| Effect of Increased Oxygen Content due to Intensive Milling on Phase and Microstructural Development of Silicon Nitride |
| Hai-Doo Kim, Ellen Y. Sun 1, Paul F. Becher 2, Hyo-Jong Kim3, Byung-Dong Han, Dong-Soo Park |
Ceramic Materials Group, Korea Institute of Machinery and Materials
1United Technology Research Center
2Metals and Ceramics Division, Oak Ridge National Laboratory
3Smart Ceramic Company |
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| ABSTRACT |
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Compacts of a mixture of fine $alpha$-Si$_3$N$_4$powders, 6% $Y_2$O$_3$and 1% $Al_2$O$_3$were attrition milled time on phase and microstructural development in silicon nitride ceramics. The sintered surface and the interior showed different behaviors in phase and microstructral developments. Increased oxygen content with increased milling time of powder mixture leads to the formation of Si$_2$$N_2$O phase at temperatures as low as 155$0^{circ}C$. Si$_2$$N_2$O is stable in the interior of the samples but unstable in the surface region of the specimen sintered at higher temperature. This results in a duplex structure where the interior consists of Si$_2$$N_2$O grains dispersed in $beta$-Si$_3$N$_4$matrix and a surface which contains only $beta$-Si$_3$N$_4$. The alpha to beta phase transformation and the microstructural development are shown to be influenced by the formation and decomposition of the Si$_2$$N_2$O. |
| Key words:
$Si_3$$N_4$, Attrition milling, Increased oxygen content, $Si_2$>$N_2$O, Duplex structure |
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