The effect of the viscosity in the precursor solution on the structure of sol-gel derived silica films containing cobalt

Silica coatings containing cobalt have been prepared from sol-gel precursor solutions having a viscosity in the range of 3 to 40 cP. The different values of viscosity were achieved by aging the solutions with various amount of solvent (ethanol). The structure of these samples was analyzed using x-ray diffraction, Raman scattering, infrared absorption and Auger depth profiles. These measurements show that, upon heat treatments in air at 500°C, the cobalt oxidizes to form small oxide particles. However, when the coatings are prepared from precursor solutions with viscosity lower than about 9 cP, the cobalt migrates to the outer surface of the coating were it is oxidized to form the particles. On the other hand, if the coatings are prepared from solutions with a higher viscosity, the oxide particles are formed in the bulk of the coating. The infrared and Raman spectra indicate that the structure of this later set samples is more ordered with fewer amount of voids.