Abstract
Polyimide or fluorine polymer that are used as heat-control materials on structures in LEO and GEO orbits, if not protected from the atomic oxygen (AO) may be severely degraded by the formation of microcracks. Carbonized materials are suitable for use in low Earth orbit (LEO) as they have excellent mechanical strength, electrical insulation, and thermal conductivity. Carbonized wood, in the form of a Japanese lacquer composed of aromatic compounds derived from the urushi tree, could potentially be used as the outer surface material of spacecraft, provided however that its resistance against AO irradiation in LEO is sufficient. The main aim of this study, therefore, is to develop the requisite technology to impart erosion resistance against AO to the carbonized wood. Specifically, increased sp2 bonding in the Si-doped diamond-like carbon introduced here is shown providing effective resistance against AO-induced erosion.
Keywords
Introduction
Highly reactive atomic oxygen (AO) is produced in the outer atmosphere of Earth by ultraviolet radiation reacting with molecular oxygen [1]. The surfaces of spacecraft in low Earth orbit (LEO; 200–700 km above the Earth) are susceptible to oxidation through ionization by ultraviolet radiation and reactions with AO. Interactions with AO and/or ultraviolet radiation lead to the rapid deterioration of the outer surface of spacecraft in LEO [2].
Polyimide or fluorine polymers that are usually employed as heat-control materials on the outer surface of spacecraft need to be protected against AO. For that reason they are coated by ceramic type of coatings. However, the protection provided by ceramic-coated polymers can be compromised by the formation of microcracks. The excellent mechanical strength, electrical insulation, and thermal conductivity provided by carbonized materials make them suitable alternatives for LEO protection [3]. Carbon materials, which are inflammable, light and robust are recognized as promising candidates for this purpose.
Previously, we carbonized organosolv lignin produced by cooking wood in l-lactic acid. We investigated its resistance to AO erosion in the presence of carbonized wood containing Si and found that aromatics in the carbonized wood played an important role in preventing damage from AO [4]. Urushi is traditionally used as paint and is extracted from the lacquer tree (Toxicodendron vernicifluum). Products coated with the lacquer are recognizable by an extremely durable and glossy finish. Our hypothesis is that carbonized urushi can also be used as an outer surface material for spacecraft.
In this study, we investigate the resistance to AO radiation of samples coated with diamond-like carbon (DLC) sputtered from a target of carbonized Urushi and Si. The erosion of the samples under AO was studied in order to identify the chemical reactions occurring between C, Si, and O in the DLC film. The DLC coat, composed of C, Si, and O was characterized by transmission electron microscopy electron energy-loss spectroscopy (TEM-EELS) and X-ray photoelectron spectroscopy (XPS) in order to reveal the mechanisms governing its resistance to erosion.
Experimental
Sample Preparation
Urushi was carbonized by heating up to 973 K at 4 K/min in a N2 atmosphere, maintaining the temperature for 1 h, and then cooling to room temperature. Carbonized urushi and Si were mixed in a glove box to a 60:40 weight ratio. The mixtures were then sintered at 1173 K and at the mechanical pressure of 40 MPa for 15 min in vacuum. Thereby, sputtering targets 30 mm in diameter and about 2 mm thick were obtained of carbonized urushi with and without Si.
A layer of DLC was deposited on a Cu microgrid by DC magnetron sputtering using the prepared targets of the carbonized urushi with or without Si, in an Ar atmosphere under 20 Pa for 5–10 min.
AO-Exposure Experiments
All the samples were exposed to an AO beam generated by exciting molecular oxygen using a CO2 laser beam (Fig. 1, wavelength: 10.6 μm; pulse energy: 5–7 J) [1]. The energy distribution of the AO beam was calculated as shown in Fig. 1. In this study, the average energy was about 5 eV and the flux was 2 × 1015 atoms/cm2. This energy is equivalent to that of the AO in LEO. Samples were placed in the system with their pressed plane perpendicular to the AO beam.
Analysis
The DLC films deposited on 200-mesh Cu microgrids with holey carbon supported films were analyzed using a TEM-EELS (JEM2100F) before and after exposure to AO. The chemical state of the carbon in the DLC is reflected in the appearance, position, and intensity of the EELS peaks in the core-loss region of the spectra. The spectra have a smooth background, modeled here using a power-low curve, which was subtracted from beneath the carbon edge. The same DLC films on Cu microgrids were also analyzed by XPS (Shimadzu/KRATOS) using MgKα radiation.
Results and Discussion
TEM-EELS
Figure 2 shows TEM images after AO irradiation of DLC films on a Cu microgrid sputtered for 5 and 10 min. While the DLC film sputtered for 5 min is damaged in part by AO exposure, the one sputtered for 10 min remains intact. Using the setup described above, a sputtering time of 10 min is therefore necessary to form a DLC film resistant to AO exposure. Figure 3a and b show core-loss EELS spectra obtained from DLC films sputtered for 5 min before and after exposure to AO, respectively. These reveal the chemical state and the concentration of the different elements in the DLC films.
The π* feature at a binding energy of 285 eV is more sharply defined in Fig. 3b, while the broader spectral feature in Fig. 3a at 290–310 eV is typical of sp2-rich amorphous carbon [5]. This increase in the π*/σ* ratio implies that AO exposure enhances sp2 bonding in the DLC films.
XPS
Figure 4 shows C1s, O1s, and Si2p XPS spectra obtained from DLC films before and after AO exposure. The atomic concentration of each element is shown in Table 1 (note that Cu and Pd come from the background). The atomic concentration of SiOxCy increases by 1.2 % after AO irradiation, whereas the atomic concentration of C–O and C=O decreases. The change in the full width at half maximum of the C1s peaks from 1.9 to 1.6 eV after AO irradiation shows that the DLC films remain relatively free of oxidation after exposure. The increase in sp2 bonding in the DLC films mentioned above for the TEM-EELS results is supported by these XPS data. The original aromatic structure in urushi may be a contributing factor.
Conclusions
DLC films obtained from carbonized urushi have been shown to successfully prevent AO-induced erosion. The formation of SiO2 and increased sp2 bonding in the DLC films are the main protecting factors. The catalytic effect of Si–O on the formation of sp2 bonds may contribute furthermore to the prevention of damage from AO irradiation.
References
Tagawa M (2001) Material degradation phenomena in low earth orbit space environment and their ground-based simulations. J Vac Soc Jpn 44(5):26–31
Yokota K, Ikeda K, Tagawa M, Okamoto A (2005) Erosion on polyimide and fluorinated polymers in combined low earth orbit space environment: simultaneous exposure effects of atomic oxygen and ultraviolet. High Temp Soc 31:318–323
Fujimoto K, Sato K, Shioya T, Seki N, Fujita K (2003) Degradation of materials by high-energy atomic oxygen. JSME Int J Ser A 46(3):283–289
Kajimoto T, Hata T, Tagawa M, Kojima H, Hayakawa H (2013) Resistance of silicon-containing carbonized lignin to atomic oxygen erosion. In: Protection of materials and structures from the space environment (Astrophysics and space science proceeding). Springer, Berlin, pp 541–546
Bruley J, Williams DB, Cuomo JJ, Pappas DP (1995) Quantitative near-edge structure analysis of diamond-like carbon in the electron microscope using a two-window method. J Microsc 180(1):22–32
Acknowledgements
This work was supported by KAKENHI (22251004), a Grant-in-Aid for Scientific Research (A) from the Japan Society for the Promotion of Science (JSPS) and a research grant for Mission Research from the Research Institute for Sustainable Humanosphere, Kyoto University.
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Kajimoto, T., Hata, T., Tagawa, M., Kojima, H., Hayakawa, H. (2017). Wood-Based, Diamond-Like Carbon for Improved Resistance Against Atomic Oxygen. In: Kleiman, J. (eds) Protection of Materials and Structures from the Space Environment. Astrophysics and Space Science Proceedings, vol 47. Springer, Cham. https://doi.org/10.1007/978-3-319-19309-0_8
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DOI: https://doi.org/10.1007/978-3-319-19309-0_8
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