Chapter 25. Effect of Gas Phase Composition of SiC and Si3N4 Formations
- John B. Wachtman Jr.
Published Online: 26 MAR 2008
Copyright © 1990 The American Ceramic Society, Inc.
14th Annual Conference on Composites and Advanced Ceramic Materials, Part 2 of 2: Ceramic Engineering and Science Proceedings, Volume 11, Issue 9/10
How to Cite
Wada, H. and Wang, L. (2008) Effect of Gas Phase Composition of SiC and Si3N4 Formations, in 14th Annual Conference on Composites and Advanced Ceramic Materials, Part 2 of 2: Ceramic Engineering and Science Proceedings, Volume 11, Issue 9/10 (ed J. B. Wachtman), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470313053.ch25
- Published Online: 26 MAR 2008
- Published Print: 1 JAN 1990
Print ISBN: 9780470374931
Online ISBN: 9780470313053
During the ceramic whiskers synthesis such as SiC, Si3N4, and sialon by the carbothermal reduction of silica through the VS mechanism, a localized formation of amorphous phase or powder oxynitride was observed beneath these whiskers. To elucidate effect of the gas-phase composition on the reaction mechanism of these phases, the oxygen partial pressure was continuously measured during the synthesis with a ZrO2 solid electrolyte. The oxygen partial pressure steadily increased with increasing temperature and reached to the maximum level of 10−11–10−12 atm in early stage of reaction at 1623 K, then decreased again toward the end of reaction. The patterns in the changing Po2 were similar in both SiC and Si3N4 formations. Both high oxygen partial pressure and high SiO partial pressure were generated by the accelerated carbothermal reduction of SiO2 by forming a molten fluorosilicate with an auxiliary bath. Effect of gas-phase composition on SiC and Si3N4formations is not the same; the Pco and Pco2 forms oxynitride phase in the Si3N4 formation.