It was recalled that information on interdiffusion in intra-lanthanide systems was limited, and that no data were available for the present system. It was of particular importance because the component elements were fission products that were generated during the irradiation of U-Pu-Zr alloys. The present elements migrated, interacted with steel cladding, and formed phases which could melt at low temperatures. In the present work, Ce-Nd diffusion couples were annealed at 425, 550, and 650C. Both intrinsic and interdiffusion data were obtained, as well as the activation energy as a function of composition. On the basis of an analysis of the results (tables 31 and 32), it was deduced that Ce-Nd interdiffusion increased in the -Ce phase and decreased in the -Ce plus -Nd phase, with increasing Nd concentration. The activation energy for Ce-Nd interdiffusion in the -Ce plus -Nd phase was about 150kJ/mol. The activation energy in the -Ce phase was lower, and changed with concentration. Interdiffusion was generally higher in the -Ce phase. The Ce intrinsic diffusivity was higher than that of Nd, and the ratio of the Ce intrinsic diffusivity to that of Nd increased with increasing temperature. Consequently, the Kirkendall plane shifted to the Ce side of diffusion couples. On the basis of discontinuities in the concentration profiles in these couples, it was suggested that the -Ce plus (-Ce, -Nd) 2-phase region of the Ce-Nd phase diagram should be shifted more towards the Nd side of the diagram.

D.D.Keiser: Scripta Metallurgica et Materialia, 1995, 33[6], 959-65

Table 31

Interdiffusion Coefficients for Ce-Nd Alloys

Table 32

Activation Energies for Interdiffusion

in Ce-Nd Alloys at 425 to 650C