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Effects of high pressure nitrogen on the thermal stability of SiC fibersPolymer-derived SiC fibers were exposed to nitrogen gas pressures of 7 and 50 atm at temperatures up to 1800 C. The fiber weight loss, chemical composition, and tensile strength were then measured at room temperature in order to understand the effects of nitrogen exposure on fiber stability. High pressure nitrogen treatments limited weight loss to 3 percent or less for temperatures up to 1800 C. The bulk Si-C-O chemical composition of the fiber remained relatively constant up to 1800 C with only a slight increase in nitrogen content after treatment at 50 atm; however, fiber strength retention was significantly improved. To further understand the effects of the nitrogen atmosphere on the fiber stability, the results of previous high pressure argon treatments were compared to those of the high pressure nitrogen treatments. High pressure inert gas can temporarily maintain fiber strength by physically inhibiting the evolution of gaseous species which result from internal reactions. In addition to this physical effect, it would appear that high pressure nitrogen further improved fiber temperature capability by chemically reacting with the fiber surface, thereby reducing the rate of gas evolution. Subsequent low pressure argon treatments following the initial nitrogen treatments resulted in stronger fibers than after argon treatment alone, further supporting the chemical reaction mechanism and its beneficial effects on fiber strength.
Document ID
19910006762
Acquisition Source
Legacy CDMS
Document Type
Preprint (Draft being sent to journal)
Authors
Jaskowiak, Martha H. (NASA Lewis Research Center Cleveland, OH, United States)
Date Acquired
September 6, 2013
Publication Date
January 1, 1991
Subject Category
Composite Materials
Report/Patent Number
E-5671
NASA-TM-103245
NAS 1.15:103245
Accession Number
91N16075
Funding Number(s)
PROJECT: RTOP 510-01-01
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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