Crystallization studies of ZrO2−SiO2 composite gels

Abstract

Composite ZrO2-SiO2 powders were prepared using a gel route. Morphological and crystallographic features of ZrO 2 particles formed during the heat treatment, and the particle sizes of the composites have been investigated. The following polymorphic changes have been observed during the heat treatment: amorphous -+ metastable-cubic/tetragonal ZrO 2 --~ tetragonal ZrO2 ~ monoclinic ZrO2. SiO2 crystallizes above 1273 K. The martensitic transformation of Zr02 (t -, m) was observed in situ, when exposed to a high-energy electron beam. These results are important in the production of ZrO2-toughened ceramics of controlled microstructure.

A Study of the Crystallization of ZrO2 in the Sol–Gel System: ZrO2–SiO2

“…At approximately 12003C, both phases react to form zircon, the excess ZrO remaining monoclinic. In general, increases in silica content in the compositions used in the present study improves the thermal stability of Z(t), which is corroborated in other studies (16,21). The upper stability limit of the tetragonal phase varied between 850 and 12003C, depending on the ZrO /SiO ratio.…”

“…This is due to the formation of microcrystalline zirconia and to preparation conditions (4, 37}39). When nanocrystalline nondoped zirconia is annealed, the tetragonal phase is transformed into the monoclinic phase (40,41), a transformation that begins at approximately 4503C (24) and can be completed between 800 and 10003C (19,21,30). In the present study, however, the formation of Z(t) was detected with XRD as beginning in the earliest stages of thermal treatment (1503C).…”

“…Silica-rich compositions were not studied, though it is known (21,28,30,48) that crystallization temperature increases up to 8003C (data denoted by ᮀ; Fig. 3).…”

“…Miranda et al (28,29), synthesized samples ranging from 10 to 55% mol ZrO annealed during 5.5 h at 550, 850, and 16003C. Nagarajan and Rao (21) utilized only three compositions (5,25, and 50% mol zirconia), annealing them for 2 h in temperatures ranging from 400 to 15003C. Andrianainarivelo et al (30) studied the crystallization behavior in four compositions (1,10,17, and 50% mol ZrO ) at temperatures between 600 and 13003C with heating times ranging from 2 to 5 h. Other studies have focused only on a small range of low zirconia content compositions (31}33) or with zirconia in amorphous state (34).…”

Highly Dispersed Mixed Zirconia and Hafnia Nanoparticles in a Silica Matrix: First Example of a ZrO2–HfO2–SiO2 Ternary Oxide System

“…[45] This phenomenon, which occurs whenever zirconia or hafnia are homogeneously dispersed in a silica matrix, has been extensively described in the literature. [7,[54][55][56][57][58][59][60][61][62] Generally, the crystallization of tetragonal zirconia has been reported to occur after calcination at 400°C, [15] while partial transformation from tetragonal to monoclinic was reported to occur at 800-900°C and the single monoclinic phase is present at temperatures higher than 1000-1200°C. However, Neumayer and Cartier [15] reported that the addition of silica to zirconium and hafnium oxide was found to increase the temperature of crystallization of zirconium oxide, to stabilize the formation of tetragonal hafnia, and to increase the temperature at which the transformation of ZrO 2 or HfO 2 from the tetragonal to the monoclinic phase occurs.…”