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Transmission electron microscopy observation of second-phase particles in β–Si3N4 grains

Published online by Cambridge University Press:  31 January 2011

Naoto Hirosaki
Affiliation:
National Institute for Research in Inorganic Materials, 1-1 Namiki, Tsukuba 305-0044, Japan
Tomohiro Saito
Affiliation:
Japan Fine Ceramic Center, 2-4-1 Mutsuno, Atsuta-ku, Nagoya 456-8578, Japan
Fumio Munakata
Affiliation:
Nissan Research Center, Nissan Motor Co., Ltd., 1 Natsushima-cho, Yokosuka 237-8523, Japan
Yoshio Akimune
Affiliation:
Nissan Research Center, Nissan Motor Co., Ltd., 1 Natsushima-cho, Yokosuka 237-8523, Japan
Yuichi Ikuhara
Affiliation:
Department of Materials Science, Faculty of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
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Abstract

Silicon nitride was fabricated by adding Y2O3 and Nd2O3 as sintering additives, sintering for 8 h at 1900 °C, and heat treating for 4 h at 2200 °C to enhance grain growth. The microstructure was investigated by scanning electron microscopy, high-resolution electron microscopy, energy dispersive x-ray spectroscopy (EDS), and electron microdiffraction. This material had a duplex microstructure composed of many fine grains and a few coarse grains. In β–Si3N4 grains, second-phase particles with the composition of liquid phase, Y–Nd–Si–O or Y–Nd–Si–O–N, in the size of 10–30 nm were observed. EDS spectra and microdiffraction patterns revealed that those were amorphous or crystalline particles of Y–Nd–apatite, (Y,Nd)10Si6O24N2. These particles were presumably formed during cooling by the precipitation of Y–Nd–Si–O–N, which was trapped in the β–Si3N4 grains as solid solution or trapped liquid. The results suggest that attention should be paid to the trace amounts of trapped elements in β–Si3N4 grains in trying to improve the thermal conductivity of sintered silicon nitride.

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Articles
Copyright
Copyright © Materials Research Society 1999

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