Transactions of Nonferrous Metals Society of China
JOURNAL OF RAILWAY SCIENCE AND ENGINEERING
|Vol. 18 No. 5 October 2008|
（1. College of Materials Science and Engineering, Hunan University, Changsha 410082, China;
2. State Key Laboratory of Power Metallurgy, Central South University, Changsha 410083, China）
Abstract:The microstructures of vapor-grown carbon nanofibers(CNFs) before and after graphitization process were analyzed by high resolution transmission electron microscopy(HRTEM), Raman spectroscopy, X-ray diffractometry(XRD), near-edge-X-ray absorption fine structure spectroscopy(NEXAFS) and thermogravimetric analysis(TGA). The results indicate that although non-graphitized CNFs have the characteristics of higher disorder, a transformation is found in the inner layer of tube wall where graphite sheets become stiff, which demonstrates the characteristics of higher graphitization of graphitized CNFs. The defects in outer tube wall disappear because the amorphous carbon changes to perfect crystalline carbon after annealing treatment at about 2 800 ℃. TGA analysis in air indicates that graphitized CNFs have excellent oxidation resistance up to 857 ℃. And the graphitization mechanism including four stages was also proposed.
Key words: carbon nanofibers; microstructure; graphitization; mechanism