Factors influencing the graphitization of polymer carbons

Abstract Carbons have been prepared by carbonization of polymers to 700°C, and subsequent heating to 2700 or 3000°C. The helium density of the high-temperature carbons indicates whether or not they are graphitic; this has been checked by X-ray examination. Whether or not a given carbon graphitizes at high temperature is determined by the behaviour in the carbonization stage, and in some cases in the very earliest stages of decomposition. A graphitizing carbon is not obtained unless fusion occurs during carbonization; substantial cross-linking therefore prevents graphitization. Such cross-linking includes that which occurs when the dehydrochlorination of polyvinyl chloride takes place at 200–250° in the presence of oxygen. For graphitization to be possible, it is probable that a fused state must be maintained over a range of temperature during carbonization. This suggests that the material decomposing at this stage should be of a heterogeneous character. This is discussed in relation to the chemical character of the polymers. Important evidence on the significance of the fusion zone is provided by examination of graphitizing and non-graphitizing carbons by polarized light.