Cathodic behavior of molten CaCl₂-CaO and CaCl₂-NaCl-CaO

Abstract

The cathodic behavior of molten CaCl₂, CaCl₂-CaO and equimolar CaCl₂-NaCl-CaO was studied by cyclic voltammograms and constant potential polarization at temperatures of 1123 to 1173 K on molybdenum and titanium electrodes. The diffusion coefficient of Ca²⁺ (CaO) in molten CaCl₂-CaO was calculated from the linear relationship between the square root of scan rate and the peak current density. The deposition potentials and the potential temperature coefficient of CaO in molten CaCl₂-0.5mol%CaO and CaCl₂-NaCl-0.5mol%CaO were also obtained from their cyclic voltammograms. The result shows that CaO is more easily reduced than CaCl₂. The addition of NaCl in molten CaCl₂-CaO induces the underpotential electrodeposition of CaO.

Keywords

molten salts / calcium oxide / cyclic voltammetry / polarization

References

[1] Okabe T.H., Nakamura M., Oishi T., Ono K. Electrochemical deoxidation of titanium. Metall. Trans. B, 1993, 24, 449.

[2] Chen C.Z., Fray D.J., Farthing T.W. Direct electrochemical reduction of titanium dioxide to titanium in molten calcium chloride. Nature, 2000, 407, 361.

[3] Ono K., Suzuki R.O. A new concept for producing Ti sponge: calciothermic reduction. JOM, 2002, 54, 59.

[4] Jiao S.Q., Zhu H.M. Novel metallurgical process for titanium production. J. Mater. Res., 2006, 21, 2172.

[5] Chen G.Z., Gordo E., Fray D.J. Direct electrolytic preparation of chromium powder. Metall. Mater. Trans. B, 2004, 35, 223.

[6] Liu M.F., Guo Z.C., Lu W.C. An investigation into electrochemical reduction of TiO₂ pellet. Trans. Inst. Min. Metall. Sect. C, 2005, 114, 87.

[7] Wang D.H., Qiu G.H., Jin X.B., et al. Electrochemical metallization of solid terbium oxide. Angew. Chem. Int. Ed., 2006, 45, 2384.

[8] Du J.H., Xi Z.P., Li Q.Y., et al. Effect of TiO₂ cathode performance on preparation of Ti by electro-deoxidation. Trans. Nonferrous Met. Soc. China, 2007, 17, s514.

[9] Guo X.L., Guo Z.C., Wang Z. Direct preparation of TiFe alloy by electrolytic reduction from TiO₂ and Fe₂O₃. J. Univ. Sci. Technol. Beijing, 2008, 30(6): 620.

[10] Schwandt C., Alexander D.T.L., Fray D.J. The electro-deoxidation of porous titanium dioxide precursors in molten calcium chloride under cathodic potential control. Electrochem. Acta, 2009, 54, 3819.

[11] Wang S.L., Li Y.J. Reaction mechanism of direct electrochemical reduction of titanium dioxide in molten calcium chloride. J. Electroanal. Chem., 2004, 571, 37.

[12] Schwandt C., Fray D.J. Determination of the kinetic pathway in the electrochemical reduction of titanium dioxide in molten calcium chloride. Electrochem. Acta, 2005, 51, 66.

[13] Alexander D.T.L., Schwandt C., Fray D.J. Microstructural kinetics of phase transformations during electrochemical reduction of titanium dioxide in molten calcium chloride. Acta Mater., 2006, 54, 2933.

[14] Freydina E.B., Fray D.J. Synthesis of Pb-Ca alloys by electrolysis of CaO in molten salts. Trans. Inst. Min. Metall. Sect. C, 2002, 111, C79.

[15] Chen G.Z., Fray D.J. Voltammetric studies of the oxygen-titanium binary system in molten calcium chloride. J. Electrochem. Soc., 2002, 249, E455.

[16] Mohamedi M., Borresen B., Haarberg G.M., Tunold R.J. Anodic behavior of carbon electrodes in CaO-CaCl₂ melts at 1123 K. J. Electrochem. Soc., 1999, 146, 1472.

[17] Me W.J., Duan S.Z., Inman D. The cathodic reduction of carbon from LiCl-KCl-NaCl molten salt. Chem. J. Chin. Univ., 1998, 9, 547.

[18] D.J. Fray, Use of thermodynamics and electrochemistry in understanding novel molten salt electrochemical process, [in] The 16th Iketani Conference, Tokyo, 2006, p.269.

[19] Levin E.M., Robbins C.R., McMurdie H.F. Phase Diagrams for Ceramists, 1969 Columbus, Ohio, The American Ceramic Society, 443.

[20] Berzins T., Delahay P. Oscillographic polarographic waves for the reversible of metals on solid electrodes. J. Am. Chem. Soc., 1953, 36, 555.