Crystallization and Transformation of Zirconia Under Hydrothermal Conditions

Abstract

During constant-rate heating to 350°C in concentrated NaOH solutions, cubic Zr02 crystallized at = 120°C from hydrated amorphous Zr02; these tine cubic Zr02 particles abruptly changed into needlelike monoclinic Zr02 single crystals at 300°C. Crystallization and phase transformation were studied by XRD, TEM, and EPMA. Cubic Zr02 appears to crystallize via collapse of the Zr02'nH20 structure and subsequent slight rearrangement of the lattice. The abrupt formation of monoclinic Zr02 was considered to result when the very tine cubic Zr02 particles coagulated in a highly oriented fashion.

Reactions of Metal Salts and Alkali Metal Nitrates. Role of the Metal Precursors and Alkali Metal Ions in the Resulting Phase of Zirconia

“…The stabilization by alkali metals has been less studied. Yet, it was observed that amorphous zirconia obtained by neutralizing zirconium oxychloride solutions by sodium hydroxide crystallizes in tetragonal or cubic zirconia according to their content in sodium when annealed (5,16 latter case, the stabilization is interpreted by the formation of a solid solution of Na O in HfO . The di!erences in the structures of the two precursors or the presence of H O and OH\ in the oxychloride cannot be put forward.…”

Martensitic Phase Transformation of Isolated HfO2, ZrO2, and HfxZr1 – xO2 (0 < x < 1) Nanocrystals

“…[7,8] Nishizawa et al [7] reported that cubic zirconia crystallizes into small mosaic particles when an amorphous zirconia gel was treated hydrothermally at 130 C, however, at reaction temperature of 320 C, an abrupt change of the particle phase and shape occursÐmonoclinic rods formed. Noh et al [8] reported that, as the reaction temperature increases from 150 to 200 C during the hydrothermal processing of amorphous zirconium hydroxide and tetragonal zirconia powder, the particle shape changes from spherical to rod-like and the particle phase changes from tetragonal to monoclinic.…”

A hydrothermal route for production of dense, nanostructured Y-TZP

“…Nishizawa et al (23) demonstrated that the crystallization process under hydrothermal conditions depends strongly on concentration and type of mineralizer. They observed that undoped zirconia crystallizes at 260°C in pure water, whereas a temperature of only 130°C is required in a 1 M NaOH solution.…”