Preparation and corrosion study of NaOH-NaNO3 composite phase change thermal energy storage material

Inorganic phase change materials (PCMs), such as common eutectic salts—solar salt (60 wt% NaNO₃+40 wt% KNO₃) and Hitec salt (53 wt% KNO₃+7 wt% NaNO₃+40 wt% NaNO₂)—are widely used in solar thermal power storage due to high stability and low cost. However, optimizing eutectic compositions requires extensive experiments, and material compatibility with pipelines/storage tanks remains a key challenge. Herein, nine NaOH-NaNO₃ mixtures of varying molar ratios were melt-cooled and screened via DSC, yielding three eutectic formulations. The 6:4 NaOH:NaNO₃ composite (NN-PCM) exhibited a phase transition temperature of 268 °C, enthalpy of 260 J/g (a 50 °C reduction from pure components), and a maximum service temperature of 480 °C. Corrosion tests at 300 °C for 1000 h in sealed vessels revealed increasing corrosion rates in 310S stainless steel, ductile iron, 304 stainless steel, and 45 steel. Post-test analyses confirmed NN-PCM retained eutectic properties: stable melting temperature (268 °C), 11–17 °C lower solidification temperature, and 7 % enthalpy reduction (20 J/g). This work offers insights into inorganic PCM applications in medium-to-high-temperature energy storage systems.