VAPOR PRESSURE AND CRYSTAL STRUCTURE OF CURIUM METAL

The vapor pressure of liquid and solid curium metal between 1179° and 2068°K and between 10-10 atm and 0.1 mm was measured by the Knudsen effusion method to be log10P(atm) = (4.74±0.37) - (18 060±590)/T(°K); Δ∐1600°K and ΔS°1600°K for vaporization are 82.6±2.7 kcal/g-atm and 21.7±1.7 eu, respectively. A previously unreported fee close-packed structure for curium metal was identified with a=4.382±0.004 Å, and a density of 19.26 g/cm3, corresponding to a+4 metallic valence. The entropy of condensed curium is indicated to be relatively high by the low heat of fusion and by the ΔH°298°K for vaporization calculated by second- and third-law methods. The heat of vaporization of curium may be explained from the opposing effects of a quadrivalent metal and a 5f66d27s2 to 5f 76d7s2 transition on vaporization.