Surface treatments of vapor-grown carbon fibers produced on a substrate

Vapor-grown carbon fibers (VGCF) were grown from a methane-hydrogen mixture on a reconstituted graphite support using different catalyst precursors, the [Fe-3(CO)(12)] complex being found to be the most efficient for the production of VGCF. The fibers thus produced were characterized and submitted to different oxidative treatments, namely nitric acid, plasma, air and carbon dioxide. From analysis performed by scanning electron microscopy (SEM), nitrogen adsorption (BET) and X-ray photon spectroscopy (XPS) it appears that the air and carbon dioxide treatments do not lead to significant increase either of the surface area, or of the quantity of surface oxygen containing groups, despite the considerable weight loss attained (50%). This peculiar observation has been interpreted by considering the presence of traces of iron at the fibers surface, which can catalyze the gasification of carbon. The presence of iron on the VGCF has been evidenced for the first time by the time-of-flight secondary ion mass spectrometry technique. The cleansing of the fibers surface with concentrated hydrochloric acid results in the removal of the iron and leads, after CO2 activation, to an improvement of the BET surface area. The use of nitric acid or plasma as oxidation agents does not affect significantly the surface morphology of the fibers, but greatly increases the number of surface oxygen functions. (C) 1998 Elsevier Science Ltd. All rights reserved.