Nanocomposite Catalysts Obtaining by Mechanochemical Technique for Synthesizing Carbon Nanotubes

Abstract

In the current research reactive milling was employed to fabricate the nanocomposite precursors for the catalytic growth of carbon nanostructures. For this purpose several mixtures of iron oxide and aluminum powders along with different amounts of graphite powders were mechanically milled for different times. The adiabatic temperature and the heat released from exothermic reaction during milling were controlled by varying the percentage of graphite. Synthesized powders were analyzed by X-ray diffraction, scanning electron microscope, transmission electron microscope, and thermogravimetric analysis. Propane gas was used in a chemical vapor deposition technique as a source of carbon to synthesize carbon nanotubes (CNTs). The results show that decomposition efficiency of propane promotes in the case of using milled powders and leads to a high yield of CNTs formation. The mechanical induced reaction between aluminum and iron oxide in the presence of graphite was used to produce micron-sized composite particles. These particles contain separated iron nanoparticles and dispersed in the matrix of ball milled graphite and alumina. It was found that the yield of fabrication of CNTs increased as decomposition temperature of propane increased from 625 to 850°C. Microscopic evaluation by SEM proved that the productivity of CNTs grown on milling derived catalysts was much high at higher annealing temperatures (700°C and 850°C) rather than that of lower temperature (625°C). The results of TGA tests showed that the amount of produced carbon nanotube depends on annealing temperature and as annealing temperature changed from 652 to 850°C carbon nanotube content increased from 13 to 85 wt%. TEM results demonstrated that CNTs were grown according to tip-growth mechanism.