I have been working with nozzles made from silicon nitride wafers for biomedical applications. Recently i am facing a problem, after the substance is being sprayed from the nozzle, its sticking to the surface of the nozzle membrane and cracking it! i have no idea how to prevent that. Does anyone have any explanation to that? whats the underlying mechanism?
Thanks in advance!
Dear Salmeen,
It is well-known that nozzles made of silicone nitride are cracked as a result of thermal stresses or thermal shocks. To eliminate the possibility of cracking new formula of silicone nitride was invented and patented:
1. Silicon nitride composite refractories consisting of:
20 to 60 wt% silicon nitride;
10to 50 wt% refractory materials in powder form selected from the group consisting of magnesia, spinel, alumina, zirconia and carbides, said refractory materials having grain sizes of 50 microns or more, and
1 to 30 wt% boron nitride,
said composite refractories containing silicon nitride bonds formed by the reaction sintering of silicon, said silicon nitride bonds being bonded structures.
For more on this topic, please use the following links:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660015713.pdf
http://www.google.com/patents/US4540674
Hoping this will be helpful,
Rafik
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