Synthesis of Narrow Diameter Multiwalled Carbon Nanotubes (MWNTs) By Catalytic Chemical Vapor Deposition For Mechanical Reinforcement Applications

Strong and versatile carbon nanotubes (CNTs) are finding new applications in improving conventional polymer-based fibers. Nanotube-reinforced composites could ultimately provide the foundation for a new class of strong and lightweight fibers with properties such as electrical and thermal conductivity unavailable in current fibers. A recent research has discovered that the best type of nanotube for polymer composite reinforcement is the small diameter multiwalled nanotubes (MWNTs). One serious weakness of all current techniques for preparing MWNTs is that they produce a wide range of tube sizes and structures, which could be a drawback in areas where specific tube structures are needed. Here, a catalytic technique has been developed that has the ability to define the diameter of bulk multiwalled carbon nanotubes grown. The method involved catalytic decomposition of methane over the catalyst at 950°C in a chemical vapor deposition (CVD) system. It includes pre-treatment of iron, nickel and cobalt catalyst with NH3 gas as the key step to vary the size of catalyst used for the growth and subsequently defined the diameter of CNTs produced. Structural characterizations including scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), thermo gravimetric analysis and Raman spectroscopy conducted on CNTs grown on three different catalysts, namely iron, cobalt and nickel have indicated that the size and type of catalyst used affects their sizes and crystallinity. With this technique, narrow diameter bulk multiwalled carbon nanotubes in the range of 19 to 38 nm has been produced. It is believed that with this diameter-controlled synthesis, bulk CNTs of certain range of diameter can be produced to fulfill the requirement needed for mechanical reinforcement of polymer composites.