Aziridination of graphitic carbon nanocapsules (CNCs) followed by pyrolysis at 700 °C at ambient pressure yields tetrahedral amorphous carbon nanoballs (CNBs, see Figure). Because of the pyramidal character of some of the double bonds in the derivatized CNCs, a radical chain mechanism is proposed to rationalize the transformation of C sp2 hybridization in the CNCs to C sp3 hybridization in the CNBs.