A Magnetic Resonance Investigation of the Process of Corundum Formation Starting from Sol–Gel Precursors
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 -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.
Document Type: Research Article
Affiliations: 1: Humboldt University of Berlin, Institute of Chemistry, D-12489 Berlin, Germany 2: 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 3: Federal Institute for Materials Research and Testing, D-12200 Berlin, Germany
Publication date: October 1, 2005