Synthesis of carbon nanotubes–Fe–Al 2O 3 powders. : Influence of the characteristics of the starting Al 1.8Fe 0.2O 3 oxide solid solution

Abstract

Al 1.8Fe 0.2O 3 amorphous solid solution have been calcined at temperatures between 1025 and 1100°C and the obtained powders have been reduced in a H 2–CH 4 gas mixture (12 mol% CH 4) at 1050°C in order to prepare carbon nanotubes (C NTs)–Fe/Fe 3C–Al 2O 3 nanocomposite powders. The calcination at 1100°C leads to powders containing an α-Al 2−2xFe 2xO 3 solid solution (x < 0.1) and some traces of a Fe-rich phase (α-Fe 2−2yAl 2yO 3) that gives, under reduction, large Fe particles which catalyze the growth of ribbon like filaments. An α-Al 1.8Fe 0.2O 3 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 C NTs or bundles of C NTs 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 C NTs 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 C NTs.