Effect of nickel addition and microstructure on absorption and desorption behavior of hydrogen in LaNi5

Hydrogen desorption behavior of LaNi5+x-H (x = 0, 1 and 3) alloys was studied by means of the thermal desorption spectrum (TDS). Two methods of arc-melting and melt-spinning were used to obtain different microstructures of the alloys. In the TDS of the arc-melted alloys, the hydrogen desorption peak which corresponds to the transformation from the γ-phase (hydride LaNi5H6) to the α-phase (solid solution) shifted to lower temperature with the increase in the nickel content. On the other hand, for the melt-spun alloys, no dependence of the peak temperatures on the nickel content was observed. The decrease of the peak temperature means the decrease in the stability of the γ-phase. With the help of measurements on the pressure-composition (P-C) isotherms and the pressure differential scanning calorimetry (PDSC), the role of the Ni phase-network formed in the arc-melted alloys is discussed.