ON THE RELATIONSHIP BETWEEN EQUILIBRIUM PRESSURES AND THE PHASE DIAGRAM OF A REACTIVE SYSTEM: THE SYSTEMS: NaCl–Na2ZrCl6, KCl–K2ZrCl6, NaCl–KCl–ZrCl4

Abstract

The binary equilibrium phase diagrams for the systems NaCl–Na2ZrCl6 and KCl–K2ZrCl were established from the combined results of cooling curve and vapor pressure measurements. A portion of the ternary NaCl–KCl–ZrCl4 has also been determined. Vapor pressure measurements on the two pure compounds, Na2ZrCl6 and K2ZrCl6, as well as on mixtures with the respective alkali metal chlorides, were taken. The vapor-producing reaction is given as[Formula: see text]where M represents, respectively, sodium and potassium.Thermodynamic relationships relating the phase diagram to the measured equilibrium pressures have been developed. The classical shape of the pressure–temperature curves, even for the pure compound, as well as mixtures of the two components, indicates a dependency on liquidus and eutectic melting. Vapor pressure measurements were also carried out over that composition of the ternary which could be of interest for the recovery of zirconium metal by fused salt electrolysis. From these data, the activities and the other partial molar properties of the components in solution were calculated for both the M2ZrCl6 and ZrCl4 species.