Some thermodynamic properties of the solutions of ZrCl4 and HfCl4 in CsCl melts

Abstract

The binary equilibrium phase diagrams of the systems CsCl—Cs2ZrCl6, CsCl—Cs2HfCl6, and CsCl—KF were established by cryoscopy. A portion of the ternary CsCl—KF—ZrCl4 has also been determined.Equilibrium vapour pressures of the two pure compounds Cs2ZrCl6 and Cs2HfCl6, as well as of mixtures of Cs2HfCl6 with CsCl, have been measured. The equilibrium reaction is given as[Formula: see text]where M represents Zr or Hf.From the results, activities of CsCl, Cs2HfCl6, and HfCl4 were calculated at 825 °C.The low escaping tendency of the MCl4 vapour from the CsCl—Cs2MCl6 type melts makes these solutions suitable as electrolytes for the recovery of Zr and Hf metal by fused salt electrolysis