High-temperature thermal stability of ternary nitrate salt(53%KNO3-40%NaNO2-7%NaNO3)in air and nitrogen is investigated by mass loss ratio

NO2- content of molten salt and thermo-gravimetric analysis.The results show the upper limit of operation temperature is 773 K in air for the ternary nitrate salt and the deterioration will appear at higher temperatures

while the thermal decomposition begins at 723 K and proceeds slowly in nitrogen.According to the thermodynamics and kinetics of molten salt

the thermal decomposition and oxidation of sodium nitrite of the ternary nitrate salt occur below 773 K in air

while the reaction for the ternary salt in nitrogen is the thermal decomposition of sodium nitrite below 723 K.Diffusion of oxygen and decomposition reaction of nitrite follow the first order reaction kinetics when the oxygen content is constant.