Ceramic materials

A method of producing a ceramic material comprising:

• mixing components consisting essentially of not more than 75% by weight of high active surface area alumina in powder form of particle size less than 10 microns, or a compound of aluminum which decomposes to give the required alumina at the elevated temperature of the process, with powdered silicon nitride of particle size less than 20 microns;
• surrounding the mixture with a protecting medium;
• and sintering the mixture at a temperature within the range of from 1600.degree.C to 2000.degree.C for at least 30 minutes, the silicon nitride and alumina combining at said temperatures to form a ceramic material consisting of a least 90% of a single phase silicon aluminum oxynitride consisting of a B-phase silicon nitride lattice having increased cell dimensions in which the silicon in the lattice has been partially replaced by aluminum and the nitrogen has been partially replaced by oxygen.

A method of producing a ceramic material including at least 90% of a single phase silicon aluminum oxynitride consisting of a .beta.-phase silicon nitride lattice having increased cell dimensions in which the silicon in the lattice has been partially replaced by aluminum and the nitrogen has been partially replaced by oxygen, comprising heating a mixture containing silicon powder and alumina powder in a nitriding atmosphere and at a temperature greater than 1250.degree. C and less than or equal to 1600.degree. C, the powders having a particle size of less than 20 microns, and the relative proportions of the silicon and alumina in the mixture being such that the atomic ratio of the silicon to aluminum is greater than or equal to 3:1.

A method of producing a ceramic material including at least 90% of a single phase silicon aluminum oxynitride consisting of a .beta.-phase silicon nitride lattice having increased cell dimensions in which the silicon in the lattice has been partially replaced by aluminum and the nitrogen has been partially replaced by oxygen, comprising heating a mixture containing silicon powder and alumina powder in a nitriding atmosphere and at a temperature greater than 1250.degree. C and less than or equal to 1600.degree. C, the powders having a particle size of less than 20 microns, and then raising the temperature above 1600.degree. C with the preheated mixture being surrounded with a protective medium, the relative proportions of the silicon and alumina in the mixture being such that the atomic ratio of the silicon to aluminum is less than 3:1 down to 1:3.