PRODUCTION OF ALUMINIUM, MAGNESIUM AND ALUMINIUM-MAGNESIUM ALLOYS BY DIRECT ELECTROCHEMICAL REDUCTION OF THEIR SOLID OXIDES

摘要

A variable composition Al:Mg alloy was made by reducing magnesium oxide tablets that were floating on a liquid aluminium cathode. Forced convection would be required to form a uniform alloy in pools deeper than 10mm due to diffusion limitations. Calcium was also deposited into the alloy by cathodic reduction of calcium ions from the salt. Reducing the calcium activity by introducing a second salt or even replacing calcium chloride completely may alleviate this parasitic reaction. In cells without the liquid cathode, increasing the calcium oxide activity in the salt encouraged calcium deposition reducing the current efficiency of the electrochemical reduction process. The subsequently formed free calcium metal did not reduce alumina or magnesia very easily with barely any penetration into the oxide tablet. An ～ 30wt% reduction of alumina was achieved by using highly porous alumina tablets. Producing magnesia tablets of comparable porosity and strength was not possible resulting in virtually no reduction.