Al Electrodeposition in Molten CaCl2 with Various Calcium Aluminates

Abstract

An innovative production process of Al metal is desired to reduce CO2 and perfluorocarbon gas generation. Our previous study showed that calcium titanate and silicate dissolved in molten CaCl2. Ti and Si metals could be electrodeposited, and it was indicated that Ti and Si reductions depended on the molar ratio of CaO to TiO2 or SiO2. In this study, direct production of liquid Al metal was attempted in molten CaCl2 with various calcium aluminates.Molten CaCl2 at 1373 ~ 1573K in an Ar atmosphere was used as a bath. Calcium aluminate (molar ratio of CaO to Al2O3, RCaO/Al2O3 =1.0, 12/7 or 3.0) was prepared by sintering a molded mixture of CaO and Al2O3, and it was added in CaCl2 beforehand. Mo and graphite rods were used a working and counter electrode, respectively. Mo wire was used as a quasi-reference electrode. The cathodic reaction was investigated by cyclic voltammetry, and potentio-static electrolysis was carried out. The electrodeposit was analyzed by XRD and SEM-EDX.Although no sharp current peak was seen, cathode current increased overall with calcium aluminate addition. The shape of CVs slightly changed with RCaO/Al2O3, but RCaO/Al2O3 seemed not to affect Al reduction significantly.Al and Al-Mo alloy were detected in the electrode after the electrolysis at -1.8V at 1573K regardless of RCaO/Al2O3, but the Al amount was very small. So, a Mo cathode with BN receiver in the bottom shown Fig.1 was used to prevent deposited Al metal from running down from the cathode. Al metal covered the surface by electrolysis, and a thick Al-Mo alloy layer was found in its cross section. It was shown that calcium aluminate dissolved in molten CaCl2 above 1573K, and that Al metal could be deposited electrochemically. The molar ratio of CaO to Al2O3 slightly affected the Al deposition though its influence have not clarified well.