Platinum Metals Rev., 1976, 20, (3), 85
High Temperature Thermodynamic Properties of Platinum-Titanium Alloys
Many of the enigmas of the interaction of platinum metal with other substances, in particular refractory oxides, are yielding to the systematic application of thermodynamic analysis, guided in no small measure by the Engel-Brewer predictions made over the past few years. Among the latest contributions to this field is the work recently reported by P. J. Meschter and W. L. Worrell (Metall. Trans. A, 1976, 7, (2), 299–305) who describe high temperature thermodynamic measurements on platinum-titanium alloys.
The study concentrated on platinum-rich alloys containing 2 to 25 atomic per cent titanium and over the temperature range 1150 to 1400K. The thermodynamic information was obtained from e.m.f. measurements, using a solid ionic conductor as the electrolyte in a cell of the type:
The e.m.f. data were used to derive the integral molar free energies, enthalpies and entropies for the range of platinum-titanium compositions studied, and also the partial molar quantities for platinum and titanium in the alloys. The activity of titanium in platinum was shown to be extremely low, that for the 20 per cent titanium alloy at 1300K being, a Ti=2.6×10−12. In accordance with Brewer ’ s predictions, the standard free energies of formation of the intermetallic compounds also proved to be highly negative , and kcal/g atom Ti at 1300K.
A tentative phase diagram is presented for the 0 to 25 atomic per cent titanium region of the system, based on the e.m.f. and X-ray data. It is proposed that TiPt8 forms peritectoidally from TiPt3 and Pt at 1350±20K.
The authors have made similar thermodynamic studies of the related systems, Pt-Zr and Pt-Hf, and expect to present these in a future publication.