The effect of the microstructure upon the diffusion of protium in 5 alloys was studied by using the desorption method. One of the alloys was the protium-absorbing alloy Ni5La; the stoichiometric composition. The others were 2-phase alloys, LaNix, where x ranged from 5.5 to 8.1 and consisted of Ni5La plus Ni. By analysing desorption curves at 353 to 573K, the protium diffusivity in the alloys was determined by assuming that the sample particles were spheres. The Arrhenius plots for diffusion in all of the alloys were linear. The diffusivity in LaNix, when x was 6.0, 6.5 and 8.1, increased with increasing x-value. It was greater than that in Ni5La, and the diffusivity in Ni5.5La was the lowest within the studied temperature range. The published value of the diffusivity in Ni5La, as obtained using the quasi-elastic neutron scattering method, fell in the middle of the coefficients for the 5 alloys. It was suggested that the effective surface area of the Ni5La desorption specimen was reduced by the formation of an oxide layer and that, in the 2-phase alloys, protium diffusion was enhanced by a network of Ni which was deformed by expansion of the Ni5La phase due to the absorption of protium. The Ni phase in Ni5.5La was insufficient to form such a network.

Protium Diffusion in La-Ni Alloys. K.Gunji, H.Takamura, M.Okada, Y.Iijima: Journal of Alloys and Compounds, 1999, 293-295, 270-4