Statistics – Applications
Scientific paper
Jan 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aipc..458..627d&link_type=abstract
Space technology and applications international forum -1999. AIP Conference Proceedings, Volume 458, pp. 627-635 (1999).
Statistics
Applications
Spaceborne And Space Research Instruments, Apparatus, And Components, Ceramics And Refractories
Scientific paper
Solar dynamic (SD) space power systems require durable, high emittance surfaces on a number of critical components, such as heat receiver interior surfaces and parasitic load radiator (PLR) elements. To enhance surface characteristics, an alumina-titania coating has been applied to 500 heat receiver thermal energy containment canisters and the PLR of NASA Lewis Research Center's (LeRC) 2 kW SD ground test demonstrator (GTD). The alumina-titania coating was chosen because it had been found to maintain its high emittance under vacuum (<=10-6 torr) at high temperatures (1457 °F (827 °C)) for an extended period (~2,700 hours). However, preflight verification of SD systems components, such as the PLR, require operation at ambient pressure and high temperatures. Therefore, the purpose of this research was to evaluate the durability of the alumina-titania coating at high temperature in air. Fifteen of sixteen alumina-titania coated Incoloy samples were exposed to high temperatures (600 °F (316 °C) to 1500 °F (816 °C)) for various durations (2 to 32 hours). Samples were characterized prior to, and after, heat treatment for reflectance, solar absorptance, room temperature emittance and emittance at 1200 °F (649 °C). Samples were also examined to detect physical defects and to determine surface chemistry using optical microscopy, scanning electron microscopy, operated with an energy dispersive spectroscopy (EDS) system, and x-ray photoelectron spectroscopy (XPS). Visual examination of the heat-treated samples showed a whitening of samples exposed to temperatures of 1000 °F (538 °C) and above. Correspondingly, the optical properties of these samples had degraded. A sample exposed to 1500 °F (816 °C) for 24 hours had whitened and the thermal emittance at 1200 °F (649 °C) had decreased from the non-heat treated value of 0.94 to 0.62. The coating on this sample had become embrittled, with spalling off the substrate noticeable at several locations. Based on this research it is recommended that preflight testing of SD components with alumina-titania coatings be restricted to temperatures no greater than 600 °F (316 °C) in air to avoid optical degradation. Moreover, components with the alumina-titania coating are likely to experience optical property degradation with direct atomic oxygen exposure in space.
de Groh Kim K.
MacLachlan Brian J.
Smith Daniela C.
Wheeler Donald R.
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