Electrodes used in electric heating are refractory conductors that do not participate in the furnace reactions. For example, graphitized electrodes used in steelmaking primarily require low resistivity, and the strength and ash content requirements are not as high as those for semiconductor and nuclear graphite. This is especially true for electrodes used in other mineral heating applications, such as in the production of calcium carbide. The raw materials are coke and quicklime, both inexpensive and impure materials. Coke contains a large amount of ash, so using electrodes with high ash content is acceptable, as impurities introduced by consumable electrodes can be decomposed by the furnace heat or expelled with the slag.
In most cases, impurities in the electrodes will either not enter the product or, if they do, will not significantly affect the product. Therefore, electrodes used in electric heating can have a high ash content, either because the ash content is unimportant or because the use of cheaper electrodes justifies the trade-off in resistance.
Increasing electric furnace capacity requires a corresponding increase in busbars and electrodes, which also means stricter requirements for electrode performance to accommodate the more sophisticated steelmaking techniques. Sulfur contamination from electrodes can be significant in electric furnace steel, so electrodes are manufactured using low-sulfur coke.
In the 1940s, there was a trend toward increasing the graphitization temperature (i.e., the degree of graphitization) and using low-ash coke to enhance electrode conductivity. Graphite coke was subsequently used to produce electrodes. As furnace capacity increased, electrode diameters increased to maintain the necessary current density, which created difficulties in electrode forming. By the 1960s, high-power and ultra-high-power electrodes were being developed, improving their quality and thus their ability to withstand high current densities.