The vapor pressures and the heat of vaporization of liquid uranium have been measured by collecting a known fraction of the vapor effusing from a Knudsen cell. The deposits were ``weighed'' by comparing the number of fissions upon thermal neutron irradiation with the fissions from a standard. The measured rate of vaporization is extremely sensitive to the residual pressure of oxygen in the vacuum at background pressures of the order of 10—7 mm Hg. With the aid of a theoretically derived expression the effusion rate can be extrapolated to zero oxygen pressure to yield for the vapor pressure the result that ,over the temperature range 1630 to 1970°K. This expression, together with heat capacity data for solid uranium, yields a value of 116.6 kcal/mole for the heat of sublimation at 0°K and predict a value of about 4.7 kcal/mole for the heat of fusion.
REFERENCES
1.
J. J. Katz and E. Rabinowitch, The Chemistry of Uranium (McGraw‐Hill Book Company, Inc., New York, 1951), p. 152.
2.
G. Derge and M. Cefola, Atomic Energy Commission Document CT‐2277, October 22, 1944.
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R. G. J. Fraser, Molecular Rays (The Macmillan Company, New York, 1931), pp. 14–15.
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D. C. Ginnings and R. J. Corruccini, Atomic Energy Commission Document MDDC‐589, January 23, 1947.
7.
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Schramm, Gordon, and Kaufmann, Atomic Energy Commission Document AECD‐2686, August 26, 1949.
9.
This second statement follows from the Raoult’s law with negative. Therefore .
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H. D. Hubbard and W. F. Meggers, Key to Periodic Chart of the Atoms (W. M. Welch Scientific Company, Chicago, Illinois, 1950).
11.
12.
E. G. Rauh and R. J. Thorn, unpublished data.
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© 1954 American Institute of Physics.
1954
American Institute of Physics
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