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

Al1.8Fe0.2O3 amorphous solid solution have been calcified at temperatures b etween 1025 and 1100 degrees C and the obtained powders have been reduced i n a H-2-CH4 gas mixture (12 mol% CH4) at 1050 degrees C in order to prepare carbon nanotubes (C-NTs)-Fe/Fe3C-Al2O3 nanocomposite powders. The calcinat ion at 1100 degrees C leads to powders containing an alpha-Al2-2xFe2xO3 sol id solution (x < 0.1) and some traces of a Fe-rich phase (alpha-Fe2-2yAl2yO 3) that gives, under reduction, large Fe particles which catalyze the growt h of ribbon like filaments. An alpha-Al1.8Fe0.2O3 monophased solid solution with a higher specific surface al ea is obtained after a calcination at on ly 1050 or 1025 degrees C. In the corresponding composite powders, all fila ments 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 greatl y enhanced in comparison with previous results. About 20% of the observed C -NTs are single wall nanotubes (SWNTs). The majority of the observed multiw all nanotubes (MWNTs) have only two walls and the inner diameters are distr ibuted 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 nanocompos ite powders containing very large quantities of high quality C-NTs. (C) 200 0 Elsevier Science Ltd. All rights reserved.