Forming a ceramic by flocculation and centrifugal casting

• US 4,624,808 A
• Filed: 05/15/1984
• Issued: 11/25/1986
• Est. Priority Date: 05/15/1984
• Status: Expired due to Fees

• Current Assignee: Rockwell International Corporation
• Original Assignee: Rockwell International Corporation
• Inventors: Lange, Frederick F.
• Primary Examiner(s): DERRINGTON, JAMES H
• Application Number:
  US06/610,378
• Time in Patent Office: 924 Days
• Field of Search: 264/311, 264/23, 264/56, 501/1
• US Class Current: 264/434
• CPC Class Codes: B28B 1/20 by centrifugal or rotational casting slip-casting involving rotation of the mould B28B1/28; for molten material B28B1/54
• CPC Class Codes: C04B 35/119 with zirconium oxide
• CPC Class Codes: C04B 35/584 based on silicon nitride
• CPC Class Codes: C04B 35/622 Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products

Abstract

A ceramic is fabricated by dispersing ceramic particles in a liquid, sedimenting the dispersion to remove large particles, and then changing its pH to flocculate the dispersed particles. The size distribution of the particles in each individual floc is similar to the size distribution of particles throughout the dispersion. The supernate is removed and the flocs are cast by centrifuging them into a mold. The cast flocs are dried and sintered to form the ceramic. To provide a multiphase ceramic, particles of two or more ceramics can be mixed together and flocced prior to centrifuging.

Claims

1. A method of fabricating a structural ceramic comprising the steps of:

dispersing ceramic particles in a liquid;

sedimenting the disposed particles to remove large particles and agglomerates;

flocculating the dispersed ceramic particles;

removing the clear supernate from the flocced ceramic particles;

centrifuging said flocced ceramic particles to produce a consolidated mass capable of retaining its shape; and

sintering the centrifuged ceramic particles.

2. The method as claimed in claim 1 wherein said step of centrifuging comprises centrifugally casting said flocced ceramic particles into a mold.

3. The method as claimed in claim 1 including the step of air drying said centrifuged ceramic particles prior to sintering.

4. The method as claimed in claim 1 wherein said step of flocculating comprises changing the pH of said liquid.

5. A method of fabricating a structural ceramic comprising the steps of:

dispersing ceramic particles in a liquid;

sedimenting said dispersed particles to remove large particles and agglomerates;

flocculating said dispersed particles by changing the pH of said liquid;

removing supernate from said flocced particles;

centrifugally casting said flocced particles into a mold to produce a consolidated mass capable of retaining its shape;

drying said cast particles; and

sintering said dried particles.

6. A method of fabricating a multiphase structural ceramic comprising the steps of:

dispersing particles of a first ceramic in a first liquid;

sedimenting said dispersed particles of a first ceramic to remove large particles and agglomerates;

flocculating the dispersed particles of said first ceramic;

dispersing particles of a second ceramic in a second liquid;

sedimenting said dispersed particles of a second ceramic to remove large particles and agglomerates;

flocculating the dispersed particles of said second ceramic;

removing clear supernate and mixing the flocced particles of said first and said second ceramics;

centrifuging the mixture of said first and said second ceramics to produce a consolidated mass capable of retaining its shape; and

sintering the centrifuged mixture.

7. The method as claimed in claim 6 wherein said step of mixing comprises shaking the flocced particles of said first and said second ceramics together and then feeding the mixture into an homogenizer.

8. The method as claimed in claim 6 wherein said step of mixing comprises shaking the flocced particles of said first and said second ceramics together and then exposing the mixture to ultrasonic agitation.

9. The method as claimed in claim 6 including the step of air drying said centrifuged mixture prior to sintering.

10. A method of fabricating a multiphase structural ceramic comprising the steps of:

dispersing particles of a first ceramic in a first liquid;

sedimenting said dispersed particles of a first ceramic to remove large particles and agglomerates;

dispersing particles of a second ceramic in a second liquid;

sedimenting said dispersed particles of a second ceramic to remove large particles and agglomerates;

mixing the dispersed particles of said first and second ceramics;

flocculating the particles of said first and second ceramics;

removing clear supernate from said flocced particles;

centrifuging the flocced particles of said first and second ceramics to produce a consolidated mass capable of retaining its shape; and

sintering the centrifuged particles of said first and second ceramics.

11. The method as claimed in claim 10 including the steps of:

flocculating the dispersed particles of said first ceramic and then redispersing them prior to said mixing step; and

flocculating the dispersed particles of said second ceramic and then redispersing them prior to said mixing step.

12. The method as claimed in claim 10 including the step of drying said centrifuged particles prior to said sintering step.