Texture and Porosity Effects on the Thermal Radiative Behavior of Alumina Ceramics

Abstract

International audienceThermal and optical properties of ceramics are dependent on radiation scattering and cannot be determined by a knowledge of their chemical composition alone, as for single crystals. In this paper, extrinsic effects, such as roughness, porosity, and texture, on the spectral emissivity of alumina ceramics are investigated. Roughness effects have an influence mainly in the opaque zone; an important porosity dependence and the presence of a critical porosity threshold were observed in the semitransparent zone. Furthermore, it was shown that two ceramics with similar total porosities, but with different textures, possess radically different emissivities, showing that grain size, pore size, and spatial repartition of the grains are also crucial for an understanding of the thermal properties of the ceramics

Thermal radiation in dust flame propagation

“…The photodiode signal increases more progressively that with pure methane air flames but the amplitude are higher (double). All of this would also suggest that the emissivity of alumina is not zero but rather low in agreement with recent data (Rozenbaum and al., 2009) With SiC particle (figure 11), the radiated flux is much higher than with the pure gaseous mixture when the dust concentration is 500 g/m 3 but smaller for a higher concentration (800 g/m 3 ). These dust concentrations might be too large since a proportion of the dust can fall down in the maps of time between the interruption of the flow and the ignition.…”

Highly enhanced infrared spectral emissivity of porous CeO2 coating

“…2. It was reported that the porosity had the positive effect on the emissivity in Si, SiO 2 and Al 2 O 3 materials [3,4,17]. The pores in the CeO 2 coating are similar to blackbody cavities.…”

Development of optical tools for the characterization of selective solar absorber at elevated temperature

“…Sample was heating by the back face with metallic heater. This configuration is known to be not well adapted for sample with poor thermal conductivity such ceramics [14,16]. In this case the surface temperature may be lower than expected and we have a wrong calculation of luminance of the sample (eq 6) which gives a lower emittance.…”

“…This choice is justified since SiC is one of the materials used for high temperature receiver (tower technology) [13]. The -Al2O3 is largely used for the emittance measurement in the range of high temperature [14,15,16] and can be considered as a reference materials. …”