Vacuum Ultraviolet Radiation in Sources of Hyperthermal Atomic Oxygen. Photodestruction of Polytetrafluoroethylene (PTFE) and Teflon FEP for hdication of this Radiation

Abstract

Most facilities for testing the stability of spacecraft materials under attack by fast atomic oxygen (AO) are based on the generation of hypersonic beams of AO in nozzle sources with the use of continuous electrical discharges or in laser pulse-induced breakdown of the gaseous oxygen. In both cases, the sources of fast AO are simultaneously quite intense sources of vacuum ultraviolet (VUV) radiation. In the present study the intensity of VUV radiation with wavelengths > 115 nm from fast AO source were directly measured in the Central Aerohydrodynamic Institute facility VAT- 103. The intensity of this VUV radiation at the nozzle exit was shown to be almost equal to the intensity of the commercial lamp XeR-2 emitting at 147.0 nm (at its window). This VUV radiation can take part in destruction and erosion of polymer materials simulating the oxydative effects of fast AO. Its contribution to observed mass losses is greatly dependent on the material under test. For polymers consisting of carbon, hydrogen, oxygen and nitrogen the main role in erosion is played by fast AO. The decisive role of VUV radiation is shown in the erosion of fully fluorinated polymers. The mass losses of Teflon and Teflon FEP films in facilities for generation of fast AO are suggested as a means of measuring the VUV radiation dose in these facilities. The main features of mass losses that depend on duration of VUV irradiation are formulated. They are based on the previously proposed model of mass losses from these polymers during VUV photodestruction. The key feature of this model is the limited rate of photofragment evaporation (sublimation) into vacuum.