Potential Response During the Formation of the La-Ni Alloy After Molten Salts Electrolysis

Abstract

Lanthanum was electrodeposited on a Ni substrate in molten chlorides and the alloying treatment between the electrodeposit and the Ni substrate was carried out to obtain hydrogen absorption alloy film such as LaNi₅. The change 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 potentials 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 each potential. These constant potentials corresponded to the equilibrium potentials between two phases consisting of La-Ni alloys or Ni substrate on the surface. The relationships between these potentials and the alloy on the surface were considered from these results.