Experimental study of catalyst nanoparticle and single walled carbon nanotube formation in a controlled premixed combustion

Abstract

In this work we investigated formation processes of both catalyst nanoparticles and single walled carbon nanotubes (SWCNTs) in a controlled premixed CH4–O2–Ar flame. Experimental measurements were conducted to study the formation mechanism of the catalyst, the interaction between the catalyst and SWCNTs, and the formation process of SWCNTs. The sampling of flame generated nanostructures was carried out at different locations in the flame. Then the as-produced sample was characterized using Raman spectroscopy, X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy and transmission electron microscopy. Two classes of nanoparticles were characterized in the sample, iron oxide (magnetite Fe3O4 or maghematite Fe2O3) and elemental iron coated with graphite layers. The iron particles were hence suggested to be the direct catalyst for the growth of SWCNTs. Thermodynamic studies and flame kinetics support the formation mechanism of nanoparticles. Three flame zones were identified for the growth of SWCNTs: an induction zone, a stable growth zone, and a growth cessation zone. The flame temperature was found to be an important factor which controls the inception and growth of SWCNTs.