Differentiation in corrosion performance of alumina forming alloys in alkali carbonate melts

Alkali carbonate melts are promising high temperature thermal storage media. In this work five alumina forming alloys have been exposed to a ternary LiNaK carbonate melt and CO2 at 800 °C. The corrosion propagation was found to depend on the formation of a slow-growing LiAlO2 scale. Furthermore, the two polymorphs contributing to the LiAlO2 phase were monitored for up to 1000 h: a dense α-LiAlO2 scale and γ-LiAlO2 crystallites. We suggest a growth stress assisted formation of α-LiAlO2 relaxing into the outwards growing γ-LiAlO2 phase. This implies a deceleration of the α-LiAlO2 scale growth towards a steady state-thickness.