• Journal of Aerospace System Engineering
• /
• v.11 no.5
• /
• pp.1-5
• /
• 2017

This objective of this study is an effort to predict atomic oxygen (ATOX) erosion as ot affects coating material(s) of LEO satellite's solar array by implementing the 'real ram direction accumulation method'. We observed the difference of ATOX Fluence between the previous 'Maximum worst case estimation method' and 'Real ram direction accumulation method' and we plan to implement these findings for the purpose of evaluating the level of compliance for design submitted by solar array suppliers. We used the SPENVIS(Space Environment Information System) served by ESA based on assumption orbit information, and applied the satellite orbit calculation software for calculating the ATOX Flux crushed solar array in real orbit surface.

• Journal of Korean Society of Environmental Engineers
• /
• v.38 no.5
• /
• pp.242-248
• /
• 2016

The overall reaction rate of fuel cell is governed by oxygen reduction reaction (ORR) in the cathode due to its slowest reaction compared to the oxidation of hydrogen in the anode. The ORR efficiency can be readily evaluated by examining the adsorption strength of atomic oxygen on the surface of catalysts (i.e., known as a descriptor) and the adsorption energy can be controlled by transforming the surface geometry of catalysts. In the current study, the effect of the surface geometry of catalysts (i.e., strain effect) on the adsorption strength of atomic oxygen on platinum catalysts was analyzed by using density functional theory (DFT). The optimized lattice constant of Pt ($3.977{\AA}$) was increased and decreased by 1% to apply tensile and compressive strain to the Pt surface. Then the oxygen adsorption strengths on the modified Pt surfaces were compared and the electron charge density of the O-adsorbed Pt surfaces was analyzed. As the interatomic distance increased, the oxygen adsorption strength became stronger and the d-band center of the Pt surface atoms was shifted toward the Fermi level, implying that anti-bonding orbitals were shifted to the conduction band from the valence band (i.e., the anti-bonding between O and Pt was less likely formed). Consequently, enhanced ORR efficiency may be expected if the surface Pt-Pt distance can be reduced by approximately 2~4% compared to the pure Pt owing to the moderately controlled oxygen binding strength for improved ORR.

• Journal of the Mineralogical Society of Korea
• /
• v.22 no.4
• /
• pp.343-352
• /
• 2009

High-resolution Solid-state NMR provides element specific and quantitative information and also resolves, otherwise overlapping atomic configurations in multi-component non-crystalline silicates. Here we report the preliminary results on the effect of composition on the structure of CMAS (CaO-MgO-$Al_2O_3-SiO_2$) silicate glasses, as a model system for basaltic magmas, using the high-resolution 1D and 2D solid-state NMR. The $^{27}Al$ MAS NMR spectra for the CMAS silicate glasses show that four-coordinated Al is predominant, demonstrating that $Al^{3+}$ is network forming cation. The peak position moves toward lower frequency about 4.7 ppm with increasing $X_{MgO}$ due to an increase in $Q^4$(4Si) fraction with increasing Si content, indicating that Al are surrounded only by bridging oxygen. $^{17}O$ MAS NMR spectra for $CaAl_2SiO_6$ and $CaMgSi_2O_6$ glasses qualitatively suggest that NBO fraction in the former is smaller than that in $CaMgSi_2O_6$ glasses. As $^{17}O$ 3QMAS NMR spectrum of model quaternary aluminosilicate glass resolved distinct bridging and non-bridging oxygen environments, atomic structure for natural magmas can also be potentially probed using high-resolution 3QMAS NMR.

• Aerospace Engineering and Technology
• /
• v.3 no.1
• /
• pp.86-96
• /
• 2004

Space environment has various hazard effects on satellite. These effects can not be experienced in earth ambient condition. In terrestrial space, plasma or atomic oxygen could erode satellite surface. Also ultra violet or particle radiation may damage surface materials or electronic parts which constitute satellite. So, in designing satellite, the natural environment of operational orbit should be investigated and appropriate mitigation should be prepared.

• Journal of the Mineralogical Society of Korea
• /
• v.19 no.4 s.50
• /
• pp.347-353
• /
• 2006

The atomic-nano scale structures of multi-component aluminosilicate glasses have not been well understood in spite of its implications fur dynamics and generation of magma in the natural system due to lack of suitable spectroscopic and scattering experiments. Here, we report O-17 MAS and isotropic projection of 3QMAS NMR spectra for quaternary Na-Ca silicate glasses $[(CaO)_x(Na_2O)_{1-x}]\;(A1_2O_3)_{0.5}(SiO_2)_6,\;CNAS)$ at 14.1 Tesla where atomic configurations around bridging oxygen (Si-O-Si, Si-O-Al) and non bridging oxygen (Na-O-Si, Ca-O-Si, (Na, Ca)-O-Si) are partially resolved. With increasing Na content, the fraction of Na-O-Si increases while those for bridging oxygens remain constant. The Na/Ca ratio apparently affects the peak widths of bridging oxygen peaks (e.g., Si-O-Si)) and thus the topological entropy as well as chemical shifts of the bridging oxygen peaks, implying that both BOs and NBOs are strongly interacting with network modifying cations The effect of cation field strength on the degree of Al-avoidance was also discussed.

• Composites Research
• /
• v.28 no.3
• /
• pp.130-135
• /
• 2015

This study investigates the property of graphene filled polymer nanocomposites in LEO(Low Earth orbit) environment conditions. In order to improve compatibility with polymer matrices and resistance of carbon material against AO(Atomic oxygen) attack, silanization of graphene oxide with organosilane was carried out. The corresponding moieties were characterized through X-ray photoelectron spectroscopy (XPS). Graphene oxide filled nanocomposites were prepared using solution based processing methods. The sets of specimen series were tested in an accelerated LEO simulated space environment facility. Graphene oxide and silane treated graphene oxide reinforced nanocomposites were compared with neat epoxy. The comparison revealed that the silane treated graphene filled polymer composite shows inherent resistance against atomic oxygen attack while the lack of silane treatment resulted in a reduction in performance.

• Journal of the Mineralogical Society of Korea
• /
• v.23 no.4
• /
• pp.403-411
• /
• 2010

Essentials of understanding the geochemical evolution and geophysical processes in Earth's system are macroscopic properties and atomistic (and electronic) structures of Earth materials. Recent advances in quantum calculations based on the density functional theory allow us to unveil the previously unknown details of local atomic structures in diverse silicates in Earth's interior. Here, we report the O K-edge ELNES (energy-loss near-edge structure; ELNES) spectra and PLDOS (partial local density of states) for oxygen atoms in ${\alpha}$-quartz and stishovite using the quantum calculations based on FP-LAPW (full potential linearized augmented plane wave). The calculated O K-edge ELNES spectrum of ${\alpha}$-quartz shows a strong peak at ~538 eV due to comer-sharing oxygen linking two $SiO_4$ tetrahedra and that for stishovite shows two distinct peaks at ~537 and ~543 eV corresponding to edge-sharing oxygen linking $SiO_6$ octahedra. The significant differences in spectral features of O K-edge ELNES spectra suggest that the O K-edge features can be useful indicator to distinguish various oxygen sites in diverse crystal and amorphous silicates in the Earth's interior.

• Nuclear Engineering and Technology
• /
• v.4 no.4
• /
• pp.294-300
• /
• 1972

CNDO/2 and INDO calculations have been carried out on varying geometries of methyl chloro-and fluoro-formates. Results show that the configuration in which halogen atom is trans to methyl group is the most stable. Atomic charges and overlap population show that the trans form is stabilized by conjugation of carbonyl double bend with the unshared pairs of the ether oxygen and by electrostatic attraction of carbonyl oxygen to methyl group. Dipole moments of the trans forms agree reasonably well with the experimental values but showed that any generalizations made with dipole moments from bond moments should be accepted with considerable reservations.

• Journal of the Korean Vacuum Society
• /
• v.19 no.1
• /
• pp.14-21
• /
• 2010

Ge is one of the attractive channel materials for the next generation high speed metal oxide semiconductor field effect transistors (MOSFETs) due to its higher carrier mobility than Si. But the absence of a chemically stable thermal oxide has been the main obstacle hindering the use of Ge channels in MOS devices. Especially, the fabrication of gate oxide on Ge with high quality interface is essential requirement. In this study, $HfO_xN_y$ thin films were prepared by plasma-enhanced atomic layer deposition on Ge substrate. The nitrogen was incorporated in situ during PE-ALD by using the mixture of nitrogen and oxygen plasma as a reactant. The effects of nitrogen to oxygen gas ratio were studied focusing on the improvements on the electrical and interface properties. When the nitrogen to oxygen gas flow ratio was 1, we obtained good quality with 10% EOT reduction. Additional analysis techniques including X-ray photoemission spectroscopy and high resolution transmission electron microscopy were used for chemical and microstructural analysis.

• Applied Chemistry for Engineering
• /
• v.5 no.4
• /
• pp.609-615
• /
• 1994

Partial oxidation of ethylene over 10wt% $Ag/{\alpha}-Al_2O_3$ catalyst was studied with a pulse reactor which was connected directly to a G. C. When ethylene was injected after oxygen injection at the temperature where molecular adsorption of oxygen is difficult ethylene oxide was evolved. From the results, it is suggested that adsorbed atomic oxygen is related with the evolution of ethylene oxide. The selectivity to ethylene oxide decreased with the decrease of the amounts of adsorbed oxygen and bulk oxygen. Ethylene oxide was either decomposed to ethylene and adsorbed oxygen or isomerized to acetaldehyde. However, the isomerization of ethylene oxide to acetaldehyde was strongly suppressed by the preadsorbed oxygen.