Corrosion interface formation in thermally cycled stainless steel 316 with high-temperature phase change material

The formation and mechanism that drive corrosion in stainless steel as a containment material in the presence of phase change materials is of importance in solar thermal energy storage systems. In our work, half-immersed stainless steel 316 tokens in a carbonate-based phase change material (PCM 638) have been investigated. The samples were thermally cycled in air and Nitrogen environment up to 500 times within a high-temperature range, allowing the PCM to transform between solid and liquid states repeatedly. As a consequence of thermal cycling, severe thickness loss on steel token was observed, indicating a degree of oxidation occurring, which depleted the uncorroded steel. Cross-sectional microstructural analysis was carried out to determine the elemental distribution and structural morphology along the corrosion layers. This study shows that thermal cycling of SS 316 in PCM results in active Ni and Cr migration to the surface, leading to a significant depletion of Cr from steel moving into the PCM. Cr and Fe on the surface are found to oxidise with varying degrees, with respect to the exposure time. The depletion of Cr was found to be higher in SS 316 immersed in PCM, while also increasing with exposure time.

Automated summary

The study reveals that thermal cycling of SS 316 in PCM leads to active migration of Ni and Cr to the surface, resulting in significant depletion of Cr from the steel. Oxidation of Cr and Fe on the surface is found to vary with exposure time. The depletion of Cr is higher in SS 316 immersed in PCM and increases with exposure time.