STRUCTURE OF MINERAL GELS

Small-angle neutron scattering (SANS) measurements have been performed to investigate the nanoscale structure of materials of the systems xT iO(2) .(1 - x)SiO2 and xZrO(2) .(1 - x)SiO2 with x less than or equal to 10 mol% at different processing stages. The materials were prepared by sol-gel processing using the alkoxides under strong acidic conditi ons. Samples were studied as xerogels heat treated at 120 degrees C an d 850 degrees C and as wet gels at gel point and after ageing. All sam ples showed identical microstructure at the gel point of extended line ar chains about 10 nm long. The aged gel has a mass fractal structure with fractal dimensions of 1.7-1.9. The 120 degrees C heat-treated xer ogels show homogeneous oxide regions with mass fractal structure. For the 850 degrees C heat-treated xerogel the average size of the oxide r egions is reduced and it has become more dense compared with the 120 d egrees C heat-treated sample.