Abstract: An aluminum nitride sintered body containing 1 to 10% by weight of an oxide of at least one element selected from a group consisting of a group IIIa element, Ca, Sr and Ba, the concentration of a Si component in the sintered body is 0.01 to 0.2% by weight and three-point bending strength is 490 MPa or more. The sintered body is characterized in that a crystal structure composed of aluminum nitride crystal grains is formed, the fracture toughness is 2.8 MN/m.sup.3/2 or more, the three-point bending strength is 490 MPa or more and the thermal conductivity is 150 W/m.multidot.k or more. In the crystal structure, the distribution of the crystal grain distribution is adequately adjusted. The growth of the AlN sintered body is restricted, thus the structure of the sintered body is fined, and the distribution of the crystal grain size is controlled adequately so that the strength and the fracture toughness of the sintered body are improved.

Abstract: A high thermal conductive silicon nitride sintered body contains: 2.0-7.5% by weight of a rare earth element in terms of the amount of an oxide thereof; at most 0.3% by weight of Li, Na, K, Fe, Ca, Mg, Sr, Ba, Mn and B as impurity cationic elements in terms of total amount thereof; and, if necessary, at most 2.0% by weight of alumina and/or at most 2.0% by weight of aluminum nitride, and comprises a beta-phase type silicon nitride crystal and a grain boundary phase. The silicon nitride sintered body has a thermal conductivity of at least 60 W/m.multidot.K. Optionally, the sintered body further contains 0.2-3.0% by weight of at least one compound selected from the group consisting of the oxides, carbides, nitrides, silicides and borides of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W. The sintered body has a porosity of at most 1.5% by volume, a thermal conductivity of at least 60 W/m.multidot.K, and a three-point bending strength of at least 80 kg/mm.sup.2 at a room temperature.

Abstract: Sintered bodies with the primary phase of .beta. and/or .alpha. prime sialon. In the sialon phase which is the primary phase, hafnium oxide and silicon carbide are dispersedly contained as dispersion phases. 1 to 60 parts by weight of hafnium oxide are contained in 100 parts by weight of the primary phase. 5 to 30 parts by weight of silicon carbide are contained in 100 parts by weight of the primary phase. Hafnium oxide suppresses decrease of sintering characteristic which is caused by silicon carbide. Thus, a large amount of silicon carbide can be added, thereby improving the fracture toughness value.

Abstract: A ceramic sinter whose mother phase substantially satisfies a sialon composition. This sialon containing ceramic sinter contains at least one kind of compound selected from the group of oxides, carbides, nitrides, and silicides of hafnium, niobium, or titanium in the range of from 0.2 to 40 weight %. The compound of hafnium, niobium, or titanium is present independently in the mother phase in particle-dispersive form. The dispersed particles contribute to improving the mechanical strength, fracture toughness, and heat impact resistance because the sinter body is reinforced by dispersion. The sialon containing ceramic sinter is so excellent in high-temperature properties that it is suitable for use in high-temperature structural materials. Further, a .beta.

Abstract: A wear-resistant member formed comprises a sintered ceramic body essentially consisting of 0.1 to 15% by weight of at least one material selected from the group comprising molybdenum carbide, niobium carbide, hafnium carbide, tantalum carbide, tungsten carbide, molybdenum silicide, niobium silicide, hafnium silicide, tantalum silicide, tungsten silicide, molybdenum boride, niobium boride, hafnium boride, tantalum boride, and tungsten boride, 2 to 20% by weight of a boundary phase selected from the group consisting of Si--Y--Al--O--N and Si--Y--Al--O--N--B, and a balance of .beta.-silicon nitride. The wear-resistant member preferably has a metal member bonded to the sintered ceramic body. The wear-resistant member can perform high-load work such as high-speed cutting.

Abstract: A sialon based composite composite essentially consists of 5 wt % to 40 wt % of SiC fibers, 0.3 wt % to 10 wt % of an Hf component which is calculated in terms of Hf oxide, and the balance of sialon as a major constituent. In this case, the sialon is .alpha.-sialon or .beta.-sialon.

Abstract: A wear-resistant member consisting of ceramics containing yttrium oxide and aluminum oxide as a sintering auxiliary component and further titanium oxide, hafnium oxide and aluminum nitride, and mainly formed of silicon nitride. Silicon nitride ceramics possesses the segregation of amorphous phase mainly consisting of the sintering auxiliary component, but its size is 100 .mu.m or below at most. By restricting the segregation size of the amorphous phase to 100 .mu.m or below, sliding property, particularly rolling fatigue properties are improved. And also variability is lowered and the reliability can be highly improved.

Abstract: A method for the production of a silicon nitride ceramics exhibiting high mechanical strength at elevated temperature is disclosed. This production is effected by a method which comprises preparing a mixture of silicon dioxide with excess carbon as a silicon nitride material for the silicon nitride ceramic, reducing this mixture in an atmosphere of nitrogen, roasting the resulting mixture of silicon nitride with carbon thereby giving rise to a silicon nitride-carbon mixture with the free carbon content thereof adjusted in the range of 0.1 to 3% by weight, molding the produced mixture in combination with a sintering aid in a prescribed shape, calcining the molded mixture, and thereafter sintering the calcined mass.

Abstract: A sintered silicon nitride ceramic article excelling in high-temperature strength and experiencing only an insignificant decline of strength at elevated temperatures particularly up to 1,300.degree. C. is produced by firing a ceramic mixture composed of not more than 10% by weight of the oxide of a rare earth element, not more than 10% by weight of at least one member selected from the group consisting of oxides, carbides, and silicides respectively of Hf, Ta, and Nb, optionally not more than 10% by weight of aluminum nitride, and the balance being silicon nitride.

Abstract: A sliding member formed of sintered silicon nitride shows improvement in strength and abrasion resistance when substantially all the .beta.-phase type fine silicon nitride particles present as a main component in the sintered silicon nitride have major diameters not exceeding 60 .mu.m and aspect ratios of not less than 5 and the aforementioned fine silicon nitride particles have a relative density of not less than 98%.

Abstract: Sintered ceramic articles and a method for the production thereof are disclosed. When a shaped Si.sub.3 N.sub.4 ceramic article is sintered in the presence of SiO.sub.2 or a SiO.sub.2 -containing substance in an inactive gas atmosphere, there is obtained a sintered ceramic article having the surface thereof coated with a thin layer formed preponderantly of silicon oxynitride (Si.sub.2 N.sub.2 O).The sintered ceramic article of this invention excels in resistance to elevated temperatures, particularly temperatures exceeding 1200.degree. C., and enjoys a good surface condition.

Abstract: A sintered ceramic body has a surface layer containing yttrium silicate, cristobalite and silicon nitride, and mainly consists of silicon nitride. The silicon ceramic body is manufactured by preparing a composition containing a silicon nitride powder and an yttrium oxide powder, forming and sintering the composition, and heat-treating the sintered body in an oxidizing atmosphere. The ceramic body has a high mechanical strength over its entire surface and has little variation in mechanical strength.

Abstract: As the aluminum nitride component of a sintering aid for powdered silicon nitride, either a spinel type compound having oxygen dissolved in aluminum nitride to form a solid solution or a poly-type aluminum nitride is used. Since the compound is highly stable in water, it can be effectively used in the form of an aqueous slurry mixture. As the sintering aid, this compound is used as effectively as aluminum nitride.

Abstract: A sintered ceramic body is manufactured first by preparing a composition containing a binder and a ceramic powder having a particle size distribution given such that 0 to 1 weight % of ceramic particles with a particle size of less than 0.2 .mu.m, 0 to 2 weight % of ceramic particles with a particle size of 0.2 .mu.m to less than 0.5 .mu.m, 5 to 15 weight % of ceramic particles with a particle size of 0.5 .mu.m to less than 1.0 .mu.m, 5 to 15 weight % of ceramic particles with a particle size of 1.0 .mu.m to less than 1.5 .mu.m, 5 to 15 weight % of ceramic particles with a particle size of 1.5 .mu.m to less than 2.0 .mu.m, and 50 to 80 weight % of ceramic particles with a particle size of not less than 2.0 .mu.m. The prepared composition is then injection-molded into a predetermined shape. The binder is removed from the molded body, and the binder-free molded body is sintered.

Abstract: Disclosed is a process for producing a sintered silicon nitride-base body, which comprises; mixing powder (A) of heat-treated or not heat-treated silicon nitride powder and powder (B) of powder obtained by heat-treating a powdery mixture of silicon nitride powder and a sintering additive in a non-oxidizing atmosphere and then grinding the resulting heat-treated products into powder; and forming the resultant powdery mixture into a desired shape, which is then sintered in a non-oxidizing atmosphere.The process is characterized by heating powder (B), or powder (A) and powder (B), before sintering, thereby producing sintered silicon nitride body of highly improved properties.

Abstract: Disclosed is a method of producing a sintered body of ceramics, wherein a powder mixture consisting, essentially of at most 10%, exclusive of 0%, by weight of yttrium oxide, at most 10%, exclusive of 0%, by weight of aluminum oxide, at most 10%, exclusive of 0%, by weight of aluminum nitride, at most 5%, exclusive of 0%, by weight of at least one material selected from the group consisting of titanium oxide, magnesium oxide and zirconium oxide, and the balance essentially of silicon nitride is sintered under a non-oxidizing atmosphere.

Abstract: There are disclosed a sintered body of ceramics, comprising 0.1 to 10% by weight of yttrium oxide; 0.1 to 10% by weight of aluminum oxide; 0.1 to 10% by weight of aluminum nitride; 0.1 to 5% by weight of at least one silicide selected from the group consisting of magnesium silicide, calcium silicide, titanium silicide, vanadium silicide, chromium silicide, manganese silicide, zirconium silicide, niobium silicide, molybdenum silicide, tantalum silicide and tungsten silicide; and the balance being silicon nitride, and a process for producing a sintered body of ceramics, which comprises molding a powder mixture of the same composition, and sintering the resultant molded compact in a non-oxidative atmosphere.According to the present invention, it is possible to manufacture sintered body having high density and excellent impact resistance.

Abstract: There are disclosed a sintered body of ceramics, comprising 0.1 to 10% by weight of Y.sub.2 O.sub.3 ; 0.1 to 10% by weight of Al.sub.2 O.sub.3 ; 0.1 to 10% by weight of AlN; 0.1 to 5% by weight of at least one oxide selected from the group consisting of Li.sub.2 O, BeO, CaO, V.sub.2 O.sub.5, MnO.sub.2, MoO.sub.3 and WO.sub.3 or a combination of at least one of these oxides with at least one oxide selected from the group consisting of B.sub.2 O.sub.3 MgO, TiO.sub.2, Cr.sub.2 O.sub.3, CoO, NiO, ZrO.sub.2, Nb.sub.2 O.sub.5, HfO.sub.2 and Ta.sub.2 O.sub.5 ; and the balance of Si.sub.3 N.sub.4, and a process for producing a sintered body of ceramics, which comprises molding a powder mixture of the same composition, and sintering the resultant molded compact in a non-oxidative atmosphere.The process of the present invention requires no hot press and therefore very suitable for bulk production.

Abstract: Ceramic powder material mainly consists of silicon nitride wherein the content of oxygen combined with generally unavoidable impurities as measured by activation analysis accounts for less than 2% by weight. The above-mentioned ceramic powder material can also be prepared preferably by the method which comprises the step of heating raw ceramic powder material mainly consisting of silicon nitride to 1,400.degree. C. to 1,900.degree. C. in the presence of a separately prepared nonsintered molding of ceramic material or sintered molding of ceramic material having a porosity of at least 10%.

Abstract: Disclosed is a method of producing a sintered body of ceramics, wherein a powder mixture consisting, essentially of at most 10%, exclusive of 0%, by weight of yttrium oxide, at most 10%, exclusive of 0%, by weight of aluminum oxide, at most 10%, exclusive of 0%, by weight of aluminum nitride, at most 5%, exclusive of 0%, by weight of at least one material selected from the group consisting of titanium oxide, magnesium oxide and zirconium oxide, and the balance essentially of silicon nitride is sintered under a non-oxidizing atmosphere.