Structure evolution of carbon microspheres from solid to hollow

Hollow carbon microspheres, several micrometers in diameter, were prepared from solid carbon microspheres by a simple oxidation-in-air process. The morphology and structure of these products were characterized by field-emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and thermogravimetry. Results indicate that heat treatment temperature in air plays a key role in the evolution of the cavity size and wall thickness of the hollow carbon microspheres with poor graphitization, and high heating temperature leads to a thin wall thickness and large inner diameter. A proposed formation mechanism reveals that the hollow carbon microspheres are formed as a result of the effect of curvature and crystallinity, i.e. the inner part of solid carbon microspheres has a large curvature and a low crystallinity, which is much more easily oxidized to form hollow carbon microspheres when subjected to air oxidation.