Abstract: A silicon nitride sintered body comprising ?-sialon expressed by a composition formula of Si6?ZAlZOZN8?Z, wherein z value being the dissolved amount is 0.1 to 1, as a main phase, a grain boundary phase and Fe silicide particles. The grain boundary phase contains RE (Group III elements in the periodic table)-Al—Si—O, and component ratios of Al, Si and RE in terms of Al2O3, SiO2, RE2O3, respectively is 5 to 50 mass % of Al2O3, 5 to 20 mass % of SiO2, and the balanced amount of RE2O3, the grain boundary phase is contained in a range of 20 volume % or less to 100 volume % of the sintered body, and the Fe silicide particles is contained in 0.02 to 3 mass % in terms of Fe to 100 mass % of the sintered body. Its high thermal shock resistance provides suitable applications to members for molten metal, hot working, and digging.

Abstract: This invention provides a protective member comprising a ceramic body comprising a plurality of first phases (2) composed mainly of silicon carbide and a plurality of second phases (3) having a composition different from the composition of the first phase (2) and containing at least boron, silicon and carbon. A part of the second phase is present in the first phase as a whole, and at least a part of the remaining part of the second phase is present between a plurality of the first phases.

Abstract: A boron carbide sintered body having a plurality of pores, comprises a boron carbide as a main component and a plurality of graphite particles dispersed in the sinter. The graphite particles is exposed to the pores or is in the vicinity of the pores.

Abstract: A silicon nitride sintered material includes a silicon nitride crystal and a grain boundary layer that contains at least two of a first metal silicide (a metal silicide having, as a first metal element, at least one selected from the group consisting of Fe, Cr, Mn and Cu), a second metal silicide (a metal silicide having, as a second metal element, at least one of W or Mo) and a third metal silicide (a metal silicide having a plurality of metal elements including the first metal element and the second metal element), wherein the grain boundary layer has neighboring phase where at least two of the first through third metal silicides exist in contact with each other.

Abstract: The compressive strength of a boron carbide sintered compact is improved by controlling crystals of the boron carbide to a polycrystalline structure having a grain size distribution in which coarse crystals with a grain size of 20 ?m or more and fine crystals with a grain size of 10 ?m or less are mixed in an appropriate ratio. Furthermore, a protective member having an improved compressive strength can be provided using the boron carbide sintered compact having a polycrystalline structure in which coarse crystals and fine crystals are mixed in an appropriate ratio or a boron carbide sintered compact containing graphite and silicon carbide.

Abstract: A silicon nitride sintered body comprising ?-sialon expressed by a composition formula of Si6-ZAlZOZN8-Z, wherein z value being the dissolved amount is 0.1 to 1, as a main phase, a grain boundary phase and Fe silicide particles. The grain boundary phase contains RE (Group III elements in the periodic table)-Al—Si—O, and component ratios of Al, Si and RE in terms of Al2O3, SiO2, RE2O3, respectively is 5 to 50 mass % of Al2O3, 5 to 20 mass % of SiO2, and the balanced amount of RE2O3, the grain boundary phase is contained in a range of 20 volume % or less to 100 volume % of the sintered body, and the Fe silicide particles is contained in 0.02 to 3 mass % in terms of Fe to 100 mass % of the sintered body. Its high thermal shock resistance provides suitable applications to members for molten metal, hot working, and digging.

Abstract: A boron carbide sintered body having a plurality of pores, comprises a boron carbide as a main component and a plurality of graphite particles dispersed in the sinter. The graphite particles is exposed to the pores or is in the vicinity of the pores.

Abstract: The compressive strength of a boron carbide sintered compact is improved by controlling crystals of the boron carbide to a polycrystalline structure having a grain size distribution in which coarse crystals with a grain size of 20 ?m or more and fine crystals with a grain size of 10 ?m or less are mixed in an appropriate ratio. Furthermore, a protective member having an improved compressive strength can be provided using the boron carbide sintered compact having a polycrystalline structure in which coarse crystals and fine crystals are mixed in an appropriate ratio or a boron carbide sintered compact containing graphite and silicon carbide.

Abstract: A silicon nitride sintered material includes a silicon nitride crystal and a grain boundary layer that contains at least two of a first metal silicide (a metal silicide having, as a first metal element, at least one selected from the group consisting of Fe, Cr, Mn and Cu), a second metal silicide (a metal silicide having, as a second metal element, at least one of W or Mo) and a third metal silicide (a metal silicide having a plurality of metal elements including the first metal element and the second metal element), wherein the grain boundary layer has neighboring phase where at least two of the first through third metal silicides exist in contact with each other.

Abstract: Ceramic granules for producing sintered products of silicon nitride that can be favorably used as structural materials for various heat engines such as automotive parts, gas turbines and the like, and as abrasion resistant materials and corrosion resistant materials. A process for preparing the ceramic granules and a process for preparing sintered products of silicon nitride by using the ceramic granules. Ceramic granules comprise a mixture of a silicon nitride powder, a silicon powder and an assistant, as well as an organic binder, said ceramic granules having an average particle diameter of from 50 to 300 .mu.m and a relative density of from 18 to 30%.

Abstract: A sintered product of silicon nitride containing not smaller than 70 mol % of a .beta.-silicon nitride as well as an element of the Group 3a at least including Lu of periodic table and impurity oxygen, wherein when the content of the element of the Group 3a of periodic table and the content of the impurity oxygen are, respectively, expressed being reckoned as the amount of an oxide of the element of the Group 3a of periodic table (RE.sub.2 O.sub.3) and as the amount of SiO.sub.2 of impurity oxygen, their total amount is from 2 to 30 mol %, the molar ratio (SiO.sub.2 /RE.sub.2 O.sub.3) of the amount of the element of the Group 3a of periodic table reckoned as the oxide (RE.sub.2 O.sub.3) thereof to the amount of impurity oxygen reckoned as SiO.sub.2 is from 1.6 to 10, and the intergranular phase of the sintered product chiefly comprises a crystal phase consisting of the element of the Group 3a of periodic table, silicon and oxygen and a process for producing the same.