Studies on high temperature corrosion reactions involving metal oxides and sodium sulfate

Abstract

PurposeThe purpose of this paper is to present the results of studies on the reaction of metal oxides such as Cr2O3 and Al2O3 with Na2SO4 in flowing SO2 (g) at 1,100 and 1,200 K.Design/methodology/approachThe oxides chosen for the studies were initial scaling products during the oxidation of industrial alloys and invariably are involved in hot‐corrosion reactions in the presence of molten salts. The thermo‐gravimetric studies for the system were carried out as a function of Na2SO4 in the mixture. The different constituents in the reaction products were identified by XRD analysis and morphologies of the reaction products were discussed on the basis of optical metallography and scanning electron microscopic studies. The pH and conductivity of the aqueous solutions of reaction products were measured and an attempt made to functionalize these parameters with Na2SO4 concentration in the mixture. Quantitative estimation of the soluble metal was carried out using an atomic absorption spectrophotometer. The formation of products was investigated by thermodynamic computation of free energies of the reactions and the study of relevant phase stability diagrams.FindingsLooking at the complex nature of the reactions, it is difficult to generalize the conductance studies, as many complex species are liable to hydrolyze in the aqueous solution. However, the break in few curves at certain mole fraction of Na2SO4 indicates the presence of soluble complex species.Originality/valueThe paper provides information regarding the reaction between a pertinent oxide and Na2SO4 and proper identification of reaction products, useful for understanding the occurrence and importance of fluxing reactions and in the interpretation of hot corrosion mechanism and the development of new protective materials.