High-energy Atomic Oxygen Research Articles

Temperature dependence of atomic‑oxygen irradiation mechanism of hydrogenated diamond-like carbon film

Hydrogenated diamond-like carbon (H-DLC) films are effective lubricants for aerospace moving parts, but the service of H-DLC is severely threatened by atomic oxygen (AO) in low Earth orbit (LEO). The interaction between AO and H-DLC strongly depends on ambient temperature; however, the interactive mechanism has not been fully understood. In this study, we report different temperature dependences of AO irradiation behavior on H-DLC film. Under the AO irradiation with low energy, the increase in ambient temperature can only increase the surfacial oxidation; while, the effect of temperature under high AO irradiation energy is more significant, resulting in the transition from the surficial oxidation to continuous carbon removal. Subsequent analysis of the AO trajectories shows that the different repulsion mechanisms of the H-DLC surface against high and low energy AO result in the different temperature dependence. For AO incident with low energy, the incident AO cannot touch the H-DLC surface anymore due to the repulsion of the surfacial oxygen in the later irradiation stage. Nevertheless, high energy AO could overcome the repulsion of oxidized surface to contact the H-DLC surface, the increase in temperature can continuously promote the AO irradiation on the H-DLC surface.

Functionalized multi-walled carbon nanotubes/hydrogen-rich benzoxazine nanocomposites for cosmic radiation shielding with enhanced mechanical properties and space environment resistance

In the new space era, cosmic radiation shielding is important for satellites equipped with highly integrated electronic equipment and astronauts participating in long-term space missions. Because hydrogen-rich benzoxazine (HRB) contains a large amount of hydrogen, it can effectively shield radiation. The mass of an HRB radiation shield is lower than that of an epoxy shield, and its mechanical properties may be enhanced by the addition of amines or carbon nanotubes. However, when HRB is exposed to a space environment, high-energy atomic oxygen erodes its surface, while ultrahigh vacuum combined with high temperature causes outgassing. To improve the mechanical properties of HRB and its space environment resistance, multi-walled carbon nanotube (MWCNT)/HRB nanocomposites with grafted amine groups have been synthesized in this study. The tensile properties of these nanocomposites were evaluated, and their space environment resistance was determined using special equipment that simulates a space environment, including high-energy atomic oxygen irradiation. The obtained results revealed that the proposed NH2–MWCNT/HRB nanocomposites were superior to HRB in terms of their tensile properties, outgassing performance, and atomic oxygen resistance. Therefore, these materials can potentially replace epoxy polymers in space missions that require cosmic radiation shielding.

Прискорення ресурсних випробувань полімерів космічних апаратів на стійкість до тривалої дії атомарного кисню в іоносфері Землі

The procedure of accelerated resource tests of spacecraft polymers for their resistance to the long-term influence of atomic oxygen (AO) in the Earth's ionosphere at altitudes from 200 to 700 km has been developed. The procedure involves irradiation of polymers with high-energy ions of atomic oxygen and the use of a kapton-H polyimide as reference material. The condition of equivalence of the " atomic oxygen - polymer" interaction in the ionosphere and on the laboratory set is the equality of tested material mass loss. The basis for substantiating the procedure of accelerated tests is the result: when irradiating the kapton-H polymer with high-energy atomic oxygen ions in the energy range from 30 to 80 eV, the degradation of polyimide is determined by the process of chemical etching of the material. To substantiate the procedure of accelerating resource tests of polymeric structural materials of spacecraft for resistance to long-term action of atomic oxygen flows, the dependences of mass loss and volumetric mass loss factor (reactivity) of kapton-H polyimide and Teflon FEP-100A on fluence and energy of the atomic oxygen ions have been obtained. It is shown that when irradiating kapton-H polyimide with atomic oxygen ions with the energy of 30 to 80 eV, the material mass loss due to chemical etching is about an order of magnitude greater than the mass loss due to kinetic sputtering. When the kapton-H polymer is irradiated with high-energy atomic oxygen ions, the coefficient of acceleration of the resource tests and the fluence of atomic oxygen are about two orders of magnitude greater than the coefficient of acceleration obtained using atomic oxygen ions with an energy of 5 eV.

The degradation behavior of C/C composites in high-energy atomic oxygen

In low earth orbit (LEO), spacecraft, space structure and other applications encounter a degradation problem induced by the impact of atomic oxygen (AO) in the space environment. C/C composites (C/Cs), which are widely applied to different applications in space systems, were tested to study the irradiation and bombardment effects of LEO space environment on the composites. The degradation was analyzed in the aspect of mass loss, morphology and flexural strength and thermal conductivity properties. Results show that the specimens are bombarded by high-speed AO with high activity during AO irradiation test. The flexural strength of C/C composites after AO irradiation test for 24 h (AO24, 150.4 MPa) is decreased by 25.8% than C/Cs (202.7 MPa). The coefficients of thermal conductivity of C/Cs after AO irradiation show an increase. Carbon fibers and pyrolytic carbon (PyC) were also exposed to AO irradiation test. Results show that the denudation rate of PyC is slower than that of C/C composites and carbon fiber. Besides, the denudation of carbon fiber (form crisscrossed ravine) is most serious. PyC shows the least damage. This work may provide not only the influence of AO irradiation on C/Cs but the protection of C/Cs from AO irradiation.

Degradation on a mechanical property of high-modulus aramid fiber due to hyperthermal atomic oxygen beam exposures

High-modulus aramid fiber was exposed to energetic (5 eV) atomic oxygen, which simulates the space environment in low Earth orbit. It was found that Young’s modulus and tensile strength decreased significantly due to the atomic oxygen exposures. X-ray photoelectron spectroscopy showed that the decomposition of amid group occured at the exposed surfaces. Scanning electron microscopy revealed that the diameter of the fiber was not influenced so much by the attack of atomic oxygen, but the exposed fiber became an extremely rough surface. The change in mechanical properties has been explained by the formation of surface texture that is characteristic to the high-energy atomic oxygen collisions.

Degradation of Materials by High-Energy Atomic Oxygen

The degradation of materials exposed in LEO (low earth orbit) is one of the most important problems in space technology because the predominant component of the atmosphere in LEO is AO (atomic oxygen) which degrades some kinds of materials. This paper presents an experimental simulation on the ground for the degradation of carbon-based materiais. In the experiment, AO produced at a plasma torch is accelerated fluid-dynamically with working gas. Graphite, C/C (carbon/carbon) composite and Si -C.C. (silicon impregnated C/C composite) were used as the target materials. The mass loss per unit area depends strongly on the temperature of the material surface. The eroded surfaces of materials were observed with SEM (scanning electron microscope) and laser fucus displacement meter. In case of C/C composite, the matrix region erodes more than carbon fiber. The mass loss of Si-C.C. is less than that of corresponding C/C composite and only the C/C region erodes deeply with almost no erosion in Si and SiC regions. In order to investigate the degradation caused by the impact of AO, numerical simulation was also conducted for graphite using MD (molecular dynamics) method.

Degradation of carbon-based materials due to impact of high-energy atomic oxygen

Spacecraft structures in low earth orbit encounter a degradation problem caused by the impact of atomic oxygen (AO) in the space environment. This paper presents an experiment of impact degradation on the ground. The experiment was carried out in a vacuum space chamber. AO produced at a plasma torch was accelerated fluid-dynamically with argon (Ar) working gas. As the target materials, several carbon-based materials were employed; i.e., graphite, carbon fiber/carbon composite (C/C composite) and silicon impregnated C/C composite (Si-C.C.). The degradation was analyzed in the aspect of macroscopic mass loss per unit area and the microscopic degradation modes. The temperature effect and the exposure time effect are investigated and the comparison among the target materials is developed. The mass loss per unit area is approximately proportional to the exposure time and depends on the temperature of material surface. The eroded surfaces of materials were observed with a scanning electron microscope and an electron probe micro-analyzer. In case of C/C composite, the matrix region erodes more than carbon fiber, however, this effect is more pronounced in the normal oxidation at the ambient atmosphere. The mass loss of Si-C.C. is less than that of the corresponding C/C composite and only the C/C composite region erodes deeply with almost no erosion in Si and SiC regions.

603 Degradation of Materials by High Energy Atomic Oxygen

The degradation of structural materials exposed in space is a new problem since various kinds of materials have been used for structures in low earth orbit (LEO). This paper presents an experiment of degradation on the ground and a simulation by the molecular dynamics (MD) method. In the experiment, atomic oxygen produced at a plasma torch is accelerated fluid-dynamically with working gas. Graphite, C/C (carbon/carbon) composite and Si-C. C. (silicon impregnated C/C composite) were used as the target materials. The mass loss per unit area depends strongly on the temperature of the material surface. The eroded surfaces of materials were observed with SEM (scanning electric microscope) and laser focus displacement meter. In case of C/C composite, the matrix region erodes substantially more than carbon fiber. The mass loss of Si-C. C. is less than that of corresponding C/C composite and only the C/C region erodes deeply with almost no erosion in Si and SiC regions. In order to investigate the degradation caused by high energy atomic oxygen, numerical simulation was performed for graphite using the MD method. The simulation model explains the influence of the impact energy of AO on the degradation of materials.

118 高エネルギ原子状酸素による材料の劣化機構に関する研究(OS 先端材料の力学特性と計測技術)

118 高エネルギ原子状酸素による材料の劣化機構に関する研究(OS 先端材料の力学特性と計測技術)

Experimental and theoretical simulation of material degradation caused by atomic oxygen impact in space

The degradation of structural material exposed in space is a new problem, since various kinds of materials have been used for structures in low earth orbit (LEO). This study presents an experiment of degradation on the ground and a simulation by the molecular dynamics. In the experiment, atomic oxygen produced at a plasma torch is accelerated fluid dynamically with working gas. Graphite, C/C composite and Si-C.C. (: Silicon impregnated C/C composite) were used as the target materials. The mass loss per unit area is approximately proportional to the exposure time and depends strongly on the temperature of material surface. The eroded surfaces of materials were observed with SEM and EPMA. In case of C/C composite, the matrix region erodes substantially more than carbon fiber. The mass loss of Si-C.C. is less than that of corresponding C/C composite and only the C/C composite region erodes deeply with almost no erosion in Si and SiC regions. In order to investigate the degradation caused by high-energy atomic oxygen, numerical simulation was conducted for graphite using the molecular dynamics method. The simulation model explains the influence of exposure time on the degradation of material.