STRUCTURE AND THERMODYNAMICS OF POTASSIUM FLUORIDE ALUMINUM FLUORIDE MELTS - RAMAN-SPECTROSCOPIC AND VAPOR-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(A IF3)degrees)<5 (for pressures), 16 (for Raman spectral for KF-AlF3 mel ts. Stoichiometric equilibrium constants are calculated for the two eq uilibria AlF63- = AlF52++F- and AlF52- - = AlF4- + F- established in t he 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 bas ed on a quantitative analysis of the Raman intensities of the AlF63-, AlF52- and AlF4- vibrational frequencies. When combined with thermodyn amic data, these results indicate a non-ideal mixture of the establish ed anions.