Idealizing γ-Al2O3: In Situ Determination of Nonstoichiometric Spinel Defect Structure
In: The Journal of Physical Chemistry - Part C, Jg. 114 (2010-08-05), Heft 30, S. 13039-13046
serialPeriodical
Zugriff:
The ideal γ-Al2O3structure is elucidated by solving the defect reaction for alumina-rich magnesium aluminate spinel. The selective reduction of nickel from NixMg1−xAl2O4spinel through reaction with hydrogen enables the in situ analysis of the defect reaction as it progresses. The reaction is described by the following equation: NixMg1−xAl2O4+ xH2→ xNi0+ Mg1−xAl2O4−x+ xVNi′′ + xVO••+ xH2O. Rietveld refinement of neutron and X-ray powder diffraction data is used to determine the following: (1) the weight percents of the products, (2) the nickel occupancy in the spinel phase, and (3) the Mg1−xAl2O4−xlattice parameter. The weight loss during the hydrogen reaction is determined using in situ thermogravimetric analysis. The hydrogen reaction is generalized to describe the defect reaction for alumina-rich spinel: Al2O3→ VMg′′ + VO••+ 2AlAlx+ 3OOx. Application of this defect equation to γ-Al2O3predicts a significantly lower number of ions per unit cell than is commonly accepted. This defect model predicts 16 Al3+ions and 24 O2−ions per unit cell versus the commonly accepted 64/3 Al3+ions and 32 O2−ions per unit cell. We relate the large concentration of vacancies to the porous microstructure of γ-Al2O3. The role of the anion and cation vacancies in oxidation and reduction reactions may be described as a Lewis acid and Bronsted-Lowry base, respectively.
Titel: |
Idealizing γ-Al2O3: In Situ Determination of Nonstoichiometric Spinel Defect Structure
|
---|---|
Autor/in / Beteiligte Person: | Miller, Michelene E. ; Misture, Scott T. |
Zeitschrift: | The Journal of Physical Chemistry - Part C, Jg. 114 (2010-08-05), Heft 30, S. 13039-13046 |
Veröffentlichung: | 2010 |
Medientyp: | serialPeriodical |
ISSN: | 1932-7447 (print) ; 1932-7455 (print) |
DOI: | 10.1021/jp102759y |
Sonstiges: |
|