EFFECTS OF OXYGEN ON THE SOLIDIFICATION MICROSTRUCTURE OF LANI5

Modern nickel/metal hydride batteries and cryogenic refrigerators base d on hydrogen absorption rely heavily on the rare-earth intermetallic compound LaNi5. Proper stoichiometry is crucial to obtain optimum perf ormance in this compound. Oxygen segregation during solidification of these materials can lead to depletion of lanthanum through the formati on La2O3. This, in turn, can greatly reduce the phase purity of these materials, thus limiting their performance in many applications. A ser ies of LaNi5 alloys were produced by nonconsumable arc melting with va rious oxygen contents. These alloys were investigated principally by A uger spectroscopy. Correlations were made between the solidification m icrostructure and the oxygen content at a known solidification rate. H ydrogen storage capacities were also measured to evaluate the absorpti on properties of the solidification-derived microstructure. Increasing oxygen content was found to reduce the hydrogen absorption capacity o f these materials.