Correlation between microstructure and hydrogen storage capacity in MmNi(5) alloys with Al, Mn and Sn substitutions

The morphology and compositions of the phases present in the microstructure s of annealed hydrogen storage MmNi(5-x)Al(x) (x = 0.4 and 0.8), MmNi(5-x)M n(x) (x = 0.4 and 0.8) and MmNi(4.6)Sn(0.4) alloys (Mm-Indian Mischmetal) h ave been studied. Al, Mn and Sn substitutions in MmNi(5) produce two-phase microstructures. The precipitates tend to become globular upon annealing. T he hydrogen storage capacity of these alloys correlates with the volume fra ction of the matrix phase. The higher the matrix volume fraction, the highe r the hydrogen storage capacity. The elements that constitute Mm are presen t in greater proportion in the major constituent matrix phase of the two ph ase structure. Only trace amounts of these elements could be found in the p recipitate phase in the Al- and Mn- substituted alloys. However, for the Sn -substituted composition, the proportion of these elements is nearly the sa me in matrix and precipitate phase. (C) 1999 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.