Superior protection by α-Al2O3/α-LiAlO2 double oxide scales against alkali carbonate corrosion

Abstract

Ferritic alumina-forming alloys showed high corrosion resistance to molten carbonates by forming a protective α-LiAlO2 scale at their surface. In this work, four ferritic alumina-forming alloys were pre-oxidised before exposure to (Li,Na,K)2CO3-melt at 800 °C for 1000 h. Only outer transient alumina, such as γ-alumina, reacts with the melt, forming LiAlO2. At the same time, the innermost α-Al2O3 scale remains intact. α-Al2O3, as well as α-LiAlO2, are slow-growing compressive stress-stabilised oxide scales. Thus, the combined presence of α-Al2O3/α-LiAlO2 improves the corrosion protection of materials investigated in this study, compared to non-pre-oxidised ones, by forming a superior double oxide scale.