D. Chartouni et al., THE INFLUENCE OF COBALT ON THE ELECTROCHEMICAL CYCLING STABILITY OF LANI5-BASED HYDRIDE FORMING ALLOYS, Journal of alloys and compounds, 241(1-2), 1996, pp. 160-166
We present an investigation of the influence of cobalt substitution fo
r nickel on the electrochemical cycle life of LaNi5-based alloys. Latt
ice expansion during hydriding was measured by means of X-ray diffract
ion for the alloys LaNi4Co, LaNi3.5CoAl0.5 and LaNi4.5Al0.5. The surfa
ce composition of the alloy grains was analysed by means of X-ray phot
oelectron spectroscopy (XPS). The XPS-depth-profiles are mentioned in
this paper. The mechanical and electrochemical properties of these all
oys and additionally of Zr0.2La0.8Ni4.5Al0.5 and Er0.2La0.8Ni4.5Al0.5
were also measured. We observed a strong correlation between the hardn
ess of these alloys and the cycling stability. Harder alloys lose capa
city more rapidly with cycling. Cobalt appears to lower the hardness a
nd therefore increase the cycle life of these alloys. It is well known
that alloys which show a large lattice expansion during hydriding, pu
lverize faster with cycling. This behaviour was clearly observed in ou
r measurements. The combination of a minimal lattice expansion and a l
ow hardness seem to have a synergetic effect in increasing the cycle l
ife.