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Heterogeneous Formation of Oriented Silicon Oxynitride on α-Si3N4 Seed Crystals : Habits And Radiation Stability

Published online by Cambridge University Press:  02 July 2020

R.W Carpenter ,
W Braue  and
M.J. Kim
R.W Carpenter
Affiliation:
Science and Engineering of Materials and Center for Solid State Science, Arizona State University, Tempe, AZ85287-1704
W Braue
Affiliation:
German Aerospace Research Establishment (DLR), Materials Research Institute, D-51147, Cologne
M.J. Kim
Affiliation:
German Aerospace Research Establishment (DLR), Materials Research Institute, D-51147, Cologne
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Lath-like silicon oxynitride crystals have often been observed in the microstructure of silicon nitride based ceramics after processing. They are usually located in glassy regions which are siliceous solidified sintering aid liquid, and usually contain a small (∼100nm) a-Si3N4 crystal. These nitride crystals are considered to be seeds, incompletely dissolved in the melt, that are heterogeneous nucleation sites for the oxynitride crystals. We present here the first observations of morphological and crystallographic habits between the seed nanocrystals and the host oxynitride laths.

Fig. 1 shows a typical oxynitride lath containing a nitride seed crystal. The lath is surrounded by glass and ß-Si3N4 particles, and a small cristobalite particle (a minor constituent). This microstructure is from an Si02-Si3N4 ceramic processed with Al2O3 sintering aid. The same oxynitride lath/seed structures were observed when other sintering aids (eg. Y2O3, MgO, ZrO2) were used, so they are independent of sintering aid.

Type
Future of Microscopy: Ceramics, Composites, and Cement
Information
Microscopy and Microanalysis , Volume 5 , Issue S2: Proceedings: Microscopy & Microanalysis '99, Microscopy Society of America 57th Annual Meeting, Microbeam Analysis Society 33rd Annual Meeting, Portland, Oregon August 1-5, 1999 , August 1999 , pp. 778 - 779
Copyright
Copyright © Microscopy Society of America

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5. This research was supported by the Division of Materials Sciences, USDOE, under grant No. DE-FG03-94ER45510, and by the German Aerospace Research Establishment.