Low-Temperature Electrolytic Production of Aluminum–REM Alloys in Cryolite Melts

The electrolytic production of Al–Y and Al–Sc alloys in an electrolyte based on the KF–NaF (10 wt %)–AlF 3 potassium cryolite with a cryolite ratio (CR) of 1.5 containing Al 2 O 3 , Sc 2 O 3 , or Y 2 O 3 oxides in a cell with vertical electrodes is studied. An Fe–Ni–Cu alloy serves as an inert anode. The wettable cathode is a graphite plate coated with aluminum diboride. Electrolysis is carried out at 830°C and a cathode current density of 0.2 A/cm 2 . The weight of an Al 2 O 3 additive is calculated at a current efficiency of 60%. A Sc 2 O 3 additive is introduced into a melt in an amount of 1 wt %. The weight of an Y 2 O 3 additive is chosen on the basis of its solubility in the melt under study. For this purpose, the influence of Y 2 O 3 additives on the liquidus temperature of a quasi-binary mixture [KF–NaF (10 wt %)–AlF 3 (CR = 1.5)]–Y 2 O 3 is determined. Unlike Sc 2 O 3 additives decreasing the liquidus temperature of the cryolite melt, small Y 2 O 3 additives lead to a sharp increase in the liquidus temperature. The efficiency of the electrolytic reduction of Y 2 O 3 is an order of magnitude higher than that of aluminothermic reduction. Under other equivalent conditions, the efficiency of the electrolytic reduction of Y 2 O 3 is higher than that of Sc 2 O 3 . Al–Y and Al–Sc alloys with a 0.6 wt % REM are formed. However, the time to reach the maximum reduction of yttrium significantly exceeds the time to reduce scandium. Metallographic studies of the prepared alloys indicate the presence of the Al 3 Sc and Al 2 Y intermetallic compounds. A conclusion is made about a principal possibility of the low-temperature electrolytic production of Al–REM alloys in cryolite melts based on potassium cryolite in vertical cells with an inert metallic anode and a wettable cathode.