The influence of ZrO2 precursor type on the structure of ZrO2-TiO2-SiO2 gels and selected thin films

Abstract

Zirconia-silica materials show valuable properties but usually they are synthesized via high temperature processes. The sol-gel method makes it possible to obtain materials of the same properties but at much lower temperatures. In the present work, tetraethyl orthosilicate TEOS Si(OC2H5)4 and titanium propoxide Ti(OC3H7)4 were used in the sol-gel method as SiO2 and TiO2 precursors, respectively. Additionally, different ZrO2 precursors were applied: zirconium acetate Zr(OOC2H3)4, zirconium propoxide Zr(OC3H7)4 or zirconium butoxide Zr(OC4H9)4. All gels were of the same molar ratio ZrO2:TiO2:SiO2 = 0.089: 0.018: 0.089, but they were synthesized using different ZrO2 precursors, as mentioned above. Because each precursor of titania, silica and zirconia shows different rates of hydrolysis and polycondensation processes, the syntheses were conducted applying ethyl alcohol (98%pure) as a solvent. All gels were then dried in air and annealed at 500 °C, 800 °C and 1200 °C. Additionally, thin films based on one of the ZrO2 precursors, zirconium propoxide Zr(OC3H7) and two sols of different degrees of dilution, but the same molar ratio of ZrO2: TiO2: SiO2 as in gels, were prepared. Coatings were deposited on steel substrates by dip coating technique. To improve mechanical properties and adhesion, all coatings were annealed at 500 °C in air.For all samples, a wide range of structural studies was carried out, covering FTIR spectroscopy, X-ray diffraction and SEM. The surface of thin films was examined using AFM to estimate the roughness and the particles size in the samples. The results allowed concluding on the influence of different types of ZrO2 precursors on the structure and morphology of the obtained gels and thin films. The focus was put especially on the presence and stabilization of the metastable tetragonal form of ZrO2, which is advantageous because of its valuable properties. Preliminary studies of hydrophilic/hydrophobic properties of thin films were undertaken by measuring the contact angle values.