Molar enthalpy at five compositions in the NaNO3NaOH system in the liquid and solid states

The molar enthalpies of the two compounds and three eutectics in the NaNO₃NaOH system were determined over the 450–630 K temperature range by means of drop calorimetry. The enthalpy changes over the 500–550 K range, which in all cases includes melting, are usefully large from the viewpoint of energy storage: 5.7 (79), 5.2 (83), 5.1 (87), 5.1 (93) and 3.5 (73) kcal mole^?1 (cal g^?1) in 0.710 NaNO₃·0.290 NaOH, 0.500 NaNO₃·0.500 NaOH, 0.411 NaNO₃·0.589 NaOH, 0.327 NaNO₃·0.673 NaOH and 0.178 NaNO₃·0.822 NaOH, respectively. At χ_NaOH = 0.822, a high, negative heat of mixing (0.7–0.8 kcal mole^?1) was noted. This is contrary to what has been observed in other common cation-mixed anion molten salt solutions.