A Magnetic Resonance Investigation of the Process of Corundum Formation Starting from Sol–Gel Precursors
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 -Al2O3 phase (four- and six-fold Al coordination). In undoped or unseeded samples, intermediate Fe species could be detected by ESR and evidence for -Al2O3 was obtained from 27Al–NMR spectroscopy.
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Document Type: Research Article
Humboldt University of Berlin, Institute of Chemistry, D-12489 Berlin, Germany
Institut de Recherche en Ingénierie Moléculaire et Matériaux Fonctionnels IRIM2F, FR CNRS No. 2575, Laboratoire de Physique de l'Etat Condensé LPEC, UMR CNRS No. 6087, 72085 Le Mans, France
Federal Institute for Materials Research and Testing, D-12200 Berlin, Germany
Publication date: 2005-10-01