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Thermoluminescence et frittage de l'alumine alpha ultra-pure dopée par le zirconium, le thorium, le calcium, ou le cérium

Abstract : Thermoluminescence is a technique of identification of the point defects that appear in a solid consecutively to its fabrication. The synthesis parameters of alpha-alumina that will be taken into account here are the atmosphere during therma1 treatment (oxidizing or reducing), and the effect of the dopants: zirconium, thorium, calcium or cerium. The aim of this work is to correlate the point defects to the reactivity of the powder, especially its sintering. The TL mechanisms of the dosimetric peak of alpha-alumina, around 200°C, were clarified: The trap is an aggregate of 2 point defects (VAl-V0), and the recombination center is Cr3+. The sensibilizing effect observed for thorium, or for cerium under reducing atmosphere, is attributed to the presence of a large emission band in the blue-green domain. Chromium is the main impurity at the origin of the E' peak (360°C) of alpha-alumina. It is acting as trap and also as recombination center. A mechanism of transfer of energy between Cr3+ and Ti4+ is also presented in order to explain the increase of the TL intensity of the E' peak when doping by a tetravalent cation. In the case of doping by calcium, TL allows the revelation of the phase CaAl12O19. A quenching was observed for alpha Al2O3:Ca and alpha Al203:Ce under reducing atmosphere. It is attributed to oxygen vacancies for the doping by calcium, and to the presence of Ce3+ for the doping by cerium. The alumina prepared under reducing conditions exhibits a perturbation of kinetics during sintering, and also abnormal grain growth in doped samples. This unusual kinetic is explained by a decrease in the concentration of aluminum vacancies under reducing atmosphere, conducting indirectly to a greater segregation of Si4+ at the grain boundaries, and to the formation of a liquid phase at the surface of grains. This phenomenon is amplified in the case of doping by calcium.
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Submitted on : Tuesday, April 16, 2013 - 6:13:45 PM
Last modification on : Wednesday, June 24, 2020 - 4:18:29 PM
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  • HAL Id : tel-00814282, version 1

Citation

Frédérique Ferey. Thermoluminescence et frittage de l'alumine alpha ultra-pure dopée par le zirconium, le thorium, le calcium, ou le cérium. Génie des procédés. Ecole Nationale Supérieure des Mines de Saint-Etienne, 2002. Français. ⟨tel-00814282⟩

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