The effect of microstructure on the diffusion of protium (hydrogen) in La-Ni alloys was studied by the desorption method. Five alloys were prepared; one was the well known protium absorbing alloy LaNi5 with the stoichiometric composition, and the others were the two phase alloys LaNix (x = 5.5-8.1) consisting of the LaNi5 phase and the Ni phase. By the analysis of the desorption curves for the temperature range 353-573 K, the diffusion coefficient of protium in the alloys was determined under the assumption that the sample particles were spheres. The Arrhenius plots of the diffusion coefficients, D, for all the alloys show linear relationships. The value of D in LaNix (x = 6.0, 6.5, 8.1) increases with increasing the value of x, and they are larger than that in LaNi5, although the value of D in LaNi5.5 is the smallest in the temperature range examined. The literature value of D in LaNi5 obtained by the quasielastic neutron scattering (QNS) method is in the middle of the coefficients of the five alloys. This suggests that the effective surface area of the LaNi5 specimen for the desorption is reduced by the formation of oxide layer and that in the two phase alloys the protium diffusion is enhanced via a network of the Ni phase deformed by the expansion of the LaNi5 phase due to the absorption of protium, although the Ni phase in LaNi5.5 is insufficient to form the network.
|Number of pages||5|
|Journal||Journal of Alloys and Compounds|
|Publication status||Published - 1999 Dec 20|
|Event||Proceedings of the 1998 International Symposium on Metal-Hydrogen Systems - Fundamentals and Applications (MH98) - Hangzhou, China|
Duration: 1998 Oct 4 → 1998 Oct 9