Preparation Of Multi-walled Carbon Nanotubes

Under certain experimental conditions multi-walled carbon nanotubes (MWNTs) were produced successfully by chemical vapor deposition method with the mixture of ferrocene and fine coal as the reactants. By orthogonal tests, the optimal condition was determined with the temperature being about 1000℃, the time 2h and the weight ratio of ferrocene to fine coal 2:1. From these orthogonal tests, it is clear that the weight ratio has the most influence in the quality and productivity of MWNT products. According to this result, the weight ratio was changed to be 3:1 and the products formed were better-quality MWNTs that had less impurities and evener inner and outer diameters. Another set of orthogonal tests was designed to instruct experiments in order to produce best-quality MWNTs with least impurites. Under this circumstance, the optimal experimental condition was as follows: the temperature: 1000℃, the time: 2h and the weight ratio of ferrocene to fine coal: 3:1. Because the amount of impurities contained in the products has great impacts on the application and properties of MWNTs, a two-step method was used to purify this best-quality MWNTs. The resutls of transmission electron microscope and X-ray diffraction showed that the majority of impurities had been removed and the magnetization curves of two kinds of products showed that the saturated magnetization and remanence of the printine MWNTs were much higher than those of the purified MWNTs. The hysteresis loops of the former product exhibited typical ferromagnetic behavior. Furthermore, separate researches into the different influences of the reaction temperature, the reaction time and the weight ratio of ferrocene to fine coal in the quality of MWNTs were conducted and the growth mechanism of MWNTs was analysed. Besides, iron phthalocyanine was used to take place of ferrocene and was mixed with fine coal. After several experiments, we found that few CNTs could be seen in such products. This means that iron phthalocyanine is less active than ferrocene.