Equilibrium between NO3~- and NO2~- in KNO3–NaNO2 melts:a Raman spectra study

We study ionic structure of KNO3–NaNO2 melts under air atmosphere by using Raman spectroscopy. Molar fraction of NO--3 and NO2 is obtained and thermal stability of this kind of melts system is then analyzed. The results show that when the temperature is increased to a certain value, equilibrium between the decomposition of NO-3 and the oxidation of NO-2 exists in KNO3–NaNO2 melts. When temperature is higher than 644 K, the molar fraction of NO-3 decreases a little with temperature increasing for the melts in which the initial fraction of KNO3 is 90 wt%, but for the melts in which the initial fraction of KNO3 is 10–80 wt%, the molar fraction of NO-3 increases with temperature, and the increasing rate is slower for a higher initial fraction of KNO-3. Molar fraction of NO3 increment increases linearly with initial fraction of NaNO2. The sample in which the initial fractions of NaNO2 are 11.3 and 14.5 wt% under air atmosphere shows the best thermal stability at 762 and 880 K, respectively.