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 total emissivity greater than 0.8 in order to ensure efficient cooling in vacuum. Only one of the investigated coatings showed sufficient long-term stability. For thermal protection of reusable space transportation systems during atmospheric reentry, in addition to high emissivity, oxidation resistance is required. SiC coatings and special polysilazane-based coatings have been tested. Results of emissivity measurements before and after flight experiments on the Russian FOTON capsule are also available. In order to improve the reliability of (high-temperature) emissivity measurements Pt–Rh alloys, SiC, Al2O3 doped with Cr2O3, and graphite have been tested to assess applicability as reference materials for comparative emissivity measurements by various facilities.