Synthesis of carbon nanotubes–Fe–Al2O3 powders.Influence of the characteristics of the starting Al1.8Fe0.2O3 oxide solid solution

Abstract

Al1.8Fe0.2O3 amorphous solid solution have been calcined at temperatures between 1025 and 1100°C and the obtained powders have been reduced in a H2–CH4 gas mixture (12 mol% CH4) at 1050°C in order to prepare carbon nanotubes (CNTs)–Fe/Fe3C–Al2O3 nanocomposite powders. The calcination at 1100°C leads to powders containing an a-Al222xFe2xO3 solid solution (x , 0.1) and some traces of a Fe-rich phase (a-Fe222yAl2yO3) that gives, under reduction, large Fe particles which catalyze the growth of ribbon like filaments. An a-Al1.8Fe0.2O3 monophased solid solution with a higher specific surface area is obtained after a calcination at only 1050 or 1025°C. In the corresponding composite powders, all filaments are isolated CNTs or bundles of CNTs and the high specific area is beneficial to both the quantity and the quality parameters which are greatly enhanced in comparison with previous results. About 20% of the observed CNTs are single wall nanotubes (SWNTs). The majority of the observed multiwall nanotubes (MWNTs) have only two walls and the inner diameters are distributed between 0.8 and 6 nm, with a peak at 2 nm. The in-situ catalysis by selective reduction of a solid solution allows for production of nanocomposite powders containing very large quantities of high quality CNTs