Diffraction studies on the size dependence of the t→m transformation of zirconia (original) (raw)
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Size-Induced Tetragonal to Monoclinic Phase Transition in Zirconia Nanocrystals
MRS Proceedings, 2003
Accurate neutron powder diffraction experiments at D20, ILL Grenoble, allowed to monitor the reconstructive tetragonal to monoclinic phase transition as a function of the size of zirconia nanoparticles. In the nanocrystals, both phases are identical to the ones generally observed in micrometric zirconia. Rietveld refinements on these samples point out an increase of the tetragonal fraction and a decrease of the lattice parameters when the size of the particle decreases. An uniaxial strain depending on the grain size is also observed. The phase transition definitely occurs above a threshold crystal size. These results are analysed within the Landau theory and they can be understood as a mechanism of size-dependent phase transition where the primary order parameter is altered by the nanoparticle size.
Journal of Solid State Chemistry, 2000
Two powdered batches of undoped zirconia, prepared by spray pyrolysis and characterized by 6.9 and 13.2 nm average crystallite size were annealed for di4erent temperatures and for di4erent times. The tetragonal+monoclinic phase transformation was monitored by Raman spectroscopy and X-ray di4raction. The evolution of parameters such as crystallite size, c/a unit cell parameter ratio, content of monoclinic and tetragonal zirconia, and Raman wavenumbers was found to di4er from one batch to the other. The destabilization of the tetragonal phase appears for the 10 to 40 nm crystallite size range and as a sudden phenomenon. The critical size range varies with preparation. The wavenumber shifts were also discussed on the basis of internal stresses associated with mechanical balance between the surface and volume states.
Effect of chemical and heat treatment on the tetragonal-to-monoclinic transformation of zirconia
Journal of Materials Research, 1993
A rapid in situ diffraction technique, synchrotron radiation-energy dispersive diffraction, has been used to obtain direct information on the kinetics of the tetragonal-to-monoclinic transformation temperatures for zirconia synthesized by heating the hydroxide up to temperatures between 900 and 1300 "C. In all cases the monoclinic phase appears only during the cooling stage. The effects of chemical (hydroxide preparation-pH) and heat treatments (top dwell temperature and dwell time) have been investigated. The transformation temperature increases with both top temperature and dwell time. For the lesser heat treatments (generally temperatures C1000 "C) the high-pH material displays the higher transformation temperatures, whereas with greater heat treatments (generally temperatures >1000) the low-pH material displays the higher transformation temperatures. These data do now give reliable indications on how to design a required metastability into the final room temperature product.
Journal of the Australian Ceramic Society, 2018
The metastable tetragonal zirconia is an interesting material exhibiting a high surface area and photoluminescence properties. The present work studies the characteristics of the metastable tetragonal zirconia nanoparticles that were successfully prepared from local zircon without using a template by a modified sodium carbonate sintering method, followed by leaching, slow hydrolysis, and calcination at a low temperature. Zircon and alkaline were combined at a mole ratio of 1:2 and sintered at 1000°C. The sintered material was washed with water to dissolve the silica and followed by leaching with sulfuric acid at pH 1-2 to dissolve the zirconia then followed by slow hydrolysis until pH 9 to precipitate zirconium hydroxide. The final product was evaluated including thermal behavior, phase transformation, chemical composition, infrared spectra, microstructure, and textural properties. Crystallization of zirconia occurred at 564.29°C. Good crystallinity of the zirconia phase was obtained at 800°C consisting of 80% tetragonal zirconia with a crystal size of 11 nm corresponding to its crystal plane of (101) and 20% monoclinic zirconia. At this temperature, zirconia attains 83.19% in purity, shows typical infrared spectrum, and consists of particles less than 40 nm in sizes that agglomerate, belongs to a mesoporous material exhibiting a high surface area of 46.990 m 2 /g. Increase in calcination temperature at 1050°C transformed the tetragonal phase to the monoclinic phase of zirconia. Overall, the present work reveals a promising template-free method on the preparation of the metastable tetragonal zirconia nanoparticles from local zircon.
Structural and textural evolution of zirconia nanocrystals induced by thermal treatment
Materials Science-poland, 2008
Nanometric tetragonal and monoclinic zirconia was synthesized from zirconyl chloride by the modified forced hydrolysis method. Phase transitions and morphological changes accompanying zirconia calcination in the temperaure range 600-1000 °C were studied by XRD, HR-TEM techniques and N 2-porosimetry. Ageing of the amorphous hydrous zirconia at 100 °C for 48 h in the mother solution and its subsequent calcination at 600 °C for 6 h strongly favoured formation of single-phase tetragonal ZrO 2 of the thermal stability enhanced by 250 °C. Influence of the calcination temperature on phase composition, grain size, grain boundaries and pore structure of the resultant ZrO 2 material was analyzed.
Complex thermal evolution of size-stabilized tetragonal zirconia
Journal of Physics and Chemistry of Solids, 2010
Zirconia nanopowder with doping YO 1.5 contents between 0 and 1 mol% were synthesized by the Pechini method. The crystallite dimensions of the powder, around 10 nm, allows for the size stabilization of the tetragonal polymorph over the thermodynamically stable monoclinic one. As the nanopowders are heated to 1200 1C and subsequently cooled back to room temperature, a complex evolution of the phase composition occurs. Upon heating the tetragonal phase transforms slowly into the monoclinic one and the transition cannot be completed before entering the stability range of the tetragonal phase (above 1150 1C). Upon cooling, on the other hand, the reaction is considerably faster and the complete transformation into the monoclinc phase occurs in a narrow temperature range. Rietveld analysis of the high temperature X-ray patterns revealed as, during heating, the transition is mainly controlled by microstructural parameters and in particular it is triggered by the release of RMS microstrain. Upon cooling, on the other hand, the transition is kinetically controlled by the doping content.
A novel method for synthesis of metastable tetragonal zirconia nano powder at low temperatures
Materials Research Bulletin
Zirconia (ZrO 2 ) nanopowder was synthesized using sucrose and fructose as a chelating agent from zirconium hydroxide. The synthesized powders were characterized by X-ray diffraction (XRD), simultaneously thermal analysis (STA), BET surface area, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The above-experimental results showed that the synthesized powders had particle sizes in the range 40-60 nm and mean crystallite sizes of 7-8 nm. Finally, in this research, chelating agents of sucrose and fructose were compared and the obtained results demonstrated that using fructose, nanopowder of zirconia with tetragonal phase was obtained.
Comparative study of nanocrystalline zirconia prepared by precipitation and sol–gel methods
Catalysis Today, 2001
The crystalline properties of zirconia synthesized by the precipitation and sol-gel methods were comparatively studied. Samples were characterized with thermoanalysis and X-ray powder diffraction techniques. The tetragonal and monoclinic crystalline structures of zirconia were refined with the Rietveld technique, which provided the quantitative information concerning the lattice cell parameters, phase concentrations, average crystallite sizes and the concentrations of the cationic and anionic vacancies. Both synthesis methods gave rise to nanocrystalline zirconia. The samples calcined at 800 • C and prepared by the precipitation had average crystallite sizes less than 18 nm, which were two times smaller than the corresponding values obtained in the sol-gel samples. Both tetragonal and monoclinic nanocrystalline phases had atomic defects in concentrations that depended on the synthesis method and annealing temperature.