New Method for the Preparation and Stabilization of Nanoparticulate t ‐ZrO 2 by a Combined Sol–Gel and Solvothermal Process

Nonstabilized and silica‐stabilized zirconia (ZrO 2 ) 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 ZrO 2 nanoparticles was approximately 5 nm. A following solvothermal process led to a crystalline fraction of the powder consisting of 31 wt% tetragonal ( t ) phase ZrO 2 . 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°C. The crystallite sizes were also confirmed by means of Brunauer–Emmett–Teller and high‐resolution transmission electron microscopy.