Dense, uniform, smooth SiO2/TiO2 hard coatings derived from a single precursor source of tetra-n-butyl titanate modified perhydropolysilazane

Abstract

SiO₂/TiO₂ composite coatings are of great interest due to their optical, photocatalytic, electrical and mechanical properties. There are many methods for preparing SiO₂/TiO₂ composite coatings. Among these, the sol–gel process is eco-friendly and easily implementable for industrial applications. However, it is still a great challenge to prepare dense, uniform and smooth SiO₂/TiO₂ composite coatings with a sol–gel process. In this work, we show a modified sol–gel process for achieving dense, uniform and smooth SiO₂/TiO₂ coatings with tetra-n-butyl titanate modified perhydropolysilazane (PHPS) as a single precursor source, in which PHPS acts as the source for SiO₂ instead of a traditional alkoxylsilane compound. The micro-morphology and composition evolution during the preparation process have been investigated; a smooth surface with a roughness average (S_a) below 4.5 nm and a uniform distribution of Ti elements over the entire coating are shown. These dense, uniform SiO₂/TiO₂ coatings exhibit excellent mechanical robustness, with hardness values as high as 9.45 GPa, excellent optical transparency and hydrophilic properties.