Nature and Thermal Evolution of Amorphous Hvdrated Zirconium Oxide

Vage, J. Li; Doi, Kotaro; Mazières, C.

doi:10.1111/j.1151-2916.1968.tb15952.x

Cited by 328 publications

(116 citation statements)

References 11 publications

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“…Sorrentino et al [29] studied a number of other oxides and concluded that coalescence of particles is responsible for the glow. On the other hand Keshavaraja et al [27] and Livage et al [40] associate the glow exotherm with crystallization. In summary, the literature does not clearly identify the reaction providing the heat for the glow.…”

Section: Events During Thermal Treatmentmentioning

confidence: 99%

Rapid genesis of active phase during calcination of promoted sulfated zirconia catalysts

Hahn

Jentoft

Ressler

et al. 2005

Journal of Catalysis

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Amorphous sulfated zirconium hydroxide was promoted with iron or manganese via the incipient wetness technique, to give 0.5-3.5 weight% promoter in the final catalyst. An exothermic reaction during the calcination temperature ramp (to 823 or 923 K) leads to a rapid overheating ("glow") of the sample. XRD shows that crystallization starts before and progresses during the overheating. The surface area shrinks during the glow, and its final size (85-120 m 2 ·g -1 ) and the porosity appear to be largely determined by the glow event. Manganese and iron ions prevent the coalescence of particles and lead to high surface areas. Variation of the batch volume (2.2, 8.4, or 17.1 ml) for calcination produced different catalysts from the same precursor. For both promoters, samples calcined in large batches exhibited the highest surface areas, interconnected mesopores (2.2-3.8 nm), and the highest maximum rate in n-butane isomerization (338 K, 1 kPa n-butane). Long term performance was independent of surface area and morphology. The concentration of the active sites depended on the calcination batch size, indicating that the active phase is formed in kinetically controlled reactions during the rapid overheating. The catalytic and textural properties of sulfated zirconia catalysts can be reproduced through controlling the batch size used for calcination.

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Section: Events During Thermal Treatmentmentioning

confidence: 99%

Rapid genesis of active phase during calcination of promoted sulfated zirconia catalysts

Hahn

Jentoft

Ressler

et al. 2005

Journal of Catalysis

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“…The stabilization of t-ZrO 2 at low temperatures are governed by several factors such as the crystallite size effect, 1,2,18,19 the existence of stabilizers (variety and amount), 20,21 the presence of anionic impurities, 18,19 the domain boundaries, 22 and structural similarities between the tetragonal phase and the amorphous phase of the precursor. 19,23,24 In comparison with pure ZrO 2 , the metastability of the tetragonal phase for the doped zirconia can be observed in a wider range of temperatures due to the presence of oxygen vacancies. 5,6 Previously, various explanations have been proposed for the observed metastability of t-ZrO 2 .…”

Section: +mentioning

confidence: 99%

Unusual calcination temperature dependent tetragonal–monoclinic transitions in rare earth-doped zirconia nanocrystals

Zhang

Han

et al. 2003

Phys. Chem. Chem. Phys.

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The dependence of tetragonal-monoclinic (t ! m) transitions in the hydrothermally prepared (ZrO 2 ) 0.98 (RE 2 O 3 ) 0.02 (RE ¼ Sc, Y) nanocrystals upon the calcination between 400-1400 C were explored by means of X-ray diffraction (XRD), high temperature X-ray diffraction (HTXRD), near infrared Fourier transform (FT) Raman and ultraviolet (UV) Raman spectroscopies. XRD and FT Raman scattering analysis indicated that the monoclinic fraction varied discontinuously with increasing the temperature from 400 to 1400 C, which is unusual and is mainly ascribed to the microstrain effect. HTXRD analyses (from room temperature to 1400 C) revealed that the as-prepared samples underwent tetragonal ! monoclinic (t ! m) transformation at 500 C for (ZrO 2 ) 0.98 (Sc 2 O 3 ) 0.02 and at 200 C for (ZrO 2 ) 0.98 (Y 2 O 3 ) 0.02 during the cooling process. UV Raman spectra suggested that the t ! m transformation initially occurred at the surface region of the calcined samples. Hence, the monoclinic phase was enriched on the surface of the zirconia grains. Finally, the size effect of the stabilizers (Y 3+ and Sc 3+ ) on the critical crystallite size and the metastability of the tetragonal phase were also discussed.

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“…Theunissen (21) used a high temperature Guinier camera for XRD (heating rate 15°C/hr) and observed the first appearance of diffraction lines of the tetragonal phase at 400°C. Livage et al (22) found from a series of isothermal experiments that the minimum temperature required for complete crystallization of pure ZrO 2 in air equals 350°C. It can thus be concluded, that temperatures of 350 -400°C are needed for complete crystallization of zirconia in air.…”

Section: Microstructures After Sinterin~ At 1050°cmentioning

confidence: 99%

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

Boutz

scholtenhuis

Winnubst

et al. 1994

Materials Research Bulletin

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Y-TZP powders were prepared either by calcination in air or crystallization under hydrothermal conditions of a hydrous gel, obtained by coprecipitation. Differences in powder properties, green compact structure and sinterability were examined. Crystallization under hydrothermal conditions occurs at temperatures as low as 190°C in the presence of ammonia. The hydrothermally treated powders are composed of soft agglomerates, that collapse under very low pressures, resulting in green bodies with high densities and small pore radii. The sinterability is greatly improved by the hydrothermal treatment and allowed the production of dense, nanostructured Y-TZP by free sintering at 1050°C.

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Nature and Thermal Evolution of Amorphous Hvdrated Zirconium Oxide

Cited by 328 publications

References 11 publications

Rapid genesis of active phase during calcination of promoted sulfated zirconia catalysts

Rapid genesis of active phase during calcination of promoted sulfated zirconia catalysts

Unusual calcination temperature dependent tetragonal–monoclinic transitions in rare earth-doped zirconia nanocrystals

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

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