Degradation of carbon-based space materials with SiO2 nano-coating due to outgassing effects

In recent years, the emphasis in space research has been focused on both exploration and commercialization of space. In order to use space for these purposes it is mandatory to guarantee the compliance with the low earth orbit (LEO) space environment that degrades the performances and functionality of materials with phenomena such as atomic oxygen (AO), ultraviolet (UV) radiation, plasma, micrometeoroids and debris, as well as severe temperature cycles. In this frame the study of Outgassing properties of space materials is of primary importance. The resistance of a material to the high vacuum and high temperatures is one of the most critical issues of spaceability of materials. A material with poor outgassing properties will de-gas volatile particles of itself and humidity with critical effects on electronic and optical devices. The resistance to high vacuum will assure the durability and the reliability of materials and structures. Carbon based materials are of common use for re-entry-from-space applications, as thermal protection systems, thanks to their resistance to high temperatures. Carbon-Carbon (C/C) composites are engineered materials principally composed by carbon fibers and carbon matrix. They offer a wide range of properties that can be tailored by the selection of constituent materials, fiber orientations, and methods of fabrication. In this paper Outgassing tests have been performed on samples obtained from high thickness C/C prototypes for employment in re-entry systems. The C/C densification has been achieved by means of a customized CVI treatment. The outgassing tests have been performed both on four "naked" and three coated samples per kind. The considered coating was a solution of 0.5% and 1% in weight of SiO2 nano-spheres mixed in a pyro-paint liquid varnish. The results show a complete compatibility of the materials under investigation with the standard. In fact for all the materials, both coated and naked, the TML is below 1 %, RML is below 1 % and the CVCM is below 0.1%.