Atomic Oxygen Resistance Research Articles

Phenylphosphine oxide containing polyimide matrix resins for atomic oxygen-resistant fiber-reinforced composites

Phenylethynyl-endcapped imide oligomers with different calculated molecular weights (calcd number average molecular weight ([Formula: see text])) and phosphorous (P) contents (P loading) were synthesized by the reaction of diethyl ester of 4,4′-oxydiphthalic acid, monoethyl ester of 4-phenylethynyl phthalic acid, and the P-containing diamines including [2,5-bis(4-aminophenoxy)phenyl] diphenylphosphine oxide and di(3-aminophenyl)methylphosphine oxide via in situ polymerization of monomeric reactant method. The amide–ester solutions were impregnated with carbon fiber (Cf) and quartz fiber (Qf) cloth to give high quality prepregs that were then thermally cured to yield the Cf-reinforced polyimide (PI) composite (Cf/PI) and Qf-reinforced PI composite (Qf/PI), respectively. The Cf/PI composites showed high mechanical properties with a flexural strength of 1554 ± 93 MPa, a flexural modulus of 112 ± 3 GPa and an interlayer shear strength of 90 ± 5 MPa, respectively. The atomic oxygen (AO) resistances of the neat resins and composites were evaluated on a ground-based simulation facility. Experimental results indicated that the P structures offer PIs with 55–75% lower weight losses and a self-healing property. The fiber-reinforced composites showed further lower erosion rates than neat resins. In addition, the effects of calcd [Formula: see text] and P loadings on the melt processabilities of the B-staged imide oligomers and the AO resistance of the cured PIs were systematically investigated.

Surface modification of POSS–polyimide hybrid films by atomic oxygen using ECR plasma

A novel polyimide (PI) hybrid nanocomposite containing polyhedral oligomeric silsesquioxane (POSS) had been prepared by copolymerization of trisilanolphenyl-POSS, 4,4′-oxydianiline (ODA), and pyromellitic dianhydride (PMDA). The atomic oxygen (AO) resistance of these PI/POSS hybrid films was tested in the ground-based AO simulation facility. Exposed and unexposed surfaces were characterized by SEM and XPS. The SEM images showed that the surface of the 20wt.% PI/POSS became much less rough than that of the pristine PI. Mass measurements of the samples showed that the erosion yield of the PI/POSS (20wt.%) hybrid film was 1.2×10−25cm3/atom, and reduced to 4.3% of that of the PI film. The XPS data indicated that the carbon content of the near-surface region was decreased from 66.0 to 7.0at.% after AO exposure. The ratio of oxygen and silicon concentrations in the near-surface region increased to 2.08 after AO exposure. The nanometer-sized structure of POSS, with its large surface area, had led AO-irradiated samples to form a SiO2 passivation layer, which protected the underlying polymer from further AO attack. The incorporation of POSS into the PI could dramatically improve the AO resistance of PI films in low earth orbit environment.

Use of hyperbranched polyethoxysiloxane to improve the resistance of thermoplastic polyimide coatings to atomic oxygen environment

Polyimide thin films both unmodified and modified with hyperbranched polyethoxysiloxane were treated with accelerated oxygen plasma flow to imitate a low Earth orbit environment. The resulting changes in the surface morphology were studied using scanning electron microscopy. The erosion yield values were calculated and the relative stability of the tested samples was established. It was shown that the polyimide-polyethoxysiloxane composites have higher atomic oxygen resistance owing to, presumably, the siloxane particles dispersed uniformly in the polyimide matrix. The study found that all plasma-treated samples exhibit the same fibrous, carpet-like surface morphology with some minor variations caused by differences in the chemical composition of polymers.

Evaluation of two new white silicone thermal control paints under atomic oxygen

The exterior optical surfaces of satellites are directly exposed to the harsh space environment. Thermal control paints are resistant to the conditions encountered at low earth orbit (LEO): vacuum, atomic oxygen, thermal cycling, and ultraviolet radiation. In this paper two white paints were prepared by ultrasonic dispersing method for application to space structures. The white paints include zinc-oxide-pigmented silicone elastomer SilGel 612 (U1) and a zinc-oxide-pigmented silicone elastomer RT604 (U2). These coatings are electrically non-conductive. We present the behavior of thermal control paints under atomic oxygen (AO). The effects of AO exposure were studied by the mass loss of paint specimens and complementary techniques including scanning electron microscopy (SEM) and atomic force microscopy (AFM). Also the optical degradation in the reflectance spectra, solar absorptance and thermal emittance for U1 and U2 samples before and after AO exposure were investigated. The paints have promising AO resistance properties that could be suitable for space applications.

Structural and Tribological Properties of Polytetrafluoroethylene Composites Filled with Glass Fiber and Al2O3 in Atomic Oxygen Environment

Effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of polytetrafluoroethylene (PTFE) composites filled with both glass fibers and Al2O3 were investigated in a ground-based simulation facility, in which the average energy of AO was about 5 eV and the flux was 5.0 × 1015/cm2 s. It was found that AO irradiation first induced the degradation of PTFE molecular chains on the sample surface, and then resulted in a change of surface morphology. The addition of Al2O3 filler significantly increased the AO resistance property of PTFE composites. Friction and wear tests indicated that AO irradiation affected the wear rate and increased the friction coefficient of specimens. The PTFE composite containing 10% Al2O3 exhibit the best AO resistance and lower wear rate after long time AO irradiation.

Structural and tribological properties of polytetrafluoroethylene composites in atomic oxygen environment

Effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of glass fiber (GF) and MoS2 filled polytetrafluoroethylene (PTFE) composites were investigated in a ground‐based simulation facility, in which the average energy of AO was about 5 eV and the flux was 5.0 × 1015 cm–2 s–1. The structural changes were characterized by XPS and attenuated total‐reflection Fourier transform infrared spectroscopy, and the tribological changes were evaluated by friction and wear tests and SEM analysis of the worn surfaces. It was found that AO irradiation induced the degradation of PTFE molecular chains, and the primary erosion mechanism is collisionally induced rather than chemically induced. The addition of MoS2 filler significantly increased the AO resistance of PTFE composites. Friction and wear tests indicated that GF and MoS2 improved the tribological properties of materials before and after AO irradiation. Short GF and MoS2 exhibited a good synergistic effect for improving the AO resistant and tribological properties of PTFE material. Copyright © 2012 John Wiley & Sons, Ltd.

Atomic oxygen erosion resistance of titania–polyimide hybrid films derived from titanium tetrabutoxide and polyamic acid

AbstractA series of polyimide/titania (PI/TiO2) hybrid films have been successfully synthesized based on titanium tetrabutoxide (Ti(OEt)4), 3,3′,4,4′‐bezonphenone tetracarboxylic dianhydride (BTDA), 4,4′‐oxydianiline (ODA), and 1,3‐bis(aminopropyl) tetramethyldisiloxane (APrTMOS) by a sol–gel process. The atomic oxygen (AO) exposure tests were carried out using a ground‐based AO effects simulation facility. The chemical structure of PI/TiO2 films was characterized by Fourier transform‐infrared (FT‐IR) spectroscope before and after AO exposure. The glass transition temperature (Tg) and mechanical properties were examined by dynamic mechanical analysis (DMA) and universal mechanical testing machine, respectively. The tensile strength and elongation of the hybrid film decreased with the increase of TiO2 content, whereas the Tg increased with the increase of TiO2 content. The effects of TiO2 content on the morphology and structure evolvement of PI/TiO2 hybrid films were also investigated using field emission scanning electron microscopy (FE‐SEM) and X‐ray photoelectron spectroscope (XPS), respectively. The results indicated that a TiO2‐rich layer resulting from the Ti(OEt)4 formed on the PI film after AO exposure, which decreased the mass loss rate and obviously improved the AO resistance of PI films. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Effects of Atomic Oxygen Irradiation on PDMS/POSS Hybrid Films in Low Earth Orbit Environment

In order to improve the atomic oxygen (AO) erosion resistance of polyimide films in low earth orbit space environment, a type PDMS/POSS hybrid coating on polyimide substrate was prepared based on a silanol terminated polydimethylsiloxane (PDMS-OH) and Octakis(trimethylsiloxy)octaprismosilsesquioxane (Q8[Si(CH3)3]8) by copolymerizing process in DMAc solution. The atomic oxygen exposure tests were carried out using a ground-based atomic oxygen simulation facility. The mass loss, surface morphology and surface chemical compositions of PDMS/POSS hybrid films before and after exposure to incremental AO flux were investigated by using microbalance and field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS), respectively. The data indicated that a silica-rich layer was formed on the surface of the hybrid coating when the coating is exposed to AO flux, which could provide a protective barrier on the surface preventing further degradation of the polymer during extended exposure to AO and obviously improved the AO resistance of polyimide films.

Atomic oxygen erosion resistance of polyimide/ZrO 2 hybrid films

A series of polyimide/zirconia (PI/ZrO 2) hybrid films were synthesized based on zirconium n-butoxide, pyromellitic acid dianhydride (PMDA) and 4,4′-oxydianiline (ODA) by a sol–gel process. The atomic oxygen (AO) exposure tests were carried out using a ground-based atomic oxygen effects simulation facility. The effects of ZrO 2 content on the morphology and structure evolvement of PI/ZrO 2 hybrid films were investigated using field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectrometer (XPS), respectively. The results indicated that a zirconia-rich layer was formed on the polyimide film sourcing from the zirconium n-butoxide after AO exposure, which decreased the erosion rate and obviously improved the AO resistance of polyimide films.

A polysilazane coating protecting polyimide from atomic oxygen and vacuum ultraviolet radiation erosion

A polysilazane coating was prepared on polyimide substrate by the polymeric precursor method to protect space materials from attack of atomic oxygen (AO) and vacuum ultraviolet radiation (VUV) in low earth orbit (LEO) environment. Erosion kinetics, surface morphologies, and surface composition investigation indicate that this polysilazane coating possesses excellent AO resistance, and displays low shrinkage tendency in AO exposure. The erosion yield of the prepared polysilazane coating is 3.5 × and 2.1 × 10 − 26 cm 3/atom during AO exposure and simultaneous AO and VUV exposure, respectively. The low AO erosion yield of the polysilazane coating results from the formation of a SiO 2-rich layer on its top surface during exposure, and the VUV radiation is able to create free radical sites on the exposed surface, promoting the formation of a uniform SiO 2-rich surface layer.

Pendent Polyimides using Mellitic Acid Dianhydride. IV. Effect of Increased Zirconium-Pendent Group Content on Polymer Properties

For co-polyimides (PIs) of mellitic acid dianhydride, 1,3-aminophenoxybenzene and 4,4′-oxydiphthalic anhydride, Zr-pendent group content could be increased to 50% (mol) improving atomic oxygen (AO) resistance while retaining good film properties. Spectral data are consistent with expected structures. Intrinsic viscosities of 0.54—0.60 dL g—1 and average molecular weights of 111 000—122 000 g mol— 1 estimated from gel permeation chromatography confirm the polymeric nature of co-polyamic acid precursors. Nuclear magnetic resonance integrations and amounts of thermogravimetric analysis residue verify pendent group concentrations. Increasing Zr-pendent group concentration from 10 to 50% (mol) caused glass transition temperatures to increase (198—245 °C), decomposition temperatures to decrease (518—455 °C), and the number of film layers able to be fabricated prior to crack formation to decrease (10 to 8). These numbers of layers were much higher than those for other PIs with comparable Zr-pendent group concentrations. Increased pendent group concentration caused the amount of protective oxide layer formed upon AO exposure to increase.

Polydimethylsiloxane/silica hybrid coatings protecting Kapton from atomic oxygen attack

In order to improve the erosion resistance of spacecraft materials in atomic oxygen (AO) environments, a kind of polydimethylsiloxane (PDMS)/SiO(2) hybrid coatings has been prepared on Kapton by a sol-gel process. The tetraethoxysilane (TEOS) and silanol-terminated PDMS were used as two main precursors. The content of inorganic silica in the PDMS/SiO(2) hybrid coatings varied, achieving a maximum value of 40 wt% under the addition of a coupling agent. The PDMS/SiO(2) hybrid coatings possessed good adhesion and flexibility, improved thermal stability. The AO resistance of the hybrid coatings was investigated by exposure tests in the AO simulator. The results showed that the hybrid coatings had excellent AO resistance. The PDMS/SiO(2) (20 wt%) hybrid coating had an erosion rate two orders of magnitude slower than the polyimide film, and did not crack during AO exposure. The coating performance was also found to improve with increasing SiO(2) content. (C) 2008 Elsevier B.V. All rights reserved.

Investigation on sol–gel boehmite-AlOOH films on Kapton and their erosion resistance to atomic oxygen

To improve the atomic oxygen (AO) erosion resistance of Kapton, boehmite-AlOOH films were deposited on it by sol–gel method and AO exposure experiments were performed in a ground-based AO simulator. The results indicate that the AlOOH-coated samples show an improved AO resistance and their erosion yield is one order of magnitude less than that of pristine Kapton. Furthermore, the AlOOH-coated Kapton remained optically stable under AO exposure. The AlOOH film structure before and after AO exposure was analyzed by scanning electronic microscope, atomic force microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. It was found that after AO exposure, the film structure tends to transfer from an octahedral coordination for AlOOH to an octahedral and tetrahedral mixed-coordination for γ-Al 2O 3. This implies that a more stable γ-Al 2O 3 structure could be formed in AlOOH film during AO exposure. The AO erosion mechanism of the coated Kapton was discussed.

An investigation on the atomic oxygen erosion resistance of surface sol–gel silica films

Ultrathin silica films were deposited on Kapton substrate by surface sol–gel (SSG) method and their atomic oxygen (AO) erosion resistance was tested in a ground-based AO simulator. The surface morphology and structure of silica films were investigated by atomic force microscopy, scanning electronic microscope, Fourier transformed infrared spectroscopy, and X-ray photoelectron spectroscopy. The results indicate that the silica films grow on Kapton substrate in an island-like manner. As the depositing cycle increases, silica films tend to become dense and smooth. The film structure is found to be not an exact equilibrium SiO 2 structure. Under AO environment, the AO erosion resistance of silica-modified Kapton is improved and enhances as the depositing cycle increases. It is noted that the silica-modified Kapton with 10 cycles shows the best AO resistance and its erosion yield is two orders of magnitude less than that of pristine Katpon. The AO erosion mechanism of silica films is analyzed in the paper.

An experimental study on improving the atomic oxygen resistance of epoxy resin/silica nanocomposites

AbstractTo improve the atomic oxygen (AO) resistance of the spacecraft resin matrix material, inorganic silica nanoparticles were filled into the epoxy resin. Samples of the epoxy/silica nanocomposites were prepared and AO exposure experiments were conducted in a ground‐based AO effects simulation facility. The samples exhibited significantly less mass loss and erosion yield than the corresponding pristine epoxy resin. Analysis of the surface morphology, composition and chemical structures showed that some organic structures still resides on the nanocomposites surface after the AO exposure experiment. The silica nanoparticles and the organic structures could serve as a barrier to resist further erosion. POLYM. ENG. SCI., 47:1156–1162, 2007. © 2007 Society of Plastics Engineers

Pendent polyimides using mellitic acid dianhydride. II. Structure–property relationships for zirconium‐containing pendent polymers

AbstractUsing mellitic acid dianhydride to prepare Zr‐containing pendent copolyimides (co‐PIs) is currently being evaluated as a means of further increasing Zr concentration and atomic oxygen resistance while retaining other desirable film properties. The immediate objectives en route to this ultimate goal are: (1) to address the increased tendency of copolyamic acids (co‐PAAs) to undergo gelation during polymerizations and upon addition of dicyclohexylcarbodiimide during the Zr appending reactions, and (2) for multilayer films, to increase the number of layers that can be applied prior to crack formation. To accomplish these two objectives, a targeted structure–property study has been performed, holding the Zr concentration constant at 10 mol %. The polymer starting materials chosen for this investigation include PMDA and OPDA (dianhydrides), and 4,4′‐ODA, 3,4′‐ODA, and 1,3‐APB (diamines). The spectroscopic data for all polymer products are consistent with the expected amic acid, imide, pendent, and nonpendent structures. Thin‐layer chromatography, viscosity, and gel permeation chromatography (GPC) results confirm the polymeric nature of the Zr pendent and nonpendent co‐PAA precursors, with intrinsic viscosities (η0) of 0.86–0.46 for the former and 0.76–0.38 for the latter. Weight‐average molecular weights are estimated from GPC to be 115,400–436,000 g/mol for the former and 38,300–111,200 g/mol for the latter. While there was little observable effect of structure change on tendency to form gel, APB‐containing Zr pendent copolyimide had the lowest glass transition temperature and allowed the largest number of layers to be cast in a single film without cracking (10 layers) of the pendent copolyimides in this study. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1641–1652, 2007

Pendent Polyimides using Mellitic Acid Dianhydride. I. An Atomic Oxygen-resistant, Pendent 4,4′-ODA/PMDA/MADA Co-polyimide Containing Zirconium

The goal of this research is to increase the metal-organic concentration in Kapton-like polyimides (PIs) to achieve increased atomic oxygen (AO) resistance while retaining desirable film properties. Co-polyamic acid (PAA) precursors were prepared using a novel polymer building block, mellitic acid dianhydride (MADA), to provide sites for pendent group attachment. Attachment of an amino group-functionalized zirconium complex to the co-PAA precursors was facilitated by a stoichiometric amount of dicyclohexylcarbodiimide. The viscous solutions which resulted were characterized by thin layer chromatography (TLC), viscosity, and gel permeation chromatography (GPC), or treated with excess poor solvent to precipitate powder samples, or cast onto glass slides and heated to produce imidized films. Powder samples were dissolved in deuterated solvent for proton nuclear magnetic resonance analysis, or characterized by thermogravimetric analysis and differential scanning calorimetry. Film samples were characterized by Fourier transform infrared and by scanning electron microscopy (SEM) before and after exposure to atomic oxygen in a plasma asher. The spectroscopic data are consistent with the expected amic acid and imide, pendent and non-pendent structures. TLC, viscosity and GPC results confirm the polymeric nature of the pendent and non-pendent co-PAA precursors, with inherent viscosities (<0)of 0.76 and 0.65 and weight average molecular weights (Mw) estimated to be 61 000 and 138 000 Dalton, respectively. As expected, visual and SEM inspections of pendent and non-pendent co-PI films reveal extensive surface roughening upon exposure to AO, with the former developing a white surface layer known from model compound studies to be predominantly zirconium dioxide. Additional reports describing the effects of polymer structure and pendent group concentration on film properties and AO resistance are in preparation.

Effect of ion implantation upon erosion resistance of polyimide films in space environment

The atomic oxygen (AO) resistance of Si ion implanted polyimide films in the ground-based AO simulation facility was investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The results show that at the initial stage of AO exposure the implanted sample has a small mass change, and then is stabilized. The erosion yield of the implanted polyimide film decreases by about two orders of magnitude compared with that of the polyimide film. The analysis through XPS and AES indicates that a continuous high-quality protective oxide-based (SiO 2) surface layer is formed on the implanted polyimide films after the AO exposure. It can provide high-quality erosion protection for these materials. The implanted polyimide fully restores its original color and the carbonization effect disappears on the whole after AO exposure. Thermal-optical properties and surface morphology of the implanted polyimide materials are not altered. The modified materials have a markedly increased erosion resistance in AO environment.

Thermal Optical Properties of Plasma-Sprayed Mullite Coatings for Space Launch Vehicles

Thermal optical properties, for example, solar absorptance a and thermal emittance e of thin plasma sprayed mullite coatings, were determined to assess the material's suitability for space application. The mullite coatings were developed in an attempt to find a new material for thermal protection systems as well as thermal barrier coatings for atmospheric reentry vehicles. All mullite coatings show the properties of a solar reflector and hence suggest a potential application as thermal control coating to protect space-bound structures from the effect of heating by solar radiation in the low Earth orbit. Preliminary space stability tests including atomic-oxygen resistance tests confirmed that the coatings show only negligible variations both in their mechanical and thermal optical properties under the conditions selected.

Resistance of polyimide/silica hybrid films to atomic oxygen attack

Polyimide/silica (PI/SiO 2) hybrid films were prepared by the sol–gel process to improve the erosion resistance of polyimide materials in atomic oxygen (AO) environments. The p-aminophenyltrimethoxysilane (APTMOS) was used as a coupling agent to enhance the compatibility between the PI and SiO 2. The effects of the APTMOS addition on the morphology and property of the PI/SiO 2 hybrids were investigated using UV–Vis spectrophotometer, FTIR spectroscopy and SEM. The thermal properties and AO resistance of the PI/SiO 2 hybrids were investigated by TGA and in the AO simulator, respectively. The results showed that the addition of APTMOS remarkably reduced the size of the silica particles, the PI/SiO 2 hybrid films became transparent, and the compatibility between the PI and SiO 2 and the thermal stability of the hybrids were significantly improved. During AO exposure, a passive inorganic SiO 2 layer was formed on the PI/SiO 2 hybrid films, causing the hybrid films to possess excellent AO resistance. The optical properties of the PI/SiO 2 hybrid films were not altered after AO exposure.