Thermal stability and microstructure of sodium nitrite in multicomponent molten salts: An experimental analysis

Abstract

LiNO₃ exhibits excellent properties in mixed molten salts but is prohibitively expensive for practical applications. In this study, we explored the feasibility of incorporating NaNO₂ as a partial substitute for LiNO₃ to reduce costs while maintaining desirable performance in thermal storage systems. Differential scanning calorimetry, thermogravimetric analysis, and Raman spectroscopy were employed to analyze nitrites composed of NaNO₃-KNO₃ (−LiNO₃) with varying NaNO₂ contents (0–20 wt%). The effect of NaNO₂ content on the thermal stability of mixed molten salts from both macro and micro perspectives was investigated. These results indicate that in the NaNO₃-KNO₃-NaNO₂ ternary molten salt system, increasing the NaNO₂ content leads to greater NO₃^– vibration and enhanced thermal stability. Upon replacing LiNO₃ with NaNO₂, the NO₃^– vibration initially decreases and then increases, with the sample containing 7 wt% NaNO₂ exhibiting the highest thermal stability differential of 488.11°C. This represents an enhancement of approximately 37 %, thereby surpassing the performance of the pure ternary LiNO₃ molten salt system. These findings suggest that the substitution of LiNO₃ with NaNO₂ possesses significant potential for the design and development of new cost-effective molten salt systems with superior thermal stability.