ИСТИНА

Most recent researches of nanotube/nanofiber growth on the surface of carbon fibers show different ways of conducting this modification and observe the properties of modified carbon fibers. The possibility of controlled growth is rarely discussed. Although we can obtain carbon fibers modified with nanostructures of fixed length and significantly reduce the cost of such production, controlling the growth of nanostructures during their synthesis. In our research we modified carbonized PAN fibers by CVD method using the mixture of benzene and cyclohexane as precursor. The particles of nickel were used as a catalyst. The activation of these particles was conducted by hydrogen right before the start of the CVD process. Syntheses were performed at different temperatures from 600 to 900˚C. The time of syntheses was varied from 5 minutes to 30 minutes. Obtained specimens were characterized by CEM, Raman spectroscopy and thermogravimetric analysis. During the longest syntheses at different temperatures (performed for 30 minutes) the samples of gases coming out of the reactor were taken each 5 minutes of synthesis and analyzed by gas chromatography–mass spectrometry. Several syntheses were performed to obtain more data for each point. The results showing cyclohexane amounts coming out of the reactor are shown on fig.1, curves for benzene show exactly the same relation. It is seen from the shown data that for all temperatures the active growth is conducted during first 20 minutes of synthesis. Most of the particles of catalyst are poisoned by that time and the process rate slows down. These results correlate very well with CEM images of obtained specimens. Thermogravimetric analysis also shows that the change of mass loss does not differ for the specimens obtained during syntheses more than 20 minutes long. Raman spectroscopy showed that specimens treated for more than 20 minutes were covered with disordered pyrolytic carbon. That fact proves the poisoning of catalyst particles after 20 minutes of synthesis and correlates with data obtained by other methods.