Nanocomposites and nanomaterials 
Some peculiarities of MWCNTs synthesis using iron as a catalyst
Khovavko A.I.1, Kotov V.G.1, Nebesniy A.A.1, Svyatenko A.M.1, Filonenko D.S.1, Nie G.2
1 Department of Thermo-chemical Processes and Nanotechnologies,
Gas Institute of the NAS of Ukraine. 
Degtyarivska, 39, Kyiv-03113, Ukraine. 
E-mail: ahova2005@ukr.net
2 School of Physics and Telecommunication Engineering, Yulin Normal University, Yulin 537000, China.
The most common carbon-containing gaseous source – natural gas was used as the feedstock for MWCNTs synthesis. Natural gas was pre-converted on a nickel catalyst, whereupon the resulting conversion products were used to synthesize MWCNTs. There were developed some decisions to improve the aggregate for MWCNTs synthesis. It’s proposed to apply consistently sluice chambers in different zones of the reactor. The distinctive feature – supporting different gas composition atmospheres in functional zones. 

Fig. 1. View of MWCNTs obtained as a result of fresh-reduced iron processing by converted natural gas at different modes
The mechanism of carbon nanomaterial formation at moderate temperatures while processing of fresh-reduced iron by products of air conversion of natural gas is considered. It is shown that under given conditions the size and the shape of the resulting carbon are depended on the temperature and the size of microscopic iron grains formed during reduction. These iron grains are the catalyzer of the reaction of carbon monoxide disproportionation. It is concluded that the formation of nucleus of the new carbon phase occurs at the contact boundaries of neighboring grains of newly reduced iron with the subsequent formation in these places of ring-shaped carbon cups. Nanotubes are forming as a result of further carbon crystallization  and separation of iron particles from the main mass is occurring i.e., there is a fragmentation of the substance of the catalyst. Our researches allow making the conclusion that in the temperature range below 700° C carbonization-decarbonation cycles in the Feγ- Feα-Fe3C system can play a crucial role in CNTs formation.