Flame synthesis of carbon nanotubes in a rotating counterflow.

The synthesis of carbon nanotubes (CNTs) in rotating counterflow diffusion flames using nickel-nitrate coated or uncoated nickel substrates was investigated. A diffusion flame at high angular velocity (low strain rate) is stronger than a weak flame at low angular velocity (high strain rate) and produces more carbon sources because of the longer residence time of the flow. Even though both the fuel and oxygen concentrations are quite low (using 86% N2-diluted C2H4 as the fuel and air as the oxidizer), CNTs can be successfully produced. Curved and entangled tubular multi-walled CNTs are harvested, which have both typical straight tubular and bamboo-like structures. Besides curved CNTs, helically coiled tubular CNTs are also synthesized. It is verified that flow rotation associated with residence time plays an important role in the synthesis of CNTs. Using a Ni(NO3)2-coated nickel substrate has advantages over uncoated Ni substrates.