Expansion of carbon artifacts during graphitization—An industrial issue—

Abstract

Petroleum-based needle coke will be losing its dominance for the production of graphite electrodes, due to the growing production capacities in the field of coal tar pitch (CTP)-based needle coke types. Up to now, CTP needle coke does not harmonize with the conditions prevailing in modern lengthwise graphitization furnaces. The reason is the volumetric expansion during graphitization—the so called puffing—caused by the removal of gaseous nitrogen. Earlier research activity has failed to depress (or even prevent) the nitrogen puffing of CTP needle coke to a similar level as found with petroleum needle coke standards. This paper gives a brief review of the research carried out in the past. It evaluates several measures to depress nitrogen puffing and reports recently obtained results. It is expected that a chemical inhibition of nitrogen puffing is not possible on an industrial scale. However, solutions are seen in physical measures—like thermal reduction of the nitrogen content and in tailoring the coke morphology by the thermal processes involved in its production.