THERMODYNAMIC PARAMETERS OF LIQUID COBALT-PALLADIUM ALLOYS BY COMPUTER-AIDED KNUDSEN CELL MASS-SPECTROMETRY

The computer-aided Knudsen cell mass spectrometry has been applied for the determination of the molar thermodynamic excess properties of liquid binary Co-Pd alloys. Thermodynamic evaluation followed the ''Digital Intensity-Ratio'' (D.I.R.)-method. Two-parameter thermodynamically adapted power (TAP) series are used for the algebraic representation of the molar excess properties. Liquid Co-Pd alloys are characterized by exothermic molar heats of mixing H(E), slight negative molar excess entropies, and negative molar excess Gibbs energies G(E). At 1850 K the minimum H(E) values is -13 000 J/mol (55.1 at.% Pd), the minimum S(E) value is -4 J/(mol K) (52.7 at.% Pd), and the minimum G(E) value is -5700 J/mol (57.9 at.% Pd). At 1850 K the thermodynamic activities of both components, Pd and Co, show slight negative deviations from Raoult's law over the entire range of composition. The Co activities of the Co-richest alloys (x(Pd) < 0.14) are nearly ideal.