Hydrothermal Synthesis of Aqueous Sols of Nanocrystalline HfO2

Nanocrystalline hafnium dioxide has been synthesized by hydrothermal treatment of X-ray amorphous hydrated hafnium dioxide in distilled water at 120–260°C for 1–7 days and in the presence of NaCl and NaOH as mineralizing agents. The size of HfO 2 crystallites has been shown to be determined by the temperature of hydrothermal treatment and the type of mineralizing agent. The size of HfO 2 crystallites obtained in alkaline medium is by 2–3 times smaller than that for HfO 2 crystallites obtained in neutral medium and constitutes ~8 nm. Dispersing of nanocrystalline HfO 2 obtained by hydrothermal treatment in water in the presence of dextrane and poly(vinylpyrrolidone) under exposure to ultrasound leads to preparation of stable sols of nanocrystalline HfO 2 .