VAPORIZATION STUDY ON LANTHANUM-CERIUM ALLOYS BY MASS-SPECTROMETRIC METHOD

The partial vapor pressures of La(g) and Ce(g) over LaxCe1-x alloys (x = 0.00, 0.05, 0.29, 0.50, 0.80, 1.00) were measured with a time-of-fl ight mass-spectrometer equipped with a tungsten Knudsen cell over the temperature range of 1592-1781 K. The thermodynamic activities of lant hanum and cerium in the liquid alloys were determined by comparing the partial vapor pressures of La(g) and Ce(g) over the alloys with those over the purl metals, respectively. The thermodynamic activities were also calculated from the ion intensity ratios of two components (lant hanum and cerium) in the alloys using the equation derived by Belton a nd Fruehan. Both activities for each element, thus obtained, were in g ood agreement with each other and almost obeyed Raoult's law. The part ial molar Gibbs free energy, and the Gibbs free energy of formation we re calculated from the thermodynamic activity values. (C) 1998 Elsevie r Science B.V.