Study on Corrosion and Thermal Alteration of MgAl$_2$O$_4$ and MgO Ceramics With Lead at 750 °C for Use in High‐Temperature Thermal Energy Storage

Thermal-energy-storage (TES) systems are promising for decarbonizing industry by storing waste heat generated by high-temperature processes. Used as heat transfer fluid (HTF), liquid-metal-based TES offer a broad liquid operating range and high thermal conductivity, making them especially attractive. Directly combining a solid storage material with metallic heat-transfer fluid in a packed bed further increases stored energy while reducing the volume of liquid metal. Ceramics can be used as storage materials. However, liquid metals are highly corrosive. This study investigates the corrosion behavior of two grades of magnesium aluminate spinel (alumina-rich spinel, fused spinel) and three grades of magnesium oxide (94%, 97%, and 99% purity) exposed to static liquid lead at 750 °C. The materials were analyzed using scanning electron microscopy and X-ray diffraction. The results show that all samples performed well overall. MgO showed better resistance than the tested spinels, with the highest-grade purity performing best. In all three grades, the magnesium oxide phase was stable; only the various calcium silicate phases observed at the grain boundaries reacted with Pb. Regarding the spinel, the fused one displayed cracks, and the alumina-rich one displayed Pb penetration and thermal alteration, resulting in a transformation of Mg$_{0.38}$Al$_{0.62}$(Al$_{1.79}$)O$_4$, MgO$_{0.388}$Al$_{2.408}$O$_4$, and corundum Al$_2$O$_3$, to ((Mg$_4$Al$_{0.6}$)Al$_{1.8}$O$_4$).