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Novel Silicon Nitride Microstructures Through Processing of Phase Separated Polysilazane Gels

Published online by Cambridge University Press:  25 February 2011

David A. Lindquist,
John S. Haggerty,
Wendell E. Rhine and
Dietmar Seyferth
David A. Lindquist
Affiliation:
Massachusetts Institute of Technology, Cambridge, MA 02139
John S. Haggerty
Affiliation:
Massachusetts Institute of Technology, Cambridge, MA 02139
Wendell E. Rhine
Affiliation:
Massachusetts Institute of Technology, Cambridge, MA 02139
Dietmar Seyferth
Affiliation:
Massachusetts Institute of Technology, Cambridge, MA 02139
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Abstract

To date, processes used to synthesize to silicon nitride and silicon carbide ceramics from polysilazane preceramic polymers have focused on techniques which seek fully dense monoliths or matrices. An alternative approach, phase separation of polysilazane solutions using appropriate gelation agents, yields infusible preceramic monoliths having controlled two-phase microstructures. Subsequent removal of the solvent phase by supercritical fluid exchange leads to aerogels with defined pore structures. Controlled pore structures were explored as a means of providing diffusional pathways for reactant and product gases during pyrolysis. Resulting changes in the gel microstructure were followed by scanning electron microscopy and surface analysis by nitrogen desorption methods. It was found that micropores present in the unpyrolyzed gels are absent after pyrolysis, but that larger pore structures are maintained.

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References

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