Effect of pH on crystallization of nanocrystalline zirconia in a microwave-hydrothermal process

Abstract

Nanocrystalline zirconia (ZrO₂) was synthesized using a microwave-hydrothermal process. The effect of pH on the crystallization of the ZrO₂ powders was investigated. The phase and microstructure of ZrO₂ powders were examined using X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). Results show that pure m-ZrO₂ can be obtained at low pH (pH<2). Pure t-ZrO₂ is formed at pH = 7 and 14. The size of the ZrO₂ crystals is in the range of 8-26 nm and decreases with increasing pH. The formation of m-ZrO₂ results from the precipitation of ZrO₂ from solution. The t-ZrO₂ is formed through the in-situ structural rearrangement of amorphous Zr(OH) _xO _y. The stabilization of t-ZrO₂ is attributed to the small crystal size and the adsorption of hydroxy ions on the surfaces of the crystals.

Keywords

microwave-hydrothermal / nanocrystalline zirconia / crystallization mechanism / pH

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