干旱区生态环境知识资源中心(Arid): Optical and Scanning Electron Microscopy of the Materials International Space Station Experiment (MISSE) Spacecraft Silicone Experiment

Arid

报告编号	NASA/TM-2012-217678, E-18353
来源ID	NTRS_Document_ID: 20120013788
	Optical and Scanning Electron Microscopy of the Materials International Space Station Experiment (MISSE) Spacecraft Silicone Experiment
	Hung, Ching-cheh; de Groh, Kim K.; Banks, Bruce A.
英文摘要	Under a microscope, atomic oxygen (AO) exposed silicone surfaces are crazed and seen as "islands" separated by numerous crack lines, much analogous to mud-tile cracks. This research characterized and compared the degree of AO degradation of silicones by analyzing optical microscope images of samples exposed to low Earth orbit (LEO) AO as part of the Spacecraft Silicone Experiment. The Spacecraft Silicone Experiment consisted of eight DC 93-500 silicone samples exposed to eight different AO fluence levels (ranged from 1.46 to 8.43 10(exp 21) atoms/sq cm) during two different Materials International Space Station Experiment (MISSE) missions. Image analysis software was used to analyze images taken using a digital camera. To describe the morphological degradation of each AO exposed flight sample, three different parameters were selected and estimated: (1) average area of islands was determined and found to be in the 1000 to 3100 sq mm range; (2) total length of crack lines per unit area of the sample surface were determined and found to be in the range of 27 to 59 mm of crack length per sq mm of sample surface; and (3) the fraction of sample surface area that is occupied by crack lines was determined and found to be in the 25 to 56 percent range. In addition, average crack width can be estimated from crack length and crack area measurements and was calculated to be about 10 mm. Among the parameters studied, the fraction of sample surface area that is occupied by crack lines is believed to be most useful in characterizing the degree of silicone conversion to silicates by AO because its value steadily increases with increasing fluence over the entire fluence range. A series of SEM images from the eight samples exposed to different AO fluences suggest a complex sequence of surface stress due to surface shrinkage and crack formation, followed by re-distribution of stress and shrinking rate on the sample surface. Energy dispersive spectra (EDS) indicated that upon AO exposure, carbon content on the surface decreased relatively quickly at the beginning, to 32 percent of the pristine value for the least exposed sample in this set of experiments (1.46 10(exp 21) atoms/sq cm), but then decreased slowly, to 22 percent of the pristine value for the most exposed sample in this set of experiment (8.43 10(exp 21) atoms/sq cm). The oxygen content appears to increase at a slower rate. The least and most AO exposed samples were, respectively, 52 and 150 percent above the pristine values. The silicone samples with the greater AO exposure (7.75 10(exp 21) atoms/sq cm and higher) appear to have a surface layer which contains SiO2 with perhaps small amounts of unreacted silicone, CO and CO2 sealed inside.
英文关键词	LOW EARTH ORBITS CARBON DIOXIDE SILICONES DEGRADATION IMAGE ANALYSIS SILICON DIOXIDE SPACEBORNE EXPERIMENTS INTERNATIONAL SPACE STATION SCANNING ELECTRON MICROSCOPY
出版年	2012
报告类型	Technical Report
语种	英语
国家	美国
URL	http://hdl.handle.net/2060/20120013788
资源类型	科技报告
条目标识符	http://119.78.100.177/qdio/handle/2XILL650/259343
推荐引用方式 GB/T 7714	Hung, Ching-cheh,de Groh, Kim K.,Banks, Bruce A.. Optical and Scanning Electron Microscopy of the Materials International Space Station Experiment (MISSE) Spacecraft Silicone Experiment,2012.