Abstract
The structure and phases of alloys of uranium and two of the light platinum metals, Pd and Rh have been studied. Using X-ray diffraction, metallography and electron microscopy, the phase diagram of the noble metal-rich end of the ternary system, U-Pd-Rh has been established. Portions of the binary systems, U-Pd and U-Rh have also been studied and the Pd-Rh phase diagram re-established. The structure of the solid phases which are stable at 1050°C, 1150°C and 1250°C have been determined. A thermodynamic calculation of the isothermal sections of the ternary U-Pd-Rh system at 1350°K, 1450°K and 1550°K was carried out. This confirms the phases that the conventional methods were used to establish. It has been suggested that UPd[4] has a defect lattice with some of the uranium sites being vacant. On addition of Rh this compound phase (UPd[4] or alpha[1]) extends continuously to include the 1:3 ratio which characterises the A-B compounds with L12 structures. It is also shown that whereas Pd is dissolved in URh[3], solubility of Rh in UPd[3] is very restricted. It has been found that the miscibility gap in the Pd-Rh system widens upon addition of uranium and that the critical point therefore rises in the ternary system although the ternary critical point is unstable. Electronic effects are responsible for the large solubility of U in Pd (delta-solid solution) as compared with the other Pt metals. The pseudo-binary system UPd[4] and URh[3] (both having the L12 structure) has a miscibility gap.