![SEM of a crack in the P4 coating (adapted from Kulig [20]),](https://www.researchgate.net/profile/Packirisamy-Shanmugam/publication/226701414/figure/fig1/AS:668916888133639@1536493622723/SEM-of-a-crack-in-the-P4-coating-adapted-from-Kulig-20_Q320.jpg)
![Mass loss of unprotected and DBP-1 protected Kapton 9 on exposure to atomic oxygen (adapted from Packirisamy et aL [50]).](https://www.researchgate.net/profile/Packirisamy-Shanmugam/publication/226701414/figure/fig4/AS:668916888129555@1536493622899/Mass-loss-of-unprotected-and-DBP-1-protected-Kapton-9-on-exposure-to-atomic-oxygen_Q320.jpg)
![SEM of broken glassy layer of DBP-1 coating ashed for 624 h (adapted from Packirisamy et aL [50]).](https://www.researchgate.net/profile/Packirisamy-Shanmugam/publication/226701414/figure/fig6/AS:668916888133644@1536493622996/SEM-of-broken-glassy-layer-of-DBP-1-coating-ashed-for-624-h-adapted-from-Packirisamy-et_Q320.jpg)
![Figure t2 SEM of a broken glassy layer in a severely bent area of the P2 coating (adapted from Schwam et aL [27]).](https://www.researchgate.net/profile/Packirisamy-Shanmugam/publication/226701414/figure/fig2/AS:668916888129551@1536493622777/Figure-t2-SEM-of-a-broken-glassy-layer-in-a-severely-bent-area-of-the-P2-coating-adapted_Q320.jpg)
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Atomic oxygen resistant coatings for low earth orbit space structures
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This review presents research in the area of polymeric coatings developed for protecting low earth orbit (LEO) space structures from atomic oxygen. Following a brief description of the LEO environment, ground-based simulation facilities for atomic oxygen and evaluation of protective coatings are discussed. Atomic oxygen resistant coatings based on different polymeric systems such as fluorinated polymers, silicones, poly (carborane-siloxane)s and decarborane-based polymers are presented. Finally, the performances of different coating systems are compared and the scope for further research to improve the performance of some of the coating systems is discussed.
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... However, the majority of the atomic oxygen exposure facilities operational today are focused on investigating the induced erosion, which is a serious concern as its effects can damage different systems such as optics and electronics with the potential of compromising whole missions [12,13]. Identifying materials that are resistant to AO erosion has been a key interest of these facilities [14,15]. To expedite the effects of AO exposure, many have increased AO flux to levels that are orders of magnitude above those experienced by spacecraft in VLEO [16]. ...
The testing of atmosphere-breathing electric propulsion intakes is an important step in the development of functional propulsion systems which provide sustained drag compensation in very low Earth orbits. To make satellite operations more sustainable, it is necessary to develop new materials which withstand erosion, long-lasting propulsion systems to overcome drag, and tools that allow for ground-based testing. Among the tools to enable these innovations is the Rarefied Orbital Aerodynamics Research facility at the University of Manchester. Here, a description of the facility is provided together with two different methodologies for testing sub-scaled intake designs for atmosphere-breathing electric propulsion systems. The first methodology is based on measurements of the pressure difference between the two extremities of the intake, while the second uses a gas sensor to measure the collection efficiency of the intake. Direct Simulation Monte Carlo models have been used to assess the viability of the proposed testing methodologies. The results of this analysis indicate that either methodology or a combination of both can provide suitable measurements to assess the performance of future intake designs.
... Therefore, the polyimide backplane of aerospace photovoltaic modules must exhibit durable AO resistance, which requires the substrate to not react with atomic oxygen, or form a selfprotective oxide coating to make the underlying material durable to atomic oxygen and achieve a lower atomic oxygen erosion yield (E y ) [9][10][11]. While the AO erosion yield of pure POLYIMIDE-ref Kapton ® film is 3.0 × 10 −24 cm 3 /atom in space flight, which needs to be further reduced to improve service life [12]. ...
Titanium oxide (TiO2) coated polyimide has broad application prospects under extreme conditions. In order to obtain a high-quality ultra-thin TiO2 coating on polyimide by atomic layer deposition (ALD), the polyimide was activated by in-situ oxygen plasma. It was found that a large number of polar oxygen functional groups, such as carboxyl, were generated on the surface of the activated polyimide, which can significantly promote the preparation of TiO2 coating by ALD. The nucleation and growth of TiO2 were studied by XPS monitoring and SEM observation. On the polyimide activated by oxygen plasma, the size of TiO2 nuclei decreased and the quantity of TiO2 nuclei increased, resulting in the growth of a highly uniform and dense TiO2 coating. This coating exhibited excellent resistance to atomic oxygen. When exposed to 3.5 × 1021 atom/cm2 atomic oxygen flux, the erosion yield of the polyimide coated with 100 ALD cycles of TiO2 was as low as 3.0 × 10−25 cm3/atom, which is one order less than that of the standard POLYIMIDE-ref Kapton® film.
High-performance polymer (HPP) blends have made it possible to reliably replace metallic components in certain tribological applications over a broad temperature range, even in the absence of liquid lubrication. The current study examines the tribological performance of an advanced HPP aromatic thermosetting copolyester (ATSP) with those of poly-hydroxybenzoic acid polymer or Ekonol® as additives for polytetrafluoroethylene (PTFE). The tribological performance of the HPP blends was evaluated using a pin-on-disk configuration under unlubricated conditions from room temperature up to 300 °C. Compared to PTFE-Ekonol composites, PTFE-ATSP blends not only showed almost 50% reduction in the wear rate at all tested temperatures, but higher wear resistance at different sliding speeds. Temperature plays a critical role in the deposition of transfer films from the blended composite to the 440C stainless steel (440C SS) disk, where it was observed a rich fluoride transfer film when tested against PTFE-ATSP. Better tribological performance of PTFE- ATSP, compared to PTFE-Ekonol is attributed to its viscoelastic stability or higher mechanical strength in the studied temperature range, which results in lower wear rates. Tribological results point out that PTFE-ATSP blends are an attractive solution for oil-less applications in the temperature range of 25-300oC.
Flexibility and lightweight are promising research topics for space science and technology, which benefit to reduce load, reduce volume, and integrate device. However, most photoelectronic devices on spacecraft are rigid devices now, because the space environment consists of irradiations and thermal cycling, with higher requirements for flexible photoelectronic materials and devices. The main bottlenecks include: the synthesis of space-durable packaging materials, the fabrication and packaging of flexible photoelectronic devices, and the effective investigation method for irradiation mechanism analysis. In view of these problems, this review presents the synthesis of bulk-phase silicon-reinforced yellow and transparent polyimides with space durability, the optical modulation of bulk-phase silicon-reinforced polyimide to ultra-black film and flexible color filters, the electrical modulation of bulk-phase silicon-reinforced polyimide into flexible transparent electrode, the integration of the bulk-phase silicon-reinforced transparent polyimide and flexible triple-junction GaAs thin-film solar cell, and the exploration of general investigation methods for irradiation mechanism based on the penetration depth and damage modes including atomic oxygen, ultraviolet, electron, proton, and thermal cycling. The material synthesis, device fabrication, and mechanism analysis method focus on the core scientific problems of space-durable flexible lightweight photoelectronic materials and devices, leading the development direction of flexible and lightweight space science and technology.
During the last decade, silicon-containing polymers such as polysilanes and polycarbosilanes have attracted much attention because of their potential applications as ceramics precursors,1 binders for ceramics2 and for powder metallurgy,3 photoresistors4 and photoinitiators,5 and non-linear optical materials.6 The first practical use of a polysilane was in the production of β-silicon carbide by the Yajima process (Eq. 1).7
Polymers of type [-B10H12·diamine]-n have been prepared by reaction of decaborane(14) with various diamines, including H2NCH2CH2NH2, Me2NCH2CH2NMe2, HN(CH2CH2)2NH, and N(CH2CH2)3N in diethyl ether solution. The polymers, all white solids, were characterized by elemental, thermogravimetric, and thermomechanical analysis and molecular weight determinations. The synthesis and characterization of copolymers and end-capped oligomers are also described. Pyrolysis of such polymers in a stream of argon to 1000°C gave boron carbonitride in high yield. Pyrolysis in a stream of ammonia gave almost carbon-free boron nitride. Heating of these amorphous ceramics to 1500°C gave a crystalline material. The pyrolysis mechanism involves early conversion of the covalent polymer, by proton transfer from boron to nitrogen, to a nonvolatile diammonium salt of the [B10H10]2- anion. These polymers serve as low-loss binders for ceramic powders and as precursors for ceramic monoliths. Short (5 cm) fibers could be drawn from syrups of such polymers in DMF; subsequent pyrolysis gave ceramic fibers.
An optical microscope study of the stress relief forms of diamond-like carbon thin films is presented in this paper. The dimensions of the stress relief patterns are shown to be proportional to the film thickness. Three stress relief forms are distinguished. They are analysed in the framework of the linear theory of plate buckling. The forms of the stress relief correspond to two different solutions of the differential equations.
The mechanical properties of thin coatings are closely coupled with the preparation techniques used. In carbon layers deposited by electron beam and ion beam techniques high compressive stresses were measured and these stresses cause debonding of the layer. In some cases amazing structures and shapes of the debonded regions were observed: wavy wrinkles with well-defined widths and shapes. The nucleation and growth of these wrinkles is caused by a very well-defined combination of internal strain, Young's modulus, coating thickness and adhesion energy. This may be used to estimate the internal strain as well as the adhesion energy. For the i-C (where i signifies the use of an ion beam) layers 200 nm thick that were investigated internal stresses of 3–6 GPa and adhesion energies in the range of 4–7 N m−1 were estimated. These adhesion energies are more than an order of magnitude higher than those measured previously.
The mechanical properties of carbon films 500–3000 Å thick deposited onto glass substrates were investigated. The average internal stress measured by the cantilever method was 5 x 108N m−2 compression. This large stress often generates wrinkles in the films. Young's modulus of the film and the adhesion energy between the film and the substrate can be estimated from the shape and size of the wrinkles. As a method of estimation, the elastic energy of the wrinkled film is considered. The dependence of the size of the wrinkles on the film thickness is deduced and compared with experimental results.
Under basic conditions B10H12((C6H5) 2P·Cl)2 and B10H12((C6H5) 2P·OH)2 were found to enter into a condensation polymerization with elimination of hydrogen chloride to form a P-O-P linked polymer, (-OP(C6H5)2B10H12P(C 6H5)2-)x. A study of the pyrolysis of this polymer and monomeric compounds of the type B10H12((C6H5) 2P·R)2 was conducted. B10H12((C6H5) 2-N·N3)2 and diphosphines reacted in refluxing benzene with evolution of nitrogen to give P=N-P linked polymers of high thermal stability, e.g., (=P(C6H5)2-C6H4-P(C 6H5)2=N-P(C6H5) 2B10H12P(C6H5)2N=) x, dec. >340deg;.