Carbon Nanotubes, Synthesis, Growth and Orientation Control in Opposed Flow Diffusion Flames

The combustion synthesis of carbon nanotubes is reviewed, examining their formation and control in diffusion flames. Much of the initial work in this area employed coflow diffusion flames and provided insight into carbon nanotube (CNT) formation. However, the inherent multidimensional nature of such coflow flames made the critical spatial location difficult to maintain. Among this early work, our UIC group demonstrated the superiority of the opposed flow diffusion flame configuration due to its uniform radial distribution that reduces such flow to a one-dimensional process. While a summary of the early coflow flame work is presented, the use of the opposed flow diffusion flame will be the focus of this review. The production of carbon nanostructures in the absence of a catalyst is discussed together with the range of morphology of nanostructures generated when a catalyst is employed. The important aspect of control of the growth and orientation of CNTs and generation of CNT arrays through the use of electric fields is examined as is the use of anodized aluminum oxide templates. Fruitful areas for further research such as the functional coating of CNTs with polymers and the application of these opposed flow flames to synthesis of other materials are discussed.