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.

Fluorine Plasma Treatments of Poly(propylene) Films, 2 – Modeling Reaction Mechanisms and Scaling

“…They found that, unlike the photolysis of PP and PE, CC bond generation is not a major process. They found CF n ( n = 1–3) in the ejecta, indicating that the polymer CC backbone undergoes scission, a process also observed by Skurat and Nikiforov 26. Ono et al estimated the quantum yield for atomic fluorine photolysis at 147 nm to be 0.0025.…”

Mechanistic Studies of Atomic Oxygen Reactions with Polymers and Combined Effects with Vacuum Ultraviolet Light

“…Extensive efforts have been undertaken in both space environments and ground-based test facilities in order to unravel the erosion mechanisms of FEP Teflon. [31][32][33][34][35][36][37][38][39][40][41] FEP Teflon has strong absorption bands at VUV wavelengths. VUV radiation breaks C-C and C-F bonds and creates fragments that become volatile.…”

Hyperthermal atomic oxygen durable transparent silicon-reinforced polyimide

“…[1][2][3][4][5][6][7] When spacecrafts travel at the first cosmic velocity in LEO, the surface materials collide with AOs at velocities of 7-8 km s À1 , with translational energies of 4-5 eV and fluxes of 10 13 -10 15 atoms cm À2 s À1 , which causes serious erosion and degradation to spacecraft materials. [8][9][10][11][12][13][14][15][16][17][18][19][20][21] Yellow polyimides Kapton H or Kapton NH have been widely used in LEO, for their low density, thermal stability, flexibility, and durability to vacuum ultraviolet (UV). However, they suffer from strong oxidation under hyperthermal AO attack when operating in orbit, for their elements of carbon (C), hydrogen (H), O, and nitrogen (N) are easily oxidized by the high-velocity AO interaction, to form volatile gas molecules and leave surface, resulting in mass loss of materials.…”