DETERMINATION OF THE FREE ENTHALPY OF FORMATION OF THE AU-TE MELTS BYKNUDSEN-CELL EFFUSION COMBINED WITH A MASS-SPECTROMETER

The vapor pressure of Te over the Au-Te melts was measured in the 0.48 less than or equal to x(Te) less than or equal to 0.67 range with the help of a Knudsen cell apparatus combined with a varian-Mat mass-spec trometer. The activity of Te and the partial Gibbs energy of Te in the melt, a(Te) and g(Te)(xs,f), were deduced respectively The integral G ibbs energy of formation of the melt, g(xs,f) was calculated from Gibb s-Duhem integration. g(xs,f) at 753K shows a minimum of -1.94 kJ.mol(- 1) at x(Te) = 0.55. From the Gibbs energy of formation of the melt and the thermodynamic properties of pure Te the phase boundary correspond ing to the liquid + pure Te was calculated in good agreement with the experimental phase diagram. From the enthalpy of formation of the AuTe 2 compound combined with Gibbs energy of the melt we also calculated t he entropy of formation of the compound at its melting point and we co uld calculate the liquidus line of the AuTe2 + liquid domain. The agre ement with the experimental phase diagram is good too.