Small metal particles in ceramic matrices by sol-gel processing of metal complexes
Composites containing metal or metal oxide particles of a few nanometers diameter are prepared by hydrolysis of a solution of tetraethoxysilan (TEOS) and a metal salt in the presence of aminoalkyl(trialkoxy)silanes, RHN(CH2)nSi(OR')3 (R = H, (CH2)2NH2) or related bifunctional compounds, followed by complete oxidative removal of all organic moieties. By this process metal oxide particles in SiO2 are formed, which then are reduced by hydrogen. The metal or metal oxide particles prepared by this method have a high and uniform dispersion and a very narrow particle size distribution. The very high metal dispersion is achieved by complexation of the metal and fixation of the metal complexes to the silica matrix by the bifunctional ligand during sol-gel processing.