Electrochemistry of UBr3 and preparation of dendrite-free uranium in LiBr-KBr-CsBr eutectic melts
The electrochemistry of UBr 3 was studied on W working electrodes in LiBr-KBr-CsBr eutectic salt at 623 K. The U(III)/U (0) redox reaction was evaluated with respect to its electrochemical behavior, diffusion and electrocrystallization properties. According to cyclic voltammetry and square wave voltammetry , the reduction of U(III) ions to U (0) metal is a one-step three-electron reaction and the oxidation of U(III) ions is an one-electron transferred reaction. Cyclic voltammograms at varied scan rates show that U(III)/U (0) redox reactions are quasi-reversible. Chronopotentiometry and Sand's equation were used to determine the diffusion coefficients of U(III) ions. The nucleation mechanisms of uranium metal deposited on W substrates with different UBr 3 concentrations were predicted by using Scharifker-Hill model, which shows that the nucleation and growth mode changes from progressive mechanism to instantaneous mechanism with an increasing concentration of UBr 3 in the salt. At 623 K, potentiostatic electrodeposition was conducted to prepare mass uranium. The current-time evolution curve indicates that the actual surface area of electrodeposits keeps stable. Furthermore, the macroscopic appearance and microcosmic morphology show compact structure, rather than dendrites. Bulk uranium metal was further analyzed by inductive coupled plasma atomic emission spectrometer and X-ray diffraction, which indicate that the compact uranium is high-purity metal.
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