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.