Cathode for a hall-heroult type electrolytic cell for producing aluminum

#This invention relates to electrolytic production of aluminum and more particularly, it relates to an improved cathode suited for use in an electrolytic cell for the production of aluminum such as Hall-Heroult electrolytic cells.

#In the electrolytic production of aluminum, there is great interest in utilizing a cathode that is highly conductive and does not react with molten aluminum deposited thereon. Carbon cathodes which are traditionally used in the Hall-Heroult cells have the problem that they are not readily wettable with molten aluminum. The carbon cathode surface reacts with the molten aluminum and forms aluminum carbide. Thus, the cathode is depleted at about 2 to 5 cm/yr. during operation of the cell. Or, the carbon cathode has the problem that it permits formation of cyanides, presenting a disposal problem. Thus, the carbon cathode has been replaced or modified with materials to improve its performance.

#For example, U.S. Pat. No. 5,961,811 discloses an improved carbonaceous material suitable for use as a cathode in an aluminum producing electrolytic cell, the cell using an electrolyte comprised of sodium containing compounds. The carbonaceous material is comprised of carbon and a reactive compound capable of suppressing the formation or accumulation of sodium cyanide during operation of the cell, of reacting with sodium to reduce problems associated with sodium intercalation, and of reacting with one of titanium or zirconium to form titanium or zirconium diboride during operation of the cell to produce aluminum.

#FIG. 1 is a cross-sectional view of a Hall-Heroult type cell in accordance with the invention.

#FIG. 2 is a cross-sectional view of an electrolytic cell showing a drained cathode in accordance with the invention.

#Referring now to FIG. 1 there is illustrated an electrolytic cell 10 for use in electrolytically reducing alumina to aluminum in accordance with the invention. Typically, cell 10 is comprised of a steel shell 20 having sides 22 and bottom 24. Sides 22 and bottom 24 may be provided with a layer of thermal insulation 26. A lining 30 is provided inside insulation layer 26 to contain molten electrolyte 40 and molten aluminum 50. Lining 30 may be comprised of carbon or graphite blocks or other suitable material. Anode 80, supported by anode rod 82, is shown immersed in molten electrolyte 40. As seen in FIG. 1, anode 80 projects through frozen electrolyte layer 42 into the electrolyte. The anode may be comprised of carbon material or cermet or other suitable material.

#The cell typically uses molten cryolite electrolyte at temperature above 900° C., e.g., in the range of 930° to 980° C. although other electrolytes may be used.

#Cathode 60 is located or positioned on top of insulation 26 and extends across the bottom of cell 10, Cathode 60 is comprised of a base material 61 having bottom surface 62 that rests on insulation 26 and a top surface 64. In accordance with the invention, top surface 64 comprises a layer 66 on which rests a layer or pool of molten aluminum 50.