Preparative Aspects of Sol-derived Oxide Glass Coatings

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Abstract
Thin, transparent coatings of amorphous SiO2 and Al2O3 were deposited on soda lime glass substrates by the dip technique, using organometallic precursor sols. The water content of the sol was found to influence its wetting behaviour, low values of H2O: Si(OC2H5)4 being preferred for SiO2 and high values of H2O: Al(OC4H9S)3 for Al2O3 coatings of sufficient uniformity and clarity. Expulsion of volatiles and polycondensation of the coated material were allowed to take place via (i) an initial baking step at 90°-100°C and (ii) a final heating step at 350°-500°C according to the sol composition. The procedure yielded homogeneous, highly transparent coatings, showing 84–93% transmission of the visible range of wavelengths.