From ceramic-matrix nanocomposites to the synthesis of carbon nanotubes

The selective reduction in Hz of oxide solid solutions produces nanocomposi te 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 a tmosphere, the metal nanoparticles that form on the surface of the oxide gr ains act as catalysts for the CH4, decomposition and, because of their smal l size at high temperatures (>800 degreesC), favor the in-situ nucleation a nd 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 spectrosco py as a complement to other characterization techniques.