Hydrothermal synthesis of yttria stabilized ZrO2 nanoparticles in subcritical and supercritical water using a flow reaction system

Yttria stabilized zirconia nanoparticles have been prepared by hydrothermal flow reaction system under subcritical and supercritical conditions. ZrO(NO3)2/Y(NO3)3 mixed solutions were used as starting materials. Reaction temperature was 300–400 °C. Reaction time was adjusted to 0.17–0.35 s. Based on the residual Zr and Y concentrations, the complete conversion of zirconium was achieved irrespective of pH and hydrothermal temperature, whereas the conversion of yttrium increased with an increase in pH and hydrothermal temperature. Stoichiometric solid solution was achieved at pH>8. XRD results revealed that tetragonal zirconia can be formed regardless of yttrium content, where the tetragonality was confirmed by Raman spectroscopy. The average particle size estimated from BET surface area was around 4–6 nm. Dynamic light scattering particle size increased with the solution pH owing to the aggregation of primary particles. TG-DTA analyses revealed that weight losses for adsorbed water and hydroxyl groups decreased with hydrothermal temperature.