SURFACE-PROPERTIES OF LANI5 - A REINVESTIGATION

Although a number of surface analysis reports are available on the LaNi5 system, yet a clear picture of the actual species involved and their consequences on the activation and deactivation processes has not been reached. Moreover, differences of opinion have been seen among the researchers. The present results distinctly indicate that the air exposed samples are completely contaminated with a variety of oxygenated species (such as oxides, hydroxides and carbonates) of the constituent elements, hitherto not reported by others. The protective nature of such species in regard to the durability of the alloy and the formation of supported-metal type species upon activation accounts for its excellent behaviour. The relative higher stability of LaNi5 over CaNi5 under cyclic operating conditions has been explained based on surface energy criteria of the constituent elements rather than the deterioration initiated by hydrogen and/or gaseous impurities alone. In addition, the specific importance of X-ray induced Auger electron spectroscopy (XAES) technique in conjunction with X-ray photoelectron spectroscopy (XPS) has been highlighted in the identification of different species.