Vapor pressures of Bi-2 (g) over La0.03Bi0.97 and two-phase mixtures of Bi
+ LaBi2. LaBi2 + LaBi, LaBi + La4Bi3, La4Bi3 + La5Bi3, and La5Bi3 + La2Bi w
ere measured in the temperature range from 795 to 1066 K with a time-of-fli
ght mass spectrometer equipped with a tungsten Knudsen cell. The vapor pres
sure of Bi-2 (g) over the two-phase mixtures of La2Bi + La could not be det
ected experimentally in this temperature range. The thermodynamic activity
of bismuth was determined from the vapor pressure of Bi-2 (g). Thermodynami
c 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 previou
s study by graphic integration of the Gibbs-Duhem equation. Thermodynamic q
uantities such as Gibbs Free energy of formation, excess enthalpy, etc., we
re also calculated from the thermodynamic activities.