Thermal Sprayed Oxide Coatings for Stainless Steel Containers Used with Molten Al–Si and Al–Cu–Si Phase Change Materials: Compatibility and Thermal Cycling Stability

The application of aluminium-based metallic phase change materials (mPCMs) in latent heat thermal energy storage is limited by the poor compatibility of molten alloys with conventional stainless steel containers. This work evaluates thermally sprayed oxide coatings deposited directly on 304 stainless steel as protective barriers for molten Al–Si and Al–Cu–Si phase change materials. Alumina (Al2O3), zirconia (ZrO2) and Al2O3/ZrO2 (60/40 wt. %) coatings were produced by atmospheric plasma spraying (APS) and high-velocity suspension flame spraying (HVSFS) and assessed through coating characterisation, long-term static compatibility tests, thermal cycling experiments and thermal contact resistance measurements. APS coatings exhibited a pronounced dependence of coating thickness on spray angle, whereas the HVSFS coating provided a more uniform thickness distribution. After two weeks of static exposure, no reaction layer formation, coating dissolution or detectable elemental interdiffusion was observed for the investigated coating systems. For the Al2O3/Al–12.3 wt. % Si system, no coating degradation or interfacial reaction was detected after approximately 300 thermal cycles. Furthermore, average liquid thermal contact resistances of 0.31 × 10−3 and 0.39 × 10−3 m2 K W−1 were measured for smooth and rough Al–Si/coating interfaces, respectively. These results demonstrate that thermally sprayed oxide coatings can effectively protect stainless steel from molten aluminium-based PCMs while providing design-relevant data for the development of high-temperature latent heat thermal energy storage systems.