Ni-silica and Cu-silica nanocomposites prepared by ball milling

Nickel-silica nanocomposites with different metal volume fractions have been prepared via solid state exchange reactions which were induced by ball milling nickel oxide and silicon powders and by direct milling mixtures of nickel and amorphous silica. A copper-silica nanocomposite has also been prepared by a solid state exchange reaction. The evolution of the systems during the preparation process has been monitored by X-ray diffraction and transmission electron microscopy. Electrical properties of the final samples are examined as a function of composition and preparation method

Preparation of aerogel and xerogel nanocomposite materials

Sol-gel method was used to prepare nickel oxide-silica and iron oxide-silica nanocomposites materials in form of aerogels and xerogels. The samples were characterized by thermal analysis, X-ray diffraction, N2 physisorption and transmission electron microscopy techniques. The variation of the supercritical solvent extraction conditions gives rise to differences in the morphological characteristics of the aerogels. These differences influence the size of the nickel oxide nanoparticles in nickel containing aerogels. On the other hand they do not affect the structure and size of the iron oxide nanoparticles in iron containing aerogels. The differences between the xerogel and aerogel nanocomposites are discussed

Iron-Cobalt-Silica aerogel nanocomposite materials

Iron-Cobalt-Silica nanocomposites were prepared in form of aerogels. X-ray diffraction, transmission electron microscopy and N2 physisorption at 77 K were used to investigate the structure, size and dispersion of the nanocrystals and the porous structure in the aerogels and in the final composites. The variation of the supercritical drying conditions gives rise to differences in the morphological features of the aerogels. These differences influence the size of the cobalt oxide nanoparticles in the aerogels. On the other hand, after the reduction treatment the average size of the alloy nanoparticles is the same in all the aerogel nanocomposites. The effect of reduction temperature on alloy formation and particle size is also discussed

An X-ray absorption spectroscopy study of the FeK edge in nanosized maghemite and in Fe2O3-SiO2 nanocomposites

The structural evolution of Fe2O3-SiO2 nanocomposite samples prepared using the sol-gel method have been studied by EXAFS (extended X-ray absorption fine structure) and XANES (X-ray absorption near edge structure) techniques in comparison with pure nanosized and microcrystalline maghemite samples. EXAFS data show that the difference between nanosized and microcrystalline maghemite is due to an increase of disorder of the superficial sites while no decrease of coordination numbers was detected. EXAFS and XANES data of the nanocomposite thermally treated at 900 degrees C indicate that the sample is constituted by maghemite nanoparticles embedded into amorphous silica while the sample thermally treated at 300 degrees C contains an amorphous precursor which is very likely to be ferrihydrite. No interactions between the metal oxide nanoparticles and the silica network are present since the EXAFS spectra of the nanocomposite samples can be interpreted as only having Fe-O and Fe-Fe interactions