Degradation of optical properties in anodic coatings exposed to vacuum-ultraviolet radiation
Sheng, Xia Yang
Master of Science
Sulfuric acid anodized aluminum coating systems possessing a low ratio of solar absorptance to infrared emittance are susceptible to vacuum-ultraviolet radiation. Vacuum-ultraviolet exposure can degrade the coating systems by increasing the solar absorptance without a commensurate increase in infrared emittance. Experimental findings from electron microprobe analysis, x-ray diffraction, exposure to vacuum, optical microscopy, and computer simulation have been used to propose the mechanisms for this degradation based on water loss from anodic coatings. It has been determined that water vaporization during vacuum-ultraviolet exposure can cause densification and cracking in a sealed anodic coating. Increased specific density and cracks reduce the reflectance in the short wavelength region and lead to an increase in absorptance.