New method for the preparation and stabilization of nanoparticulate t-ZrO2 by a combined sol-gel and solvothermal process

Nonstabilized and silica-stabilized zirconia (ZrO2) crystallites with sizes between 3 and 4 nm were synthesized by a novel combined sol-gel and solvothermal process. After adding zirconium n-propoxide to a solution of isobutanol, propionic acid, and water, a transparent nanoparticulate sol was synthesized by a sol-gel process. The average hydrodynamic diameter of the amorphous ZrO2 nanoparticles was approximately 5 nm. A following solvothermal process led to a crystalline fraction of the powder consisting of 31 wt% tetragonal (t) phase ZrO2. This fraction was doubled to 61 wt% by adding 10 mol% 3-methacryloxypropyl trimethoxysilane (MPTS) and increased to 96 wt% by a subsequent calcination at 800 degrees C. The crystallite sizes were also confirmed by means of Brunauer-Emmett-Teller and high-resolution transmission electron microscopy.