Description
Large Carbon electrode are used in the electrochemical industry in the production of Aluminum, Magnesium, Alkalis and chlorine; in electrothermal processes for graphite calcium and silicon carbides; and in manufacturing steel and some none ferrous alloys. Small electrodes are employed in electric are lighting and primary batteries. This term “Electrode” signifies application where the function is primarily conduction of current.
The pitch binder, preferably in liquid form is blended with the filler in a sigma-bladed mixer or a high shear kneader of the Baker-Perkins or Werner Plainer type at a temperature well above the softening point of the pitch. For larger electrodes typical mixes consists of Calcined Petroleum Coke, varying in size from 1-2 cm or more to finder that #200 ASTM mesh, and 15 to 35wt % of coal tar pitch. The carbon paste or green mix may be compression molded or extruded to give products which are then baked at a gradually increasing temperature to maximum of 750 to 1250 degree Celsius depending on the end use.
The green strength of carbon paste, both hot and cold, is important since on carbonization a strong dense structure free of cracks must result. Green strength depends on many factors-the nature and particle size distribution of the filler; mixing condition, extrusion/molding temperature and pressure; and the amount and properties of the binder Characteristics of the carbonized article are, in addition, a function of the heat-up rate during baking, the maximum temperature and the cooling rate.
