Sang Ge

A Surface Analytical Study on Poisoning of LaNi4.7AL0.3 by CO

ABSTRACT In this paper, studies have been made concerning the poisoning mechanism. The processes of poisoning of LaNi47Al0.3 alloy are analyzed in detail by means of X-ray photoelectron spectroscopy (XPS), second ion mass spectroscopy (SIMS), Auger-energy spectroscopy (AES) and X-ray diffraction (XRD). The changes of the valence and the concentration distribution of the elements of the alloy LaNi4.7Al0.3 poisoned by CO are studied. The process and the mechanism of CO’s poisoning of alloy LaNi47Al0.3 are proposed as follows: CO is absorbed on the surface of alloy, part of which reacts with La forming LaC2 and La2O3, or reacts with Ni forming NiO and C in the surface layer, the rest of the CO is decomposed into C and O, which diffuse into the bulk to react with La, Ni and Al. These results in phase-split reaction in surface layer of the particle, and enrichment of La and impoverishment Ni on the surface have taken place. The poisoning effect decreases with a increase of depth. The diffusion depth of C is within 600 Å in the surface layer, and that of O is within 1000 Å. The oxide film and carbonizing film prevent the H-storage alloys from further absorbing hydrogen, which leads to a deceleration of the H-storage capability. Moreover, The formation of a new phase with poor H-absorption capability is caused by the phase split reactions, which is one of reasons for the decrease of H-absorption property of the H-storage alloys.