Abstract: The present invention provides a wear resistant member composed of silicon nitride sintered body containing 2–10 mass % of rare earth element in terms of oxide thereof as sintering agent, 2–7 mass % of MgAl2O4 spinel, 1–10 mass % of silicon carbide, and 5 mass % or less of at least one element selected from the group consisting of Ti, Zr, Hf, W, Mo, Ta, Nb and Cr in terms of oxide thereof, wherein a porosity of said silicon nitride sintered body is 1 vol. % or less, a three-point bending strength is 900 MPa or more, and a fracture toughness is 6.3 MPa·m1/2 or more. According to the above structure of the present invention, there can be provided a silicon nitride wear resistant member and a method of manufacturing the member having a high strength and a toughness property, and particularly excellent in rolling and sliding characteristics.

Abstract: The invention provides porous silicon nitride ceramics that having uniform, fine closed pores and a manufacturing method thereof. Metal Si powder is mixed with a sintering additive, followed by thermal treatment, which is a pre-process for forming a specific grain boundary phase. Two-stage thermal treatment is thereafter performed by microwave heating at a temperature of 1000° C. or more. The metal Si powder is thereafter subjected to a nitriding reaction from its surface, the metal Si is thereafter diffused to nitride formed on the outer shell thereof such that porous silicon nitride ceramics having uniform, fine closed pores can be produced. Having a high ratio of closed pores and being superior in electrical/mechanical characteristics, the porous silicon nitride ceramics can display excellent characteristics if used, for example, for an electronic circuit board that requires an anti-hygroscopicity, a low dielectric constant, a low dielectric loss, and mechanical strength.

Abstract: Sintered silicon nitride products comprising predominantly ?-silicon nitride grains in combination with from about 0.1 to 30 mole % silicon carbide, and grain boundary secondary phases of scandium oxide and scandium disilicate. Such products have high fracture toughness, resistance to recession, and resistance to oxidation at temperatures of at least 1500° C. Methods for preparing sintered silicon nitride products are also disclosed.

Abstract: A silicon nitride porous body (5) obtained by nitriding a molded body having metallic silicon (3) as a main component, the porous body having a porous structure with an average pore diameter of 3 ?m or above, and wherein the total content of silicon and nitrogen is 95% or above and the nitridation ratio of silicon is 90% or above. The silicon nitride porous body has a porous structure with a large average pore diameter, with a test specimen cut out from the porous body exhibiting large thermal conductivity and a small thermal expansion coefficient, and can be suitably used in a component for purifying gas and/or solution such as a ceramic filter.

Abstract: Sintered silicon nitride and a silicon nitride tool. The mean major axis length, the mean minor axis length, and the aspect ratio, represented by (mean major axis length/mean minor axis length) of constituent sintered silicon nitride grains in a silicon nitride tool are controlled, and the thermal conductivity and/or fracture toughness Kc thereof are enhanced, thereby providing a tool having a cutting edge which is not prone to chipping.

Abstract: A silicon nitride porous body which is obtained by nitriding a molded body having metallic silicon as a main component and by performing a high temperature heating treatment at a temperature higher than the nitriding temperature, and which has a porous structure with an average pore diameter of 3 ?m or above, and contains at least one kind of element selected from the group consisting of the groups 2A, 3A, 3B inclusive of lanthanoid elements, and 4B. The silicon nitride porous body has a porous structure with a large average pore diameter, a test specimen cut out from the porous body exhibiting a high thermal conductivity and a small thermal expansion coefficient, and can be suitably used in a component for purifying gas and/or solution such as a ceramic filter.

Abstract: A silicon nitride sintered body comprising Mg and at least one rare earth element selected from the group consisting of La, Y, Gd and Yb, the total oxide-converted content of the above elements being 0.6-7 weight %, with Mg converted to MgO and rare earth elements converted to rare earth oxides RExOy. The silicon nitride sintered body is produced by mixing 1-50 parts by weight of a first silicon nitride powder having a particle ratio of 30-100%, an oxygen content of 0.5 weight % or less, an average particle size of 0.2-10 ?m, and an aspect ratio of 10 or less, with 99?50 parts by weight of ?-silicon nitride powder having an average particle size of 0.2-4 ?m; and sintering the resultant mixture at a temperature of 1,800° C. or higher and pressure of 5 atm or more in a nitrogen atmosphere.

Abstract: The object of the present invention is to provide a ceramic body that can support a required amount of a catalyst component, without lowering the characteristics such as strength, being manufactured without forming a coating layer and providing a high performance ceramic catalyst that is excellent in practical utility and durability. A noble metal catalyst is supported directly on the surface of the ceramic body and the second component, consisting of compound or composite compound of element having d or f orbit in the electron orbits thereof such as W, Co, Ti, Fe, Ga and Nb, is dispersed in the first component made of cordierite or the like that constitutes the substrate ceramic. The noble metal catalyst can be directly supported by bonding strength generated by sharing the d or f orbits of the second component, or through interaction with the dangling bond that is generated in the interface between the first component and the second component.

Abstract: The invention relates to cast parts which contain at least 87 wt. % silicon nitride and up to 13 wt. % of an additive combination comprised of Al2O3 and Y2O3. The initial composition of the mass formulation starts with Y2O3/Al2O3 ratios of less than 1.1, preferably with Y2O3 Al2O3 ratios of 0.2 to 1.09. 1% to 20% of the Y2O3 portion can thus be substituted by an additional element group of IVb of the periodic table or by the oxide thereof. The cast parts can comprise up to 1.0 wt. % HfO2 and/or ZrO2. Said cast parts preferably have a thickness >98% of the theoretic thickness. At room temperature, the bending strength of the inventive cast parts amounts to ≧1100 MPa and amounts to ≧850 MPa at 1000° C. The inventive cast parts correspond to the formula Si6-zAlzOzN8-z. The degree of substitution z thus amounts to 0.20 to 0.60, preferably from 0.22 to 0.54, especially from 0.3 to 0.35.

Abstract: Wear resistant member comprises a silicon nitride sintered body. Silicon nitride sintered body contains from 75 to 97% by mass of silicon nitride, from 0.2 to 5% by mass of titanium nitride and from 2 to 20% by mass of a grain boundary phase essentially containing Si—R—Al—O—N compound (R: rare earth element). Particles of titanium nitride are 1 &mgr;m or less in long axis. Particles of titanium nitride are mainly spherical particles of which aspect ratio is in the range of from 1.0 to 1.2, surface thereof being formed edgeless and roundish. Wear resistant member formed of such silicon nitride sintered body is excellent in strength, fracture toughness and rolling fatigue life. In particular, being excellent in rolling fatigue life, it is suitable for bearing member such as bearing balls.

Abstract: The present invention provides a silicon nitride wear resistant member composed of silicon nitride sintered body containing 1-10 mass % of rare earth element in terms of oxide thereof as sintering agent, wherein a total oxygen content of the silicon nitride sintered body is 6 mass % or less, a porosity of the silicon nitride sintered body is 0.5 vol. % or less, and a maximum size of pore existing in grain boundary phase of the silicon nitride sintered body is 0.3 &mgr;m or less. According to the above structure of the present invention, there can be provided a silicon nitride wear resistant member and a method of manufacturing the member having a high strength and a toughness property, and particularly excellent in sliding characteristics.

Abstract: A producing method of a porous Si3N4 having high porosity and formed of Si3N4 particles having a high aspect ratio includes the following steps. A compound of a rare earth element as a first sintering agent is mixed in an amount of 7.5-45 parts by mass, in terms of an oxide of the element, with respect to 100 parts by mass of Si powder to obtain mixed powder. A binder is added to the mixed powder, which is then molded into a molded body. The molded body is heated in a nitrogen atmosphere to 300-500° C. to remove the binder. The binder-removed body is heated in a nitrogen atmosphere to 1350-1500° C. for nitriding. The nitrided body is then sintered at 1750-1900° C. at a nitrogen pressure of 0.1-1 atmosphere.

Abstract: A corrosion-resistive member is provided, including a corrosion-resistive face that is exposed to a corrosive gas causing ion bombardmemt. At least a part of the corrosion-resistive member is composed of a sintered silicon nitride body having an open porosity of not more than 5%. The sintered silicon nitride body constitutes the corrosion-resistive face, and if two auxiliary planes are formed by cutting the corrosion-resistive member to intersect vertically with the corrosion-resistive face and to be located vertically with respect to each other, the orientation index between the two auxiliary planes is in a range of 0.8 to 1.2, and the orientation index between the corrosion-resistive face and each of the auxiliary faces is at least 1.5.

Abstract: A silicon nitride sintered product comprising silicon nitride grains and a grain boundary phase, wherein the grain boundary phase consists essentially of a single phase of a Lu4Si2O7N2 crystal phase, and the composition of the silicon nitride sintered product is a composition in or around a triangle ABC having point A: Si3N4, point B: 28 mol % SiO2-72 mol % Lu2O3 and point C: 16 mol % SiO2-84 mol % Lu2O3, as three apexes, in a ternary system phase diagram of a Si3N4—SiO2—Lu2O3 system. Also disclosed is a silicon nitride sintered product comprising silicon nitride grains and a grain boundary phase of an oxynitride, wherein the composition of the sintered product is a composition in a triangle having point A: Si3N4, point B: 40 mol % SiO2-60 mol % Lu2O3 and point C: 60 mol % SiO2-40 mol % Lu2O3, as three apexes, in a ternary system phase diagram of a Si3N4—SiO2—Lu2O3 system.

Abstract: An optical waveguide amplifier fiber comprises a core region at least in part comprises Er2O3, Al2O3, GeO2 and Ga2O3. The amplifier fiber also comprises an inner clad surrounding the core region, and an outer clad surrounding the inner clad. The relative refractive index percentages and radii of the core region, inner clad and outer clad are chosen from the following ranges: the relative refractive index percent of the core segment within the range of from about 0.5% to about 1.2%; the relative refractive index percent of the inner clad within the range of from about 0.0% to about 0.3%; the outer radius of the core region within the range of from about 2.0 &mgr;m to about 5.0 &mgr;m; and, the outer radius of the inner clad within the range of from about 3.8 &mgr;m to about 10.2 &mgr;m.

Abstract: Sintered silicon nitride containing silicon nitride substantially as a primary component and containing substantially no Al2O3. The sintered silicon nitride further contains at least one element selected from among a Group 4 element of the periodic table, a rare earth element and Mg. The amount of the selected element as converted to its oxide is at least 0.5 mol % and less than 2.6 mol % based on the entirety of the sintered silicon nitride. Also disclosed is a cutting tip, a wear-resistant member, a cutting tool and a method for producing the sintered silicon nitride.

Abstract: Corrosion-resistive ceramic materials include a silicon based ceramic, wherein a percentage of respective metal elements other than metal elements constituting sintering agents and silicon is not more than 10 weight ppm. The corrosion-resistive ceramic materials show a high corrosion resistance with respect to corrosive substances and suppress particle generation due to an exposure to corrosive substances. Therefore, chippings and cracks do not occur easily during machining work.

Abstract: A silicon nitride sintered material includes a polycrystal material having silicon nitride crystal grains and a grain boundary phase. The sintered material contains a Yb element in an amount of 2 to 30% by weight in terms of its oxide and an Al element in an amount of 1 to 20% by weight in terms of its oxide and has a thermal conductivity of 40 W/mK or less at room temperature, a resistivity of 1×105to 1×1012 &OHgr;·cm at room temperature, and a porosity of 0.5% or less.

Abstract: A silicon nitride sintered material containing silicon nitride, a Group 4a through 6a element, a rare earth element, and silicon carbide, characterized in that the amount of the rare earth element as reduced to a certain oxide thereof is 5.7-10.3 mol %; the ratio by mol of subtraction remainder oxygen amount calculated in relation to the oxygen contained in the sintered material, the remainder oxygen amount being expressed in terms of silicon dioxide, to the amount of oxygen contained in the sintered material is at least 0.50 and less than 0.70; a four-component crystalline phase of rare earth element-silicon-oxygen-nitrogen is not present; and the thermal expansion coefficient is at least 3.7 ppm/° C. between room temperature and 1,000° C.

Abstract: A surface-coated sintered body of silicon nitride wherein a coating layer on the surface comprises a crystalline phase of RE2Si2O7 and/or RE2SiO5 (RE=rare earth element), the crystalline phase having an average crystalline particle diameter of not smaller than 0.1 &mgr;m, and the excess amount of SiO2 contained in the coating layer being not larger than 10 mole %. The coating layer formed on the surfaces of the sintered body exhibits excellent adhering force even in a high-temperature zone of around 1500° C. and features a long life.

Abstract: A silicon nitride porous body which is obtained by nitriding a molded body having metallic silicon as a main component and by performing a high temperature heating treatment at a temperature higher than the nitriding temperature, and which has a porous structure with an average pore diameter of 3 &mgr;m or above, and contains at least one kind of element selected from the group consisting of the groups 2A, 3A, 3B inclusive of lanthanoid elements, and 4B. The silicon nitride porous body has a porous structure with a large average pore diameter, a test specimen cut out from the porous body exhibiting a high thermal conductivity and a small thermal expansion coefficient, and can be suitably used in a component for purifying gas and/or solution such as a ceramic filter.

Abstract: An Si3N4 sintered body produced by reactive sintering of silicon, wherein a compound of at least one element selected from the group consisting of Y, Yb and Sm is contained by 0.6 to 13% by weight as Ln2O3 (wherein Ln=Y, Yb or Sm), an oxygen content in Si3N4 crystal grains is not more than 1% by weight, a ratio of Si and Ln in the Si3N4 sintered body is within a range of 0.1 to 0.8 in a molar ratio of SiO2/Ln2O3 of the Si in terms of SiO2 to the oxide Ln2O3, and the sintered body has a relative density of 85 to 99.9%, a thermal conductivity of at least 70 W/m.K or more and a three-point bending strength of at least 600 MPa. The Si3N4 sintered body is produced by mixing 80 to 99% by weight of silicon powder and 1 to 20% by weight of powder of oxide of at least one element of Y, Yb and SM, by nitriding a molded body of the powder mixture in an atmosphere containing nitrogen at 1400° C.

Abstract: A silicon nitride sintered material includes a polycrystal material having silicon nitride crystal grains and a grain boundary phase. The sintered material contains a Yb element in an amount of 2 to 30% by weight in terms of its oxide and an Al element in an amount of 1 to 20% by weight in terms of its oxide and has a thermal conductivity of 40 W/mK or less at room temperature, a resistivity of 1×105 to 1×1012 &OHgr;·cm at room temperature, and a porosity of 0.5% or less.

Abstract: A Si3N4 composite substrate which manifests no generation of cracking on the substrate even by mechanical shock or thermal shock, and is excellent in heat radiation property and heat-cycle-resistance property is obtained by using a Si3N4 substrate as a ceramic substrate. A Si3N4 substrate having a thermal conductivity of 90 W/m·K or more and a three-point flexural strength of 700 MPa or more is used, and the thickness tm of a metal layer connected on one major surface of the substrate and the thickness tc of the Si3N4 substrate are controlled so as to satisfy the relation formula: 2 tm≦tc≦20 tm. When metal layers are connected to both major surfaces of the Si3N4 substrate, the thickness tc and the total thickness ttm of the metal layers on both major surfaces are controlled so as to satisfy the relation formula: ttm≦tc≦10 ttm.

Abstract: A silicon nitride sintered product comprising silicon nitride grains and a grain boundary phase, wherein the grain boundary phase consists essentially of a single phase of a Lu4Si2O7N2 crystal phase, and the composition of the silicon nitride sintered product is a composition in or around a triangle ABC having point A: Si3N4, point B: 28 mol % SiO2-72 mol % Lu2O3 and point C: 16 mol % SiO2-84 mol % Lu2O3, as three apexes, in a ternary system phase diagram of a Si3N4—SiO2—Lu2O3 system. Also disclosed is a silicon nitride sintered product comprising silicon nitride grains and a grain boundary phase of an oxynitride, wherein the composition of the sintered product is a composition in a triangle having point A: Si3N4, point B: 40 mol % SiO2-60 mol % Lu2O3 and point C: 60 mol % SiO2-40 mol % Lu2O3, as three apexes, in a ternary system phase diagram of a Si3N4—SiO2—Lu2O3 system.

Abstract: The invention relates to silicon nitride substances containing sintering additives and SiO2, a method for producing them and the use of the same.

Abstract: Metal oxides particularly useful for the manufacture of catalytic membranes for gas-phase oxygen separation processes having the formula: AxA′x′A″2-(x+x′)ByFey′B″2-(y+y′)O5+z where: x and x′ are greater than 0; y and y′ are greater than 0; x+x′ is equal to 2; y+y′ is less than or equal to 2; z is a number that makes the metal oxide charge neutral; A is an element selected from the lanthanide elements; A′ is an element selected from Be, Mg, Ca, Sr, Ba and Ra; A″ is an element selected from the f block lanthanides, Be, Mg, Ca, Sr, Ba and Ra; B is an element selected from the group consisting of Al, Ga, In or mixtures thereof and B″ is Co or Mg, with the exception that when B″ is Mg, A′ and A″ are not Mg. The metal oxides are useful for preparation of dense membranes which may be formed from dense thin films of the mixed metal oxide on a porous metal oxide element.

Abstract: A silicon nitride sintered product comprising silicon nitride grains and a grain boundary phase, wherein the grain boundary phase consists essentially of a single phase of a Lu4Si2O7N2 crystal phase, and the composition of the silicon nitride sintered product is a composition in or around a triangle ABC having point A: Si3N4, point B: 28 mol % SiO2-72 mol % Lu2O3 and point C: 16 mol % SiO2-84 mol % Lu2O3, as three apexes, in a ternary system phase diagram of a Si3N4—SiO2—Lu2O3 system. Also disclosed is a silicon nitride sintered product comprising silicon nitride grains and a grain boundary phase of an oxynitride, wherein the composition of the sintered product is a composition in a triangle having point A: Si3N4, point B: 40 mol % SiO2-60 mol % Lu2O3 and point C: 60 mol % SiO2-40 mol % Lu2O3, as three apexes, in a ternary system phase diagram of a Si3N4—SiO2—Lu2O3 system.

Abstract: A low-thermal-expansion, rigid and wear-resistant ceramic is provided.

Abstract: Sintered silicon nitride and a silicon nitride tool. The mean major axis length, the mean minor axis length, and the aspect ratio, represented by (mean major axis length/mean minor axis length) of constituent sintered silicon nitride grains in a silicon nitride tool are controlled, and the thermal conductivity and/or fracture toughness Kc thereof are enhanced, thereby providing a tool having a cutting edge which is not prone to chipping.

Abstract: The invention provides a slurry composition suitable for the manufacture of Si3N4 sintered bodies, wherein the dispersion properties and oxidation resistance of Si powder in water are improved, resulting in the homogenous dispersion of a sintering aid powder and a fine Si powder with less oxygen. Si powder, a sintering aid, water in an amount of 50 to 90 wt % relative to the total weight of the composition, and a surface coating agent in an amount of 0.05 to 10 wt % relative to the Si powder are added, the pH is adjusted to between 3 and 8, and the ingredients are milled and mixed. Trivalent metal ions such as Fe or Ga, or a polysiloxane with a BHL of no more than 10 is used as the surface coating agent. The resulting slurry composition can be used to prepare Si3N4 sintered bodies with better electrical, thermal, and mechanical properties.

Abstract: A silicon nitride sintered material includes a polycrystal material having silicon nitride crystal grains and a grain boundary phase. The sintered material contains a Yb element in an amount of 2 to 30% by weight in terms of its oxide and an Al element in an amount of 1 to 20% by weight in terms of its oxide and has a thermal conductivity of 40 W/mK or less at room temperature, a resistivity of 1×105 to 1×1012 &OHgr;·cm at room temperature, and a porosity of 0.5% or less.

Abstract: A dry refractory composition having superior insulating value. The dry refractory composition also may have excellent resistance to molten metals and slags. The composition includes filler lightweight material, which may be selected from perlite, vermiculite, expanded shale, expanded fireclay, expanded alumina silica hollow spheres, bubble alumina, sintered porous alumina, alumina spinel insulating aggregate, calcium alumina insulating aggregate, expanded mulllite, cordierite, and anorthite, and matrix material, which may be selected from calcined alumina, fused alumina, sintered magnesia, fused magnesia, silica fume, fused silica, silicon carbide, boron carbide, titanium diboride, zirconium boride, boron nitride, aluminum nitride, silicon nitride, Sialon, titanium oxide, barium sulfate, zircon, a sillimanite group mineral, pyrophyllite, fireclay, carbon, and calcium fluoride.

Abstract: The present invention relates to a titanium diboride sintered body and a method for manufacturing thereof wherein silicon nitride is added to a titanium diboride as a sintering aid. The sintered body according to the present invention has a fine structure and excellent physical characteristics such as a strength, hardness, etc. Therefore, the sintered body according to the present invention may be applicable to certain materials which requires high strength and hardness.

Abstract: A ceramic material which is an orthorhombic boride of the general formula: AlMgB14:X, with X being a doping agent. The ceramic is a superabrasive, and in most instances provides a hardness of 40 GPa or greater.

Abstract: A slurry Si-base composition comprising an Si powder having a thickness of a surface oxide film ranging from 1.5 to 15 nm, 50 to 90% by weight of water, 0.2 to 7.5% by weight, in terms of oxide, of a sintering aid and 0.05 to 3% by weight of a dispersant, the Si-base composition having a pH value adjusted to 8-12. This slurry Si-base composition is produced by a process which comprises subjecting Si powder to oxidation treatment at 200 to 800° C. in air, adding 50 to 90% by weight of water, 0.2 to 7.5% by weight, in terms of oxide, of a sintering aid and 0.05 to 3% by weight of a dispersant to the oxidized Si powder and performing such a pH adjustment that the resultant mixture has a pH value of 8 to 12. The slurry Si-base composition not only enables producing a ceramic of Si3N4 at a lowered cost without the need to install explosionproof facilities but also allows the obtained Si3N4 ceramic having a relative density of at least 96% and a flexural strength of at least 800 MPa can be obtained.

Abstract: A sintered Si3N4 material, valves and components made with the material, and methods for making same.

Abstract: A silicon nitride sintered product comprising silicon nitride grains and a grain boundary phase, wherein the grain boundary phase consists essentially of a single phase of a LU4Si2O7N2 crystal phase, and the composition of the silicon nitride sintered product is a composition in or around a triangle ABC having point A: Si3N4, point B: 28 mol % SiO2-72 mol % LU2O3 and point C: 16 mol % SiO2-84 mol % LU2O3, as three apexes, in a ternary system phase diagram of a Si3N4—SiO2—LU2O3 system. Also disclosed is a silicon nitride sintered product comprising silicon nitride grains and a grain boundary phase of an oxynitride, wherein the composition of the sintered product is a composition in a triangle having point A: Si3N4, point B: 40 mol % SiO2-60 mol % LU2O3 and point C: 60 mol % SiO2-40 mol % LU2O3, as three apexes, in a ternary system phase diagram of a Si3N4-SiO2-LU2O3 system.

Abstract: Wear resistant member comprises a silicon nitride sintered body. Silicon nitride sintered body contains from 75 to 97% by mass of silicon nitride, from 0.2 to 5% by mass of titanium nitride and from 2 to 20% by mass of a grain boundary phase essentially containing Si—R—Al—O—N compound (R: rare earth element). Particles of titanium nitride are 1 &mgr;m or less in long axis. Particles of titanium nitride are mainly spherical particles of which aspect ratio is in the range of from 1.0 to 1.2, surface thereof being formed edgeless and roundish. Wear resistant member formed of such silicon nitride sintered body is excellent in strength, fracture toughness and rolling fatigue life. In particular, being excellent in rolling fatigue life, it is suitable for bearing member such as bearing balls.

Abstract: The present invention provides a silicon nitride sintered body having characteristics such as excellent wear resistance, a method for manufacturing the sintered body, and a cutting insert formed thereof. The silicon nitride sintered body is formed of a polycrystalline sintered body of predominantly &bgr;-Si3N4, wherein the oxygen content is 1.2-1.5 wt. %. The method for manufacturing the silicon nitride sintered body includes the following steps: adding an organic binder to a composition containing silicon nitride as an essential component and exhibiting a theoretical oxygen content of 2.0-3.0 wt. %; heating to remove the binder; introducing an oxygen-containing gas so as to control the carbon content to 0.10-0.60 wt. %; and sintering a resultant compact in an nitrogen atmosphere to control the oxygen content to 1.2-1.5 wt. %. The cutting insert of the present invention has excellent wear resistance.

Abstract: An Si3N4 sintered body produced by reactive sintering of silicon, wherein a compound of at least one element selected from the group consisting of Y, Yb and Sm is contained by 0.6 to 13% by weight as Ln2O3 (wherein Ln=Y, Yb or Sm), an oxygen content in Si3N4 crystal grains is not more than 1% by weight, a ratio of Si and Ln in the Si3N4 sintered body is within a range of 0.1 to 0.8 in a molar ratio of SiO2/Ln2O3 of the Si in terms of SiO2 to the oxide Ln2O3, and the sintered body has a relative density of 85 to 99.9%, a thermal conductivity of at least 70 W/m.K or more and a three-point bending strength of at least 600 MPa. The Si3N4 sintered body is produced by mixing 80 to 99% by weight of silicon powder and 1 to 20% by weight of powder of oxide of at least one element of Y, Yb and SM, by nitriding a molded body of the powder mixture in an atmosphere containing nitrogen at 1400° C.

Abstract: A sintered product of silicon nitride has a crystal phase of RE2Si3N2O5 or RE3AlSi2O7N2 (RE is an element of the Group 3a of periodic table) precipitated on the grain boundaries of the silicon nitride crystal phase, and exhibits a high strength over a wide temperature region of from normal temperature to a temperature of as high as 1000° C., as well as excellent oxidation resistance and static fatigue property. The sintered product of silicon nitride is very useful as parts for heat engines, such as parts for engines and parts for gas turbines.

Abstract: A slurry Si-base composition comprising an Si powder having a thickness of a surface oxide film ranging from 1.5 to 15 nm, 50 to 90% by weight of water, 0.2 to 7.5% by weight, in terms of oxide, of a sintering aid and 0.05 to 3% by weight of a dispersant, the Si-base composition having a pH value adjusted to 8-12. This slurry Si-base composition is produced by a process which comprises subjecting Si powder to oxidation treatment at 200 to 800° C. in air, adding 50 to 90% by weight of water, 0.2 to 7.5% by weight, in terms of oxide, of a sintering aid and 0.05 to 3% by weight of a dispersant to the oxidized Si powder and performing such a pH adjustment that the resultant mixture has a pH value of 8 to 12. The slurry Si-base composition not only enables producing a ceramic of Si3N4 at a lowered cost without the need to install explosionproof facilities but also allows the obtained Si3N4 ceramic having a relative density of at least 96% and a flexural strength of at least 800 MPa can be obtained.

Abstract: A high thermal conductive silicon nitride sintered body of this invention is characterized by containing: 2.0 to 17.5% by weight of a rare earth element in terms of the amount of an oxide thereof; 0.3 to 3.0% by weight of Mg in terms of the amount of an oxide thereof; if necessary, at most 1.5% by weight of at least one of calcium (Ca) and strontium (Sr) in terms of an oxide thereof, if necessary at most 1.5% by weight of at least one element selected from the group consisting of Ti, Zr, V, Nb, Ta, Cr, Mo and W in terms of the amount of an oxide thereof, and at most 0.3% by weight of Al, Li, Na, K, Fe, Ba, Mn and B as impurity cationic elements in terms of total amount thereof, comprising a silicon nitride crystal and a grain boundary phase. The sintered body has a ratio of a crystal compound phase formed in the grain boundary phase to the entire grain boundary phase of at least 20%, a porosity of at most 2.

Abstract: Provided with a method for preparing a silicon nitride ceramic with high strength and toughness including: mixing 0.2-0.9 wt % of carbon (C) powder with silicon nitride powder containing 5.0-6.0 wt % of yttria (Y2O3) and 1.0-2.0 wt % of alumina (Al2O3) added thereto as a sintering agent, and preparing a molding; subjecting the molding to a carbothermal reduction treatment at 1400-1500° C.; and gas pressure sintering the molding at a temperature above 1850° C. after the carbothermal reduction treatment.

Abstract: A fiber-reinforced ceramic green body having enough green strength and handling strength. The fiber-reinforced ceramic green body is obtained by molding a ceramic composition comprising a ceramic powder, a sintering aid powder, an organic fiber, an aqueous dispersion medium and an optional dispersant. The organic fiber is contained in the ceramic green body in an amount of 0.2-3 parts by weight based on 100 parts by weight of a total of the ceramic powder and the sintering aid powder and uniformly dispersed throughout it. The average length of the organic fiber is 300-1000 &mgr;m and the average diameter is 2.5-30 &mgr;m. The organic fiber is preferably a synthetic high polymer such as polyester, nylon, etc., and preferably has a hydrophilic nature imparted by surface treatment.

Abstract: There is disclosed a silicon nitride sintered body produced by sintering a molded article which comprises a mixture of a silicon nitride powder as the main component and plural kinds of sintering additives, wherein said silicon nitride powder is set to be 0.1 to 1.0 &mgr;m in average grain size, and said plural kinds of sintering additives includes first and second sintering additives, said first sintering additive comprising oxide powders of at least one element of Group 3a element, said second sintering additive comprising oxide powders of at least one element selected from Zr (zirconium), Hf (hafnium), Nb (niobium), Ta (tantalum) and W (tungsten), said first sintering additive having the average grain size set to be 0.1 to 10 times as large as the average grain size of said silicon nitride powder and being incorporated in an amount ranging from 0.