C - Chemistry – Metallurgy – 04 – B
Patent
C - Chemistry, Metallurgy
04
B
25/128
C04B 35/58 (2006.01) C01B 21/06 (2006.01)
Patent
CA 1221526
ABSTRACT OF THE DISCLOSURE A method of making a reaction bonded/hot pressed silicon nitride comprising object is disclosed. To form a protective amorphous glass on crystallites in the final product, an Al2O3/SiO2 ratio must be maintained which is greater than 2. Second phase crystallites are formed prior to hot pressing. a mixture of silicon, SiO2, and .4-2.3 molar percent (by weight of the silicon) of oxygen carrying agents, i.e., Y2O3 and Al2O3, is preformed and reaction nitrided to form discs or billets having at least 60% alpha Si3N4 and a high proportion of second phase crystallites which displace substantially all silicate glass except for a controlled small quantity (.2-1% by weight). The reactive amounts of Y2O3, Al2O3 and SiO2 are controlled to assure formation of substantially YlSi12O24N4 as the second phase crystallite. Al2O3 is controlled in an amount of .4-4% by weight to insure that the small proportion of glass has little or no microporosity associated therewith and serves to protect the oxynitrides against linear oxidation kinetics.
433861
Beckwith Elaine C.
Ezis Andre
Ford Motor Company Of Canada Limited
Sim & Mcburney
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