Wide angles X-ray scattering (W.A.X.S.) and H.R.E.M. studies on nanoscale cobalt and cobalt oxide colloids

Monodispersed cobalt nanoparticles have been synthesised by an original method using the decomposition under hydrogen of an organometallic precursor in the presence of a stabilising polymer. Using W.A.X.S. and H.R.E.M. techniques we have characterized the structure of two particle batches, 1.5 and 5nm average size. The finest particles (1.5nm) present a bcc core and a disordered surface whereas the biggest ones (5 nm) are hep as the bulk structure. We then have followed very precisely the air oxidation kinetics at room and moderate temperatures. Room temperature leads to CoO divalent cobalt oxide whereas oxidation at 130°C drives to the Co₃O₄ spinel form.