Vapor Pressure Measurements of Lanthanum–Bismuth Alloys by Mass-Spectrometric Method1

Vapor pressures of Bi2 (g) over La0.03Bi0.97 and two-phase mixtures of Bi+LaBi2 , LaBi2+LaBi, LaBi+La4Bi3, La4Bi3+La5Bi3 , and La5Bi3+La2Bi were measured in the temperature range from 795 to 1066 K with a time-of- flight mass spectrometer equipped with a tungsten Knudsen cell. The vapor pressure of Bi2 (g) over the two-phase mixtures of La2Bi+La could not be detected experimentally in this temperature range. The thermodynamic activity of bismuth was determined from the vapor pressure of Bi2 (g). Thermodynamic activities of lanthanum over alloys were derived from those of bismuth in the alloys in this study and that of lanthanum in the bismuth in a previous study by graphic iIntegration of the Gibbs Duhem equation. Thermodynamic quan- tities such as Gibbs free energy of formation, excess enthalpy, etc., were also calculated from the thermodynamic activities.