Structure and thermodynamics of potassium fluoride aluminium fluoride melts. Raman spectroscopic and vapour pressure studies

Raman spectra and vapour pressures have been obtained as functions of temperature, 860<T/degrees C<1000, and composition, 1<n(KF)degrees/n(AIF3)degrees)<5 (for pressures), 16 (for Raman spectral for KF-AlF3 melts. Stoichiometric equilibrium constants are calculated for the two equilibria AlF63- = AlF52++F- and AlF52- - = AlF4- + F- established in the melt. The temperature variation of these constants is given as In K'= -7698/T/K+7.46 and -5894/T/K+2.29, respectively. These data are based on a quantitative analysis of the Raman intensities of the AlF63-, AlF52- and AlF4- vibrational frequencies. When combined with thermodynamic data, these results indicate a non-ideal mixture of the established anions.