SOME ASPECTS OF THE THERMODYNAMICS OF MELTS

A modified Gibbs-Duhem equation has been derived with a view to evalu- ating activities of both components of a binary system from the measured ratios of the activities of the two components.This equation has been applied to a num- ber of melts of systems PbCl_2-SnCl_2,PbCl_2-CdCl_2,AgCl-CuCl,Cu_2S-FeS,PbO-BiO_(1.5), PbO-SbO_(1.5),CaO-CaF_2 and CaO-SiO_2-CaF_2 on the basis of our own experimental data as well as those reported in the literature. The method of evaluating activities of Ag and Pb from the binary phase diagram developed a long time ago has been extended to binary systems having a single AB compound.Activities in the In-Sb and Sn-Te systems have been eval- uated in this way. The use of a properly chosen non-ferrous metal instead of Fe as the solvent in the study of slag-metal equilibria with a view to evaluating activities in some ferrous slags has been shown to help in overcoming certain experimental difficul- ties.The systems CaO-SiO_2,CaO-Al_2O_3 and CaO-SiO_2-Al_2O_3 have been investiga- ted by bringing Sn or Cu into equilibrium with the slags.Our recent data on the CaO-SiO_2 system are believed to be sufficiently accurate for the first time to provide a basis for testing the validity of the Masson model.