Thermal stability of sodium nitrate-sodium nitrite melts: A Raman spectra study

A molten mixture of sodium nitrate-sodium nitrite is an important heat transfer and storage medium. It is important to research the thermal stability of such melts. In the present study, the equilibrium between nitrate and nitrite ion in sodium nitrate-sodium nitrite melts under air atmosphere was studied by Raman spectroscopy and the thermal stability of the melts was analyzed. The results show that when the temperature was greater than 644K, for melts in which the weighted-in content of sodium nitrate is 90 mass %, the content of nitrate ion decreased slightly with temperature. However, for melts in which the weighted-in content of sodium nitrate was 10-80 mass %, the content of nitrate ion increased with temperature. Melts in which the weighted-in fraction of sodium nitrite were 15.22%, 14.71%, and 14.60% under air atmosphere showed optimal thermal stability at 644K, 762K, and 880K, respectively. The findings of this study have provided a foundation for optimizing the composition of molten salts and for providing molten mixtures applicable to important industrial processes.