GB749698A - Improvements in or relating to carbon electrodes - Google Patents

Abstract

A calcined briquette of crystalline carbon having a sulphur and ash content each less than 1 per cent, a real specific gravity of at least 1.96, preferably 2.02-2.08, a volume resistivity of not greater than 0.008, preferably 0.00615-0.0055, ohms per c.c. and a hardness of at least 6, and preferably 7, Moh, is made by compressing and calcining a mixture of finely divided, amorphous and substantially water-free carbon having a sulphur and ash content each less than 1 per cent, and uncalcined carbonaceous binder material. The calcined briquette may be made in a weight of 23-116 grm. The amorphous carbon preferably comprises at least 25 per cent, preferably 50 per cent, or more of "coarse and crude oil carbon black" having a particle size of 200-600 millimicrons. Other materials which may be used are petroleum, pitch or tar coke, retort carbon, graphite and lamp black. The binder material may be a residual pitch of asphalt base petroleum softening at 70-127 DEG C. Mixing may be effected at 149-204 DEG C. and the proportions may be such as to produce a powder (e.g. 80 per cent carbon and 12 per cent binder) or a paste (e.g. 77 per cent carbon and 15 per cent binder). The volatile organic matter of the carbon black is preferably retained during the mixing. Calcining is effected in the absence of air. It may include a period of at least 45 min. at a temperature of at least 1288 DEG C. A number of the calcined briquettes, in an amount of 40-90 per cent, may be mixed with a mixture of carbon filler, preferably comprising crushed briquettes, and carbonaceous binder material and charged into a metal shell so that the briquettes abut one another and the inner surface of the metal shell, thus forming a Söderburg electrode.