Abstract
Cyclic hydrogenation of an LmNi 5 -based alloy up to 3000 cycles at room temperature was conducted. Based on the (P-C-T) curve of the activated alloy, the initial charging pressures were set at four different values so that the saturated hydrogen loadings in equilibrium were controlled at H/M=1.0, 0.75, 0.50, and 0.25. The cyclic hydrogenation test was made for each loading. The absorption kinetic curves, hydrogen contents, and (P-C-T) curves after 1000, 2000, and 3000 cycles of testing were collected and compared with those of the activated sample. It is observed that the maximum hydrogenation capacities are reduced to 0.95, 0.92, 0.82, and 0.74 for the loadings of 0.25, 0.50, 0.75, and 1.0, respectively. The plateaus for the loadings of 0.25 and 0.50 do not change much, but are lowered and become more sloped for the loadings of 0.75 and 1.0, indicating that non-homogeneous chemical modification has been induced. The X-ray diffraction patterns show broadening of the peaks for all samples, and even the presence of some second phase for the loading of 1.0. The degradation is explained based on reduction of grain size, phase separation, and accumulation of strain energy in the alloy. © 2003 Elsevier B.V. All rights reserved.