Abstract: In a method of forming a ceramic material of the kind including at least 90% by weight of a single phase silicon aluminium oxynitride which has a crystal structure based on .beta. silicon nitride but of increased unit cell dimensions and which obeys the general formula:Si.sub.6-z Al.sub.z N.sub.8-z O.sub.zwhere z is greater than 0 and less than or equal to 5, a ceramic intermediary is produced which contains a silicon aluminium oxynitride which obeys a different formula from said general formula. The intermediary is then heated in powder form at a temperature between 1200.degree. C and 2000.degree. C in a protective environment with at least one compound containing two or more of the elements silicon, aluminium, oxygen and nitrogen, the composition of said intermediary and the amount of said at least one compound being such that said intermediary is converted at said temperature into said ceramic material.

Abstract: In a method of forming a refractory product wherein a mixture consisting of effective amounts of silica, alumina, aluminium nitride, and with or without silicon nitride, is provided, the mixture is surrounded with a protective medium and sintered at a temperature between 1200.degree.-2000.degree. C to form a single phase silicon aluminium oxynitride corresponding to the formula: Si.sub.6.sub.-z Al.sub.z N.sub.8.sub.-z O.sub.z, where z is greater than zero and less than or equal to 5, and when there is no silicon nitride in the mixture z is greater than or equal to 4 and less than or equal to 5, the improvement being the step of introducing into said mixture magnesium oxide in an amount of not more than 5% by weight to form a magnesium silicate glass and aid in densification of the ceramic material.

Abstract: A method of producing hot pressed products, especially products of complex shapes, wherein the material from which the component is formed is hot pressed between a plurality of die parts of which at least one is of substantially uniform density and substantially compressible. This enables the shape of the die part to conform exactly or nearly so to the shape of the body being sintered throughout hot pressing, thereby resulting in obtainment of products of complex shapes.

Abstract: In a method of forming a sintered, ceramic product, aluminium nitride is reacted with silica at a temperature of between 1200.degree. and 2000.degree. C to form a single phase silicon aluminium oxynitride ceramic material, the reaction mixture at said temperature containing not more than 60% by weight of the aluminium nitride and also containing first and second metal oxides other than silica. The metal oxides are arranged so that they do not introduce into the mixture a combination of magnesium oxide and alumina alone and further are arranged so that during the reaction they combine with part of said silica to form a silicate glass having a liquidus temperature below that of the silicate glass which would be formed from silica with either of said metal oxides alone. The silicate glass formed then aids densification of the ceramic material during sintering.

Abstract: A method of manufacturing a silicon nitride powder comprises heating a bed of silicon powder in a furnace having an atmosphere containing nitrogen so that the silicon reacts with the nitrogen to produce silicon nitride. The exothermic reaction between the silicon and the nitrogen is monitored, either by comparing the temperature in the reaction bed with the temperature at another point in the furnace, or by allowing the nitrogen containing atmosphere to flow through the furnace and measuring the rates of flow of the atmosphere into and out of the furnace. The partial pressure of the nitrogen in the furnace atmosphere is then controlled in accordance with the exothermic reaction so as to ensure that the temperature in the bed does not exceed a predetermined value above which .beta.-phase silicon nitride is formed, the partial pressure of the nitrogen in the furnace being controlled by effecting at least one of the steps of:A. diluting the nitrogen in the furnace atmosphere and,B. evacuating the furnace.