Equilibrium decomposition pressures of the compounds K2ZrCl6 and K2HfCl6

The chemical equilibria representing the reactions K2ZrClsub(6(S or L)) >= 2KClsub((S or L)) + ZrClsub(4(vap,P,T)) and K2HfClsub(6(S or L)) >2KClsub((S or L)) + HfClsub(4(vap,P,T)) were investigated by direct vapour pressure measurements. The thermodynamic data for these reactions, such as free energies and enthalpies of reaction, have been calculated. With reference to the separation of Hf from Zr by a recently developed process based on the selective reactivity of ZrCl4 and HfCl4 vapours with alkali chlorides, it is shown that KCl is a better separating agent than LiCl. (author)