Characterization of tin oxide based sol-gel coatings on borosilicate glasses by X-ray reflectivity

The X-ray reflectivity technique was applied in the study of tin oxide film s deposited by sol-gel dip-coating on borosilicate glasses. The influence o f the withdrawal speed and temperature of thermal treatment on the film str ucture was analyzed. We have compared the thermal evolution of the density and the shrinkage of the films with these properties measured for the monol ithic xerogel by helium picnometry and thermomechanical analysis. In agreem ent with the Landau-Levich model, the layer thickness increases by increasi ng the withdrawal speed. Nevertheless, it decreases with the increase of th e thermal treatment temperature, due to the densification process. The valu es of apparent density are smaller than the skeletal density, which shows t hat the films are porous. The comparison between the film and the monolith indicates that shrinkage during firing is anisotropic, occurring essentiall y perpendicular to the coating surface.