Hexafluoride vapor pressure

Tungsten hexafluoride is shipped as a Hquid under its own vapor pressure in nickel or steel cylinders in quantities of 45 kilograms per cylinder or less however, it has been shown that the purity of WF packaged in steel cylinders can degrade over time (21). It is classified as a corrosive Hquid by the... 

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. 

Dimethylamino Tellurinm Pentafluoride2 8.0 g (33 mmol) of tellurium hexafluoride, 2.25 g (3 ml, 19 mmol) of dimethylaminotrimethylsilane, and 4 ml of fluorotrichloromethane are condensed into a U-trap fitted with a breakseal, the trap is sealed, warmed slowly to —78°, and held at this temperature for 12 h with occasional shaking. The breakseal is opened and the products are distilled through traps at —78° and —196°. The yellow liquid that condenses in the —78° trap is the product. It decomposes above 35° but can be stored without decomposition at —80° for several months2 yield 100% vapor pressure 3 torr at 20°. 

The quantity of molybdenum hexafluoride may be measured either in a preweighed vessel or by vapor-pressure measurements in a previously calibrated volume on the line. It was pointed out by the checker that while molybdenum hexafluoride is being handled in the line the stopcock D should normally be kept closed. 

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 ... 

The physical properties of tungsten hexafluoride are given in Table 5 [54-57], Tungsten hexafluoride is a colorless gas at room temperature and is ten times as heavy as air. It condenses into a pale yellow liquid at 17.5 C and forms a white solid below 2.3°C [54]. The vapor pressure is given by the following equations [56] ... 

It was clear that if the formulation O2+ [PtF,]- were true, then platinum hexafluoride should oxidize molecular oxygen. A sample of platinum hexafluoride was therefore prepared, and since it has a vapor pressure of 80 mm. at room temperature, the interaction with molecular oxygen was followed tensimetrically. The deep red (bromine colored) platinum hexafluoride vapor reacted instantly with the oxygen in a 1 1 molar ratio to give the familiar red compound. Interestingly, the solid made by this method at low temperatures, is iso-morphous and almost isodimensional with rhombohedral potassium hexafluoroplatinate (V). At higher temperatures transition to the cubic phase occurs. 

Xenon hexafluoride is a colorless solid with a vapor pressure of about 30 mm. at 25°. In a poly (chiorotrifluoro-... 

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

By the sublimation of sulfur hexafluoride in 1933 Denbigh and Whytlaw-Gray (66, 67) found a small liquid residue which they identified as S2Fh>. From 20 liters of crude SF6 gas they recovered only about 20 ml of S2Fio vapor. This method of preparation has been confirmed by others (34, 100, 101, 269, 270, 307). The substance is a colorless volatile liquid which has a surface tension of 13.9 dyne/cm at 0°C. From its vapor pressure, logw Pmm = 7.95 — 1530/T, its heat of vaporization is calculated to be 7000 cal/mole (67). Liquid S2Fi0 has a specific electrical conductivity somewhere between 10 12 and 10 14 ohm-1 cm-1, a dielectric constant of 2.030 at 10° and a density of 2.081, 2.054, and 2.028 gm/ml at 4°, 12°, and 20°, respectively. Its dipole moment is 0 (155). Each sulfur atom is linked octahedrally to five fluorine atoms at a distance of 1.56 A and to the other sulfur atom at a distance of 2.21 A (7, 129). 

Weinstock et al. (87) have made an exceedingly thorough study of the vapor pressure of neptunium and plutonium hexafluorides (Table X). The vapor pressures of NpF6 and PuF6 are compared to the UF6 vapor pressures... 

Vapor Pressure Data for Actinide Element Hexafluorides 1... 

Malm that the volatility anomaly of solid NpFe is related to the fact that of the three actinide hexafluorides, neptunium hexafluoride is the only one found to be paramagnetic. If the paramagnetism of neptunium hexafluoride is reflected in a higher magnetic entropy for the solid than either its vapor or liquid possesses, an increase in magnetic entropy would also tend to decrease the vapor pressure of the solid. This is in the opposite direction to that actually observed. It may, therefore, be necessary to account for... 

Krypton difluoride is a white crystalline solid with a vapor pressure of about 40 mbar at 0°C. It is thermally unstable and decomposes slowly at room temperature. Therefore, it should be stored preferably in nickel or Monel containers held at low temperature (below — 60°C). Krypton difluoride is stronger oxidizing agent than elemental fluorine, dioxygen difluoride, or xenon hexafluoride. 

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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. 

Note that aluminum trifluoride, silicon tetrafluoride. and sulfur hexafluoride have the interesting property, as does carbon dioxide, of subliming at I atm pressure without melting. The temperatures given in the table as the boiling points of these two substances are in fact the subliming points, when the vapor pressure of the crystals becomes equal to 1 atm. 

Sulfur hexafluoride is a colorless, odorless, nontoxic, nonflammable gas that has a high dielectric strength and serves widely as an insulating gas in electrical equipment. At atmospheric pressures it sublimes directly from the solid to the gas phase and does not have a stable liquid phase unless under a pressure of more than 32 psia (221 kPa, abs). It is shipped as a liquefied compressed gas at its vapor pressure of 298 psig at 70°F (2050 kPa at 21.1°C). 

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