Effect of the sixth period elements on the melting and transformation temperatures of praseodymium: Part II. Thermodynamic analysis

A thermodynamic analysis of the praseodymium-rich alloys containing Os, Ir, Pt, Au, Hg, Tl, Pb, and Bi indicated that most of the solutes dissolved in praseodymium follow ideal solution theory over a limited range of temperatures up to 40° to 135°C below the melting point of praseodymium (or concentrations out to 3 to 8 at. pct solute). The activity coefficients, activities, and excess partial free energies were calculated for liquid praseodymium at its melting point and for β-Pr at its α to β transformation temperature. The so-calledQ parameter has also been determined for these praseodymium systems, and it was found to exhibit the usual periodic dependence on the solute metal. As a result of these analyses a method has been developed which makes it possible to calculate phase boundaries for undetermined systems. This technique is shown to be especially valuable in calculating unknown phase boundaries for lanthanide-rich alloys, but for other metal solvents this method will probably be of a lesser utility.