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Des revêtements autoportés en aluminosilicates jusqu'à 1 cm d'épaisseur et 80 % de porosité par projection plasma : développement et caractérisation thermomécanique

Abstract : Considerable attention is now being focused on porous ceramics in the industrial field as used in a large variety of applications, such as thermal insulation, filter membranes, catalysts, heat exchangers, bioreactors, and refractories. As part of thermal insulating function, this study evaluates the plasma spraying process for the realization of materials that combine high porosity rates, higher than 70%, with good mechanical strength, so these materials could be machined. Operating temperatures around 1 200 °C and mass minimization stresses influence sprayed material choice to aluminum silicates. Considering the expected porosity rates, different pore formers were used in plasma spraying. Depending on the pore former nature, the plasma spraying parameters and the powder morphologies, several organized porous microstructures with a thickness of one millimeter and porosity rates between 70 and 80% were obtained. To satisfy the functional requirements, the 80% microstructure, resulting from the evacuation of aromatic polyester was obtained over one centimeter. This required a thorough study of residual stresses induced during plasma spraying and cooling steps, carried out by the deflection measurement method on standardized specimens. Understanding the mechanism that generated these stresses and minimizing them allowed the spraying of thick, flat and cylindrical microstructures. The thermomechanical behavior associated with such microstructures was analysed with different porous mullite shades. Thermal conductivities of 80 mW.m-1.K-1 were measured at room temperature on amorphous microstructures and then at temperature up to 800 °C on crystallized and amorphous structures. Young modulus, flexural stress and strain at rupture were evaluated by destructive (bending 3 – 4 points) and non-destructive (acoustic wave testing) methods. Finally, empirical relationships describing thermal and mechanical behaviour of free standing mullite microstructures following porosity and heat treatments were presented. In the end, coatings obtained by plasma spraying process have similar thermal and mechanical properties to those traditionally obtained in the literature by more conventional processes, such as gelcasting.
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Submitted on : Friday, September 3, 2021 - 6:04:10 PM
Last modification on : Saturday, September 4, 2021 - 3:20:19 AM

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Vincent Fournier. Des revêtements autoportés en aluminosilicates jusqu'à 1 cm d'épaisseur et 80 % de porosité par projection plasma : développement et caractérisation thermomécanique. Matériaux. Université de Limoges, 2021. Français. ⟨NNT : 2021LIMO0043⟩. ⟨tel-03334456⟩

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