Electrodeposition of Ho and Electrochemical Formation of Ho–Al Alloys from the Eutectic LiCl–KCl

The electrochemistry of a melt at inert and reactive electrodes has been studied at temperatures between 673 and . At a W electrode the electroreduction of Ho(III) proceeds in a single step and electrocrystallization plays an important role. Experimental current-time transients followed the theoretical models based on instantaneous nucleation with three-dimensional growth of the nuclei whatever the applied overpotential. Mass transport toward the electrode is a diffusion process, and the validity of the Arrhenius law was verified. For an Al electrode, the electroreduction of Ho(III) takes place at less cathodic potential values than at the inert W electrode which indicated the formation of Ho–Al intermetallic compounds. Ho–Al alloy films were obtained by potentiostatic electrolysis, and the samples were characterized by X-ray diffraction and scanning electron microscopy. The activity of Ho in the aluminium phase as well as the standard Gibbs energy of formation for were estimated from open-circuit chronopotentiometric measurements.