Silica-Zirconia Alkali-Resistant Coatings by Sol-Gel Route

Generally, to make the surface hydrophobic, silicabased coatings are preferred in various fields. When the coatings on glass or metal are exposed to alkaline surrounding, the silica network starts to deteriorate and its hydrophobic character ceases. To overcome this problem, we developed a silica-based coating along with zirconia which sustains the alkali attack and hydrophobicity is preserved. The chemicals involved in the synthesis were methyl tetraethoxysilane (MTMS), zirconium propoxide (ZP), methanol (MeOH) and acetyl acetone (Hacac) as a chelating agent for ZP, oxalic acid and ammonium hydroxide as acid and base catalysts respectively. A simple two-stage sol-gel method and deep-coating technique was employed to obtain the coatings. The hydrolysis time of MTMS was varied and its effect on wetting behaviour of the coatings was noted. The optimized coating was characterized by FTIR, EDAX, SEM, optical transmittance and wetting properties were studied. The water contact angle before and after exposure to alkali for bare silica and silica-zirconia coating was measured to be 120°, <10° and 100°, 93° respectively, showing improvement in the potency of coating in alkaline surroundings.