VISIBLE AND NEAR-INFRARED EMITTANCE OF ABLATION CHARS AND CARBON

Initial results of an experimental study of the visible and near-infrared spectral reflectance and emittance of ablation chars, carbon, and graphite at temperatures ranging from 2200° to 3500° K are presented. Reflectance measurements were made with a double-ellipsoidalmirror reflectometer that utilizes a carbon arc to heat and to irradiate the materials. The ablation materials, from which the chars were formed by thermal degradation in atmosphericentry- simulation facilities, included high-density and low-density phenolic-nylon, carbonfiber- reinforced phenolic, and honeycomb-reinforced, low-density filled epoxy. Measurements were made on a dense high-purity and a porous grade of carbon and on high-purity, structural, and pyrolytic grades of graphite. A photomultiplier and a lead sulfide cell were used as detectors for the visible and infrared measurements, respectively. The results indicate that emittance for all the materials is maximum in the visible spectrum and decreases with wavelength in the near-infrared spectrum. The angular distributions of radiation fluxes incident on, reflected from, and radiated from, each material, were measured with an array of solar cells. The distribution measurements showed that the materials whose surfaces are porous or have been roughened by oxidation obey Lambert's cosine law approximately in the emission of radiation, and also in reflecting the arc incident radiation, although the incident radiation is nonuniform in distribution. © 1968 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.