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- Title
A Magnetic Resonance Investigation of the Process of Corundum Formation Starting from Sol–Gel Precursors.
- Authors
Stösser, Reinhard; Scholz, Gudrun; Buzaré, Jean-Yves; Silly, Gilles; Nofz, Marianne; Schultze, Dietrich
- Abstract
27Al–MAS (magic angle spinning)–NMR and Fe3+ EPR measurements have been performed to follow the local process of corundum formation starting from xerogel on the Al3+ and Fe3+ sites yielding complementary information. Different heat treatments have been applied to the samples: an isochronous procedure and thermoanalytical measurements stopped by quenching. Despite the different mechanisms of the phase transitions deduced, both seeding and Fe3+ doping under the conditions of isochronous procedure favor the formation of α-Al2O3 at remarkably low temperatures. The first observed temperature of corundum formation following the isochronous procedure with iron-doped samples is as low as 750°C. The transition alumina, which could be clearly evidenced, is the γ-Al2O3 phase (four- and six-fold Al coordination). In undoped or unseeded samples, intermediate Fe species could be detected by ESR and evidence for θ-Al2O3 was obtained from 27Al–NMR spectroscopy.
- Subjects
XEROGELS; CORUNDUM; THERMAL analysis; GEMS &; precious stones; HEMATITE; CERAMIC materials; COLLOIDS
- Publication
Journal of the American Ceramic Society, 2005, Vol 88, Issue 10, p2913
- ISSN
0002-7820
- Publication type
Article
- DOI
10.1111/j.1551-2916.2005.00516.x