Emittance of RSI Coatings Determined from Radiation Measurements in Arc Jet Tests

Simultaneous measurements were made on three surface insulation coatings for total surface radiation and radiation at discrete wavelengths between 0.88 and 4.5 microns. The mullite coating radiated all the applied heat at convective heat rates of 204 and 295 kw/sq m. Radiation from the ceramic mullite fiber coating was 170 kw/sq m at a heat rate of 454 kw/sq m. Effective total emissivity and spectral emissivity values were evaluated; all three coatings were significantly non-grey. Effective total emissivity values were 0.79 for mullite, 0.50 for ceramic mullite fiber, and 0.78 for silica composite.