Silica-Zirconia Sol–Gel Coatings Obtained by Different Synthesis Routes

Abstract

Homogeneous xSiO2-(1−x)ZrO2 coatings have been prepared onto glass-slides, monocrystalline Si and stainless steel (AISI 304) using sols prepared via acid and basic catalysis. Zirconium tetrabutoxide (TBOZr), zirconium n-propoxide (TPZ), tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) were used as precursors of zirconia and silica, respectively. The different parameters involved in the synthesis procedure, as molar ratios H2O/alkoxides, NaOH/alkoxides, and sintering temperature have been analysed, correlating the stability and rheological properties of the sols. The evolution and structure of the sols and coatings have been studied by FTIR. Coatings have been prepared by dipping from acid and basic sols. Electrophoretic Deposition (EPD) technique has also been used to prepare coatings onto stainless steel from basic particulate sols in order to increase the critical thickness. A maximum thickness of 0.5 μ m was reached by both dipping and EPD process for 75SiO2: 25 ZrO2 composition. The critical thickness decreases with ZrO2 amount depending strongly of the drying conditions. Si–O–Zr bonds have been identified by FTIR, indicating the existence of mixed network Si–O–Zr in the coatings obtained by the different routes. Crystallisation of ZrO2(t) was only observed at high sintering temperature (900∘C) by FTIR and confirmed by DRX.