Carbon Nanotubes synthesized at LACER by Catalytic Chemical Vapor Deposition (CCVD)





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                     About Carbon Nanotubes




        Carbon Nanotubes (CNT) are a new material class discovered at 1991 by Sumio Iiijime and they present extraordinary mechanical, electrical and thermal properties. CNT has the highest tensile strength known, approximately 200 Gpa, 100 times stronger than the strongest steel with only 1/6 of it density. Several synthesis processes were developed  and most common are electrode discharge, laser ablation and the Catalytic Chemical Vapor Deposition (CCVD). The CCVD is the technique with the highest potential for mass production of CNT. Transition metals like Fe, Ni, Co e Mo are used as catalyst.





Mechanical strengh of different engineering materials compared to the carbon nanotubes





 Nanotubes with distintc helicities




        These catalyst are nanoparticles with diameters inferiors to 20nm. The catalyst are submitted to a rich carbon atmosphere in temperatures between 600-1200°C. The metallic nanoparticles adsorbed the carbon and become saturated, than occurs the precipitation of carbon in a shape of a curved graphitic plane, like a tube. This tube of sp2 hybridization carbon is the carbon nanotubes and can have one wall (Single walled nanotube, SWNT) or several walls (multi-walled nanotube, MWNT). The catalyst are generally dispersed over a flat substrate, like a silicon wafer, or a large area inert material. Several ceramics oxides can be used as support for the catalyst, like Al2O3, SiO2 and MgO. The composition of the support materials can affect the nanotubes characteristic, like the diameter. Strong interaction between the metallic catalyst particles and the support materials enhance de dispersion of the metallic particle and prevent the agglomeration. The agglomeration increase de diameters of the catalyst particles and the diameters of the nanotubes. The catalyst particles must be smaller than 20-15nm to produce carbon nanotubes


                       Synthesis of Carbon Nanotubes at LACER


        Actually single walled and multiwalled carbon nanotubes are synthesized by Catalytic Chemical Vapor Deposition. The synthesized nanotubes are not oriented and large superficial area oxides are used as support for the metallic catalyst, for increasing the efficient ness of the synthesis. Also are been developed purifications methods for the synthesized carbon nanotubes.

        The produced carbon nanotubes are been employed in production of composites of polymeric and ceramic matrix





Reactor of Catalytic Chemical Vapor Deposition used in the synthesis of carbon nanotubes. Electric furnace (A), Tubular reactor (B), humidity absorber (C), bubbler for liquid precursors (D), command panel (E), internal vision of the reaction chamber during the synthesis of carbon nanotubes (F).