Kh. B. Kushkhov, M. K. Vindizheva, R. A. Mukozheva, F. A. Kisheva.
ABSTRACT
Using the methods of cyclic chronovoltammetry, chronopotentiometry, and open-circuit chronopotentiometry (turn-on and turn-off curves), the joint electroreduction of lanthanum and nickel ions on a tungsten electrode in an equimolar melt of potassium and sodium chlorides at a temperature of 973 K was studied. It was investigating that on an inert tungsten electrode the joint electroreduction is released at potentials of – 2.1…–2.2 V relative to the silver chloride reference electrode. The mechanism of the process in one three-electron stage which controlled by diffusion transfer stage at polarization rates less than 0.1 V/s. At higher polarization rates, the charge transfer stage is slower.
With a shared content of lanthanum and nickel ions in an equimolar KCl-NaCl melt at 973 K, the current-voltage dependences show a wave of nickel reduction at potentials of 0.0…–0.1 V, lanthanum ions at potentials of – 1.85…–1.9 V. In addition to these waves, there are two recovery waves on the current-voltage dependence at potentials of –1.5…–1.6 V and –1.75…–1.8 V. The appearance of the last two waves is associated with the reduction of lanthanum ions with depolarization on pre-deposited metallic nickel on a tungsten electrode, with further formation of intermetallic phases of lanthanum and nickel LaxNiy (various compositions):
At a wave at potentials of –1.85…–1.9 V, electroreduction of LaCl63- (chloride complexes on the LaxNiy intermetallic compound takes place with the formation of intermetallic phases with a higher content of lanthanum due to the interaction of the LaxNiy intermetallic compound with metallic lanthanum: .
The (E–t) dependences of open circuit chronopotentiometry (on and off curves) revealed potential delay plateaus corresponding to the dissolution of individual phases of lanthanum and nickel intermetallic compounds.
Based on the results of the analysis of the cyclic current-voltage dependences of the molten system KCl-NaCl–LaCl3–NiCl2, (E–t) dependences obtained by the direct chronopotentiometric method and open circuit chronopotentiometry, it can be concluded that the electrochemical synthesis of lanthanum- nickel intermetallides can be realized only in the kinetic mode, namely, electroreduction of LaCl63- ions on pre-deposited metallic nickel on a tungsten electrode with the formation of LaxNiy intermetallic phases as a result of diffusion reaction.
KEYWORDS
lanthanum chloride, nickel chloride, joint electroreduction, cyclic chronovoltammetry, chronopotentiometry, open circuit chronopotentiometry, chloride melt.
DOI: 10.31857/S0235010622060081