Making a triple density article of silicon nitride

Claim 1

A method of making a triple density article of silicon nitride which comprises the steps of: compacting a mixture consisting of from about 95 to 99.5% by weight silicon nitride particles and from about 5 to 0.5% by weight of a densification aid to at least 98% of theoretical density by use of heat and pressure thereby to form a first element of silicon nitride; forming the general shape of a second element by (a) injection molding silicon metal particles and a carrier to form the general shape of said second element, and (b) heating said second element to burn out said carrier; forming the general shape of a third element by a slip casting operation, said slip casting being accomplished from a slip containing silicon metal particles suspended in a vehicle; sintering said third element in an inert atmosphere for a time and at a temperature sufficient to increase the strength of said third element, the inert atmosphere being formed of a gas which will not react with the silicon metal particles; positioning said third element adjacent at least a portion of the surface area of said second element in a manner such that a small space exists between at least a portion of said two elements; bonding said second element to said third element by a slip casting operation in which a slip containing silicon metal particles suspended in a vehicle is applied to said space existing between said two elements to build up sIlicon metal particles in said space; nitriding said bonded second and said third elements in a single operation so that both of said elements are converted substantially to pure silicon nitride and are joined to one another at the area of the slip cast bonding operation; bringing a surface area of said first element into close association with a surface area of said third element; holding said associated surfaces of said first and said third elements so they do not move with respect to one another; and forming a bond between said associated surfaces of said first and said third elements by applying heat to both elements and pressure on one of said elements while the other of said elements is held thereby to force a portion of the silicon nitride forming said surface area of said one element into bonding relationship with said surface area of the other element.

Claim 2

A method of making a triple density article of silicon nitride which comprises the steps of: compacting a mixture consisting of from about 95 to 99.5% by weight silicon nitride particles and from about 5 to 0.5% by weight of a densification aid to at least 98% of theoretical density by use of heat and pressure thereby to form a first element of silicon nitride; forming the general shape of a second element by (a) injection molding silicon metal particles and a carrier to form the general shape of said second element, and (b) heating said second element to burn out said carrier; forming the general shape of a third element by a slip casting operation, said slip casting being accomplished from a slip containing silicon metal particles suspended in a vehicle; sintering said third element in an inert atmosphere for a time and at a temperature sufficient to increase the strength of said third element, the inert atmosphere being formed of a gas which will not react with the silicon metal particles; positioning said third element adjacent at least a portion of the surface area of said second element in a manner such that a small space exists between at least a portion of said two elements; bonding said second element to said third element by a slip casting operation in which a slip containing silicon metal particles suspended in a vehicle is applied to said space existing between said two elements to build up sIlicon metal particles in said space; nitriding said bonded second and said third elements in a single operation so that both of said elements are converted substantially to pure silicon nitride and are joined to one another at the area of the slip cast bonding operation; bringing a surface area of said first element into close association with a surface area of said third element; holding said associated surfaces of said first and said third elements so they do not move with respect to one another; and forming a bond between said associated surfaces of said first and said third elements by applying heat to both elements and pressure on one of said elements while the other of said elements is held thereby to force a portion of the silicon nitride forming said surface area of said one element into bonding relationship with said surface area of the other element.

Claim 3

A METHOD OF MAKING A TRIPLE DENSITY ARTICLE OF SILICON NITRIDE WHICH COMPRISES THE STEPS OF: COMPACTING A MIXTURE CONSISTING OF FROM ABOUT 95 TO 99.5% BY WEIGHT SILICON NITRIDE PARTICLES AND FROM ABOUT 5 TO 0.5% BY WEIGHT OF A DENSIFICATION AID TO AT LEAST 98% OF THEORETICAL DENSITY BY USE OF HEAT AND PRESSURE THEREBY TO FORM A FIRST ELEMENT OF SILICON NITRIDE; FORMING THE GENERAL SHAPE OF A SECOND ELEMENT BY (A) INJECTION MOLDING SILICON METAL PARTICLES AND A CARRIER TO FORM THE GENERAL SHAPE OF SAID SECOND ELEMENT, AND (B) HEATING SAID SECOND ELEMENT TO BURN OUT SAID CARRIER; FORMING THE GENERAL SHAPE OF A THIRD ELEMENT BY A SLIP CASTING OPERATION, SAID SLIP CASTING BEING ACCOMPLISHED FROM A SLIP CONTAINING SILICON METAL PARTICLES SUSPENDED IN A VEHICLE; SINTERING SAID THIRD ELEMENT IN AN INERT ATMOSPHERE FOR A TIME AND AT A TEMPERATRE SUFFICIENT TO INCREASE THE STRENGTH OF SAID THIRD ELEMENT, THE INERT ATMOSPHERE BEING FORMED OF A GAS WHICH WILL NOT REACT WITH THE SILICON METAL PARTICLES; POSITIONING SAID THIRD ELEMENT ADJACENT AT LEAST A PORTION OF THE SURFACE AREA OF SAID SECOND ELEMENT IN A MANNER SUCH THAT A SMALL SPACE EXISTS BETWEEN AT LEAST A PORTION OF SAID TWO ELEMENTS; BONDING SAID SECOND ELEMENT TO SAID THIRD ELEMENT BY A SLIP CASTING OPERATION IN WHICH A SLIP CONTAINING SILICON METAL PARTICLES SUSPENDED IN A VEHICLE IS APPLIED TO SAID SPACE EXISTING BETWEEN SAID TWO ELEMENTS TO BUILD UP SILICON METAL PARTICLES IN SAID SPACE; NITRIDING SAID BONDED SECOND AND SAID THIRD ELEMENTS IN A SINGLE OPERATION SO THAT BOTH OF SAID ELEMENT ARE CONVERTED SUBSTANTIALLY TO PURE SILICON NITRIDE AND ARE JOINED TO ONE ANOTHER AT THE AREA OF THE SLIP CAST BONDING OPERATION; BRINGING A SURFACE AREA OF SAID FIRST ELEMENT INTO CLOSE ASSOCIATION WITH A SURFACE AREA OF SAID THIRD ELEMENT; HOLDING SAID ASSOCIATED SURFACES OF SAID FIRST AND SAID THIRD ELEMENTS SO THEY DO NOT MOVE WITH RESPECT TO ONE ANOTHER; AND FORMING A BOND BETWEEN SAID ASSOCIATED SURFACES OF SAID FIRST AND SAID THIRD ELEMENTS BY APPLYING HEAT TO BOTH ELEMENTS AND PRESSURE ON ONE OF SAID ELEMENTS WHILE THE OTHER OF SAID ELEMENTS IS HELD THEREBY TO FORCE A PORTION OF THE SILICON NITRIDE FORMING SAID SURFACE AREA OF SAID ONE ELEMENT INTO BONDING RELATIONSHIP WITH SAID SURFACE AREA OF THE OTHER ELEMENT.

Claim 4

A METHOD OF MAKING A TRIPLE DENSITY ARTICLE OF SILICON NITRIDE WHICH COMPRISES THE STEPS OF: COMPACTING A MIXTURE CONSISTING OF FROM ABOUT 95 TO 99.5% BY WEIGHT SILICON NITRIDE PARTICLES AND FROM ABOUT 5 TO 0.5% BY WEIGHT OF A DENSIFICATION AID TO AT LEAST 98% OF THEORETICAL DENSITY BY USE OF HEAT AND PRESSURE THEREBY TO FORM A FIRST ELEMENT OF SILICON NITRIDE; FORMING THE GENERAL SHAPE OF A SECOND ELEMENT BY (A) INJECTION MOLDING SILICON METAL PARTICLES AND A CARRIER TO FORM THE GENERAL SHAPE OF SAID SECOND ELEMENT, AND (B) HEATING SAID SECOND ELEMENT TO BURN OUT SAID CARRIER; FORMING THE GENERAL SHAPE OF A THIRD ELEMENT BY A SLIP CASTING OPERATION, SAID SLIP CASTING BEING ACCOMPLISHED FROM A SLIP CONTAINING SILICON METAL PARTICLES SUSPENDED IN A VEHICLE; SINTERING SAID THIRD ELEMENT IN AN INERT ATMOSPHERE FOR A TIME AND AT A TEMPERATRE SUFFICIENT TO INCREASE THE STRENGTH OF SAID THIRD ELEMENT, THE INERT ATMOSPHERE BEING FORMED OF A GAS WHICH WILL NOT REACT WITH THE SILICON METAL PARTICLES; POSITIONING SAID THIRD ELEMENT ADJACENT AT LEAST A PORTION OF THE SURFACE AREA OF SAID SECOND ELEMENT IN A MANNER SUCH THAT A SMALL SPACE EXISTS BETWEEN AT LEAST A PORTION OF SAID TWO ELEMENTS; BONDING SAID SECOND ELEMENT TO SAID THIRD ELEMENT BY A SLIP CASTING OPERATION IN WHICH A SLIP CONTAINING SILICON METAL PARTICLES SUSPENDED IN A VEHICLE IS APPLIED TO SAID SPACE EXISTING BETWEEN SAID TWO ELEMENTS TO BUILD UP SILICON METAL PARTICLES IN SAID SPACE; NITRIDING SAID BONDED SECOND AND SAID THIRD ELEMENTS IN A SINGLE OPERATION SO THAT BOTH OF SAID ELEMENT ARE CONVERTED SUBSTANTIALLY TO PURE SILICON NITRIDE AND ARE JOINED TO ONE ANOTHER AT THE AREA OF THE SLIP CAST BONDING OPERATION; BRINGING A SURFACE AREA OF SAID FIRST ELEMENT INTO CLOSE ASSOCIATION WITH A SURFACE AREA OF SAID THIRD ELEMENT; HOLDING SAID ASSOCIATED SURFACES OF SAID FIRST AND SAID THIRD ELEMENTS SO THEY DO NOT MOVE WITH RESPECT TO ONE ANOTHER; AND FORMING A BOND BETWEEN SAID ASSOCIATED SURFACES OF SAID FIRST AND SAID THIRD ELEMENTS BY APPLYING HEAT TO BOTH ELEMENTS AND PRESSURE ON ONE OF SAID ELEMENTS WHILE THE OTHER OF SAID ELEMENTS IS HELD THEREBY TO FORCE A PORTION OF THE SILICON NITRIDE FORMING SAID SURFACE AREA OF SAID ONE ELEMENT INTO BONDING RELATIONSHIP WITH SAID SURFACE AREA OF THE OTHER ELEMENT.