Abstract: A device for producing a ceramic sintered body consisting essentially of a mixing trough for mixing ceramic powder with water to form a slurry, the mixing trough having stirring blades, a separate slurry circulation conduit and a slurry mixing deflocculating unit, said separate slurry circulation conduit connecting said mixing trough and said deflocculating unit, said slurry mixing unit deflocculating said powder which has been flocculated with no grinding of powder by means of causing a high-speed shear flow and a high-speed contraction flow in the slurry, said slurry being repeatedly circulated form said slurry mixing unit to said mixing trough through said separate slurry circulation conduit.

Abstract: Silicon nitride sintered bodies consisting of prismatic crystal grains of Si.sub.3 N.sub.4 and/or sialon, equi-axed crystal grains of Si.sub.3 N.sub.4 and/or sialon, a grain boundary phase existing among the prismatic and equi-axed crystal grains and dispersed particles in the grain boundary phase, in which the prismatic crystal grains have an average grain size of 0.3 .mu.m or less in minor axis and an average grain size of 5 .mu.m or less in major axis, the equi-axed crystal grains have an average grain size of 0.5 .mu.m or less and the dispersed particles have an average size of 0.1 .mu.m or less, the volume of the dispersed particles being 0.05% by volume or more based on the total volume of the rest of the sintered body. The silicon nitride sintered bodies have a strength sufficient for use as structural materials of machine parts or members, with a minimized scattering of the strength as well as high reliability, superior productivity and advantageous production cost.

Abstract: A silicon nitride composite sintered which comprises crystal grains of silicon nitride and/or sialon having an average minor axis length of 0.05 to 3 .mu.m and an aspect ratio of 10 or less and foreign particles dispersed in the crystal grains and/or the grain boundary phase, said particles having a thermal expansion coefficient of 5.times.10.sup.-6 /.degree.C. or more and an average particle size of 1 to 500 nm. The sintered body is produced by wet mixing silicon nitride powder, at least two sintering aids selected from among Y.sub.2 O.sub.3, Al.sub.2 O.sub.3, AlN and MgO and at least one compound selected from among the oxides, nitrides, carbides and silicides of the elements, excluding Si and C, of the groups IIa, IIIa, IVa, Va, VIa, IIb, IIIb and IVb of the Periodic Table to form a molding; and heat treating under the specified conditions.

Abstract: A silicon sintered body comprising a matrix phase consisting of silicon nitride and a grain boundary phase in which the silicon nitride consists of 66 to 99% by volume of .beta.-Si.sub.3 N.sub.4 and/or .beta.'-sialon with the balance being .alpha.-Si.sub.3 N.sub.4 and/or .alpha.'-sialon, the .beta.-Si.sub.3 N.sub.4 and/or .beta.'-sialon consisting of hexagonal rod-like grains having a diameter of 500 nm or less in the minor axis and an aspect ratio 5 to 25, the .alpha.-Si.sub.3 N.sub.4 and/or .alpha.'-sialon consisting of equi-axed grains having an average diameter of 300 nm or less, and titanium compounds are contained within the grains of the matrix phase and in the grain boundary phase. The sintered body is produced by mixing (1) 100 parts by weight of .alpha.-Si.sub.3 N.sub.4 powder, (2) 0.

Abstract: A composite silicon nitride sintered body formed of silicon nitride as a matrix and silicon carbide having particle sizes of 5 to 500 nm as a phase dispersed in the sintered body, wherein the total amount of dispersed silicon carbide is 1 to 40% by volume based on the sintered body, the proportion by volume of the silicon carbide dispersed in the silicon nitride particles is 5 to 99% based on the total amount dispersed, the remainder being present only in the grain boundary of the silicon nitride, and a process for producing a silicon nitride composite sintered body which includes the steps of adding a sintering aid to amorphous composite powders as starting materials consisting of silicon, nitrogen and carbon to form a green compact; firing the green compact in a nitrogen atmosphere at 1350.degree. to 1650.degree. C. as the primary sintering; firing the same at 1600.degree. to 1900.degree. C. as the secondary sintering; and firing the same at 1800.degree. to 2200.degree. C.