A study on the microstructural change of surface of the intermetallic compound LaNi5 by hydrogen absorption

Abstract

It is well known that the surfaces of metals and intermetallics that form hydrides play a crucial role in hydrogen absorption and desorption processes. There has been considerable interest in the surface of LaNi[sub 5] due to its high reactivity with hydrogen. Schlapbach et al. used x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and magnetic properties measurement techniques to investigate the surface of LaNi[sub 5]. In their experiments, surface segregation and decomposition were found to occur after hydriding which they concluded was due to the small amount of oxygen present as an impurity. Stucki et al. reported that a surface decomposition layer of 10 nm in thickness formed after several hydrogen absorption-desorption cycles at room temperature with 99.999% H[sub 2]. It is very difficult to prepare the TEM specimen of LaNi[sub 5] because it is brittle and breaks down into powder of 4-20 [mu]m particle size on first hydriding. This is believed to be the major difficulty for TEM studies. The conventional crushing methods for TEM specimen preparation of a powder samples damages the surface of LaNi[sub 5] particles. In the present study, TEM specimens of LaNi[sub 5] powders are prepared by a ion beam thinning methods, and analytical more » electron microscopy (AEM) analysis on the surface of LaNi[sub 5] is carried out in order to understand better the surface decomposition phenomena. « less