Evaluation of the corrosion of metal-based containers in contact with molten salts at high temperature under inert atmosphere

Abstract

The reliable deployment of high-temperature thermal energy storage (TES) systems in concentrated solar power (CSP) plants requires an accurate assessment of material compatibility under realistic operating conditions. However, conventional corrosion testing in air atmosphere does not adequately represent the inert environments typically used in TES tanks, potentially leading to overly conservative material selection. This study experimentally evaluates the corrosion behaviour of PCM–metal wool composite materials under inert atmosphere conditions representative of CSP operation. Sixteen molten salt formulations, including nitrate-, carbonate-, chloride-, and sulphate-based systems, were tested in contact with metallic fibres and structural alloys (SS 314, SS 434, and Alloy 20) over a wide temperature range. The results demonstrate that inert atmosphere significantly alters material compatibility. Several PCM formulations that previously failed under air conditions exhibit acceptable behaviour under inert atmosphere, highlighting the limitations of conventional testing approaches. Nitrate- and carbonate-based systems operating between 300 and 500 °C show good compatibility with conventional alloys, whereas chloride-rich systems above 500 °C remain highly corrosive regardless of the atmosphere. These findings define a clear operational window for safe material selection. Importantly, the incorporation of metallic wool as a conductive matrix does not introduce additional corrosion penalties within this window, supporting the feasibility of PCM–metal wool composites for enhanced TES performance. This work provides experimental validation of TES materials under representative conditions and demonstrates that inert atmosphere is a critical factor for realistic material qualification in CSP applications.