| 摘要 |
Porous graphite electrodes which may be impregnated with metal salt solutions are prepared by mixing 100 to 150 parts by weight of a finely divided washable filler such as zinc oxide, calcium phosphate or sodium chloride with 100 to 125 parts by weight of a source of carbon such as tar, moulding the resulting mixture into shapes, heating the shapes for conversion into carbon at a temperature of about 650 DEG C, and not above 700 DEG C, leaching the filler to produce a carbon body having a porosity of 75 to 80 per cent and graphitizing at 2400C DEG to 2700 DEG C to produce graphite bodies of the same porosity. The bodies may now be placed in an autoclave under reduced pressure and a 10 to 20 per cent solution of the active material for a battery electrode, such as nickel chloride, a mixture of cadmium chloride and ferric sulphate, lead nitrate or a mixture of ferric and mercuric sulphates, is added. The pressure is increased to atmospheric, the bodies washed and treated with an alkali such as caustic soda to precipitate the active material as a metal hydroxide. The electrodes are then washed and the process repeated to give a final impregnation of 100 grams of graphite with 200 grams of nickel hydroxide for example. In the preferred form, tar, having a residual carbon content of about 40 per cent by weight is mixed with sodium chloride reduced to 1 to 3 microns size either by grinding in admixture with petroleum distillate or in admixture with the tar. Mixing is continued and heat applied to remove volatiles; a graphitization catalyst such as dried kaolin may be added at this stage, but preferably before, in admixture with the washable filler. The mixture is cooled to 30 DEG C to solidify it, cold ground and moulded under 500 to 1,000 kilograms/square centimetre pressure. The shaped bodies are carbonized preferably in an oxygen-free or reducing atmosphere, or surrounded by fine charcoal, at a temperature below 700 DEG C for five to six days. The filler is then leached with hot water or dilute acid and the shaped bodies graphitized either by heating to 600 DEG C, increasing to 800-1000 DEG C at the rate of 50 DEG C per day followed by heating to 2400 to 2700 DEG C at 200 DEG C per day, or alternatively heated to 1200 DEG C at a rate of 200 DEG C per hour, followed after four hours at this temperature by heating at the same rate to 2400-2700 DEG C. The graphited bodies are washed and may be impregnated. Preferably during graphitization the bodies are surrounded by carbon and silica whereby a small proportion of silicon carbide is deposited in the pores. Broken pieces of impregnated graphite electrode may be packed in perforated tubes after grinding to 1 to 1.5 millimetre size, and pressed around a central nickel core. |
