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Title: Thermodynamics of Cr2O3, FeCrO4, ZnCrO4, and CoCrO4

Authors:
 [1];  [2];  [1];  [3]
  1. Lockheed Martin Corporation
  2. {Larry} M [ORNL
  3. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
936811
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Thermodynamics; Journal Volume: 39; Journal Issue: 11
Country of Publication:
United States
Language:
English

Citation Formats

Ziemniak, S. E., Anovitz, Lawrence, Castelli, R. A., and Porter, Wallace D. Thermodynamics of Cr2O3, FeCrO4, ZnCrO4, and CoCrO4. United States: N. p., 2007. Web. doi:10.1016/j.jct.2007.03.001.
Ziemniak, S. E., Anovitz, Lawrence, Castelli, R. A., & Porter, Wallace D. Thermodynamics of Cr2O3, FeCrO4, ZnCrO4, and CoCrO4. United States. doi:10.1016/j.jct.2007.03.001.
Ziemniak, S. E., Anovitz, Lawrence, Castelli, R. A., and Porter, Wallace D. Mon . "Thermodynamics of Cr2O3, FeCrO4, ZnCrO4, and CoCrO4". United States. doi:10.1016/j.jct.2007.03.001.
@article{osti_936811,
title = {Thermodynamics of Cr2O3, FeCrO4, ZnCrO4, and CoCrO4},
author = {Ziemniak, S. E. and Anovitz, Lawrence and Castelli, R. A. and Porter, Wallace D},
abstractNote = {},
doi = {10.1016/j.jct.2007.03.001},
journal = {Journal of Chemical Thermodynamics},
number = 11,
volume = 39,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • High temperature heat capacity measurements were obtained for Cr{sub 2}O{sub 3}, FeCr{sub 2}O{sub 4}, ZnCr{sub 2}O{sub 4} and CoCr{sub 2}O{sub 4} using a differential scanning calorimeter. These data were combined with previously-available, overlapping heat capacity data at temperatures up to 400 K and fitted to 5-parameter Maier-Kelley C{sub p}(T) equations. Expressions for molar entropy were then derived by suitable integration of the Maier-Kelley equations in combination with recent S{sup o}(298) evaluations. Finally, a database of high temperature equilibrium measurements on the formation of these oxides was constructed and critically evaluated. Gibbs energies of Cr{sub 2}O{sub 3}, FeCr{sub 2}O{sub 4} andmore » CoCr{sub 2}O{sub 4} were referenced by averaging the most reliable results at reference temperatures of 1100, 1400 and 1373 K, respectively, while Gibbs energies for ZnCr{sub 2}O{sub 4} were referenced to the results of Jacob [Thermochim. Acta 15 (1976) 79-87] at 1100 K. Thermodynamic extrapolations from the high temperature reference points to 298.15 K by application of the heat capacity correlations gave {Delta}{sub f}G{sup o}(298) = -1049.96, -1339.40, -1428.35 and -1326.75 kJ mol{sup -1} for Cr{sub 2}O{sub 3}, FeCr{sub 2}O{sub 4}, ZnCr{sub 2}O{sub 4} and CoCr{sub 2}O{sub 4}, respectively.« less
  • No abstract prepared.
  • In this work ?-Cr2O3/?-Fe2O3 core-shell polycrystalline nanostructures were synthesized using ?-Cr2O3 nanoparticles as seed crystals during aqueous nucleation. The formation of ?-Fe2O3 polycrystallites on ?-Cr2O3 surfaces were confirmed by x-ray diffraction, transmission electron microscopy, and energy dispersive x-ray analysis. The excited state relaxation dynamics of as-grown core-shell structures and ''pure'' ?-Fe2O3 particles of the same size were measured using femtosecond transient absorption spectroscopy. The results show the carrier lifetimes decay within a few picoseconds regardless of sample. This is likely due to fast recombination/trapping of carriers to defects and iron d-states.
  • An impedancemetric method for NO{sub x} sensing using an yttria-stabilized zirconia (YSZ) based electrochemical cell is described. The sensor cell consists of a planar YSZ electrolyte and two identical YSZ/Cr{sub 2}O{sub 3} composite electrodes exposed to the test gas. The sensor response to a sinusoidal ac signal applied between the two electrodes is measured via two parameters calculated from the complex impedance, the modulus |Z| and phase angle {Theta}. While either of these parameters can be correlated to the NO{sub x} concentration in the test gas, {Theta} was found to provide a more robust metric than |Z|. At frequencies belowmore » approximately 100 Hz, {Theta} is sensitive to both the NO{sub x} and O{sub 2} concentrations. At higher frequencies, {Theta} is predominantly affected by the O{sub 2} concentration. A dual frequency measurement is demonstrated to compensate for changes in the O{sub 2} background between 2 and 18.9%. Excellent sensor performance is obtained for NO{sub x} concentrations in the range of 8-50 ppm in background. An equivalent circuit model was used to extract fitting parameters from the impedance spectra for a preliminary analysis of NO{sub x} sensing mechanisms.« less