Energetics of X-ray-amorphous zirconia and the role of surface energy in its formation

Molodetsky, Irina; Navrotsky, Alexandra; Paskowitz, Michael J.; Leppert, Valerie J.; Risbud, Subhash H.

doi:10.1016/s0022-3093(99)00690-0

Cited by 48 publications

(39 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This phenomenon was in agreement with a previous report on the electron beam sensitivity of amorphous zirconia, with nanoparticles growing to approximately 5.4 nm in diameter after electron irradiation, and diffraction rings developing in the SAED patterns. 25 phenomenon was observed with the time varying EDS experiment. As-deposited coating composition was slightly oxygen deficient with respect to the ZrO 2 stoichiometry, as was measured by using XPS.…”

Section: B In Situ Tem Studies Of Ysz-au Composite Coatingsmentioning

confidence: 72%

Application of in situ Transmission Electron Microscopyfor Tribological Investigations of Magnetron Sputter Assisted Pulsed Laser Deposition of Yttria-stabilized Zirconia-gold Composite Coatings

Voevodin

Zabinski

2005

J. Mater. Res.

View full text Add to dashboard Cite

Yttria-stabilized zirconia (YSZ)-Au composite coatings have great potential as solid film lubricants for aerospace applications over a wide range of environmental conditions. They were grown on steel disks or silicon wafers by pulsed laser ablation of YSZ and simultaneous magnetron sputtering of a Au target. Such a combination of ceramics with soft metals improved the toughness of the composite coating and increased its ability to lubricate at high temperature. Information on the time-dependent response of these microstructures to changes in temperature is essential to tribological investigations of high temperature performance. In situ transmission electron microscopy was used to directly measure the dynamic change of YSZ-Au coating structure at elevated temperatures. High-resolution electron microscopy and electron diffraction showed that amorphous YSZ-5 at.% Au coatings proceeded to crystallize under the irradiation of electron beams. Time varying x-ray energy dispersive spectra measured a loss of oxygen in the sample during about 10 min of irradiation with subsequent slight oxygen recovery. This behavior was related to the activation of oxygen diffusion under electron irradiation. X-ray diffraction patterns from vacuum annealed samples verified crystallization of the coatings at 500°C. Real-time growth of Au nanograins in the sample was observed as the temperature was increased to 500°C in a TEM specimen holder that could be heated. The grain growth process was recorded using a charge-coupled device camera installed on the transmission electron microscope. The crystallization and growth of zirconia and Au nanograins resulted in low friction during tribological tests. The nucleation of Au islands on heated ball-on-flat specimens was responsible for lowering friction.

show abstract

Section: B In Situ Tem Studies Of Ysz-au Composite Coatingsmentioning

confidence: 72%

Application of in situ Transmission Electron Microscopyfor Tribological Investigations of Magnetron Sputter Assisted Pulsed Laser Deposition of Yttria-stabilized Zirconia-gold Composite Coatings

Voevodin

Zabinski

2005

J. Mater. Res.

View full text Add to dashboard Cite

show abstract

“…[4] The tendency of very thin films not to form the tetragonal phase may be explained by the surface energy stabilisation of amorphous relative to tetragonal zirconia. [54] Some of the experiments (specifically, measurements of isobars by XPS) were performed with the thin and thus only partially crystallised samples, and the interpretation of these experiments must consider the small tetragonal fraction of the films. The size of the tetragonal crystallites is equivalent to those of active sulfated zirconia powders.…”

Section: Validation Of Thin Films As Modelmentioning

confidence: 99%

Adsorption–desorption equilibrium investigations of n-butane on nanocrystalline sulfated zirconia thin films

Lloyd

Hansen

Ranke

et al. 2011

Applied Catalysis A: General

View full text Add to dashboard Cite

Nanocrystalline thin films of the alkane skeletal isomerisation catalyst sulfated zirconia were successfully deposited on a silicon substrate in order to allow the application of surface science techniques. Thermal treatment of the films was optimised to chemically mimic the powder preparation process, resulting in films possessing the essential features (including tetragonal phase, nanocrystallinity and sulfur content of ~3 atomic %) of active powder catalysts. The n-butane adsorption-desorption equilibrium under isobaric conditions (10 -8 to 10 -6 hPa) over the temperature range 300-100 K was monitored by photoelectron spectroscopy. Analysis of the isobars revealed strong and weak n-butane chemisorption sites, releasing heats of between 59-40 and 47-34 kJ/mol, corresponding to 5 and 25% of a monolayer coverage, respectively. The total amount of chemisorbed n-butane coincides with the estimated number of surface sulfate groups. An increase in adsorption heat was observed between coverages of ~5-8% of a monolayer, indicating adsorbate-adsorbate interactions. It follows that adjacent sites are present and isomerisation by a bimolecular surface reaction is feasible. Physisorption on the films generates heats of ~28 kJ/mol, for coverages from 30% up to a complete monolayer. Multilayer adsorption results in the formation of an electrically insulating adsorbate structure. It is proposed that the strong chemisorption sites correspond to an interaction with a minority disulfate species.

show abstract

“…As for measured heats of reaction, neither the initial nor the final state is usually exactly defined in a thermodynamic sense with known composition, fraction of crystalline material, and particle or crystallite size. Molodetsky et al [47] have tried to distinguish surface area from crystallization effects. They report an increase in surface energy for the transition from amorphous to tetragonal zirconia, specifically 14.6 kJ·mol -1 for a material with 100 m 2 ·g -1 surface area, and an enthalpy of crystallization of tetragonal zirconia of -53 kJ·mol -1 .…”

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

View full text Add to dashboard Cite

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.

show abstract

Energetics of X-ray-amorphous zirconia and the role of surface energy in its formation

Cited by 48 publications

References 14 publications

Application of in situ Transmission Electron Microscopyfor Tribological Investigations of Magnetron Sputter Assisted Pulsed Laser Deposition of Yttria-stabilized Zirconia-gold Composite Coatings

Application of in situ Transmission Electron Microscopyfor Tribological Investigations of Magnetron Sputter Assisted Pulsed Laser Deposition of Yttria-stabilized Zirconia-gold Composite Coatings

Adsorption–desorption equilibrium investigations of n-butane on nanocrystalline sulfated zirconia thin films

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

Contact Info

Product

Resources

About