Radiative energy transfer through Si3N4 ablation layers.

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The equilibrium compositions, special absorption coefficient, emittance and transmittance of Si3N4 ablation layer plasmas have been calculated for temperatures of 3000K and 5000K, thickness of 0.01, 0.1 and pressures of 0.1, 1 and 10 atmospheres. Calculations of radiation include molecular bands, atomic lines, and continuum processes. The emittance and transmittance results are applied to a simple shock layer model to predict the effectiveness of the Si3N4, ablation layers for a blockage of the high-temperature stagnation shock layer radiation. The results show that the photoionization process in Si atom is most effective in blocking the radiation and the Si3N4 ablation layers are very effective in reducing the radiative heating to a vehicle.