Thermodynamic Investigation of the Eutectic Mixture of the $$\hbox {LiNO}_{3}$$ LiNO 3 – $$\hbox {NaNO}_{3}$$ NaNO 3 – $$\hbox {KNO}_{3}$$ KNO 3 – $$\hbox {Ca}(\hbox {NO}_{3})_{2}$$ Ca ( NO 3 ) 2 System

Abstract

Molten nitrate salt is usually employed as heat transfer or energy storage medium in concentrating solar power systems to improve the overall efficiency of thermoelectric conversion. In the present work, the liquidus curves of the $$\hbox {LiNO}_{3}$$ – $$\hbox {NaNO}_{3}$$ – $$\hbox {KNO}_{3}$$ – $$\hbox {Ca}(\hbox {NO}_{3})_{2}$$ system is determined by conformal ionic solution theory according to the solid–liquid equilibrium state of the binary mixture. The calculated eutectic temperature of the mixture is $$93.17\,{^{\circ }}\hbox {C}$$ , which is close to the experimental value of $$93.22\,{^{\circ }}\hbox {C}$$ obtained from differential scanning calorimetry (DSC). Visualization observation experiments reveal that the quaternary eutectic mixture begins to partially melt when the temperature reaches $$50\,{^{\circ }}\hbox {C}$$ , and the degree of melting increases with temperature. The mixture is completely melted at $$\hbox {130}\,{^{\circ }}\hbox {C}$$ . The observed changes in the dissolved state at different temperatures correlate well with the DSC heat flow curve fluctuations.