Effect of additives on the structure of SiO2 sol-gel spray coatings

Abstract

SiO2 coatings were prepared from alkoxide sols by means of spray coating. Coatings prepared from sols solely containing ethanol as solvent showed heterogeneous structures. This is supposedly due to solvent evaporation during spray coating. When reaching the substrate, the droplets possess too high viscosity to enable them to disperse on the substrate. However, when additives, such as 1.3-butanediol, ethylene glycol or glycerol, with high boiling temperatures were used, smooth coatings exhibiting small surface roughness were obtained. It is shown that best results were obtained when 1.3-butanediol was used. With increasing additive concentration, the surface roughness decreased.