Structural Transformations of Few-Layer Graphene Fragments during Spark Plasma Sintering and Plasma Treatment

Few-layer graphene (FLG) with varying carbon layer contents, oxidized FLG, and FLG containing Fe as a catalyst have been consolidated by spark plasma sintering (SPS). All products have been characterized by Raman and X-ray photoelectron spectroscopy, as well as transmission electron microscopy. Spark plasma sintering of FLG particles results in the formation of a morphologically heterogeneous material. During sintering of oxidized FLG, surface oxygen-containing groups are eliminated. Iron particles promote the formation of core–shell structures, in which the core is Fe and the shell consists of several carbon layers. The mechanical and electrical works of the SPS process have been calculated. The electrical work, which leads to resistive heating of the materials and the generation of plasma, makes the largest contribution. The effect of inductively coupled radiofrequency discharge plasma has been studied separately. Plasma treatment of FLG, oxidized FLG, and Fe-doped FLG does not result in significant structural changes. However, plasma treatment of activated carbon or a mixture of activated carbon with nanographite yielded particles with folded carbon layers that bear resemblance to onion-like carbon structures.