Local Structure of Amorphous and Highly Dispersed Zirconium Hydroxides and Oxides

Abstract

The local structure of amorphous and highly dispersed hydroxide and oxide zirconium compounds prepared from zirconyl nitrate solutions by precipitation was studied by an X-ray diffraction technique of radial electron distribution. It was found that X-ray amorphous precipitates were formed at 383 K. These precipitates were polynuclear hydroxo complexes, whose short-range ordering was similar to the structure of a cubic ZrO₂ phase. A special feature of these formations, compared with the cubic oxide phase, is that the closest Zr–Zr distance in them is shortened by 0.2 Å, NO₃ and OH groups are the constituents of an anionic sublattice, and the coordination number of Zr–anion distances is increased. Calcination at 653 K followed by cooling to room temperature resulted in the appearance of a monoclinic ZrO₂ phase with a crystallite size of ∼60 Å along with the cubic phase. The amount of the former phase depended on the pH of precipitation and on the presence of residual NO₃ and OH groups in precipitates.