Tetragonal zirconia-based phases

Sr, Ba), no solid solutions with fluorite structure were produced at temperatures below 1500 °C. The conductivity of such multiphase ceramic systems containing monoclinic or tetragonal zirconia-based phases was considerably low. 

Fig. 52. Raman spectra of various phases in zirconia-based ceramics (a) monoclinic (pure ZrOa) [255] (b) tetragonal (Zr02 + 2 mol% Y2O3) [256] and (c) cubic (Z1O2 + 9.5 mol% Y2O3) [257]. Gradual broadening of the spectral features upon increasing content of Y2O3 is due to the lattice mismatch caused by the differences in size between Zr and Y atoms.

Hirvonen A Nowak R. Yamamoto Y. (2006). Fabrication, Structure, Mechanical and Thermal Properties of Zirconia-based Ceramic Nanocomposites. Journal of the European Ceramic Society, Vol. 26, No. 8, May, 2006, pp. 1497-1505, ISSN 09552219 Gupta T. K. Bechtold J. FI. Kuznicki R. C.(1977). Stabilization of Tetragonal Phase in Polycrystalline Zirconia. Journal of Materials Science, Vol.l2, No.l2. Dec, 1977,pp.2421-2426, ISSN 00222461... 

The case of alumina is relatively simple since at least as first approximation, the reinforcement depends only on the crack length. Other cases are more complex, and the reinforcement can also depend on the applied stress. This is the case of the mechanisms acting at the crack front, such as microcracking and phase transformation toughening. A good example of the last case is the reinforcement in zirconia based ceramics. It is based on the tetragonal to monoclinic transformation of particles at the crack tip due to the local high stresses. The associated volume... 

The cubic pyrochlore-based ceria-zirconia solid solution is a good material. However, it has been reported that the reduction temperature has become higher after the high-temperature oxidation.This is due to the transformation from pyrochlore-based-cubic to r -tetragonal phase which is more stable than it, and r ... 

SZl sample, reference materials of this work, is constituted by pure tetragonal ZrOz, with an average crystal size (determined with the classical Scherrer equation) of 85 A (Table 1). The stabilisation of the tetragonal ZrOz depends on the presence of TPAOH in the reaction mixture. In fact, variable amounts of monoclinic phase are detected in the products synthesised in the absence of organic base (SZ2 sample. Table 1). This is probably related to the pH of the sol, but this hypothesis should be confirmed. Basic medium usually enhances the condensation reactions [15], but at the same time the ability of sulphates to form complexes with Zr precursors up to pH = 11 [16] and the low water content in the sol prevent the growth of zirconia particles. 

The pyrocholre-based cubic metastable phases can be obtained by the hydrogen reduction and subsequent reoxidation of tetragonal ceria-zirconia mixed oxides. In addition, these solid solutions can be synthesized by means of the thermal... 

Mesoporous aerogels based rai sidfated zirconia doped with chromium have been synthesized by sol-gel method and dried in supercritical conditions of the solvent by Ghorbel et al. [45]. The characterization results revealed that Zr02 tetragonal phase is stabilized by both sulfate groups and metal at high temperature. The physisorption of N2 showed that the sol-gel procedure coupled to the drying under supercritical conditions of the... 

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