The Vapor Pressures of Zirconium Tetrachloride and Hafnium Tetrachloride

Abstract

Two methods were used to measure the vapor pressures of zirconium tetrachloride and hafnium tetrachloride over the range from 10 to 10,000 mm Hg. The lower pressures (10-1000 mm) were measured in a nickel diaphragm apparatus1 which has been used successfully on other compounds by this laboratory and others2 recently. The higher pressures were obtained using a modification of the capillary "bridge" apparatus which was used by the U. S. Bureau of Mines3 in the extensive investi gation of the vapor pressures of common metal chlorides.The charge materials were prepared from oxides purchased from De Rewal International Metals Company. The ZrO2 contained less than 0.1 per cent HfO2 and the HiO2 was 98.7 per cent pure.l The oxides were purified by a mandelic acid precipitation4 to remove impurities such as iron, titanium, and calcium.The vapor pressure curves of both salts are shown on the accompanying graph. The equations for the curves are: zrci4 10g P = -5'Ír00 + 11.76Hfc14 log P = -sïooThe melting points were found to be 437°C for ZrCl4 and 434°C for HfCl4.By extrapolation, the vapor pressure of ZrCl4 at its melting point is 14,500 mm, and the vapor pressure of HfCl4 at the same temperature is 25,000 mm.The data of this report are in close agreement with and appreciably extend the range of the data of the Ames Laboratory.5The investigation of the high pressure range is being continued and it is hoped that it will be possible to obtain data above the melting points in the near future. In any event, this brief memo randum will be followed by a complete technical report which will be issued before January 1, 1950.

A thermochemical study of addition complexes of zirconium and hafnium tetrahalides

“…1 which shows the enthalpy cycle. The heats of sublimation of the tetrahalides are experimental values (5,6). These are somewhat lower than the values which may be obtained from the calculated enthalpies of formation for the ideal monomeric gases (7).…”

Design of an Extractive Distillation Column for the Environmentally Benign Separation of Zirconium and Hafnium Tetrachloride for Nuclear Power Reactor Applications

“…A large portion of the entire processing facility for the production of Zr and Hf metals is dedicated to handling a multiple-step solvent extraction process in the presence of a solvent. Furthermore, it also generates a huge volume of liquid waste, which is difficult to dispose of due to stringent environmental protection laws [17][18][19][20]. For example, isobutyl methylketone (MIBK), which is the most popular solvents used for Zr-Hf extraction, requires environmentally harmful cyanogen (CN) chemicals as an additive.…”

“…Distillation has attracted considerable attention for Zr purification because of its potential for clean separation and many other advantages for a large scale production, such as fewer unit operations and chemical consumption, higher overall yield, and less effluent [17,18]. On the other hand, because distillation utilizes the volatility difference of the components associated with the vapor-liquid equilibrium (VLE), the close boiling points of ZrCl4 and HfCl4 with narrow and harsh conditions for the vapor-liquid phase existence limits the distillation applications: a large number of separation stages are required in the column to bring HfCl4 to an acceptably low level; stringent temperature control and a confining pressure are needed to manage the VLE; and the column material must withstand high temperatures and pressures.…”

The Chemical Vapor Deposition of Zirconium Carbide onto Ceramic Substrates

“…Substoichiometric zirconium carbide has a very high melting point (3540"C), good thermal conductivity, and is resistant to chemical attack. Unfortunately, the deposition of zirconium carbide continues to be difficult due to the low vapor pressure of zirconium tetrachloride [4], the hazards associated with generating zirconium tetrachloride in-situ, and the lack of alternative precursors which yield substoichiometric zirconium carbide [5]. in this paper, a summary of efforts to understand and control deposition of substoichiometric, stoichiometric, and superstoichiometric zirconium carbide from zirconium tetrachloride and methane gaseous precursors and a discussion of how physical properties such as morphology, and density, change with zirconium carbide stoichiometry are presented.…”