Preparation of Fine Monoclinic Hafnia Powders by Hydrothermal Oxidation

Abstract

Fine single‐phase monoclinic HfO2 powders were prepared from Hf metal chips and high‐temperature high‐pressure water by hydrothermal oxidation in closed and open systems. In the closed system, Hf metal was converted to HfO2 by treatment at ≥600°C under 100 MPa for 3 h. At 500°C half the Hf reacted to produce Hf hydride and a small amount of HfO2. In the open system, Hf metal scarcely reacted at 500°C, but at 600°C the reaction was more rapid than the corresponding run in the closed system.