SPECTRAL AND TOTAL EMISSIVITY OF HIGH-TEMPERATURE MATERIALS

A number of various high emissivity coatings has been investigated in detail. Oxide ceramic coatings for rotating x-ray anodes must have a t otal emissivity greater than 0.8 in order to ensure efficient cooling in vacuum, Only one of the investigated coatings showed sufficient lon g-term stability. For thermal protection of reusable space transportat ion systems during atmospheric reentry, in addition to high emissivity , oxidation resistance is required. SiC coatings and special polysilaz ane-based coatings have been tested. Results of emissivity measurement s before and after flight experiments on the Russian FOTON capsule are also available. In order to improve the reliability of (high-temperat ure) emissivity measurements Pt-Rh alloys, SIG, Al2O3 doped with Cr2O3 , and graphite have been tested to assess applicability as reference m aterials for comparative emissivity measurements by various facilities .