Preparation of Nano-ZrO2 powder via a microwave-assisted hydrothermal method

Abstract ZrO2 nanocrystals were synthesised by a microwave-assisted hydrothermal method using zirconium oxychloride (ZrOCl2·8H2O), yttrium chloride (YCl3·6H2O), and liquor ammonia (NH3·H2O) as raw materials, triethanolamine (TEOA) as mineraliser, and polyethylene glycol (PEG) as dispersant. The obtained products were characterised with thermogravimetry-differential scanning calorimetry (TG-DSC), Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that the concentration of ZrOCl2·8H2O had little effect on the material properties, whereas the PEG molecular weight, microwave hydrothermal time and temperature, and the concentration of TEOA greatly influenced the dispersibility of the nano-sized zirconia powders. XRD and FT-IR analyses indicated that the ZrO2 nanocrystals synthesised by the microwave hydrothermal method had a tetragonal phase without any trace of monoclinic or cubic phases. The optimal parameters for preparing nano-zirconia powders with appreciable crystallinity and crystal forms included the use of PEG1000/PEG2000/PEG4000 dispersants, a microwave hydrothermal time of 30–50 min and a temperature of 200–240 °C, and a TEOA concentration of 0.3–0.5 M. Nano-ZrO2 powder prepared via our optimised microwave hydrothermal method contained mostly tetrahedral, spherically shaped, highly homogeneous, and well-dispersed 20–30 nm particles.