Computerunterstützte Knudsenzellen‐Massenspektrometrie: Die thermodynamischen Mischungsfunktionen flüssiger Gold‐Palladium‐Legierungen

Abstract

AbstractThermodynamic investigations on liquid Au—Pd alloys have been performed by means of a computer‐aided mass spectrometer in combination with a high temperature Knudsen cell unit with improved temperature measurement. A further development of the “Algebraic Intensity‐Ratio”‐method (A.I.R.) has been applied for determining the thermodynamic excess functions. T.A.P.‐series (Thermodynamically adapted power series) with three adjustable parameters are used for the algebraic representation of the thermodynamic excess properties. At 1850 K the molar excess Gibbs energy GE is negative (minimum: — 1300 J/mol at 33.9 at.% Pd) nearly over the whole range of concentration, only the alloys with more than 85 at.% Pd show slight positive GE‐values (maximum: 78 J/mol at 93.2 at.% Pd). The molar heats of mixing HE, and the molar excess entropies SE show at 1850 K a similar behaviour. These quantities are mainly negative; slightly positive values occur only for alloys with more than 70 at.% Pd. The minimum HE‐value is —8220 J/mol (28.7 at.% Pd), and the minimum SE‐value is —3.8 J/mol · K (28 at.% Pd). The maximum HE‐value is 1390 J/mol at 88.15 at.% Pd. and the maximum SE‐value is 0.7 J/mol · K (87.5 at.% Pd). At 1850 K the thermodynamic Au‐activities aAu are found to show slight negative deviations from ideality over the whole concentration range. The same behaviour is observed for the Pd‐activities for Pd‐concentrations less than 50 at.‐% Pd. The Pd‐activities of alloys with more than 50 at.‐% Pd show slight positive deviations from Result's law.