Study On Preparation Of Nano-Carbon Materials By Chemical Vapor Deposition Using K/Na/Ca Salts Catalysts

In this study,the precursor KHCO₃ and NaHCO₃ as well as their compound, the catalysts Na₂O₂,CaCO₃ and CaO, and carbon source C2H2 were used to prepare the nano-carbon materials by CVD method. The factors influencing the deposition of nano-carbon materials, for example the type of catalyst and reaction time were studied and the obtained materials were characterized using SEM and TEM.KHCO₃ and NaHCO₃ and their compound were respectively used as the precursor to preparation of nano-carbon materials with different structures, and the obtained materials were in-situ grown integral carbon nano-arrays with carbon as the base. This kind of structure endows the carbon nanofibers and carbon nanotubes with macro shapes and sizes, in the meantime, the integral structure of the carbon nano-arrays has greatly increased the strength between the carbon nanofibers and carbon nanotubes and the base, which thus expands the application of carbon nanofibers and carbon nanotubes in various fields such as industrial catalysis and field emission. By characterizing the products, we found that, the carbon nano-material deposited with KHCO₃ as the precursor had branch-shape fibers on its carbon base, and these fibers only grew on one side of the carbon base with smooth fiber surface and less impurities; it had a length of around 100nm, with even diameters, which was around 200nm. The carbon nano-material deposited with NaHCO₃ as the precursor had uneven fibers on its carbon base, with short ones with a length of less than dozens of nanometers and long fibers with a length of more than 200nm; the long and short fibers had evenly distributed diameters, which were around 20nm. When the reaction time prolonged from 1h to 4h, products prepared by these two salts as the precursors both increased in length, but the diameters did not have significant change and the surface smoothness decreased. The structure and shape of the carbon nano-material prepared by the compound of KHCO₃ and NaHCO₃ as the precursor are closely related to the ratio between KHCO₃ and NaHCO₃ in the precursor; when the ratio between KHCO₃ and NaHCO₃ was small, short fibers grew on the carbon base, and they were close to each other; when the ratio between KHCO₃ and NaHCO₃ was big, scattered nanotubes grew on the carbon base with a long length. With prolonging of the reaction time, there was no significant change to the diameters of the fibers or tubes on the carbon base, but the length was significantly increased; however, with further prolonging of the growing time, the orientation of the fiber or tube became more and more irregular, and the surface smoothness decreased.With Na₂O₂, CaCO₃ and CaO as the catalysts and with acetylene as the carbon source, this experiment used the CVD (Chemical Vapor Deposition) to prepare carbon nano-materials. We found: when Na₂O₂ was used as the catalyst, carbon nanofibers cannot be prepared under low temperature, and when the reaction temperature was increased to be around its melting point, nanofibers with a micrometer-level length and diameters around 100nm were prepared; with the increase of the reaction temperature, impurities on the fiber surface decreased. Nano-materials with good shapes cannot be prepared by using CaCO₃ as the catalyst, and when calcium oxide calcined by calcium carbonate was used as the catalyst, granular porous carbon materials were deposited under a temperature of 600℃.