Non-equilibrium radiation during SiC-CO2 plasma interaction
Résumé
The radiation of a pure CO2 inductive plasma was recorded between 190 and 920 nm during its interaction with a SiC sample under a pressure equal to 6 kPa and an estimated global specific enthalpy close to 12 MJ kg(-1). The plasma electronic excitation was found to be out of equilibrium. The main radiators were found to be O, C, C-2 and, mainly, CO. The radiation is especially significant where the plasma chemically interacts with the material revealing a stronger electronic excitation close to the surface. Excitation temperatures were also found to increase in the chemical boundary layer, which is four times smaller than the thermal boundary layer. This raises questions about the energy exchange processes of the excited states and about chemical behaviour independent of their respective ground states. The surface is found to be covered by an inhomogeneous silica layer revealing a passive oxidation, but also by bubble structures, indicative of the transition towards active oxidation. The surface temperature is estimated to be 1800-1900 K. Raman spectroscopy measurements on the surface and optical spectroscopy measurements in the boundary layer provide proof of carbon production coming from the SiC.