Abstract: A complex-shaped bonded body of silicon nitride having a high bonding strength of more than 30 kg/mm.sup.2 as flexural strength and continuously homogenous microstructure through the bonded portion can be obtained by the method comprising the following five steps:(a) molding a body from a mixture of silicon powder having a diameter of less than 44 .mu.m and non-oxide ceramics powder having a diameter of less than 44 .mu.m,(b) heating a molded body obtained by step (a) at a temperature of 600 to 1500.degree. C. in a non-oxide atmosphere such as nitrogen or argon gas to sinter said silicon powder and partially convert to silicon nitride retaining 60 to 100 wt. % unreacted silicon powder therein,(c) grinding a surface to be bonded together with other bodies of said presintered body obtained by step (b) to dispose of unreacted silicon thereon,(d) placing a bonding agent containing silicon powder having a diameter of less than 44 .mu.

Abstract: A shaped body of silicon nitride enjoying high density, ample shrinkage, and outstanding mechanical strength is produced in a desired pattern by a method of preparing a shaped body comprising Si particles and a compound capable of remaining as SiC or C in the form of film on the surface of the Si particles in a non-oxidative atmosphere at a temperature in the range of 900.degree. to 1,400.degree. C., subjecting the shaped body to sintering and shrinkage of not less than 1% in an atmosphere of inert gas at a temperature exceeding 900.degree. C., and not exceeding the softening point of Si, and subsequently subjecting the resultant sintered shaped body to nitriding in a nitriding atmosphere at a pressure exceeding atmospheric pressure and at a temperature in the range of 1,200.degree. to 1,500.degree. C.

Abstract: Method produces reaction sintered silicon nitride complex shapes. Parent material (moldings of silicon powder-cured resin) and bonding or joint material (silicon powder-uncured resin) are integrally connected by steps of heat-curing the resin in the joint, heating the body thus bonded together to pyrolyze the cured resin and sinter the silicon powder, the pyrolysis gas reducing oxide film on silicon, and sintered parent material and joint material are simultaneously nitrided and integrally connected by continuous silicon nitride.

Abstract: After sintering, ceramic body of Si.sub.3 N.sub.4 -SiC is heat-treated at 500.degree.-1500.degree. C. in atmosphere of gas mixture of chlorine and nitrogen whereby SiC is converted into silicon chloride which in turn is nitrided to form Si.sub.3 N.sub.4 in the pores of the ceramic body to provide closed pore structure. Gas mixture may contain oxygen. Heat treatment may be conducted in pressurized atmosphere of gas mixture.

Abstract: Flaky .beta.-SiC mainly composed of .beta.-SiC which is obtained from an organic silicon polymer containing the carbon and silicon atoms as the major skeletal component and the method for producing such flaky .beta.-SiC are disclosed. Such .beta.-SiC is especially utilized as the starting material for ceramics having a laminar structure as well as for the refractories. The ceramics and refractories provided with such .beta.-SiC have excellent resistance to thermal shock, to thermal fatigue as well as to oxidation.

Abstract: Flaky .beta.-SiC mainly composed of .beta.-SiC which is obtained from an organic silicon polymer containing the carbon and silicon atoms as the major skeletal component and the method for producing such flaky .beta.-SiC are disclosed. Such .beta.-SiC is especially utilized as the starting material for ceramics having a laminar structure as well as for the refractories. The ceramics and refractories provided with such .beta.-SiC have excellent resistance to thermal shock, to thermal fatigue as well as to oxidation.

Abstract: Flaky .beta.-SiC mainly composed of .beta.-SiC which is obtained from an organic silicon polymer containing the carbon and silicon atoms as the major skeletal component and the method for producing such flaky .beta.-SiC are disclosed. Such .beta.-SiC is especially utilized as the starting material for ceramics having a laminar structure as well as for the refractories. The ceramics and refractories provided with such .beta.-SiC have excellent resistance to thermal shock, to thermal fatigue as well as to oxidation.

Abstract: A SiC-Si.sub.3 N.sub.4 composite system for special heat-resisting ceramic materials which is fabricated by firing in a nitriding gas atmosphere a green compact prepared from and composed of, as starting materials, silicon powder and an organic silicon polymer containing carbon and silicon atoms as the major skeletal components, whereby said composite system, as a final fired compact has an interwoven texture of SiC and Si.sub.3 N.sub.4 with sufficient micro gaps to absorb thermal stresses, wherein the quantitative ratio by weight of SiC to Si.sub.3 N.sub.4 in said composite system being in the range of 5%-20%:95%-80%.

Abstract: A process by which dense structure refractories that have resistance to spalling may be produced which comprises building up secondary particulates from fine and/or ultra-fine particles of primary particulate, separating the thus prepared secondary particulates, reconstituting the batch within a definite range and proportion of particle size composition, molding the thus reconstituted batch under a predetermined pressure and finally firing the above molded material is disclosed.

Abstract: This invention relates to dense structure refractories having heterogeneous structure and resistance to spalling whose heterogeneous structure is composed of major high density areas of (1) coarse and intermediate grains of secondary particulate and minor low density areas of (2) fine grains and fine powders of secondary particulate distributed in a zigzag random way at the boundaries between the coarse and intermediate grains, which are fabricated from an overall batch mixture consisting of more than 60% by weight of particles of secondary particulate larger than 0.5 mm and less than 40% by weight of particles of secondary particulate smaller than 0.5 mm in size.