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  • 1
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effect of oxide crystallinity on the oxidation rate of silicon carbide was investigated. CVD SiC coupons were oxidized in a clean TGA reactor system at 1300°C initially in flowing oxygen, immediately annealed in argon, and then reoxidized, all in situ and without cooling (so as to preserve oxide integrity). The parabolic rate constants determined for the preoxidation regime (of mainly amorphous oxide film) and reoxidation regime (of devitrified oxide) were compared. The oxidation rate decreased by a factor of }30 following full oxide crystallization induced by the anneal.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The oxidative durability of a SiC-SiC composite with Hi-Nicalon fiber and a BN interphase was investigated at 800°C (where pesting is known to occur in SiC-SiC composites) for exposure durations of up to 500 h and in a variety of oxidant mixes and flow rates, ranging from quasi-stagnant room air, through slow-flowing oxygen that contained 30%-90% H2O, to the high-velocity flame of a burner rig. Degradation of the composite was determined from residual strength and fracture stain in post-exposure mechanical tests and correlated with microstructural evidence of damage to the fiber and interphase. The most-severe degradation of composite behavior occurred in the burner rig and has been shown to be associated with the high oxidant velocity and substantial moisture content, as well as a thin sublayer of carbon that is indicated to form between the fiber and the interphase during composite processing.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 1995-05-01
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Wiley on behalf of American Ceramic Society.
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  • 4
    Publication Date: 1995-05-01
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Wiley on behalf of American Ceramic Society.
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  • 5
    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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  • 6
    Publication Date: 2019-07-10
    Description: The oxidative durability of a SiC-SiC composite with Hi-Nicalon fiber and BN interphase was investigated at 800 C (where pesting is known to occur in SiC-SiC composites) for exposure durations of up to 500 hours and in a variety of oxidant mixes and flow rates, ranging from quasi-stagnant room air, through slow flowing O2 containing 30-90% H2O, to the high-velocity flame of a burner rig. Degradation of the composite was determined from residual strength and fracture strain in post-exposure mechanical tests and correlated with microstructural evidence of damage to fiber and interphase. The severest degradation of composite behavior was found to occur in the bumer rig, and is shown to be connected with the high oxidant velocity and substantial moisture content, as well as a thin sublayer of carbon indicated to form between fiber and interphase during composite processing.
    Keywords: Composite Materials
    Type: Journal of the American Ceramic Society
    Format: application/pdf
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  • 7
    Publication Date: 2019-08-15
    Description: A suitable interphase material for non-oxide ceramic-matrix composites must be resistant to oxidation. This means it must exhibit a slow rate of oxidation, and its oxidation product must be such as to ensure that the system survives oxidation when it does occur. Because the current benchmark interphase materials, carbon and boron nitride, lack these qualities, a porous fiber coating was developed to satisfy both the mechanical and oxidative requirements of an interphase for the SiC/SiC and SiC/Si2N4 composites that are of interest to NASA. This report presents the interphase microstructure achieved and the resulting characteristics of fiber push-out from a matrix of reaction-bonded silicon nitride (RBSN), both as-fabricated and after substantial annealing and oxidation treatments.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA-CR-198425 , NAS 1.26:198425 , E-10013 , NIPS-95-06250
    Format: application/pdf
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  • 8
    Publication Date: 2019-07-13
    Description: SiC-SiC composites are prone to pest degradation at intermediate temperatures where the formation of a protective scale of silica by direct oxidation of SiC is too slow to offer effective protection from attack by ambient gases. The attack results in the removal of the BN interphase and its replacement by a borosilicate liquid (which dissolves and weakens the fiber) and finally by SiO2, (which embrittles the composite by bonding fiber to fiber or to matrix). This paper reports a study aimed at mapping out the temperature range of such pest degradation and the severity of its effect.
    Keywords: Composite Materials
    Type: CIMTEC-9: World Ceramic Congress 1998; Jun 14, 1998 - Jun 19, 1998; Florence; Italy
    Format: text
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