R. C. Tennyson

Influence of content and structure of hydrocarbon polymers on erosion by atomic oxygen

From a comprehensive analysis of erosion data for materials exposed to low-Earth-orbit space environment, to fast atomic-oxygen beams, and in plasma facilities it is shown that different correlations can be found between the thermal and hyperthermal atomic-oxygen erosion yield of hydrocarbon polymers and their chemical structure and content. Correlations have been found of the hyperthermal atomic-oxygen erosion yield of many polymeric materials in flight experiments with their inverse mass density of effective (not bonded with oxygen) carbon atoms, and with their degree of aromaticity. These correlations were used to identify the rate-limiting factors of erosion processes and to predict the erosion rate for polymer-based materials in low Earth orbit. The first correlation was not found in the interaction of thermal atomic oxygen with a number of polymers, and the second is strongly pronounced. The results are explained on the basis of physical and chemical processes affecting differently the erosion rates of polymers by thermal and by fast atomic oxygen. Subthreshold bombardment-induced and -enhanced degradation and surface chemical etching are proposed to be the major mechanisms of erosion by fast atomic oxygen.

Erosion resistance and durability improvement of polymers and composites in space environment by ion implantation

Abstract Spacecraft designers use polymers and polymer-based composite materials extensively in electrical, thermal, and structural applications to address both weight and performance demands. Without protection from the deleterious effects of the space environment, in particular hyperthermal atomic oxygen (HAO), these materials suffer accelerated erosion from chemical interaction and experience a loss of mass and deterioration of performance. High dose implantation at energies in the 10–100 keV range using ions of metal or semiconductor materials was used as a method of modifying the surface of these polymeric materials to produce changes that can yield dramatic improvements in space environmental durability. The results of this study show that computer modelling of the ion implantation process combined with reasonable fluence estimates give a good basis for the choice of implantation conditions. This study presents the results for high-performance materials including Kapton ® , Mylar ® , PEEK, Lexan ® , and PEEK/carbon fibre composites using X-ray electron spectroscopy, scanning electron microscopy, and other surface analysis techniques, before and after treatment. The results show that implantation of silicon and aluminum (singly, binary, or in combination with boron) or yttrium implantation produces a stable, protective oxide-based layer following exposure to HAO. The improvement in chemical resistance of these materials assures performance without deterioration in long duration space missions and shows promise for improvement in terrestrial performance in highly reactive oxidative environments.

Protective coatings for LEO environments in spacecraft applications

Abstract Spacecraft operating in the low Earth orbit (LEO) are exposed to an environment characterized by very low pressure, various atomic species, temperature extremes, ultraviolet (UV) radiation, electromagnetic radiation and atomic oxygen (AO), which is produced by the dissociation of molecular oxygen by UV radiation. The destructive influence of AO on polymer-based materials and composites and the synergistic effects between AO and other environmental factors have been dramatically demonstrated in LEO flights and ground-based simulators. This paper investigates the effects of contamination, structure and the synergism between temperature and AO fluence on polymer-based materials, and provides an overview of the recent developments in the design and use of protective coatings for polymer and composite materials in the LEO environment and their testing in ground-based space environment simulators. Three trends in protective coatings research are identified and discussed: (a) the improvement of technologies for high-performance oxide-based coatings; (b) self-healing coatings based on special semi-organic polymers; (c) protective multilayered structures. An evaluation is made of the properties and behaviour of different protective coatings on the polymers and composite materials used in spacecraft applications.

METAL ION IMPLANTATION AND DYNAMIC ION MIXING FOR THE PROTECTION OF HIGH-PERFORMANCE POLYMERS FROM SEVERE OXIDATIVE ENVIRONMENT

Low energy high-dose Plasma Immersion Ion Implantation, combining both ion and recoil implantation (dynamic ion mixing), was used to enrich thin surface layers of high-performance polymers with an appropriate amount of specially selected reactive metal element such as Al. Both oxygen plasma and fast (E∼2–3 eV) atomic oxygen (FAO) beam have been used as aggressive environments for testing the implanted polymers. The modified materials successfully survived these test environments, including FAO, which is the main danger for carbon-based materials in space, in low Earth orbit. The retained doses of implanted and recoil implanted elements were controlled by RBS. The content, structure and morphology of the modified protective surface layers were examined by XPS and scanning electron microscopy (SEM). It was shown that protective oxide(s)-based surface structures were formed. Implantation and conversion conditions were found for which the appearance and important thermo-optical properties of treated polymer films, such as solar absorptance and thermal emittance, were practically unchanged.

Comparison of surface modification of polymeric materials for protection from severe oxidative environments using different ion sources

Abstract Mid-energy monoenergetic conventional single-, dual-, or triple ion implantation, implantation with a MEVVA ion source, as well as Metal Plasma Immersion Ion Implantation have been used for the treatment of high-performance polymers at specially selected regimes, derived from the results of computer simulation. Testing of the implanted advanced polymers and carbon fiber reinforced composites has been performed in a Space Simulator for accelerated testing by exposure to fast ( E ∼2–3 eV) atomic oxygen beam, as well as by exposure to oxygen plasma, and ozone+UV. After an intermediate stage of surface conversion, the treated materials did not show any mass loss or surface morphology change, thus indicating high-quality protection from these severe oxidative environments. A variety of complementary surface analysis techniques, such as RBS, SIMS, XPS and SEM have been used to examine the surface content and structure of the modified subsurface layers.

Improvement of oxidation and erosion resistance of polymers and composites in space environment by ion implantation

Abstract A novel approach based on ion implantation has been developed and used to investigate the influence of a selection of metal and semi-metal ions or their combinations with selected non-metal elements, the implantation energy range, and ion fluencies, on the behaviour of implanted materials under fast atomic oxygen fluxes (FAO). The preferential conditions of single- or multiple-ion implantation in a number of high-performance polymers, graphite and composite materials were examined. Highly stable, oxidation- and erosion-resistant new surface structures were created on graphite, Kapton, PEEK and Mylar, and on carbon-fibre/PEEK composites by exposing the implanted materials to FAO in a unique atomic oxygen beam facility. A number of complementary surface analysis techniques such as RBS, XPS, SEM/EDS were used to study the content and structure of the modified surfaces, and their resistance to oxidation and erosion in FAO conditions.

Surface Modification of Polymer-Based Materials by Ion Implantation - a New Approach for Protection in Leo

Atomic oxygen is known to be the most prominent hazard for polymers and carbon- based materials in low Earth orbit (LEO), causing accelerated erosion and surface texturing. Vacuum ultraviolet (VUV) radiation is another important LEO environmental hazard for many of these materials. This study presents a new approach for protection of these structural materials for space applications.

Enhancement of Space durability of materials and external components through surface modification

Results of surface modification treatment to improve space durability of main space-related thin polymer films, a lacing tape, and several organic-based thermal-control paints by a patented Photosil process are presented.Results of ground-based testing in an oxygen plasma asher and in a fast atomic-oxygen beam facility imitating low-Earth-orbit environment are also discussed. Characterization data before and after testing that include functional properties measurement, surface analyses, and durability evaluation are presented, and the protective mechanisms for Photosil treatment are discussed. Some of the samples that were treated in the program are similar to those in the Materials on International Space Station Experiment-1, being exposed now on the International Space Station. A number of space components including lacing tape and some external painted components of the Mobile Servicing System of the International Space Station were treated by Photosil, and the results will be discussed briefly.

Modification of Thermal Control Paints by PHOTOSIL™ Technology

A study was conducted at UTIAS/ITL to use the recently developed PHOTOSIL™ technology [1] for fast atomic oxygen (FAO) erosion resistance improvement of polymer-based thermal control paints. A modified version of PHOTOSIL™ process was used to treat the painted samples. Aeroglaze A276 white paint, Aeroglaze Z306 black polyurethane coating and epoxy-polyamide primer were used in the study. The paints were applied to stainless steel coupons, approximately 50 (im thick. White paints for thermal control application are generally used on the outer surfaces and black paints on internal spacecraft components.

Pristine and Surface‐Modified Polymers in LEO: MISSE Results versus Predictive Models and Ground‐Based Testing

Space flight data, collected and published by NASA Glenn Research Center (GRC) team for a set of pristine polymeric materials selected, compiled, and tested in two LEO flight experiments at the International Space Station, as part of the “Materials International Space Station Experiment” (MISSE), has been used for comparison with previously developed atomic oxygen erosion predictive models. The same set of materials was used for a ground‐based fast atomic beam (FAO) experimental erosion study at ITL/UTIAS, where the FAO exposure was performed mostly at a standard fluence of 2×1020 cm−2, with the results collected in a database for the development of a prototype of predictive software. A comparison of MISSE‐1 flight data with two predictive correlations has shown good agreement, confirming the developed approach to polymers erosion resistance forecast that might be used also for newly developed or untested in space polymeric materials. A number of surface‐modified thin film space polymers, treated by two I...