Molten salts and their vapours : a thermodynamic study of some high temperature halides and sulphates.

Reciprocal sulphate-halide liquid salt mixtures have been investigated using transpiration vapour pressure measurements. Liass spectrometric methods have also been used to investigate the binary halide mixtures in the vapour phase. Where possible the applicability of theory to the prediction of the thermodynamic properties of these systems has been studied. An activity study of the liquid reciprocal salt system: ZnC12 + Na2 SO 4 = ZNSO4 + 2 NaC1 has been carried out. Behaviour in this system is quite complex; the best fit to the data is made with the Conformal Ionic Solution Theory which contains terms involving (1) the free energy change for the above exchange reaction (2) binary type interaction terms and (3) ternary excess terms. This theory has also been found to fit some lead sulphate-alkali halide mixtures. Vapour phase mixtures PbEr 2-MBr, ZnC12-MC1, (M = Na, K, Rb, Cs) were found to contain complex species of the type MAX 3 . Possible structures of these:, species were estimated with the aid of Extended Huckel, rlolecular Orbital calculations. Conclusions concerning the formation of vapour phase complexes are drawn from available information.