Thickness controlled SiO2/TiO2 sol-gel coating by spraying

Abstract SiO2/TiO2 composite sol-gel coatings can be used in many industrial applications for their self-cleaning and photocatalytic properties. In this study, SiO2/TiO2 composite sol-gel coatings were deposited by spray coating as it allows a better thickness control than dip coating, which is now mostly used. The most critical spray coating parameters were first determined by a fractional factorial experimental design for a TiO2 sol coating. Then, the effect of silica addition in combination with a hydrophobic precursor on the thickness, the water contact angle and the adhesion strength of the coatings was studied. The most critical spray parameters for controlling the thickness of the coating were the reservoir pressure and the height of the spray gun above the substrate, while the atomisation pressure had almost no effect. A thin coating can be obtained by using a great height in combination with a low reservoir pressure.