Dip Coating of Zirconia and Mixed Zirconia Films

When glycols (except ethylenglycol) were added to an isopropanol solution of zirconium n-butoxide, the corresponding glycolates were formed by the alcohol exchange reaction, and the precipitation of oxide by hydrolysis was strongly suppressed. Diethylene glycol was most effective as the glycol additive for the precipitation retarder. At the glycol/alkoxide ratio of 2 in the presence of water (water/alkoxide ratio=0-5), a stable sol was obtained from which transparent zirconia sol-gel films can be obtained. The film thickness can be controlled by the alkoxide concentration, water/alkoxide ratio, and the pulling-up rate of the substrate plate. The maximum thickness of uniform transparent zirconia films obtained in one dipping-drying-heating cycle was about 1500Å. Much thicker films can be obtained by repeating the cycle. The crystal form of the zirconia films obtained at 600°-650°C on a glass substrate was tetragonal, and transformed into monoclinic above 800°C. The refractive indices and densities of the films obtained at 600°-650°C were 1.9-2.0 and 4.7-5.5, respectively. The density increased to 5.8-6.0g/cm3 by the heat treatment at 1000°C. In the present system, an aqueous solution of yttrium or calcium nitrate could be added so as to prepare tetragonal of cubic transparent films of doped zirconia, respectively. When silver nitrate solution was added, the tetragonal AgO-doped zirconia films were obtained. Furthermore, it was found that the addition of titanium and aluminium-magnesium alkoxides allowed to form mixed oxide films ZrTiO4 and spinel-doped ZrO2.