Effects Of Atomic Oxygen Research Articles

Atomic oxygen effects on silvered polyimide films and their surface modification by poly(siloxane amic acid) ammonium salts.

The tolerance of silvered polyimide films synthesized by an in situ self-metalization method against atomic oxygen (AO) was evaluated. The results showed that the mass loss of R–Ag/PI was markedly increased as the AO fluence increased; Ag/PI showed an identical trend. SEM data showed that the silver particles on the surfaces of R–Ag/PI and Ag/PI disappeared. The surfaces achieved a “carpet condition” that was more obvious as the AO fluence increased. Poly(siloxane amic acid) ammonium salt was synthesized and made via imidization to produce a flexible organic coating that was characterized by ATR-FTIR, 1HNMR, TGA, and XPS. This could be used to improve the tolerance of silvered polyimide films against AO. The AO resistance and the impacts on mass loss, surface morphology, and surface compositions were also evaluated after surface modification by poly(siloxane amic acid) ammonium salts. 20 wt% Foc/Ag/PI had a lower mass loss and smoother surface than the others due to the formation of a compact surface-SiO2-type layer. This flexible organic coating can be produced via an environmentally-friendly method, and it maintains the inherent thermal stability of the polyimide which cannot be achieved by other anti-AO coatings.

Impact of oxygen chemistry on model interstellar grain surfaces.

Temperature-programmed desorption (TPD) and reflection-absorption infrared spectroscopy (RAIRS) are used to probe the effect of atomic and molecular oxygen (O and O2) beams on amorphous silica (aSiO2) and water (H2O) surfaces (porous-amorphous solid water; p-ASW, compact amorphous solid water; c-ASW, and crystalline solid water; CSW). Altering the deposition method of O2 is shown to result in different desorption energies of O2 due to differences in O2 film morphology when deposited on the aSiO2 surface. O2 enthalpy of formation is dissipated into the aSiO2 substrate without changes in the silica network. However, on the H2O surfaces, O2 formation enthalpy release is dissipated into the H-bonded matrix leading to morphological changes, possibly compacting p-ASW into c-ASW while CSW appears to undergo amorphisation. The enthalpy release from O2 formation is, however, not enough to result in reactive desorption of O2 or H2O under the current experimental circumstances. Further to this, O2 formation on sub-monolayer quantities of H2O leads to enhanced de-wetting and a greater degree of H-bond reconnection in H2O agglomerates. Lastly, O3 is observed from the O + O2 reaction on all surfaces studied.

空间原子氧对保偏反射镜偏振对比度的影响

空间原子氧对保偏反射镜偏振对比度的影响

Analysis of atomic oxygen and ultraviolet exposure effects on cycloaliphatic epoxy resins reinforced with octa-functional POSS

In this study, novel nanocomposites were created by incorporation of Silsesquioxane containing eight glycidylether groups (octa-POSS) into a cycloaliphatic epoxy cured by an anhydride. The developed resin system, with different nanoparticle concentrations, was used on the outer layers of an ultra-thin CFRP structure in order to provide better environmental resistance to the environment of low Earth orbit (LEO) which was tested in a ground-simulation facility. The developed resins were subjected to space-like degrading factors and their response to corrosion, radiation and elevated temperatures was monitored by mass loss, together with measuring changes in surface chemistry (ATR-FTIR), functionality development (contact angle measurement and XPS), roughness (scanning laser microscopy) and morphology (SEM). The influence of increasing octa-POSS content on thermo-mechanical properties was measured with DMTA and the strength and modulus of elasticity were determined by flexural test. The addition of octa-POSS in any loading improves the environmental resistance, however, the most significant retention of mass and mechanical and surface properties after space-like exposure was observed in the 20 wt% octa-POSS reinforced cycloaliphatic epoxy. The results presented here may contribute to the development of novel class of nanocomposites which can offer an extended service life in LEO.

Effects of atomic oxygen on epoxy-based shape memory polymer in low earth orbit

Atomic oxygen is a dominant component of the low earth orbit and can erode most spacecraft polymeric material. In this article, the atomic oxygen erosion resistance tests of an epoxy-based shape memory polymer are carried out in a ground-based atomic oxygen simulator with a vacuum space chamber. The samples, before and after the atomic oxygen exposure, are compared in appearance, surface morphology, mass, main component, dynamical and static mechanical properties, and shape memory properties. The atomic oxygen exposure causes oxidization reaction of the material, which leads to surface roughen and mass loss, while the shape memory polymer main components remain same. The results of dynamical and static mechanical tests indicate that the atomic oxygen exposure has little effect on the storage modulus and glassy transition temperature (Tg), whereas the elongation, elastic modulus, tensile strength, and yield strength decrease since the atomic oxygen exposure gives rise to tiny cracks. The shape memory property has rarely changed since the atomic oxygen erosion is mainly located near the surface of the sample.

The influence of diamond blend on the resistance of polyimide films to atomic oxygen

Poly-pyromellitimide and polyamideimide film samples and their modifications obtained with a carbon filler (diamond blend) were irradiated with atomic oxygen flow at an average particle energy of 20 eV. Weight erosion coefficients were calculated for the initial and modified polyimides and a comparative analysis of the resistance of the film samples was carried out. The morphology of the film surface was studied after irradiation with atomic oxygen via scanning electron microscopy. An increase in the percentage of filler in the polymer matrix caused a slight increase in the resistance of the film samples to the effect of atomic oxygen.

Silicon solar cell performance deposited by diamond like carbon thin film “Atomic oxygen effects”

In this research, a diamond-like carbon thin film was deposited on p-type polycrystalline silicon solar cell via plasma-enhanced chemical vapor deposition method by using methane and hydrogen gases. The effect of atomic oxygen on the functioning of silicon coated DLC thin film and silicon was investigated. Raman spectroscopy, field emission scanning electron microscopy, atomic force microscopy and attenuated total reflection–Fourier transform infrared spectroscopy were used to characterize the structure and morphology of the DLC thin film. Photocurrent–voltage characteristics of the silicon solar cell were carried out using a solar simulator. The results showed that atomic oxygen exposure induced the including oxidation, structural changes, cross-linking reactions and bond breaking of the DLC film; thus reducing the optical properties. The photocurrent–voltage characteristics showed that although the properties of the fabricated thin film were decreased after being exposed to destructive rays, when compared with solar cell without any coating, it could protect it in atomic oxygen condition enhancing solar cell efficiency up to 12%. Thus, it can be said that diamond-like carbon thin layer protect the solar cell against atomic oxygen exposure.

CVD nano-coating of carbon composites for space materials atomic oxygen shielding

Abstract: The present work analyzes the possibility to employ carbon nanostructures as a basic material to prevent the erosion effects of atomic oxygen suffered by the carbon fiber reinforced polymeric material used in low earth orbit space environment. The application of thin protecting coatings to base materials is a widely used method for preventing the atomic oxygen induced erosion, and thus degradation. The generic purpose is to integrate carbon nanostructures onto carbon composites surface in order to develop the basic substrate of advanced nanocomposite for atomic oxygen protection. The final goal is the characterization of carbon nanostructures-reinforced carbon composites by means of on-ground atomic oxygen simulation facility, with the future objective to assess and optimize the process of carbon-multiscale advanced composites production. With such an aim, a wide investigation on the methane chemical vapor deposition (CVD) over catalyzed carbon fiber-based substrates has been carried out. The as grown nanostructures have been analyzed in terms of morphology, as well as regarding the main features of the resulting growth (yield, purity, homogeneity, coating uniformity, etc.) and the influence of the deposition route operating parameters (catalyst typology, gas flowing rate, growth time/temperature, etc.). A high degree of reproducibility in terms of the relationship between the carbon deposit type/yield and the main process variables (catalyst and protocol) has been thus obtained. Finally, atomic oxygen ground tests have been conducted in order to evaluate the coating process effectiveness. The on-ground test in atomic oxygen environment, with respect to the performances of the reference carbon composites (in terms of total mass loss and atomic oxygen rate of erosion), showed a worsening for the disordered carbon deposit, while an intriguing improvement was achieved by the high-yield carbon nano-filaments deposition.

Characterization of carbon nanotube yarn after exposure to hyperthermal atomic oxygen and thermal fatigue

Carbon nanotube (CNT)-yarn was evaluated for the survivability under hazardous space environmental conditions which were thermal fatigue, atomic oxygen and additive effect of these two exposures. Its tensile strength, tenacity, stiffness, strain to failure and electrical conductivity were characterized at the two extreme space temperatures of −150 and 120°C before and after exposure to these environmental conditions. Tensile strength, stiffness and electrical conductivity of unexposed CNT yarn increased at the cryogenic temperature relative to at the elevated temperature. There was no change in the tensile properties after exposure to the space environmental conditions when measured at the elevated and cryogenic temperatures. Electrical conductivity decreased after exposure to three hazardous environments involving thermal fatigue, but it had no or small decrease when exposed to atomic oxygen only. No additive effect of thermal fatigue followed by atomic oxygen or by atomic oxygen followed by thermal fatigue environments on the CNTs’ tensile properties and electrical conductivity was observed. Considering the low density 0.59g/cc and good resistant to the extreme hazardous space environment, CNT-yarns have potential for applications in spacecraft and satellites.

Effect of atomic oxygen irradiation on the structural and tribological characteristics of polytetrafluoroethylene and its composites

Based on the ground-based simulation facility, the effects of atomic oxygen (AO) irradiation on the structural and tribological properties of pure polytetrafluoroethylene (PTFE) and carbon fiber and MoS2-filled PTFE composites were studied by scanning electron microscopy, X-ray photoelectron spectroscopy, and a ball-on-disc tribometer. The results shown that AO irradiation had significant effects on the structural and tribological properties of pure PTFE, in which the surface morphologies, mass loss, friction coefficient, and wear rate had been changed greatly after AO irradiation. However, it was noticeable that the addition of carbon fiber and MoS2 filler to PTFE could improve the AO resist capacity and tribological properties of PTFE composites significantly. Copyright © 2016 John Wiley & Sons, Ltd.

The effect of vacuum atomic oxygen and ultraviolet radiations on Ag/a-C:H nanocomposite film

Ag/a-C:H nanocomposite film with nanosized Ag particles (about 2–5nm) embedded in a-C:H matrix is deposited by the medium frequency unbalanced magnetron sputtering. The effects of vacuum atomic oxygen and ultraviolet radiations on the composition, microstructure, morphology and vacuum tribological properties of the Ag/a-C:H nanocomposite film have been investigated. Results show that the radiations can induce the oxidation and decomposition of carbon matrix, which lead the high Ag content nearby surface, the increased sp2 carbon content, as well as the reconstruction of microstructure. As a result, the diffusion rate of Ag atoms increases while the connectivity and rigid of the carbon network decrease. The composite film exhibits low friction and high wear performance after radiations.

The effects of low earth orbit atomic oxygen on the properties of Polytetrafluoroethylene

Polymers are widely used in space systems as the structural materials. The low earth orbit (LEO) space environment includes hazards such as atomic oxygen. Exposure of polymeric materials to atomic oxygen results in destructive effects on the chemical, electrical, thermal, optical and mechanical properties as well as surface degradation. In the present work, the effects of atomic oxygen on the mechanical, thermal, and optical properties of Polytetrafluoroethylene film have been investigated. The atomic oxygen density was calculated by SPENVIS tool. After the atomic oxygen exposure by using radio-frequency (RF) plasma source, the appearance of the samples changed, and the mass of the samples reduced because of outgassing. The results of thermal analysis showed that atomic oxygen flux does not affect thermal degradation of samples regarding TGA diagrams. By increasing the atomic oxygen flux, the amount of absorbance increased showing that atomic oxygen had damaged the surface of Polytetrafluoroethylene, and it had oxidized the surface of the polymer.

Selective production of atomic oxygen by laser photolysis as a tool for studying the effect of atomic oxygen in plasma medicine

We propose a method for selectively producing O atoms by the laser photolysis of O as a tool for studying the therapeutic effect of O atoms in plasma medicine. A KrF excimer laser (248 nm) irradiates an O/He mixture flowing in a quartz tube to photodissociate O, which leads to the production of O atoms. The effluent from the quartz tube nozzle can be applied to a target (cells, bacteria, or an affected part). Simulations show that 500 ppm O atoms can be continuously supplied to a target surface at a distance of 3 mm from the quartz tube nozzle if an O(2000 ppm)/He mixture is used. The effluent contains only O, O, and O, and does not contain other types of reactive species in contrast to a plasma. Therefore, it can be used to examine the therapeutic effects of O atoms in isolation. Part of the simulation results are experimentally verified by irradiating an O/He mixture with a KrF excimer laser.

Tribological Performance and Lubrication Mechanism of Solid–Liquid Lubricating Materials in High-Vacuum and Irradiation Environments

In this paper, six solid–liquid lubricating materials have been prepared based on two kinds of liquid lubricants including perfluoropolyethers oil (PFPE) and chlorinated-phenyl and methyl-terminated silicone oil (CPSO) and three different solid lubrication materials [polyimide (PI), polytetrafluoroethylene and Cu-based alloy] by the dip-coating method. The tribological behaviors of these lubricating materials were comparatively investigated in high-vacuum condition. The results showed that the polymer-based solid–liquid lubricating materials exhibited the excellent tribological properties, which mainly attributed to the hydrodynamic lubrication. Moreover, as for the same solid substrate, the smaller the value of the steady-state contact angle was, the higher the friction coefficient was. Meanwhile, the effect of atomic oxygen (AO) and proton (H+) irradiations on structure and tribological properties of the PI/CPSO and PI/PFPE was further investigated in this work. The experimental results indicated that irradiations induced the degradation of the lubricating oil, which resulted in the increment of the friction coefficient and wear rate, thus decreasing the lubricating performance. In addition, the effect induced by H+ irradiation was more serious than that by AO irradiation. PI/CPSO solid–liquid lubricating material has good irradiation stability compared with PI/PFPE.

Ultraviolet or Atomic Oxygen Effects on Tribological Properties of the Carbon Fibers/Polyimide Composites

Carbon fibers-reinforced polyimide composites (CF-PI) were fabricated by means of a hot press molding technique. To contrast the effects of ultraviolet and atomic oxygen irradiation under high vacuum on the tribological properties of CF-PI composites, the friction and wear properties of the composites sliding against GCr15 steel ball before and after irradiation were conducted in high vacuum on a ball-on-disk test rig. The experimental results revealed that CF-PI composites exhibited higher modulus and lower coefficient of friction and worn rate value than pure polyimide under high vacuum. However, the coefficient of friction of composites increased and the worn rate value decreased after ultraviolet or atomic oxygen irradiation, which slightly affected the tribological properties of CF-PI composites. The chemical composition of the composites changed after irradiation was inspected by X-ray photoelectron spectroscopy. Microstructure of the worn surfaces of the tested composites was investigated by scanning electron microscopy to reveal the wear mechanism.

Densification of High Thickness C/C Composites by Chemical Vapor Infiltration

In the last decades the research on composite materials have been acquiring importance due to the possibility of increasing the material mechanical performances while contemporary decreasing both mass and volume of the structures. Composites are widely used in space vehicles and systems as structural materials, thermal blankets, thermal control and conformal coatings, adhesives, lubricants, etc. Exposure of composites to the space environment may result in different detrimental effects via modification of their chemical, electrical, thermal, optical and mechanical properties as well as surface erosion. The major degradation effects in composites are due to the exposure to atomic oxygen, vacuum ultraviolet, thermal cycling and combined effects during orbit period and plasma during re-entry phase. Among all, carbon-based ceramic composites are the most promising materials for space applications, due to their impressive thermal stability and lightweight. Carbon-Carbon (C/C) composites have already shown their extraordinary features in terms of high stability and excellent mechanical properties, almost unchanged at high temperatures. C/C is used also in engine applications such as nozzle throat section for launchers. The main feature for this application is the high resistance at high temperatures. In these applications high thickness composites are required, but one of the main criticalities is the uniformity of material and its final characteristics. Up to now, there's no standard for the manufacturing of high thickness C/C structures. In this paper a manufacturing method based on the chemical vapor infiltration (CVI) process is described, following each phase of the process from the preform preparation to the infiltration, and providing a detailedanalysis of the material densification.

Determination of active species in the modification of hardwood samples in the flowing afterglow of N2 dielectric barrier discharges open to ambient air

Sugar maple (Acer saccharum, Mill.) wood samples were exposed to the flowing afterglow of a N2 dielectric barrier discharge (DBD) open to ambient air. Freshly-sanded wood surfaces were hydrophilized by the treatment. The dynamic behaviour of water droplets on hardwood samples further reveals a volumetric effect of treatment as well as a modification of the topmost surface. Analysis of the discharge properties by optical emission spectroscopy (OES) indicates that the neutral gas temperature (determined from the rovibrational spectrum of N2) was close to room temperature, thus ruling out wood modification due to heat transfer. OES spectra combined with a collisional-radiative model also reveals significant concentration of metastable N2(A) states and UV photons (in particular those from the NOγ system in the 200–300 nm range) in the discharge. To better examine the role of UV irradiation, wood samples were exposed to the late afterglow of a low-pressure N2/O2 plasma optimized for UV emission from the NO systems. Wood hydrophilization was observed only for samples directly exposed to the late afterglow and not for those contained in a UV-transparent enclosure. Wood hydrophilization in the DBD is thus not directly related to UV irradiation; these energetic photons rather participate [along with N2(A) metastables] in the formation of other active species, in particular atomic oxygen and ozone due to the open-air configuration. The role of ozone was confirmed by treatments in an ozone generator, showing dynamic wettability comparable to the ones achieved after treatment in the flowing afterglows of the atmospheric-pressure N2 DBD and low-pressure N2–O2 plasma. FTIR spectra of wood samples treated in the three systems (DBD, N2–O2 plasma, and ozone generator) indicate an increased lignin content due to the possible development of lignin precipitates, corroborating the effect of atomic oxygen and ozone.

Structural and Tribological Properties of MoS<sub>2</sub>/Polyimide Composites Exposed to Atomic Oxygen Environment

Effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of MoS2filled polyimide (PI) composites were studied by using ball-on-disc tribometer, infrared spectra, X-ray photoelectron spectroscopy and scanning electron microscopy. It was found that the irradiation of AO induced the destruction of polymer molecular structures and formation of volatile products which induced the change of the structure, morphology and tribological properties of samples. The addition of MoS2filler significantly increased the AO resistance of PI composites due to the formation of MoO3-rich skin layers during AO process. The addition of MoS2improved the tribological properties of PI before and after AO irradiation.

Effects of oxygen partial pressure and atomic oxygen on the microstructure of oxide scale of ZrB2–SiC composites at 1500 °C

The oxidation behaviour of ZrB2-20vol.% SiC composites was investigated based on the microstructural evolution of oxide scale under different oxygen partial pressures at 1500°C, and the similar experiment was performed in atomic oxygen for comparison. The thickness of the oxide scale increases first and then gradually decreases as the pressure decreases, which is strongly dependent on both total pressure and oxygen partial pressure. The atomic oxygen significantly enhances the oxidation of ZrB2–SiC composites, but has little effect on the microstructure of oxide scale. The oxidation mechanism of ZrB2–SiC composites is also discussed in detail.

Chemical composition dependence of atomic oxygen erosion resistance in Cu-rich bulk metallic glasses

The effect of atomic oxygen (AO) on the surface oxidation of several typical Cu-based bulk metallic glasses (BMGs) was studied in the present work. The AO source using in this study is generated by discharge plasma type ground simulation equipment. The AO erosion/oxidation resistances of the amorphous alloy samples were assessed based on the analysis of mass loss, surface color and microstructure. It is found that these Cu-based BMGs possess good AO erosion/oxidation resistance and their resistance to AO erosion/oxidation strongly depends on the chemical composition. For the samples containing more Ag and/or Cu, the AO erosion/oxidation resistance is weaker. The present result is important for designing new metallic glasses using as space materials.