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  • 1
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    Microstructure and Mechanical Properties of Reaction-Formed Joints in Reaction Bonded Silicon Carbide Ceramics (1998)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: A reaction-bonded silicon carbide (RB-SiC) ceramic material (Carborundum's Cerastar RB-SIC) has been joined using a reaction forming approach. Microstructure and mechanical properties of three types of reaction-formed joints (350 micron, 50-55 micron, and 20-25 micron thick) have been evaluated. Thick (approximately 350 micron) joints consist mainly of silicon with a small amount of silicon carbide. The flexural strength of thick joints is about 44 plus or minus 2 MPa, and fracture always occurs at the joints. The microscopic examination of fracture surfaces of specimens with thick joints tested at room temperature revealed the failure mode to be typically brittle. Thin joints (〈50-55 micron) consist of silicon carbide and silicon phases. The room and high temperature flexural strengths of thin (〈50-55 micron) reaction-formed joints have been found to be at least equal to that of the bulk Cerastar RB-SIC materials because the flexure bars fracture away from the joint regions. In this case, the fracture origins appear to be inhomogeneities inside the parent material. This was always found to be the case for thin joints tested at temperatures up to 1350C in air. This observation suggests that the strength of Cerastar RB-SIC material containing a thin joint is not limited by the joint strength but by the strength of the bulk (parent) materials.
    Keywords: Nonmetallic Materials
    Type: Journal of Materials Science (ISSN 0022-2461); Volume 33; 5781-5787
    Format: text
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  • 2
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    Drag of a sphere oscillating in a conducting viscous medium. (1965)
    In:  Other Sources
    Details
    Publication Date: 2011-08-10
    Description: Rotation, magnetic field and compressibility effects on disturbances due to slow oscillations of conducting sphere in viscous medium
    Keywords: FLUID MECHANICS
    Format: text
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  • 3
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    Equatorial irregularity belt and its movement during a magnetic storm (1978)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Evidence for an equatorial irregularity belt and its movement during a magnetic storm has been obtained from Faraday rotation measurements at a chain of 140-MHz radio beacons receiving from the ATS-6 satellite. The stations covered a latitude region from the magnetic equator to the 45 deg N dip on the Indian subcontinent. An irregularity belt extending from the magnetic equator to about 27 deg N latitude was observed during the main phase of the magnetic storm of 10 January, 1976.
    Keywords: GEOPHYSICS
    Type: Nature; 272; Mar. 23
    Format: text
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  • 4
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    Design, Fabrication and Characterization of High Temperature Joints in Ceramic Composites (1999)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: Ceramic joining has been recognized as one of the enabling technologies for the successful utilization of ceramic components in a number of demanding, high temperature applications. Various joint design philosophies and design issues have been discussed along with an affordable, robust ceramic joining technology (ARCJoinT). A wide variety of silicon carbide-based composite materials, in different shapes and sizes, have been joined using this technology. This technique is capable of producing joints with tailorable thickness and composition. The room and high temperature mechanical properties and fractography of ceramic joints have been reported. These joints maintain their mechanical strength up to 1200 C in air. This technology is suitable for the joining of large and complex shaped ceramic composite components and with certain modifications, can be applied to repair of ceramic components damaged in service.
    Keywords: Composite Materials
    Type: Key Engineering Materials; Volumes 164-165; 415-420
    Format: text
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  • 5
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    An investigation of ionospheric irregularity effects on SIR-B image processing and information extraction (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Ionospheric irregularities and associated effects on space-time synthetic aperture radar (SAR) image processing and information extraction, including sensor calibration, target statistics determination, resolution, distortion, and overall image integrity were investigated.
    Keywords: GEOPHYSICS
    Type: JPL The SIR-B Sci. Invest. Plan; 4 p
    Format: text
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  • 6
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    High-temperature oxidation behavior of reaction-formed silicon carbide ceramics (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The oxidation behavior of reaction-formed silicon carbide (RFSC) ceramics was investigated in the temperature range of 1100 to 1400 C. The oxidation weight change was recorded by TGA; the oxidized materials were examined by light and electron microscopy, and the oxidation product by x-ray diffraction analysis (XRD). The materials exhibited initial weight loss, followed by passive weight gain (with enhanced parabolic rates, k(sub p)), and ending with a negative (logarithmic) deviation from the parabolic law. The weight loss arose from the oxidation of residual carbon, and the enhanced k(sub p) values from internal oxidation and the oxidation of residual silicon, while the logarithmic kinetics is thought to have resulted from crystallization of the oxide. The presence of a small amount of MoSi, in the RFSC material caused a further increase in the oxidation rate. The only solid oxidation product for all temperatures studied was silica.
    Keywords: Nonmetallic Materials
    Type: NASA-TM-111682 , NAS 1.15:111682
    Format: application/pdf
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  • 7
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    Microstructural Characterization of Reaction-Formed Silicon Carbide Ceramics (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Microstructural characterization of two reaction-formed silicon carbide ceramics has been carried out by interference layering, plasma etching, and microscopy. These specimens contained free silicon and niobium disilicide as minor phases with silicon carbide as the major phase. In conventionally prepared samples, the niobium disilicide cannot be distinguished from silicon in optical micrographs. After interference layering, all phases are clearly distinguishable. Back scattered electron (BSE) imaging and energy dispersive spectrometry (EDS) confirmed the results obtained by interference layering. Plasma etching with CF4 plus 4% O2 selectively attacks silicon in these specimens. It is demonstrated that interference layering and plasma etching are very useful techniques in the phase identification and microstructural characterization of multiphase ceramic materials.
    Keywords: Nonmetallic Materials
    Type: NASA-TM-111692 , NAS 1.15:111692 , E-9674
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  • 8
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    Microstructures of BN/SiC coatings on nicalon fibers (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The microstructures of Nicalon silicon carbide (SiC) fibers and layered coatings of boron nitride (BN) followed by chemical vapor infiltrated silicon carbide (CVI-SiC) were characterized using optical and electron microscopy. Two different precursors and reactions were used to produce the BN layers while the deposition of CVI silicon carbide was nearly identical. Coated tows were examined in cross-section to characterize the chemistry and structures of the constituents and the interfaces. One BN precursor yielded three sublayers while the other gave a relatively homogeneous nanocrystalline layer.
    Keywords: METALLIC MATERIALS
    Type: NASA-CR-200047 , NAS 1.26:200047 , NIPS-96-07287
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  • 9
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    Reactive melt infiltration of silicon-molybdenum alloys into microporous carbon preforms (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Investigations on the reactive melt infiltration of silicon-1.7 and 3.2 at.% molybdenum alloys into microporous carbon preforms have been carried out by modeling, differential thermal analysis (DTA), and melt infiltration experiments. These results indicate that the pore volume fraction of the carbon preform is a very important parameter in determining the final composition of the reaction-formed silicon carbide and the secondary phases. Various undesirable melt infiltration results, e.g. choking-off, specimen cracking, silicon veins, and lake formation, and their correlation with inadequate preform properties are presented. The liquid silicon-carbon reaction exotherm temperatures are influenced by the pore and carbon particle size of the preform and the compositions of infiltrants. Room temperature flexural strength and fracture toughness of materials made by the silicon-3.2 at.% molybdenum alloy infiltration of medium pore size preforms are also discussed.
    Keywords: METALLIC MATERIALS
    Type: NASA-TM-111193 , NAS 1.15:111193 , NIPS-96-07166
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  • 10
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    An NNSS satellite timing receiver (1982)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The U.S. Navy Navigation Satellite System, NNSS, offers a unique worldwide facility for precise time synchronization. Space Applications Centre (SAC) developed a simple timing receiver. Using this timing receiver first the internal time consistency of NNSS was studied and then its performance to synchronize time was compared with that of National Time Standard. The methodology of data analysis, results, and various sources of error which affect the time transfer accuracy were studied and described. The main source of error was found to be the receiver delay which varies with signal strength. It is possible to apply that this delay correction empirically provided signal strength is recorded.
    Keywords: LASERS AND MASERS
    Type: NASA. Goddard Space Flight Center Proc. of the 13th Ann. Precise Time and Time Interval (PTTI) Appl. and Planning Meeting; p 817-830
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