General Electric Company

John A Palm

Charles D Greskovich

Svante Prochazka

A silicon nitride compact with a density of 95% to 100% is produced by forming a particulate dispersion of silicon nitride and beryllium additive into a compact, firstly sintering the compact from about 1900.degree. C. to about 2200.degree. C. in nitrogen at superatmospheric pressure sufficient to prevent thermal decomposition of the silicon nitride until the entire outside surface of the compact becomes impermeable to nitrogen gas, and then secondly sintering the compact from about 1800.degree. C. to about 2200.degree. C. under a nitrogen pressure having a value at least twice the first nitrogen sintering pressure.

Sintering of silicon nitride to high density

A polycrystalline silicon nitride body having a density of at least 99.5% of the theoretical density of silicon nitride, a thickness ranging from about 0.15 mm up to but less than 0.4 mm, a minimum in-line transmission of about 5% of radiant energy at wavelengths ranging from about 0.9 micron to about 2.5 microns, and a minimum in-line transmission of about 10% at wavelengths ranging from about 2.5 microns to about 4.5 microns.

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Clifton Park, NY, United States of America

John A Palm