(400b) Dynamic Method along with Capillary Electrophoresis Analysis for Solid/Vapor Equilibrium Study of Hafnium Tetrachloride

Hafnium and zirconium two similar chemical elements exist naturally together in a mixed crystal lattice. Pure zirconium, Zr, has a low thermal cross section of neutron capture (1.80.10-29 m2) and an exceptional resistance to corrosion so that its principal use is the coating of the nuclear reactors. The associated hafnium, Hf, on the other hand, has high thermal neutron cross section (1.05.10-26 m2) and is undesirable for structural use in nuclear reactors. So the limit content of Hf in a Zr coated reactor is below 100 ppm. Zirconium-hafnium separation via direct distillation of ZrCl4 and HfCl4 is possible only at elevated pressures, on the order of (2.5 to 3) MPa, in the relatively narrow liquid range of the tetrachlorides. This is a major impediment to the practical use of this potentially attractive process. A possible alternative to the direct separation of ZrCl4 and HfCl4 is extractive distillation, a process that utilizes a low-melting solvent with a relatively low vapor pressure. Thus the knowledge of the solid-vapor equilibrium of pure HfCl4 is indispensable to calculate and to optimize the distillation. With this aim, we carried out sublimation pressure measurements of HfCl4 using a gas saturation apparatus, fig.1. The obtained results are in a good agreement with the available literature data.