Activities in the system KF-AlF3

Activities in the system KF-AlF3 have been measured. In the acidic melts (n(KF)/n(KAlF4) <3) activities of KAlF4 were calculated as a(i) = p(i)/p(i)(o), p(i) being obtained from a combination of vapour pressures and vapour composition data. In basic melts (n(KF)/n(KAlF4) >3), the measured vapour pressures were, however, too low to give accurate pressure data. For this range vapour pressures of KAlF4 were calculated from composition data of the vapour over the melts. A ratio R = (p(KAlF4)/x(KAlF4)(o))/(p(KF)/x(KF)(o)), where x(i)(o) is the weight in mole fraction, can be obtained using the composition data. LnR is a linear function of x(KAlF4)(o) up to x(Alf3)(o) approximate to 0.33. This enabled us to calculate partial pressures of K-AlF4. Activities of K-AlF4 in the basic region could then be obtained. The activities of KF in the range 0<x(AlF3)(o)<0.5 were obtained from the activities of KAlF4 using the Gibbs-Duhems equation. Thereafter, Raman based activity coefficients of KAlF4 and KF were calculated as gamma(i)(RS) = a(i)/x(i), where x(i) are the real mole fractions of KA1F, and KF as obtained by Raman spectroscopy and gamma(i)(RS) the corresponding Raman based activity coefficients.