ABSTRACT

It is not necessary to know the activity of HF(/) in the KF • kHF melt, because of the equilibrium between the gaseous and liquid phases. Thus

P hf is the partial pressure of HF and / hf the fugacity coefficient. The variations of AG°f(HFig)) with the temperature t, expressed in °C, are given by

For the molten KF • nHF system with n « 2, the pressure of HF in equilib­ rium with the melt, P hf? is often lower than 1.5 X 104 Pa; HF molecules are not too much associated, and it is possible to neglect the term containing fugacity coefficients. In industrial cells, P H2 = P F2 = P — P hf with P = 1 atm (1.013 X 105 Pa). The values of P hf have been determined for KF • nHF melts by Cady [10].