Experimental Research On Pyrolysis Flame Synthesis Of Carbon Nanotubes Via Catalytic Decomposition Of Methane

Carbon nanotubes are one-dimensional materials. Since carbon nanotubes were discovered by Iijama in 1991, preparation of carbon nanotubes has been one of the hot carbon nanotube research. Carbon nanotubes have many excellent properties and broad application prospects. Carbon nanotubes were synthesized from methane, using Fe/Mo/Al2O3 as catalyst, by pyrolysis flame. By changing the experimental conditions, the preparation of carbon nanotubes were explored and optimized, and the products were characterized. Oxy-acetylene flame temperature, sampling height, sampling time, the gas flow ratio and catalyst calcination temperature were studied. After determining the better experimental conditions, the growth of carbon nanotubes oriented were explored. Finally, the synthetic product of two different carbon sources carbon monoxide and methane are compared.The result shows that:(1)With an oxygen-acetylene flame temperature increasing, the yield is increased and the morphology of the carbon nanotubes changes greatly.1100℃ is the most suitable flame temperature for synthesis of carbon nanotubes. And sampling height was studied with the oxy-acetylene flame temperature of 1100℃. It is found that the yield with sampling height 80 mm is greater than sampling height 60 mm. However, when the sampling height is 60 mm, carbon nanotubes synthesis is more straight. (2) When sampling time is 1min, the carbon nanotube products is rare. With the sampling time increasing, the yield is increased. the most 9min product sampling time. The yield of carbon nanotubes is highest, When the sampling time is at 9min. (3)He flow rate change will affect the morphology of the carbon nanotubes. CH4, H2 flow rate change does not affect the morphology of the carbon nanotubes. He, H2, CH4 flow rate change affects the yield of carbon nanotubes. When He, H2, CH4 flow rate was 2:3:6, the yield of carbon nanotubes is the highest and the product is mainly single-, double- and triple-wall carbon nanotubes. (4)When the catalyst is in air calcined at 550℃ and 700℃, the yield of carbon nanotubes is low. When the catalyst is in air calcined at 800℃,700℃ and 1000℃, the yield of carbon nanotubes is high. And the yield of carbon nanotubes is highest When the catalyst is in air calcined at 900℃. Raman spectra shows that the catalyst calcined at 800℃,900℃ and 1000℃, carbon nanotubes of good quality are synthesized. And single-walled carbon nanotubes are synthesized. When the catalyst is in air calcined at 800℃, products are most double-walled carbon nanotubes. When the catalyst is in air calcined at 900℃, products are most single-walled carbon nanotubes and double-walled carbon nanotubes. When the catalyst is in air calcined at 1000℃, products are most single-, dobuble- and triple-walled carbon nanotubes. (5)Growth of carbon nanotubes show some directionality with influence of the electric field.(6)respectively, carbon monoxide and methane as carbon source, types and forms of the synthesized product are different.