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.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (No. 51674120, 51874141), the Natural Science Foundation of Hebei Province (No. E2016209163, E2018209266), and the High School Science and Technology Research Project of Hebei Province (No. BJ2017050). The authors gratefully acknowledged the financial support from NSF and the University of Alabama, AL, USA.
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