Abstract Method and apparatus for producing silicon nitride molded bodies by means of a pseudoisostatic hot pressing process. Silicon nitride is initially ground in a grinding vessel with grinding elements wherein the vessel is lined with the same material from which the grinding elements are made, e.g., hot pressed silicon nitride. Grinding is continued until a specific surface area greater than 15 m 2 is obtained. The grinding takes place in the presence of a grinding liquid to prevent oxidation of the freshly ground silicon nitride. The silicon nitride suspension is then treated in a pressure vessel to remove the grinding liquid therefrom and form a blank. The blank is thereafter embedded within a pressure transfer medium, e.g., boron nitride, and inserted into the die of a hot pressing furnace to obtain the desired hot pressed silicon nitride. The pressure vessel used in this method comprises a chamber for the silicon nitride suspension, an outlet means connected to the bottom of the chamber to permit the vacuum removal of the grinding fluid from said suspension; and an inlet means connected to the chamber for admitting an inert gas, e.g., nitrogen, into the chamber.
A method for producing silicon nitride molded bodies by means of pseudoisostatic hot pressing wherein carbon is used as the die of the hot pressing furnace, comprising: (1) grinding a silicon nitride starting material to a specific surface area greater than 15 m 2 per gram in combination with a sufficient amount of grinding liquid in the form of a suspension to keep air and the humidity of the air away from said starting material, said grinding being done by grinding elements made of silicon nitride in a vessel lined with silicon nitride; (2) removing said grinding liquid from said ground silicon nitride to form a filter cake or blank; and (3) embedding said filter cake or blank within a pressure transfer medium within a hot pressing furnace and pseudoisostatically hot pressing the embedded blank to form a hot pressed silicon nitride molded body.
Claim 2
Independent Claim
144 words
A method for producing silicon nitride molded bodies by means of pseudoisostatic hot pressing wherein carbon is used as the die of the hot pressing furnace, comprising: (1) grinding a silicon nitride starting material to a specific surface area greater than 15 m 2 per gram in combination with a sufficient amount of grinding liquid in the form of a suspension to keep air and the humidity of the air away from said starting material, said grinding being done by grinding elements made of silicon nitride in a vessel lined with silicon nitride; (2) removing said grinding liquid from said ground silicon nitride to form a filter cake or blank; and (3) embedding said filter cake or blank within a pressure transfer medium within a hot pressing furnace and pseudoisostatically hot pressing the embedded blank to form a hot pressed silicon nitride molded body.
Claim 3
Dependent Claim
13 words
The method of claim 1 wherein said pressure transfer medium is boron nitride.
Claim 4
Dependent Claim
23 words
The method of claim 1 wherein said grinding liquid is an organic liquid capable of preventing the oxidation of freshly ground silicon nitride.
Claim 5
Dependent Claim
13 words
The method of claim 1, wherein said grinding liquid is acetone or cyclohexane.
Claim 6
Dependent Claim
40 words
The method of claim 1 further comprising removing said grinding liquid by means of a vacuum and introducing, under pressure, an inert gas to provide turbulence and prevent sedimentation of said silicon nitride during the removal of the grinding liquid.
Claim 7
Dependent Claim
11 words
The method of claim 5 wherein said inert gas is nitrogen.
Claim 8
Dependent Claim
21 words
The method of claim 1 wherein said vessel lining and said grinding elements are both made of hot pressed silicon nitride.
Claim 9
Dependent Claim
31 words
The method of claim 1 further comprising hot pressing said silicon nitride filter cake or blank at a temperature between 1750° and 1850° C. in the presence of an inert atmosphere.