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Microwave Sintering of Alumina at 915 MHz: Modeling, Process Control, and Microstructure Distribution

1
Normandie Univ, ENSICAEN, UNICAEN, CNRS, CRISMAT, 14000 Caen, France
2
Laboratoire Georges Friedel, École des Mines de Saint-Étienne, 42023 Saint-Etienne, France
3
SOLCERA, ZI n 1 Rue de l’industrie, 27000 Evreux, France
4
DGA (Direction Générale de l’Armement), Echangeur de Guerry, 18000 Bourges, France
*
Author to whom correspondence should be addressed.
Materials 2019, 12(16), 2544; https://doi.org/10.3390/ma12162544
Received: 3 July 2019 / Revised: 2 August 2019 / Accepted: 7 August 2019 / Published: 9 August 2019
(This article belongs to the Special Issue Conventional and Microwave Sintering Techniques in Materials)
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PDF [4540 KB, uploaded 9 August 2019]
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Abstract

Microwave energy can be advantageously used for materials processing as it provides high heating rates and homogeneous temperature field distribution. These features are partly due to the large microwave penetration depth into dielectric materials which is, at room temperature, a few centimeters in most dielectric materials. However, up to now, this technology is not widely spread for high-temperature material processing applications (>1200 °C), because its reproducibly and ability to sinter large size samples (>30 cm3) still needs to be improved. In this context, this paper describes both an empirically designed 915 MHz single-mode cavity made from SiC susceptors and refractory thermal insulation, and the 3D modeling of the process in order to improve our understanding of it. Different susceptors geometries and coupling slit position were numerically tested in order to better understand how these parameters impact the field homogeneity and the process stability. It was found that positioning the largest surface of the susceptors parallel to the electrical field allows a very uniform and hybrid heating of the material, while avoiding plasma or thermal instabilities. This was correlated to the 3D modeling results. Finally, thanks to a fully-automatized system this apparatus was used to sinter large size (~30 cm3) low-loss dielectric alumina samples. The sintered materials were subsequently characterized in terms of density, grain size distribution, and homogeneity. The reproducibility was also discussed, demonstrating the process efficiency and reliability. View Full-Text
Keywords: microwave sintering; resonant applicator; process control; alumina; hybrid heating; modeling microwave sintering; resonant applicator; process control; alumina; hybrid heating; modeling
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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MDPI and ACS Style

Marinel, S.; Manière, C.; Bilot, A.; Bilot, C.; Harnois, C.; Riquet, G.; Valdivieso, F.; Meunier, C.; Coureau, C.; Barthélemy, F. Microwave Sintering of Alumina at 915 MHz: Modeling, Process Control, and Microstructure Distribution. Materials 2019, 12, 2544.

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