Abstract
The vapor pressure of liquid cerium has been redetermined because the results of previous studies are not consistent with the thermodynamic properties of gaseous and liquid cerium. Both mass effusion and mass spectrometric measurements have been combined to yield the vapor pressure equation: log 10{p( Ce/ atm}=(5.500±0.029)−(21070±55)K/T, (1525 to 2225K) The mass effusion results were obtained by the total mass loss method and by neutron activation analysis of collected samples of the vapor. The mass spectrometric observations also demonstrated that oxygen contamination which vaporizes as CeO(g) could be reduced to an insignificant level only after approximately 20 per cent of the sample had been evaporated. The enthalpy of vaporization of cerium and its standard deviation at 2000 K evaluated from the temperature dependence of the vapor pressure is (96 420±250) cal mol −1, and that evaluated from the measured values of the vapor pressure combined with the free energy functions of liquid and gaseous cerium is (96 125±50) cal mol −1. The enthalpy of sublimation calculated at 0 K is (99 350±500) cal mol −1. The measured value of the entropy of vaporization and its standard deviation at 2000 K is (25.17±0.13) cal K −1 mol −1 compared with the value (25.00±0.15) cal K −1 mol −1 calculated from absolute entropies.
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