Chemical degradation in Thermally Cycled Stainless Steel 316 with High-Temperature Phase Change Material

Abstract Analysis of stainless steel 316 as a containment material in the presence of a phase change material (PCM) cycled at high temperature was carried out through a combination of X-ray photoelectron spectroscopy and X-ray diffraction methods. In this work, stainless steel tokens were half-immersed in a chloride carbonate-based PCM, which were then thermally cycled in an air or a nitrogen environment up to 500 times, allowing the PCM to repeatedly transform between solid and liquid phases. Spectroscopy and diffraction methods were applied on the tokens, as well as the cycled PCM, to investigate the extent and nature of corrosion in such steel alloys. With varying sputtering conditions, the oxidation state at different depths of token surfaces was quantified. From the outermost corroded layer through to the bulk, this study shows a gradual change in distribution in both Cr and oxidation of Fe, while Cr was specifically found to have depleted and migrated into the PCM. The oxidation and depletion have been found to increase with increasing exposure time to PCM while sigma-phase structure embrittled in the corrosion layer.