Effect of electron exposure on optical properties of aluminized polyimide film
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M.M. Mikhailov Space Materials Laboratory, Tomsk State University of Control and Electronic Technology, Tomsk 634043, Russia (Received 23 May 2002; accepted 26 June 2002)
The effect of the irradiation of electrons with 10–70 keV on optical properties, including spectral reflectance and solar absorptance as, of aluminized polyimide films was investigated. The spectral reflectance was measured in situ before and after electron exposure. Experimental results showed that the reflective properties of aluminized polyimide film were apparently degraded in the 500–1200 nm wavelength range of the solar spectrum. Under the exposure of electrons, no charging effects were found on the aluminized polyimide film serving as an ion-conductive polymer. After the exposure, an “annealing” or “bleaching” effect occurred. At a given irradiation fluence, the change in solar absorptance (⌬as) of the aluminized polyimide film was increased with electron energy. There is a threshold value of electron flux cr which affects the change in ⌬as of the aluminized polyimide film, approximately cr ⳱ 6 × 1012 electrons/cm2s. When < cr, the change in ⌬as is independent from the flux; when > cr, ⌬as increases with the flux monotonically. The change in ⌬as with electron fluence ⌽ can be expressed in the form of a power function: ⌬as ⳱ ␣⌽. The factors ␣ and  are related to electron energy and show a maximum and a minimum value at 50 keV, respectively.
I. INTRODUCTION
Aluminized polyimide is a polymer material with excellent properties, such as high temperature resistance, high dielectric coefficients, good mechanical properties, and unique processability. The polyimide consists of molecules with benzenoid structure, which possesses high capability of absorbing radiative rays, and thus is often used in the industries of atomic energy and aerospace as a material with strong resistance to radiation. For instance, the aluminized polyimide film is widely used for spacecraft applications as an aluminized flexible optical solar reflector (FOSR),1,2 solar sails,3 and reflective mirrors for a space solar power plant and space garbage collecting bins.4,5 The thermal control surface coatings of spacecrafts are subjected to the damage caused by high vacuum, solar electromagnetic rays, and electrons and protons in orbit,1,6–8 resulting in degradation of optical properties such as the spectral reflectance and solar absorptance as. Since such a degradation would destroy the thermal balance of spacecrafts, it is
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J. Mater. Res., Vol. 17, No. 9, Sep 2002 Downloaded: 14 Mar 2015
important to reveal the evolution of properties of thermal control coatings in orbit through ground simulation9,10 to improve the service reliability and lifetime of spacecrafts. The aim of this study was to investigate the effect of electron irradiation in geostationary orbit on optical properties of aluminized polyimide film through ground simulation. The degradation in spectral reflectance (⌬) and s
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