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Formation of porous surface layers in reaction bonded silicon nitride during processingAn effort was undertaken to determine if the formation of the generally observed layer of large porosity adjacent to the as-nitride surfaces of reaction bonded silicon nitrides could be prevented during processing. Isostatically pressed test bars were prepared from wet vibratory milled Si powder. Sintering and nitriding were each done under three different conditions:(1) bars directly exposed to the furnance atmosphere; (2) bars packed in Si powder; (3) bars packed in Si3N4 powder. Packing the bars in either Si of Si3N4 powder during sintering retarded formation of the layer of large porosity. Only packing the bars in Si prevented formation of the layer during nitridation. The strongest bars (316 MPa) were those sintered in Si and nitrided in Si3N4 despite their having a layer of large surface porosity; failure initiated at very large pores and inclusions. The alpha/beta ratio was found to be directly proportional to the oxygen content; a possible explanation for this relationship is discussed.
Document ID
19800014966
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Shaw, N. J.
(NASA Lewis Research Center Cleveland, OH, United States)
Glasgow, T. K.
(NASA Lewis Research Center Cleveland, OH, United States)
Date Acquired
September 4, 2013
Publication Date
January 1, 1979
Subject Category
Nonmetallic Materials
Report/Patent Number
E-431
NASA-TM-81493
Meeting Information
Meeting: Fall Meeting of the Basic Sci. and Nucl. Div. of the Am. Ceramic Soc.
Location: New Orleans
Start Date: October 14, 1979
End Date: October 17, 1979
Accession Number
80N23456
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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