X-ray reflectivity of zirconia based sol-gel coatings on borosilicate glasses

In this work the technique of X-ray reflectometry was applied to study zirc oniumsulfate films deposited by sol-gel dip-coating process on a borosilica te glass surface. The influence of withdrawal speed and temperature of ther mal treatment on the film structure are analyzed. The thermal evolution of the density and thickness of the film was compared with these properties me asured for a monolithic xerogel by helium picnometry and thermomechanical a nalysis. The fitting of experimental curves by classical reflectivity model showed the presence of an additional layer at the top surface of the coati ng. Layer thickness increases with increase of withdrawal speed in agreemen t with the Landau-Levich model. The apparent and real densities are similar for coatings fired below 400 degrees C, which shows that the films are fre e of pores. The shrinkage during firing is anisotropic, occurring essential ly perpendicular to the coating surface. (C) 1999 Elsevier Science B.V. All rights reserved.