Eutectoid decomposition of Co5Ce

Diffusion couples formed between cobalt and cerium provide useful information about the eutectoid transformation involving Co
5
Ce. The presence of Co
5
Ce in the couple formed at 700°C and its absence in the couple formed at 650°C provides supporting evidence for the instability of Co
5
Ce. A transformation of an unknown nature was observed in the Co
17
Ce
2
phase held for a long period at 650°C.