Sol-gel-derived thick coatings and their thermomechanical and optical properties

The preparation of crackfree and transparent SiO2 coatings on soda lime glass with thicknesses of about 8 µm after densification at 500°C is presented. The high thickness can be obtained by using on 80:20 mixture of methyltriethoxysilane and tetraethyl orthosilicate as alkoxide precursors in combination with an aqueous colloidal SiO2 sol with particle sizes of about 7 nm. This principle of synthesis is also applied to ZrO2 containing coatings yielding to thickness of about 3 µm. Refractive index measurements indicate that the coatings are nearly completely densified. At higher temperatures tensile stresses appear within the layers and are transmitted to the substrate, increasing its thermal stability.