Carbon block for cathodes of aluminum

Claim 1

In an electrolytic process for producing aluminum which comprises dissolving alumina in a molten salt bath containing cryolite at an elevated temperature in an electrolytic cell and electrolyzing said alumina by passing a direct current through the molten salt bath through a carbon anode to a carbon cathode constructed by lining baked carbon blocks on the bottom of the electrolytic cell to deposit aluminum on the bottom of the electrolytic cell, the improvement which comprises prolonging the life of the electrolytic cell by constructing said cathode of at least one carbon block having a stability constant of 0.7-1.0, said block consisting of at least 50% by weight of petroleum coke and less than 50% by weight of at least one other carbonaceous material selected from the group consisting of calcined anthracite, cokes other than petroleum coke, and other graphitized carbonaceous materials, based on the weight of a dry aggregate of the coke and said other materials, which has been kneaded with pitch, formed and baked at a temperature higher than 2000° C. but lower than about 2400° C. to yield said carbon block.