A.N. Danilin, S.M. Nikitin, L.N. Rabinsky, Yu.G. Yanovsky
This article gives a brief review of existing methods for the synthesis of carbon nanotubes (CNT). The Catalytic Vapor Deposition method (CVD) is considered in detail as of the most efficient and promising one for industrial development, which consists in CNT forming from the vapor by passing a carbon feedstock in the vapor over a heated catalyst. There are a number of shortcomings of the traditional technology of this method, one of which is its periodicity (the inability to implement continuous process) and the inefficient consumption of carbon-containing raw materials and associated inert gases.
The modified CVD method is described, which allows to improve efficiency and achieve greater productivity in the process continuity. It is proposed to use a rotary tube furnace with devices for continuous feeding of catalyst and gas mixture in the active furnace zone and removing of the product and waste gases.
The catalyst is fed continuously to the unheated part of the furnace where it is pre-heated gases emanating from the hot part of the furnace. Hot gases are transferred toward the catalyst, which improves the heat transfer. The catalyst is mixed and blown on by a gas mixture continuously and uniformly in all the way passing through the tube furnace. This eliminates stagnant areas. Coming out of the active zone of the furnace, the reaction products are cooled in a stream is fed gas mixture at the same time making its preheating. There is a significant difference from well-known implementations of CVD: the gas composition leaving the reactor is adjusted accordingly, and the gas is then sent back to the reactor.
The installation was designed and manufactured for the CNT synthesis according to the new technology. The installation allows synthesizing CNT continuously without significant loss of carbon and related materials with a capacity of 0,5 to 1 tons per year.
The resulting nanoproducts are agglomerates of bound CNT with inclusions of metal clusters (Fe, Co), which were part of the catalytic systems Fe/Al2O3 and Co/Al2O3.
Results of CNT structure studies on the electron microscopes are given. The sizes of CNT agglomerates are estimated and their magnetic properties investigated.