IRON-SILICA AND NICKEL-SILICA NANOCOMPOSITES PREPARED BY HIGH-ENERGY BALL-MILLING

Metal-silica nanocomposites with different metal volume fractions have been prepared via solid state exchange reactions induced by ball mill ing followed by a reduction treatment in H-2 flux. In nickel-containin g mixtures oxygen transfers directly from NiO to Si while NiO is reduc ed to Ni. When NiO is present in a large ratio, its excess can be redu ced by a thermal treatment in H-2 flux. Nickel crystallites are obtain ed with nanometer size in the milling process and there is no signific ant growth during thermal treatment. Similar process conditions applie d to Fe-containing mixtures give rise to a more complex reaction path which prevents the complete conversion of Fe(III) to Fe. Nickel-silica and iron-silica nanocomposites are also produced by ball milling mixt ures of either nickel or iron with amorphous silica.