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Role of Si2N2O in the passive oxidation of chemically-vapor-deposited Si3N4The results of two-step oxidation experiments on chemically-vapor-deposited Si3N4 and SiC at 1350 C show that a correlation exists between the presence of a Si2N2O interphase and the strong oxidation resistance of Si3N4. During normal oxidation, k sub p for SiC was 15 times higher than that for Si3N4, and the oxide scale on Si3N4 was found by SEM and TEM to contain a prominent Si2N2O inner layer. However, when oxidized samples are annealed in Ar for 1.5 h at 1500 C and reoxidized at 1350 C as before, three things happen: the oxidation k sub p increases over 55-fold for Si3N4, and 3.5-fold for SiC; the Si3N4 and SiC oxidize with nearly equal k sub p's; and, most significantly, the oxide scale on Si3N4 is found to be lacking an inner Si2N2O layer. The implications of this correlation for the competing models of Si3N4 oxidation are discussed.
Document ID
19930032523
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Ogbuji, Linus U. J. T.
(NASA Lewis Research Center Cleveland, OH, United States)
Date Acquired
August 15, 2013
Publication Date
November 1, 1992
Publication Information
Publication: American Ceramic Society, Journal
Volume: 75
Issue: 11
ISSN: 0002-7820
Subject Category
Nonmetallic Materials
Accession Number
93A16520
Distribution Limits
Public
Copyright
Other

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