Temperature dependence study of FEP Teflon and Kapton H erosion in a simulated LEO atomic-oxygen environment

Abstract

Polymer degradation occurs as a result of exposure to atomic oxygen in low Earth orbit (LEO). The damaging effects of the space environment on materials have prompted the simulation of LEO to study polymer erosion. The laboratory setting provides a method of evaluating material erosion by atomic oxygen attack in an affordable and time-efficient manner: This study investigates the temperature dependence of the erosion of Kapton H and FEP Teflon when exposed to hyperthermal 5 eV atomic oxygen beam. This study extends earlier investigations of the temperature dependence of Kapton H erosion and helps unveil the reaction mechanisms that lead to erosion of Kapton H and FEP Teflon in LEO. The investigations reported in thesis relied on the use of Kapton H to calibrate the atomic oxygen exposures, so an additional study was performed to verify the linear dependence of Kapton H erosion. Surface characterizations of the eroded samples in this study were performed by surface profilometry and atomic force microscopy. The Kapton H erosion yield grew exponentially with temperature in the range 298 K to 573 K. The temperature dependence of Kapton H erosion could be explained by temperature-dependent and -independent mechanisms. The temperature-independent mechanism dominates at lower temperatures and involves the direct reaction of O atoms with the polymer surface, with an activation energy that is easily overcome by the O-atom collision energy with the surface. The temperature-dependent mechanism becomes important at higher temperatures. Apparently, at high surface temperatures, material is removed through reactions that occur in thermal equilibrium with the surface and have an effective activation energy of 0.31 eV. From 298 K to 423 K the erosion yield of FEP Teflon grew exponentially. The nonlinear Arrhenius behavior suggested a two-term mechanism analogous to that used to describe the temperature dependent erosion of Kapton H. At temperatures lower than 373 K the temperature-independent mechanism dominates the material erosion and at higher temperatures, a mechanism becomes important that occurs in thermal equilibrium with the surface and has an activation energy of 0.24 eV.