments. An equation is proposed to predict the conditions under which this form of attack can occur. Because the vapor pressure of iron chloride increases rapidly with temperature, this form of corrosion can only occur in a narrow range of temperatures just above the melting point of FeCl₂.