Thermal hydriding of some Ni-based intermetallic compounds

Abstract

The behavior of various types of Ni-based intermetallic alloys, namely NiZr, NiZr 2 and LaNi 5 , in thermal hydriding-dehydriding cycles has been investigated from room temperature to 1173K at various initial pressures ranging from 0.2 to 3.3 MPa absolute. It has been found that, upon hydriding, the rate of hydrogen absorption becomes enormous at specific temperatures, regardless of the initial hydrogen pressure over the samples. The same phenomenon has been observed upon dehydriding (i.e. the rate of hydrogen release becomes high at certain temperatures). The incident has been found to be reproducible. The specific temperature changes from one alloy to another during hydriding cycles. A method by which to record and present the phenomenon has been suggested, plotting the rate of change of hydrogen in the hydride with the temperature, where these sudden changes appear as sharp and distinctive peaks. This phenomenon has been attributed to the formation of a stable hydride phase in the case of LaNi 5 , and a phase transition in both NiZr and NiZr 2 .