Inorganic White Thermal-Control Coatings for Extreme Space Environments

摘要

White paints and clear anodizing are often used as thermal-control coatings. Inorganic white ceramic coating on AA2219 alloy prepared using novel Keronite plasma-electrolytic-oxidation technology was used in this study for the BepiColombo mission. The Keronite coating on a high copper-containing 2219 aluminum alloy was investigated in terms of its resistance to environmental exposures, such as corrosion, humidity, and high-temperature (400 degrees C) UV/VUV radiation. The coating was characterized in terms of its microstructure, porosity, and adhesion, and their relations to the overall thermooptical performance and space suitability. Optical reflectivity, spectrophotometer color, solar absorptance, and hemispherical emittance have been measured and compared against that of currently used white silicone paint. The Keronite white coating has been shown to offer thermooptical characteristics acceptable as a space thermal-control material, while offering all the added benefits of 1) inorganic ceramic coating with extremely good adhesion, 2) environmentally friendly process with no toxic substances and heavy metals, 3) capability to coat shapes with complex geometries and non-line-of-sight areas, and 4) resistance to harsh space environment. The ceramic white coating has now been applied on Mercury Planetary Orbiter solar-array thermal shields.