From ceramic-matrix nanocomposites to the synthesis of carbon nanotubes

The selective reduction in Hz of oxide solid solutions produces nanocomposite powders in which transition metal nanoparticles are dispersed inside and on the surface of the oxide matrix grains. When using a H-2/CH4 reducing atmosphere, the metal nanoparticles that form on the surface of the oxide grains act as catalysts for the CH4, decomposition and, because of their small size at high temperatures (>800 degreesC), favor the in-situ nucleation and growth of single-wall and thin multiwall carbon nanotubes. This article reviews our results on the synthesis and characterization of M-MgAl2O4 (M = Fe, Fe/Co, Fe/Ni) nanocomposite powders, without and with carbon nanotubes, emphasizing the information that can be derived from Mossbauer spectroscopy as a complement to other characterization techniques.