GB800092A - Improvements relating to the electrolysis of fused salt, particularly alumina - Google Patents

Abstract

800,092. Electrode furnaces. MONTECATINI SOC. GENERALE PER L'INDUSTRIA MINERARIA E CHIMICA, and VARDA, G. DE. Jan. 17, 1955 [Jan. 19, 1954], No. 1369/55. Class 39(3) [Also in Group XXXVI] A fused salt electrolytic furnace, e.g. for producing aluminium, employing a consumable anode 16, comprises a cell gap 13 formed by two opposed, parallel, plane faces inclined to the vertical presented each by one of two stationary carbon electrodes 15, 16, the face of the anode 16 being accessible from the top of the furnace, and a collecting chamber 14 below the gap 13 for molten aluminium. The anode 16, eg. an agglomerate block of amorphous carbon, and the cathode 15, e.g. of graphite, are each connected by metal, e.g. iron, stubs 17 to a conductive plate 21<SP>1</SP> contacted by a terminal bar 21. The top surface of each electrode, which may be inclined slightly down towards the top of the gap 13, is covered by an inert layer or plate, insulating layers 18 of sintered alumina, aluminium nitride or magnesia, and 19 of calcinated magnesite, surrounding the cell in a layer of powdered alumina 20. Molten metal 23 is tapped off at 22 or drawn off by suction from the top of the cell. As the anode 16 is consumed its operative face may be re-covered by a plate or a number of strips of carbon caused to adhere thereto by pitch or graphitic dust. A cover may be provided, and the cell may be heated by an external source. In a modification, a number of intermediate bipolar electrodes of graphite or electrodic carbon are interposed between the anode and cathode, insulating partitions separating adjacent chambers 14. The voltage across each cell in such a multi-cell furnace may be 2.8 to 3.6, a current of 2,000 amps being employed to give current densities of 0.3 to 0.6 amps per sq. cm. Such a cell should be operated so that the sum of the gap width of the cells, which individually vary between 12 cms and 2 cms as the anodes are consumed, is kept constant. In both embodiments, the upper walls of the cell may diverge as shown, and in the multi-cell apparatus partitions may define separate upper chambers, gas exit ducts being provided. Alumina in powder form may be spread on the top of the electrodes 15, 16 or on the bath for preheating prior to delivery to the bath.