Potential response during the formation of the La-Ni alloy after molten salts electrolysis

Lanthanum was electrodeposited on a Ni substrate in molten chlorides and th e alloying treatment between the electrodeposit and the Ni substrate was ca rried out to obtain hydrogen absorption alloy film such as LaNi5. The chang e of open-circuit potential of the Ni substrate during the alloying process was also measured after the electrolysis in the molten salts. It was found that the potential shifted to noble direction with time and several potent ials showing constant values for a while were observed at -1.88 V, -1.76 V, -1.45 V and -0.50 V until reaching the rest potential of the Ni substrate, -0.27 V. The specimens were picked up at these various plateau potentials, cooled rapidly and subjected to the X-ray diffraction analysis, the EPMA. line analysis and SEM observation to identify the alloy phase formed at eac h potential. These constant potentials corresponded to the equilibrium pote ntials between two phases consisting of La-Ni alloys or Ni substrate on the surface. The relationships between these potentials and the alloy on the s urface were considered from these results.