Study On Erosion Effect Of Atomic Oxygen On Ployimide And Its Protective Technology In LEO Environmen

Kapton is used extensively on spacecraft primarily as flexible substrates forlilghtweight, high-power solar arrays because of its inherent strength, temperature stability, excellent insulation properties, ultraviolet (UV) stability and infrared (IR) transparency. However, Atomic oxygen (AO) is the most dangerous factor to space materials in low earth oribit (LEO). It can erode most polymers and polymer-based materials in spacecraft. In this work, a ground-based simulation AO facility has been established in our laboratory, the AO erosion resistance of POSS/PI films, PDMS/PI hybrid coatings, and polysiloxane coating modified by Si ion implantation techinique are systematically investigated by the AO simulator.A ground-based simulation AO facility has been established in our laboratory, in which, the relationship of polyimide between atomic oxygen erosion rate and impingement angle was in-situ studied by using QCM. In situ mass loss measurements clearly indicated that the impingement angle dependence of the erosion rate of polyimide follow a cosine law.The POSS/PI and PDMS/POSS hybrid coatings were prepared on Kapton substrates in situ polymerization and their erosion resistance was evaluated through exposure test. They were investigated by using scanning electron microscopy (SEM), photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and so on. AO exposure test results showed that the both coatings could protect Kapton substrate from AO attack effectively. The data indicated that a silica-rich layer was formed on the surface of the hybrid coating when the coating is exposed to AO flux, which could provide a protective barrier on the surface preventing further degradation of the polymer during extended exposure to AO and obviously improved the AO resistance of polyimide films, The erosion yield of the two coatings decreased by one and two order of magnitude respectively, compared with the value of3.0×10-24cm3/atom of the polyimide film.The AO resistance of Si ion implanted siloxane coatings on the polyimide substrate was tested in the ground-based AO simulation facility. In initial stage of AO exposure, the implanted sample had a mass change, and then was stabilized. The erosion yield of the Si implanted siloxane coatings decreased by more than two orders of magnitude compared with the polyimide film. The results through SEM and XPS indicated that a continuous high-quality protective oxide-based (SiO2) surface layer formed on the implanted siloxane coatings after the AO exposure. It can prevent further degradation of the underlying polymer with increased exposure to the AO flux. The Si implanted materials have a markedly increased erosion resistance than unimpalnted siloxane coatings, and its exposed surface does not show any pin-holes in AO environment.