Graphitization-induced microstructural changes in tetrahydrofuran-derived pyrolytic carbon spheres

This article is a study of monodispersed, submeter-sized solid carbon spheres having smooth surfaces and almost perfectly round shapes. These spheres were synthesized by pyrolysis of tetrahydrofuran in the absence of a catalyst. Microstructures of carbon spheres before and after graphitization were systematically investigated using electron microscopy, thermogravimetric analysis, and x-ray diffraction. The sphere is believed to consist of an underdeveloped spiral-shell core and a surface with discrete fragments of concentrically arranged graphene layers. Under lower temperature heat treatment, the underdeveloped spiral-shell structure changes to a well-developed spiral-shell structure. After graphitization, the spiral-shell core is shown to transform into continuous and closed polyhedral secondary shells, whereas the exterior discrete fragments of graphene sheets transform into discontinuous polyhedral surface shells. The mechanisms of these microstructural changes are discussed.