Surface characterization of tetragonal ZrO2 (original) (raw)

Influence of SO42−, Cr2O3, MoO3, and WO3 on the stability of ZrO2-tetragonal phase

2000

Zirconia is an oxide with high melting point (2973 K), a low thermal conductivity, and a high resistance for corrosion. Therefore, it has been widely used for various purposes such as refractors, pigment, piezo electric devices, ceramic condensers, and oxygen sensors. ZrO 2 is increasingly used in catalysis both as a support and as a catalyst . It efficiently catalyzes hydrogenation of CO , olefins , and dienes . Among the notable, the sulfated zirconia has attracted much attention recently because of its ability to catalyze many acid catalyzed reactions such as cracking, alkylation, isomerization, and condensation . Recently, Hino and Arata reported that WO 3 doped ZrO 2 is another alternative catalyst in reactions requiring stronger acid sites. Reddy et al. observed that MoO 3 incorporated ZrO 2 also catalyzes various acid catalyzed reactions more effectively. The major advantages of Moor W-modified ZrO 2 over sulfated zirconia are that the former catalysts do not suffer from dopent loss during thermal treatments and also undergo significantly less deactivation during catalytic reactions. However, the exact role of these dopents on the genesis and stabilization of strong acidic properties of zirconia is not fully understood.

Thermodynamics of some ZrO2-containing ceramics

Journal of Shanghai University (English Edition), 2006

Thermodynaufic assessment in the ternary systems ZrO=,-CeOe-Y~ O8, ZrO2-CeOe-Ce2 O3 and the limiting binaries ZrO2-Y203, ZrO2-CeOe. CeO2-Y2 O3, ZrO2-Ce~ O3, CeO2-Ce20:~ as well as the modeling for oxides are reviewed comprehensively. Based on the recent estimations on the YOI.5-CeOe, ZrO~-CeO2 and ZrO2-YO~ 5 systems, isothermal sections at 1 273 and 1 973 K of the ternary CeO2-ZrOe-YO~. 5 system are calculated. In the system of ZrOe-CeO2-Ce~O ~ , the complex relation between the nonstoichiometry (y) in CeO2 ~, the composition of the ZrOe -CeO~ solid solution and the oxygen partial pressure ( P% ) for different ZrO2 containing solid solutions Ce~ Zr~ _ ~ Oe ~ ~ are evaluated from 1 473 to 1 773 K. The relation between the degree of Ce + 4 reduction to Ce "3 under different Poe in the fluorite CeO2 y and Ce: Zr~ _ ~ O2 ~. solid solutions at different temperatures can be used as a guide in the development of functional ceramics.

Factors Influencing the Stability of Low Temperature Tetragonal ZrO 2

Croatica Chemica Acta

Various factors that influence the appearance of a tetragonal (t-) ZrO 2 polymorph at room temperature have been extensively inves-tigated. Several proposed models emphasize the role of anionic im-purities (SO 4 2– , OH –), crystallite size (surface energy), structural similarities between the starting material and t-ZrO 2 , lattice strains, water vapor, lattice defects (oxygen vacancies), etc. Our in-vestigations, focused on the stability of low temperature t-ZrO 2 , showed that, regardless of the structural differences in the starting zirconium materials, their thermal decomposition products crystal-lized into a metastable t-ZrO 2 . The t-ZrO 2 ® m-ZrO 2 transforma-tion occurred during the cooling or further calcination in the pres-ence of air at atmospheric pressure. On the other hand, if these processes are performed in vacuum, the metastable phase is pre-served. These observations indicate that a metastable t-ZrO 2 ap-pears at room temperature as a result of stabilization cause...

Structural and textural study on ZrO2-Y2O3 powders

Journal of the European Ceramic Society, 1998

Microporous gels of ZrOz, ZrOz02mol% YzO, and ZrOz.Smol% YzO, were treated in air and under vacuum at temperatures ranging from 450 to 1300°C. X-ray and electron dtflraction results seem to indicate that both, pure and doped zirconia gels crystallize in the cubic form of ZrOz. On lengthening of the thermal treatment at 450°C or after treatment at higher temperatures, the transformations cubic-ttetragonal-tmonoclinic occur, but those are delayed as the yttria content in the sample increases. In some treatment conditions, cubic and tetragonal phases can also been retained to some extent in pure zirconia. Moreover, a rhombohedral deformation of the cubic cell along the (1 I I> directions has been observed in some crystals of pure zirconia samples. Textural degradation takes place in both, pure and doped zirconia, due to particle growth and also the loss of porosity and therefore, the observed structural stabilization does not improve textural stability. The dtxerences in the texture of pure and doped samples have been related to dehydration and crystal growth processes, and to the properties of primary particles in the gels.

Microstructural Evolution in a ZrO2 Wt% Y2O3 Ceramic

Journal of the American Ceramic Society, 1985

Several unusual microstructural features, i.e., 90" tetragonal ZrOz twins containing antiphase domain boundaries, tetragonal Zr02 precipitates in a colony morphology, and precipitatefree zones at the perimeter of cubic ZrOz grains containing fine tetragonal Zr02 precipitates, were observed in a single ZrOZ-12 wt% YzOJ ceramic annealed at 1550", 1400", and 1250"C, respectively. The type of phase transformation responsible for each microstructural feature is described.

ZrO2 phase structure in coating films and powders obtained by sol-gel process

Journal of Sol-Gel Science and Technology, 1994

Zirconia coating film and powder obtained by the sol-gel route using zirconium n-propoxide as starting material and acid catalyst were investigated by the Perturbed Angular Correlations method, X-Ray Diffraction and Differential Scanning Calorimetry and Differential Thermal Analyses. The hyperfine interaction, measured after annealing the samples at increasing temperatures up to 1100°C, allowed to distinguish five different zirconium neighborhoods. Two of them describe rather disordered material which, on heating, crystallizes to the tetragonal phase and end finally in monoclinic zirconia. As compared with the powder, the film exhibits a minor fraction of an unidentified ordered form and a higher and more stable fraction of tetragonal phase. In addition, the tetragonal to monoclinic conversion takes place at higher temperatures and with a larger activation energy.

A structural study of metastable tetragonal zirconia in an Al2O3-ZrO2-SiO2-Na2O glass ceramic system

Journal of Materials Science, 1980

The structural and microstructural properties (crystalline system at the beginning of crystallization, lattice disorder and crystallite size) of metastable zirconia have been studied by an X-ray line broadening analysis using simplified methods based on suitably assumed functions describing the diffraction profiles. Metastable tetragonal zirconia has been crystallized at 970, 1000 and 1050 ~ C, respectively, starting from an AI203-ZrO=-SiO2-Na20 glassy system with a chemical composition very close to that of well known electromelted refractory materials. In the present work we have definitely shown the presence, inside the crystallized zirconia phase, of internal microstrains having values ranging approximately between 2 and 4 • 10-3. Moreover, we have confirmed the peculiar smallness in size of precipitated zirconia crystallites (~< 200A). Therefore, in the present system, the stabilization of the tetragonal form of ZrO2 with respect to the stable monoclinic one can be explained in terms of a contribution to the amount of free energy due to strain energy, in addition to the previously hypothesized surface energy. The observed strong line broadening for some samples treated at lower temperatures (970 and 1000 ~ C) gives rise to an apparent cubic lattice pattern; but the asymmetry of each apparent single line masks unequivocally a tetragonal doublet. This latter conclusion disagrees with some hypotheses on the existence of a cubic metastable form of ZrO2 which could originate at the beginning of zirconia crystallization.

Novel Fabrication of High-Quality ZrO2 Ceramic Thin Films from Aqueous Solution

Journal of the American Ceramic Society, 2005

... Rev. B, 65, 144302 (2002). CrossRef. 15 R. Brenier, J. Mugnier, and E. Mirica, “XPS Study of Amorphous Zirconium Oxide Films Prepared by Sol–Gel,”Appl. Sur. Sci., 143 [1–4] 85–91 (1999). ... 36 AE Bohé, J. Andrade-Gamboa, DM Pasquevich, AJ Tolley, and JL Pelegrina ...

Thermal behavior of ZrO2 precursors obtained by sol–gel processing

Journal of Molecular Structure, 1999

Three different zirconia precursors were synthesized from zirconium(IV)-propoxide by sol-gel processing at pH 1.5, 5.5 and 10.5. The first crystallization products, obtained after the calcination of ZrO 2 precursors at 400ЊC, contained metastable t-ZrO 2 as a dominant phase. The sensitivities of metastable t-ZrO 2 products to the influence of temperature (600ЊCand 800ЊC) or pressure (500, 1000 and 1350 MPa) were monitored by laser Raman and FT-IR spectroscopies. X-ray powder diffraction was used as a complementary technique. It was found that the pH, used during the sol-gel processing of the ZrO 2 precursor strongly influenced the sensitivity of the metastable t-ZrO 2 products to the influence of temperature or pressure. The most stable t-ZrO 2 product was obtained from the ZrO 2 precursor precipitated at pH 1.5 and the most susceptible from the precursor precipitated at pH 5.5. ᭧