Synthesis Of Carbon Nanofibers In Solid State

Carbon nanofibers (CNFs) possess unique morphology, structure and physi-chemical properties, and have exhibited widely potential applications in the fields including nano-fabrication, electronical materials and devices, biomedicine, chemistry, Physics, composites, energy storage, electron resource and so on.In this thesis, carbon nanofibers with high graphitization degree were synthesized by the Solid state Method carbonized at1500℃using expanded graphite (EG)、artificiated graphite (AG)、carbon black (CB)、and mesocarbon microbeads (MCMB) as the carbon source and nitrate nickel and chlorine ferric as the catalyst precursors, respectively. The products were characterized by SEM, TEM, XRD and HRTEM measurements. The formation mechanism of CNFs was deduced.The CNFs produced in the present of Nitrate nickel as catalyst precursor are2-30um long with the diameter of50-200nm, whereas, the CNFs produced in the present of chlorine ferric as catalyst precursor are2um-40um long with the diameter of around30nm. It was found that different kinds of carbon sources with various grain sizes show different reactivities. Especially the way and degree of pretreatment、the addition content of catalyst precursor、the composite manner of the carbon sources with the catalyst precursor、 carbonization temperature and preservation time have great effects on the formation of CNFs, according to a series of experiments. The optimized synthetic parameters using AG as the carbon source are as follows:mixed acid is sulfur acid and nitrate acid, volume ratio=3:1, pre-treat time is100hrs, AG:catalyst precursor is1:1, carbonization temperature is1500℃, and the preservation time is1hr. The conversion efficiency is70%.With the help of XRD,we deduced the growth mechanism of CNFs: metal particles were reduced by carbon, and because of small and have good binding capacity with the metal particles, carbon dig into the metal particles to form an eutectic film,then,the carbon diffused through the metal partical until the temperature goes down, finally CNFs were found when the carbon released from Ni(111) or Fe (200)(211)It could be known by SEM analysis that these CNFs were abide the bottom-based and top-based growth mechanism which were bring forward by Baker. Meanwhile, we find out that the CNFs are abide grobal-based and block-based growth mechanism, these are because of the whisk、erode、 oxidation of mixed acid, which result in havoc of the carbon sources’original structure, with the havoc, carbon raw material reassemble into ball or block, then the new CNFs grow on the ball or block.