A eutectic salt high temperature phase change material: Thermal stability and corrosion of SS316 with respect to thermal cycling

- Its thermo-physical properties did not vary significantly over 1000 thermal cycles.
- Corrosion products were identified and the thickness of the products were measured.
- The mass-loss corrosion rate on SS316 increases linearly up to 350 cycles.
- The corrosion rate stabilizes at 70 mg/cm2 after 350 cycles.

Thermal energy storage (TES) is a critical component in a concentrated solar power (CSP) plant since it is able to provide dispatchability and increase the capacity factor of the plant. Recently the Brayton power cycle using supercritical carbon dioxide (s-CO2) has attracted considerable attention as it allows a higher thermal to electric power conversion efficiency compared to the conventional Rankine cycle using subcritical steam. However, no commercial TES has yet been developed for integration with a s-CO2 based plant. One reason is the lack of a suitable storage material. This work explores the use of a eutectic NaCl-Na2CO3 salt as a reliable high temperature phase change material (PCM). The PCM has been thermally cycled up to 1000 times. Its thermo-physical properties have been measured before and after it has been subjected to the thermal cycling and its corrosion behavior has been investigated. This eutectic salt shows good thermal stability without degradation after cycling 1000 times between 600 and 650 °C. The corrosion rate on stainless steel 316 (SS316) increases linearly up to 350 cycles, and thereafter it stabilizes at 70 mg/cm2.