Behavior of yttria-stabilized zirconia in the presence of molten salts: Part 1 - Dissolution and recrystallization phenomena

Yttria‐stabilized zirconia is supposed to be a promising candidate as anti‐corrosion coating on steel tubes in waste‐to‐energy (WTE) plants. Since the formation of low‐melting eutectic salt melts on the surface of those tubes is a common process within WTE plants, the performance of yttria‐stabilized zirconia under these conditions was evaluated. Beads of 5 wt.‐% Y2O3 stabilized zirconia were embedded in an equimolar mixture of KCl-K2SO4-ZnCl2-ZnSO4. In a temperature range between 600 and 700 °C under an atmosphere of N2-2.55 vol.‐% HCl-0.45 vol.‐% O2, a dissolution and recrystallization of the zirconia was observed. The driving force of this process is a changing electromotive force in combination with an increasing basicity of the melt, controlled by reactions between melt and atmosphere. With respect to an application as anti‐corrosion coating, the recrystallization process can enable the material to act as a self‐healing coating.