Uranium hexafluoride, vapor pressure

Uranium hexafluoride is probably the most interesting of the uranium fluorides. Under ordinary conditions, it is a dense, white solid with a vapor pressure of about 120 hull ai room temperature. It can readily be sublimed or distilled, and it is by far the most volatile uranium compound known. Despite its high molecular weight, gaseous UFg is almost a perfect gas, and many of the properties of the vapor can be predicted from kinetic theory. 

A laboratory preparation is the reaction of uranium metal and CIF3.20 The hexafluoride forms colorless crystals (mp 64.1°C) with a vapor pressure of 115 mm Hg at 25°C. It is a powerful fluorinating agent (e.g., it converts CS2 to SF4) and is rapidly hydrolyzed by water. The hexafluoride is also used to make UF4 and UF5 by the following reactions ... 

B7. Brooks, A. A., and P. Wood Vapor Pressure Tables for Liquid Uranium Hexafluoride, Report K-722, Nov. 21, 1957. 

The triple points are seen to decrease in the order UF, NpF , and PuF. It can also be seen that, unlike uranium hexafluoride, neptunium hexafluoride and plutonium hexafluoride possess a liquid range at atmospheric pressure. Heats of sublimation and vaporization are shown in Fig. 9, also taken from the paper of Weinstock et al. (87). 

While other materials have been used as feed to uranium-enrichment processes, the most widely used volatile compound of uranium is the hexafluoride. At room temperature, UFe is a colorless solid with a density of 5.1 g/cm. It sublimes at atmospheric pressure, and at room temperature has a vapor pressure of 100 torr. The main disadvantage of working with UFe is its high chemical reactivity. It reacts vigorously with water, but is not very reactive with dry air. UF5 reacts with most metals however, nickel, copper, and aluminum are resistant. This holds only for pure UFg the presence of even small amounts of HF increases the rate of attack on even the resistant metals. 

Uranium hexafluoride (UF ), also called hex, is probably the best known and most widely investigated compound of uranium mainly because it is the only uranium compound with significant vapor pressure at ambient temperatures and therefore an essential raw material for most commercial isotope enrichment processes. UFg is a white monoclinic crystalline solid that sublimes directly to a gas (reaches atmospheric pressure at 56.5°C), but when heated in a closed vessel will melt at 64.05°C, which is the triple point where the solid, liquid, and gas phases coexist, as shown in Figure 1.8. This is probably one of the most weU-recognized phase diagrams in the chemical literature. 

Uranium hexafluoride, UFg, is a white solid that sublimes (vaporizes without melting) at 57°C under normal atmospheric pressure. The compound is used to separate uranium isotopes by effusion. What is the rms speed (in m/s) of a uranium hexafluoride molecule at 57°C ... 

Uranium hexafluoride has a vapor pressure at 56°C equal to 765 torr, so UEs is a gas at 60°C and 1.000 atm. Various diffusion and thermal diffusion processes were used in the Manhattan Project of the United States in World War II to separate gaseous UEs molecules from UFg molecules. 

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