SILICA GELS AND GEL GLASSES CONTAINING SILVER AND PLATINUM METAL PARTICLES

Abstract

Silica gels containing between 0.05 and 20.0 mol% Ag2O and between 0.1 and 1.0 mol% PtO2 have been synthesized using TEOS, C2H5OH, H2O, HNO3, HCl, AgNO3 and PtCl4 as precursors. The gels obtained with Ag2O are colorless, while the gels containing PtO2 are yellow. The gels have been heat treated in the 25–1000°C temperature range. The processes of structural evolution of gels have been studied by means of IR-spectroscopy, X-ray diffraction analysis, transmission electron microscopy (TEM) and transmission electron microdiffraction (TEMD). It has been established that the temperature of gel to gel-glass transition decreases when the Ag2O content of the gels increases. The same tendency was established for the gel to gel-glass transition in the SiO2-PtO2 system. Special attention was paid to the formation of silver and platinum metallic particles in amorphous materials. The microstructure of the gels has been observed and the sizes of the metal particles were determined to be from 3 to 25 nm. The crystallization processes in the gels heat treated at 1000–1200°C have been examined and besides the silver and platinum particles α-cristobalite was formed. It has been shown that nanocomposite materials containing ultrafine silver and platinum particles in SiO2 amorphous or polycrystalline matrixes can be obtained.