On the cyclic hydrogenation stability of an Lm(NiAl)5-based alloy with different hydrogen loadings

Cyclic hydrogenation of an LmNi(4.8)Al(0.2) alloy with different hydrogen loadings up to 3000 cycles at room temperature was conducted, and the performance is compared with that of a similar alloy containing no Al. The saturated hydrogen loadings in equilibrium were controlled at H/M = 0.75 and 1.00. The P-C-T curves after 1000, 2000, and 3000 cycles of test were collected at T = 30, 50, and 70 degrees C and were compared with those of the activated sample. After 3000 cycles, it is observed that the maximum hydrogenation capacities for the loadings of 0.75 and 1.00 are reduced to 0.89 and 0.87, respectively. The plateaus do not change much for T = 30 and 50 degrees C, but become little sloped with no observable split at 70 degrees C, indicating that the formation of an intermediate phase beta-LmNi(5)H(3) may be suppressed by substitution of Al for Ni. The X-ray diffraction patterns indicate that the strains associated with repeated hydrogenation are isotropic for all samples. It is concluded that partial replacement of Ni by Al has substantially improved the cyclic hydrogenation stability of the Lm(NiAl)(5)-based alloy. The degradation in cyclic stability for the alloy containing no Al is related to the formation of the P-hydride and phase separation. (c) 2004 Elsevier B.V. All rights reserved.