Title

Cerium LIII-Edge XAS Investigation of the Structure of Crystalline and Amorphous Cerium Oxides

Abstract

>Cerium oxide solid samples were prepared via precipitation from aqueous solution of hydrous cerium-(III) nitrate in the presence of different percentages of hydrogen peroxide (H2O2) as model corrosion inhibiting coatings materials for aluminum alloys. X-ray absorption spectroscopy at the Ce LIII-edge was applied for the characterization of crystalline anhydrous CeO2, nanocrystalline hydrous CeO 2, nanocrystalline CeO2 sample I precipitated in the presence of H2O2, and an amorphous CeO2 sample II precipitated at a higher H2O2 concentration. An analysis by X-ray absorption near-edge structure (XANES) for cerium oxides did not indicate a broad variation in cerium valence state in the precipitated samples as compared to anhydrous CeO2. Furthermore, XANES analysis revealed a decrease in the intensity of the white line peaks for the precipitated samples relative to those in anhydrous CeO2. The EXAFS spectra of the oxides showed that H2O2 reduced the precipitate's particle diameter and bulk crystallinity. Growth in the coordination number of the first, Ce-O, shell was observed with an increased bond distance RCe-O in hydrous and precipitated CeO2 samples. However, the coordination numbers of the second, Ce-Ce, and third, Ce-O, shells were reduced in comparison with anhydrous CeO2. Increasing concentration of H2O2 during alkaline precipitation of cerium oxides caused increased hydration, corresponding to a reduced outer-shell coordination number and reduced bulk crystallinity but no corresponding change in the cerium valence state.

Department(s)

Chemistry

Sponsor(s)

Air Force Research Laboratory (Wright-Patterson Air Force Base, Ohio)
National Center for Research Resources (U.S.)
National Institute of Health (U.S.)
United States. Department of Energy

Keywords and Phrases

Absorption Spectroscopy; Aluminum Alloys; Amorphous Materials; Chemical Bonds; Coatings; Coordination Reactions; Corrosion; Crystal Structure; Hydrogen Peroxide; Nanostructured Materials; Precipitation (Chemical); Solutions; X Ray Spectroscopy; Bond Distance; Cerium Oxides; Coordination Number; Crystallinity; Cerium Compounds; Aluminum; Cerium; Cerium Nitrate; Cerium Oxide; Coordination Compound; Hydrogen Peroxide; Oxide; Oxygen; Unclassified Drug; Alkalinity; Aqueous Solution; Chemical Bond; Concentration (Parameters); Corrosion; Crystal Structure; Extended X Ray Absorption Fine Structure; Hydration; Nanop Particle Size; Precipitation; Solid State; Spectroscopy; Synthesis; X Ray Absorption Near Edge Structure; X Ray Absorption Spectroscopy

International Standard Serial Number (ISSN)

8974756

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2005 American Chemical Society (ACS), All rights reserved.


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