Degradation of white anodic-oxide coatings in UV irradiation in vacuum

Photostimulated degradation of the reflectivity of white anodic-oxide coatings on Al alloy (Al-AOCs) that are used as thermal-regulating coatings of space vehicles is investigated by spectroscopy of diffuse reflection in the region of 0.5–6 eV. It is established that irradiation in vaccum when λ≤300 nm leads to the appearance in diffuse-reflection spectra of the absorption bands at 4.0 and ∼4.6 eV that are similar to these induced by vacuum heating for T≥350 K. A growth in the absorption bands is accompanied by gas release from the coatings. These processes have a common excitation spectrum, basic kinetic regularities, and a thermoactivated character. UV irradiation in vacuum is assumed to initiate Al-AOC destruction with the formation of color centers. This process is accompanied by the desorption of molecular products.