Thermodynamic Properties of Alloys of Phosphorus with Calcium, Barium, Chromium, Manganese and Iron

Knudsen effusion mass-spectrometry has been applied to study the thermodynamic properties of alloys of with Ca, Ba, Cr, Mn and Fe in the solid and liquid state. Evaporation was accompanied by decomposition of the alloys to the components. Complex molecules (FeP and Fe P) were discovered only over Fe–P alloys. In addition to the Knudsen experiments heat capacities of some phosphides were obtained in the temperature range of 113 to 873 K using a DSC thermal analyzer. The absolute entropies of the phosphides calculated according to the second and the third law of thermodynamics agreed within the limits of experimental error. The thermodynamic properties of the melts were approximated by the associated-solution model. The Gibbs energies of formation of the associative complexes were found to correlate with those of the phosphides. Both these functions altered in accordance with the electronegativity of the metal component. The calculated phase diagrams of the studied systems are in good agreement with published data.