Graphitization Control Using Additives in Pitch Composites-Part II: Effect of Size, Stacking, Loading, and Composition of Graphene and Graphene Oxide on Crystallite Sizes

As a continuation of our study into temperature-dependent crystallite size evolution, carbonization reactions, and mesophase formation upon graphene addition, this paper reports graphenic additive structural parameter effects on crystallite sizes in graphitized pitch composites. Eight different graphenic additives (four graphenes and four graphene oxides) were added to commercial coal tar and petroleum pitches, whereafter the composites were graphitized at 2500 °C. The crystallite sizes of the composites were analyzed using X-ray diffraction with confirmation provided by Raman spectroscopy. The crystallite sizes greatly varied as a function of graphene lateral size, stacking height, composition, and loading. Notably, an inverse correlation between crystallite sizes and the lateral size and loading of graphenic additives was observed. Additionally, the stacking height of graphene exhibited a positive correlation with crystallite sizes. In contrast, variations in the stacking height of graphene oxide additives resulted in similar crystallite sizes. Intriguingly, all graphene oxide additives consistently yield crystallite sizes smaller than those produced by graphene additives, manifesting in a distinct size range. Moreover, the higher oxygen content in graphene oxide additives demonstrates an inverse correlation with crystallite sizes, underscoring the profound impact of additive composition on the crystallite formation process. Mechanisms behind these effects are proposed and discussed.