Graphitation partielle de quelques carbones durs. Etude en microscopie et microdiffraction electronique

This paper gives more complete and more general results than an earlier paper by the same authors. Graphitization of hard C atoms is always a three phase process. This means that outside each grain of non-graphitizable carbon (the matrix) two new phases suddenly appear: graphite (platelets) and graphitizable carbon (conical rolled spirals), the percentage of which depends on both the origin of the carbon and its granularity (compact samples give no crystalline phases). The temperature at which the graphite and graphitizable phases appear depends on the purity of the original sample (for instance the presence of iron decreases the temperature from 2200 to 2000° and even to 1600°C). Finally as the heat treatment temperature increases the small turbostratic stacks of carbon layers forming the matrix produce fibers by mutual rearrangement and thus some macropores develop. This phenomenon becomes pronounced as the proportion of graphite and the graphitizable phase increases. These results lead to an improvement in the model for hard C atoms proposed in the previous paper and to its endorsement.