Effect of Hyperthermal Atomic Oxygen on Space-Grade CV-1144-0 Silicone

Despite the fact that silicone-based coatings are often used to protect satellite materials from atomic oxygen (AO) in low Earth orbit (LEO), a quantitative understanding of the effects of AO on such coatings has been lacking. We have thus investigated the chemical and morphological changes to a commonly used commercial silicone, NuSil CV-1144-0, when it is subjected to bombardment by a beam of AO traveling at orbital velocities. The AO beam was generated with a well-characterized laser-detonation source, which, for this experimental study, produced a pulsed beam of oxygen atoms with an average translational energy of similar to 5 eV and an average flux of 4.6 x 10(15) O atoms cm(-2) s(-1). The morphology and chemical composition of CV-1144-0 before and after AO exposure at room temperature (RT) and at 300 degrees C were studied with scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). After exposure to an AO fluence of similar to 2 x 10(20) O atoms cm(-2), both shallow and deep cracks were observed, and the surface was largely transformed to silicon oxide. The mass change of CV-1144-0 at 25 degrees C as a function of AO fluence, studied with a quartz crystal microbalance (QCM), showed an initial mass gain followed by a slow and constant mass-loss rate. An average mass-loss rate of 6.2 x 10(-27) g O atom(-1) was observed after the mass gain. This mass-loss rate is about 3 orders of magnitude lower than that of Kapton H, which is typically used as a reference material for reporting AO-induced mass loss of LEO spacecraft materials. The investigation presented here provides both a quantitative measure of the mass loss of CV-1144-0 as well as a basic understanding of the complex AO effects on this polysiloxane coating, which are expected to be similar for all polydimethylsiloxane (PDMS)-based materials.