Conditions Extrêmes et Matériaux : Haute Température et Irradiation
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2009

ACLN
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B.Rousseau, H.Gomart, D.De Sousa Meneses, P.Echegut, 'Material parameters influencing the radiative properties of heterogeneous optically thick oxide ceramics', ASME 2009 Heat Transfer Summer Conference HT2009-88574 403-410 (2009) doi:10.1115/ht2009-88574

Knowledge of the thermal radiative properties of heterogeneous materials is crucial for the design of efficient systems operating at high temperatures. Examples include zirconia stabilized yttria thermal barrier coatings for aero-engine parts, carbide ceramics used in space shuttle re-entry shields or metallic foams used in heat exchangers. Costly experimental trial-and-error campaigns are often required to elaborate a material endowed with the desired radiative properties. An alternative way to speed up the development of these systems is to model their optical response by taking account their internal structure from the atomic scale to the macroscopic scale. From a material viewpoint, this task requires for a given compound, to thoroughly characterize its material parameters such as its chemical composition, its texture with relevant morphological descriptors, and its macroscopic size. Here, the term texture stands for the spatial organization and the size distribution of the scatterers (grains, pores) that constitutes the architecture of the porous material. In the other hand, from a modelling viewpoint, an important task is to appreciate the magnitude of the optical mechanisms that are connected to the latter material parameters. This investigation is primordial and allows, in return, the development of modelling strategies giving reliable radiative data performed with commercial computers. In the following, a general approach is proposed to treat this tricky issue. It is applied to the case of two opaque rough coatings based on conducting oxides belonging to the LnMO4+d family (Ln is a rare earth, M is a transition metal and d corresponds to the excess of oxygen). The first coating is used in the design of plate black body furnaces, and the seconds ones are used as cathodic layers for SOFC. After characterizing their chemical and textural properties, a strategy of modelling based on a Monte Carlo Ray Tracing code will be detailed. In particular, it directly runs in the two–dimensional image of the surface. According to the length scale of the scatterers, adaptation of the previous code based on the use of the effective-medium approximation will be proposed. The pertinence of this hybrid computing approach will be discussed by comparing the calculated spectra with the experimental ones acquired with a set-up based on infrared spectrometer Bruker IFS 113 v. At least, this work opens the possibility to discuss the design of ceramics with prescribed thermal radiative properties