Leveling effect of sol-gel SiO2 coatings onto metallic foil substrates

The leveling capability of sol-gel SiO2 layers onto titanium and Kovar (Fe5 4 Ni29 Co17) foil substrates has been analyzed by atomic force microscopy ( AFM) and profilometer roughness measurements as a function of the sol-gel p reparation parameters. SiO2 coatings have been prepared by immersion of met allic foils in a solution where the [alkoxide]/[EtOH] ratio was between 0.0 5 to 0.7, and subsequent withdrawal of the samples at a constant rate betwe en 8 and 49 cm/min. By increasing the [alkoxide]/[EtOH] ratio and/or the wi thdrawal velocity, the SiO2 layer thickness and leveling capability increas e but its mechanical integrity decreases. By increasing SiO2 film thickness , better coverage of large-scale heterogeneities but poorer coverage of sho rt-scale features have been observed. A compact (cracks and striations free ) coverage which minimizes the roughness sample surface at short and large scales has been obtained by applying successive SiO2 layers with various th icknesses. (C) 2001 Elsevier Science B.V. All rights reserved.