HIGH-TEMPERATURE PROPERTIES AND ALLOYING BEHAVIOR OF THE REFRACTORY PLATINUM-GROUP METALS
BATTELLE MEMORIAL INST COLUMBUS OH
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The occurrence of many phases in platinum-group metal alloys, or even more generally in transition metal alloys, correlates amazingly simply with electronatom ratio or as we have preferred to call it, group number. One example is the HCP structure that occurs in alloys in the average group number range 7-8.5. The axial ratio, ca, was a sensitive measure of the electronic state. The ca-composition relationship in some 20 HCP alloys containing platinum-group metals was determined. The axial ratio appears to correlate well with phase stability the smaller the axial ratio, the more stable the phase, with the HCP phase becoming unstable relative to cubic phases as ca approaches 1.61. A theoretical study of Laves phases based on an elastic model was performed. A theoretical study of allotropism was initiated and is continuing. This study was very productive in providing clues to the phase-stabilizing factors. It has been tentatively concluded that the low temperature phases are generally characterized by a high density of states at the Fermi level and that the high temperature phases are characterized by high vibrational entropies.
- Properties of Metals and Alloys
- Atomic and Molecular Physics and Spectroscopy