Electrochemical Behavior of Fe3O4 in NaCl-CaCl2 Melts

Abstract

Abstract The reduction and dissolution mechanism of Fe3O4 in NaCl-CaCl2 melts system are analyzed by thermodynamics. The electrochemical methods of Fe3O4 in NaCl-CaCl2 melts are studied by cyclic voltammetry, square wave voltammetry and open-circuit chronopotentiometry. The effects of temperature on reduction potential and peak current are investigated. The diffusion coefficients of Fe3+ and Fe2+ at different temperatures are calculated, and the activation energy E is obtained. Electrolytic products are obtained after 10 min of potentiostatic electrolysis in the melts of NaCl-CaCl2-Fe3O4 at 1073 K and 1.9 V. The results of XRD show that no other compounds are formed in the melts, indicating that Fe3O4 do not react chemically in the NaCl-CaCl2 melts system at 973 K, which is consistent with the theoretical analysis. Fe3O4 is reduced by two-step quasi-reversible reaction in the melts of NaCl-CaCl2 at 973 K to obtain iron: Fe3+ → Fe2+ → Fe. The two-step reaction is controlled by diffusion. The diffusion coefficients are 4.53 × 10–6 cm2·s–1 and 1.17 × 10–6 cm2·s–1, respectively. Fe3O4 is reduced in two steps. The potential shifts with temperature and decreases with the increase of the proportion of Fe3O4. The activation energies of the two-step reaction are 62.38 kJ·mol–1 and 77.52 kJ·mol–1. A deposited layer of uniform distribution, high coverage and dense iron is prepared.