TEMPERATURE AND EMISSIVITY DETERMINATION OF Si-B MATERIALS BY IN-SITU MEASUREMENTS: APPLICATION TO CATALYSIS

摘要

For catalysis application, it is useful to measure precisely the TPS (Thermal Protection System) surface temperature and wall heat fluxes. In the most of cases, wall heat fluxes measurements are carried out thanks to pyrometers or, in our case, infrared camera. First, the surface temperature is deduced from the radiative intensity due to the material emissivity. The wall heat flux is then calculated by the Planck's law which depends too on the emissivity. So a good knowledge of the material emissivity is needed. The only values of this parameter available in the literature have been determined in particular conditions, like argon atmosphere. In the ICP (Inductively Coupled Plasma) facility of the CORIA, Sintered SiC samples have been studied under dissociated air atmosphere. The infra-red spectra of the SiC samples has been recorded from 1.1 to 5 μm and concerns temperature range 1300 - 1900 K. Due to this original measurements, in a first time the surface temperature can be deduced without the emissivity by the two colours method. This very precise method give a good calibration of our IR camera (between 7-12 μm the SiC emissivity is not precisely known). In a second time, the emissivity is deduced by comparison of the spectral emission of the sample with the black body radiation at the sample surface temperature. The results show a monotonous increase of the emissivity from 0.6 to 0.9. This is in contradiction with the common value of 0.8 taken for pyrometric measurements around 1 μm in wavelength. The final aim is to calibrate the camera to have a simple efficient and precise tool for temperatures and wall heat fluxes determinations. In addition, to validate the modelling used to derive the sample catalysis, spontaneous Raman spectroscopy on N_2 have been carried out in the boundary layer above a fully catalytic wall. We obtain a surprising result : the boundary layer seems in equilibrium.