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Vapour-pressures of NpF6 and PuF6; thermodynamic calculations with UF6, NpF6 and PuF6

1959; Pergamon Press; Volume: 11; Issue: 2 Linguagem: Inglês

10.1016/0022-1902(59)80054-3

1878-1225

Bernard Weinstock, Edward Weaver, John G. Malm,

Nuclear Materials and Properties

The vapour-pressures of NpF6 and PuF6 have been measured from 0° to 77°C with a quartz sickle-gauge. The data have been fitted to interpolation formulas from which the triple points, 55·10°C, 758·0 mm Hg for NpF6 and 51·59°C, 533·0 mm Hg for PuF6, and boiling points, 55·18°C for NpF6 and 62·16°C for PuF6, have been calculated. The derived heat and entropy of fusion for NpF6 and PuF6 are 4198 and 4456 cal mole−1 and 12·79 and 13·72 cal mole−1 deg−1 respectively. Upon comparison with UF6 several anomalies appear which are discussed and partially explained in the text. The heats of sublimation and vaporization of UF6, NpF6 and PuF6 are calculated from 273·15° to 350°K. Satisfactory agreement with the Third Law of thermodynamics is obtained from the thermodynamic data of UF6. The heat of vaporization of UF6 at 0°K is calculated to be 12965 cal mole−1 using the value of b = −3·6 × 103T−2cal mole−1 (mm Hg)−1 for the second virial-coefficient and a new assignment for the fundamental vibration frequencies of UF6; ν1 = 667, ν2 = 535, ν3 = 623, ν4 = 181, ν5 = 202, and ν6 = 140 cm−1. The vapour-pressure of UF6 at 0°C is remeasured to be 17·65 mm in agreement with a thermodynamic calculation.