Effects of oxygen on the solidification microstructure of LaNi5

Abstract

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