GB784695A - Improvements in or relating to electrolytic cells for the production of aluminium - Google Patents

Abstract

The free carbon content in zirconium carbide is reduced by a process similar to that described in Specification 784,697 with respect to titanium carbide, but the final firing temperature is 2700 DEG C. Specification 784,696 also is referred to.ALSO:A compact mass of titanium carbide for use as a cathode in a fused-electrolytic cell for obtaining aluminium is made by first mixing the powdered material having a mean particle diameter of 1-2 microns with a binder such as 1 per cent of paraffin wax dissolved in benzene. This is heated to evaporate the benzene and melt the wax and compacted with a pressure 0.5-5 tons per sq. inch. Compacting may be effected between male and female dies at an ordinary or an elevated temperature, or the material may be p extruded into the desired shape. The mass is then prefired in vacuum to a temperature of 1100 DEG C. If not already formed to the desired shape it may be worked by sawing, filing or like operation. It is then fired in vacuum at 1600 DEG C., or in a neutral gas, e.g. hydrogen. A compact mass of zirconium carbide may be similarly made, the prefiring temperature being in this case 1600 DEG C. and the subsequent firing temperature 2200 DEG C. The free carbon content of the product must be below 0.5 per cent, preferably below 0.1 per cent. If commercial titanium carbide powder containing 1-2 per cent of carbon with some titanium oxide is employed the free carbon content is reduced by mixing with the powder about 2-3 per cent of alumina before the operation above described, and employing higher sintering temperatures. Specifications 784,696 and 784,697 are referred to.ALSO:A compact mass of titanium carbide for use as a cathode in a fused-electrolytic cell for obtaining aluminium is made by first mixing the powdered material having a mean particle diameter of 1-2 microns with a binder such as 1 per cent of paraffin wax dissolved in benzene. This is heated to evaporate the benzene and melt the wax and compacted with a pressure 0,5-5 tons per sq. inch. Compacting may be effected between male and female dies at an ordinary or an elevated temperature, or the material may be extruded into the desired shape. The mass is then pre-fired in vacuum to a temperature of 1100 DEG C. If not already formed to the desired shape it may be worked by sawing, filing or like operation. It is then fired in vacuum at 1600 DEG C., or in a neutral gas, e.g., hydrogen. A compact mass of zirconium carbide may be similarly made, the pre-firing temperature being in this case 1600 DEG C. and the subsequent firing temperature 2200 DEG C. The free carbon content of the product must be below 0,5 per cent, preferably below 0,1 per cent. If commercial titanium carbide powder containing 1-2 per cent of carbon with some titanium oxide is employed the free carbon content is reduced by mixing with the powder about 2-3 per cent of alumina before the operations above described, and employing higher sintering temperatures. Specifications 784,696 and 784,697 are referred to.