Diffusion of 54Mn in stainless steel and nickel in the presence of sodium

Tracer diffusion of 54Mn in austenitic stainless steel and nickel has been measured in the temperature range of 673 to 1023 K in presence of argon or sodium. 54Mn is deposited by vacuum sublimation-condensation. After annealing the samples are sectioned using a glow discharge system and the surface concentration of 54Mn is determined with a windowless flow counter. In this temperature range, these studies show that the lattice diffusion is unimportant, while the grain-boundary diffusion is the principal process of 54Mn penetration in both nickel and stainless steel. For the same temperature and annealing-time the diffusivity of 54Mn in both nickel and stainless steel in presence of sodium is different from that in argon. It is necessary to consider the influence of the medium in contact with the metal surface (argon, vacuum, sodium, etc.) on the diffusivity of an element in a metal. In our case the distribution of 54Mn between the liquid sodium and a solid metal is important in relation to their diffusivity in the solid metal. (author)