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A Magnetic Resonance Investigation of the Process of Corundum Formation Starting from Sol–Gel Precursors
Author(s) -
Stösser Reinhard,
Scholz Gudrun,
Buzaré JeanYves,
Silly Gilles,
Nofz Marianne,
Schultze Dietrich
Publication year - 2005
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2005.00516.x
Subject(s) - corundum , magic angle spinning , electron paramagnetic resonance , phase transition , calcination , quenching (fluorescence) , doping , chemistry , analytical chemistry (journal) , materials science , mineralogy , nuclear magnetic resonance spectroscopy , nuclear magnetic resonance , condensed matter physics , catalysis , physics , stereochemistry , optics , organic chemistry , fluorescence
27 Al–MAS (magic angle spinning)–NMR and Fe 3+ EPR measurements have been performed to follow the local process of corundum formation starting from xerogel on the Al 3+ and Fe 3+ 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 Fe 3+ doping under the conditions of isochronous procedure favor the formation of α‐Al 2 O 3 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‐Al 2 O 3 phase (four‐ and six‐fold Al coordination). In undoped or unseeded samples, intermediate Fe species could be detected by ESR and evidence for θ‐Al 2 O 3 was obtained from 27 Al–NMR spectroscopy.