High-temperature thermodynamic properties of the alkali-metal fluorides

Abstract

The enthalpies of LiF, NaF, KF, RbF and CsF have been measured in the temperature range 500 to 1600 K by means of an adiabatic vacuum drop calorimeter. All temperatures are based on 1PTS-48. The results have been correlated with existing or estimated low-temperature heat capacity data and are represented by quadratic equations of the type H°(T)–H°(298.15 K)=aT+bT²+CT^–1+d from which the molar thermodynamic functions of the alkali metal fluorides have been calculated in the range 300 to 2000 K.

Enthalpies of fusion of the fluorides have also been determined accurately and the values obtained are (in cal mol^–1): LiF, 6380; NaF, 8030; KF, 7050; RbF, 6180; CsF, 3350.