Chapter 30. Nitridation Mechanisms of Silicon Powder Compacts
- John B. Wachtman Jr.
Published Online: 26 MAR 2008
Copyright © 1989 The American Ceramic Society, Inc.
A Collection of Papers Presented at the 13th Annual Conference on Composites and Advanced Ceramic Materials, Part 1 of 2: Ceramic Engineering and Science Proceedings, Volume 10, Issue 7/8
How to Cite
Barsoum, M., Kangutar, P. and Koczak, M. J. (1989) Nitridation Mechanisms of Silicon Powder Compacts, in A Collection of Papers Presented at the 13th Annual Conference on Composites and Advanced Ceramic Materials, Part 1 of 2: Ceramic Engineering and Science Proceedings, Volume 10, Issue 7/8 (ed J. B. Wachtman), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470310557.ch30
- Published Online: 26 MAR 2008
- Published Print: 1 JAN 1989
Print ISBN: 9780470374863
Online ISBN: 9780470310557
- chemical vapor infiltration;
- si powder compacts;
- reaction bonded silicon nitride;
- nitridation kinetics;
The nitridation of Si powder compacts was examined by measuring the flow rate dependence of nitrogen and N2/H2 gas mixtures during slow heating of the compacts while simultaneously monitoring the oxygen partial pressure of the exiting gas. The reaction was found to occur in two stages: an initial stage, the temperature (1215°C) of which was found to be independent of oxygen partial pressure and gas composition, and a second higher temperature stage. Small (4%) additions of hydrogen gas greatly enhanced the extent of reaction at lower temperature. It is believed that the first stage is initiated as a result of devitrification of the native SiO2 layer, catalyzed by Fe impurities, and the exposure of the underlying Si. The reaction sequence at that point has been unequivocally shown to be: [equations] as evidenced by a large increase in the oxygen partial pressure simultaneously with the onset of the initial stage. In the absence of hydrogen, both reactions are rapidly suppressed as the liberated oxygen competes with the nitrogen for the exposed Si surface and reoxidizes it. In the presence of hydrogen, however, this stage is quite pronounced and the role of hydrogen appears to be, in addition to aiding in the formation of SiO, to react with the oxygen and prevent reoxidation of the Si allowing for more extensive nitridation at lower temperatures. The main nitridation reaction at 1300°–1400°C appears to be a time dependent diffusion controlled process that depends on the nature of the passivating layer that forms during the initial stage, which in turn depends on gas composition, i.e., vol% H2.