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Interface Nanochemistry in Mg-Doped Al2O3

Published online by Cambridge University Press:  15 March 2011

Georgette Petot-Ervas
Affiliation:
Laboratoire Structures Propriétés et Modélisation des Solides, CNRS-Ecole Centrale Paris, Grande voie des vignes, F-92295 Châtenay-Malabry cedex, gpetot@spms.ecp.fr, baldinozzi@spms.ecp.fr
Gianguido Baldinozzi
Affiliation:
Laboratoire Structures Propriétés et Modélisation des Solides, CNRS-Ecole Centrale Paris, Grande voie des vignes, F-92295 Châtenay-Malabry cedex, gpetot@spms.ecp.fr, baldinozzi@spms.ecp.fr
Claude Petot
Affiliation:
Laboratoire Structures Propriétés et Modélisation des Solides, CNRS-Ecole Centrale Paris, Grande voie des vignes, F-92295 Châtenay-Malabry cedex
Mike J. Graham
Affiliation:
Institute for Microstructural Sciences NRC, K1A 0R6, Ottawa, Ontario, Canada
Irwin G. Sproule
Affiliation:
Institute for Microstructural Sciences NRC, K1A 0R6, Ottawa, Ontario, Canada
Moussa Tebtoub
Affiliation:
Laboratoire Structures Propriétés et Modélisation des Solides, CNRS-Ecole Centrale Paris, Grande voie des vignes, F-92295 Châtenay-Malabry cedex
Jean-Marc Raulot
Affiliation:
Laboratoire Structures Propriétés et Modélisation des Solides, CNRS-Ecole Centrale Paris, Grande voie des vignes, F-92295 Châtenay-Malabry cedex
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Abstract

In this experimental paper the influence of the grain size, of the thermal history and of the nominal composition on the nanochemistry at the interfaces in α-alumina submicronic powders are analyzed. The consequences on the physical and chemical properties are also discussed. Nanocrystalline Mg-doped α-alumina powders (550 and 1650 ppm by wt MgO) were prepared by the alum process. These powders (10-400 nm) were characterized by X-ray diffraction, SEM, TEM, XPS and surface area measurements (BET). In agreement with BET analysis, SEM observations show that the grain size increases with annealing time and annealing temperature. This effect is less pronounced in the highly doped samples. The less doped samples are also less aggregated and sintering bridges between the grains are still observed. XPS shows that Mg segregates at the periphery of the grains on a depth ≤0.5 nm. The dopant segregation is stronger when the nominal amount of Mg increases, leading eventually to the formation of MgAl2O4 precipitates near the grain surface. It is possible to observe an increase of the dopant segregation with grain size in the low Mg concentration powders. Other impurities like Si or higher cooling rates also favour this Mg segregation. However, the rate of cooling is so effective that it can overshadow all the other parameters (grain size, impurities,…), suggesting that this is certainly the key parameter for obtaining a perfect sintering of these ceramics, as experimentally shown.

Type
Research Article
Copyright
Copyright © Materials Research Society 2004

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References

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