Abstract: A process for producing a SiC ceramic microtube, comprising the steps of oxidizing the surface of an organosilicon polymer to become infusible by exposure to an ionizing radiation, extracting the uncrosslinked central portion of the fiber with an organic solvent to make a hollow silicon polymer fiber, and firing it in an inert gas so that it acquires a ceramic nature.

Abstract: A process for forming a porous silicon nitride-silicon carbide body, the process comprising (a) forming a plasticizable batch mixture comprising (1) powdered silicon metal; (2) a silicon-containing source selected from the group consisting of silicon carbide, silicon nitride and mixtures thereof; (3) a water soluble crosslinking thermoset resin having a viscosity of about 50-300 centipoise; and, (4) a water soluble thermoplastic temporary binder; (b) shaping the plasticizable batch mixture to form a green body; (c) drying the green body; (d) firing the green body in nitrogen at a temperature of 1400° C. to 1600° C. for a time sufficient to obtain a silicon nitride-silicon carbide structure.

Abstract: A continuous process for the manufacture of a ceramic sintered compact wherein the process comprises the steps of: forming a green compact from a powder mixture comprising a first component comprising compounds which contain elements of silicon, aluminum, oxygen and nitrogen; and the powder mixture further comprising a second component comprising a compound of at least one element selected from the group consisting of yttrium, scandium, cerium, lanthanum and the metals of the lanthanide series, and the second component comprising between 0.1 and 10 weight percent of the powder mixture; heat treating the green compact wherein the heat treatment comprises continuously passing the green compact through at least one heating zone so as to produce a sintered compact.

Abstract: A method of making spherical bodies from powder, which comprises (1) preparing an adjusted powder so as to have at least one powder characteristic selected from the group consisting of an average particle size, a powder particle size distribution and a BET specific surface area, (2) preparing nuclei having a particle size larger than that of the adjusted powder, (3) rotating the nuclei, and (4) adding the adjusted powder and a solvent to the rotating nuclei so that particles of the adjusted powder accumulate on the nuclei to form granular bodies. Also disclosed is a spherical body having a core or nucleus formed in the spherical body, an adjusted powder composition for forming a spherical body, and a method for manufacturing spherical sintered bodies of silicon nitride.

Abstract: The invention comprehends a silicon nitride sintered body having consistent qualities, a process for producing the same, a ceramic heater employing the silicon nitride sintered body as a substrate and a glow plug containing the ceramic heater as a heat source. In the production of a silicon nitride sintered body through a hot press method, a sintering aid protecting agent is added to the raw material. The employable protecting agents are metallic elements such as Ta, W and Mo and compounds of the metallic elements such as nitrides and silicides. Conversion of these elements and compounds to carbides occurs preferentially to reduction of the sintering aid. Thus, it becomes possible to suppress reduction of the sintering aid in a reducing atmosphere formed, for example, of carbon monoxide, which is generated particularly when a graphite pressing die is employed.

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 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 method of producing the silicon nitride sintered body includes the steps of forming a compact of molding materials including silicon nitride powder, a Mg component and a sintering aid, and sintering the molding materials at 1,800 to 2,000° C. under a nitrogen atmosphere. The materials at least include an oxide of Mg in a range of 0.3 to 10 wt. %. A constant temperature is kept for at least 0.5 hours in a temperature range of 1,400 to 1,700° C. before the temperature is increased to the sintering temperature. A silicon nitride body having high thermal conductivity and excellent electrical insulation properties at high temperature can thus be provided.

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: A method comprising incorporation of an inorganic polymer precursor of a grain growth inhibitor into nanostructured materials or intermediates useful for the production of nanostructured materials. The precursor/nanostructured material composite is optionally heat treated at a temperature below the grain growth temperature of the nanostructured material in order to more effectively disperse the precursor. The composites are then heat treated at a temperature effective to decompose the precursor and to form nanostructured materials having grain growth inhibitors uniformly distributed at the grain boundaries. Synthesis of the inorganic polymer solution comprises forming an inorganic polymer from a solution of metal salts, filtering the polymer, and drying. Alloying additives as well as grain growth inhibitors may be incorporated into the nanostructured materials.

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: 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.

Abstract: A method for making an alpha prime SiAlON-based ceramic article, including the steps of providing an admixture of starting materials and densifying said admixture. The admixture includes: beta silicon nitride; a source of aluminum selected from the group consisting of aluminum nitride, alumina, and mixtures thereof; at least one oxide compound; and a plurality of alpha prime SiAlON seeds.

Abstract: A silicon nitride sintered body is obtained by mixing 2.about.16 wt % of Yb.sub.2 O.sub.3 as a sintering additive with Si.sub.3 N.sub.4 powders including unavoidable impuirities, pressing the mixed powder into a desired form, and gas-pressure sintering the thusly pressed form, whereby an inner region of the sintered body has a fine microstructure, and an outer region thereof has a mixed microstructure in which elongated grains and fine grains co-exist and a method for manufacturing a silicon nitride sintered body, includes the steps of: adding and mixing 2.about.16 wt % of Yb.sub.2 O.sub.3 powder as a sintering additive into a silicon nitride (Si.sub.3 N.sub.4) powder; ball-milling the mixed powder to obtain a slurry; drying and classifying the slurry; press-forming the resultant powder in a die uniaxially and isostatically; and gas-pressure sintering the resultant compact body at a temperature in the range of 1800.about.2000.degree. C.

Abstract: A process for producing a bonded article of ceramic bodies comprising steps of: machining the ceramic bodies to be bonded to form machined surfaces with average surface roughnesses (Ra) of not more than 0.2 .mu.m and flatnesses of not more than 0.2 .mu.m; applying solution containing a bonding aid on at least one of the machined surfaces; contacting the machined surfaces with each other to produce an assembly; and subjecting the assembly to a heat treatment to produce the bonded article. The roughnesses and the flatnesses may preferably be not more than 0.1 .mu.m. The bonding aid may preferably be a sintering aid applicable to at least one of the ceramic bodies. The ceramic bodies may preferably be one or more material selected from a group consisting of aluminum nitride and silicon nitride. The bonding aid may preferably be one or more bonding aid selected from a group consisting of a substance of yttrium and a substance of ytterbium.

Abstract: The ceramic cutting tool material according to the present invention comprises a beta silicon nitride matrix with total amount of 0.5-10 weight %, preferably 0.5-6 weight %, of an intergranular phase and 0.05-3 weight % of at least one secondary crystalline phase of a transition metal carbide, nitride, carbonitride and/or silicide present as spherical particles with a size of 0.1-2 .mu.m, preferably submicron (0.01-1 .mu.m). The transition metal is preferably niobium and/or tantalum. The material has less than 1 volume %, preferably less than 0.3 volume %, porosity. The beta silicon nitride grains are to at least 10%, preferably more than 20%, elongated with an aspect ratio greater than 3, preferably greater than 5. The grain diameter of the beta silicon nitride grains is in the range of 0.2-10 .mu.m, preferably 0.2-5 .mu.m, and most preferably 0.2-3 .mu.m.

Abstract: A sintered ceramic material for high speed machining of heat resistant alloys is provided comprising SiAlON grains and 0.2-20 v/o intergranular phase. At least 80 v/o of said SiAlON phase is beta SiAlON having a z-value greater than 1.0, but less than 1.5. The ceramic material has a Vickers Hardness HV1 of more than 1530 and it is produced by gas pressure sintering.

Abstract: Titanium carbo-nitride complex silicon nitride tool is composed mainly of titanium carbo-nitride and silicon nitride and contains 10 to 56 wt % of Ti, 11.6 to 51 wt % of Si and 1 to 21 wt % in total of one or two or more of Ce, Y, Yb and Dy. The tool is mainly composed of Si.sub.3 N.sub.4 superior in both strength and resistance against thermal shock and TiCN superior in the effect of suppressing reactivity of Si.sub.3 N.sub.4 with Fe and exhibiting high hardness. By using oxides CeO.sub.2, Y.sub.2 O.sub.3, Yb.sub.2 O.sub.3 and Dy.sub.2 O.sub.3 as sintering aid so that the sum of the amounts of Ce, Y, Yb and Dy will be in the above range, both the resistance against flank notch (wear) of the end edge and resistance against thermal shock are improved resulting in improved durability as compared to the conventional silicon nitride cutting tool.

Abstract: A silicon nitride sintered body prepared through a nitriding reaction of Si, consists of crystal grains mainly composed of silicon nitride and/or SIALON and a grain boundary phase. The grain boundary phase includes a first component including at least one element selected from a group of Na, K, Mg, Ca and Sr and a second component including at least one element selected from a group of Y and lanthanoid series elements. The molar ratio of the first component to the second component is in the range of 1:1 to 6:1 in terms of oxides. The mean breadth and the mean length of the crystal grains are not more than 0.1 .mu.m and not more than 3 .mu.m respectively, and the standard deviation of the mean length in the sintered body is within 1.5 .mu.m. Especially, the mean breadth of the crystal grains is at least 0.4 .mu.m and not more than 0.9 .mu.m.

Abstract: By providing a new method of producing sintered silicon nitride, this invention takes into account the fact that parts made of Si.sub.3 N.sub.4 are often used in temperature ranges below 1200.degree. C. and sometimes even below 500.degree. C. and therefore needn't be designed to withstand temperatures above 1200.degree. C. The sintered silicon nitride for these low-temperature applications is obtained by sintering silicon nitride powder of <2 .mu.m with 5 to 20 wt. % of one or more glass components of the same particle size at temperatures below 1400.degree. C. It is a prerequisite that the glass components used, preferably alkali metal borate glasses with a coefficient of thermal expansion .alpha. which matches that of Si.sub.3 N.sub.4, have a transformation point T.sub.g which is below 750.degree. C., and that the individual glass components have a free enthalpy .DELTA.G which is at least 60% of the free enthalpy of SiO.sub.2. For low-temperature applications, Si.sub.3 N.sub.

Abstract: The present invention relates to a method for producing a porous silicon nitride sintered body having high strength and low thermal conductivity, which comprises of adding more than 10 volume % of rodlike beta-silicon nitride single crystals with a larger mean diameter than that of a silicon nitride raw powder into a mixture comprising the silicon nitride raw powder and a sintering additive, preparing a formed body with rodlike beta-silicon nitride single crystals oriented parallel to the casting plane according to a forming technique such as sheet casting and extrusion forming, sintering said formed body to develop elongated silicon nitride grains from the added rodlike beta-silicon nitride single crystals as nuclei and obtain the sintered body with the elongated grains being dispersed in a complicated state.

Abstract: The invention discloses a dense silicon nitride composite material which may be used as a high-temperature component in building armatures and motors with a long service life and high reliability even at higher temperatures. More specifically, the invention discloses a dense silicon nitride composite material containing 3 to 50 wt. % of a reinforcing component, in which the reinforcing component contains 10 to 90 wt. % Me.sub.5 Si.sub.3 and the remaining portion is either MeSi.sub.2 or MeSi.sub.2 and silicides with other stoichiometries and Me is a metal or a mixture of metals. The present invention is made by a method in which the material is produced by sintering and/or hot pressing and/or hot isostatic pressing and the reinforcing components are added as Me.sub.5 Si.sub.3 and MeSi.sub.

Abstract: A silicon nitride reaction-sintered body having a high mechanical strength without surface working can be produced by (1) forming a silicon powder mixture of at least two types of silicon powders having substantially independent particle size distribution ranges into a green body, the silicon powder mixture having an average particle size ranging from 5 .mu.m to 300 .mu.m; (2) heating the green body in a nitrogen-containing atmosphere for nitrogenation; and (3) sintering the nitrogenated green body at a temperature of 1900.degree. C. or higher.

Abstract: A silicon nitride ceramic sliding material comprising silicon nitride crystal grains and a grain boundary phase and having a porosity of 2 to 10% and a maximum pore size of 20 to 100 .mu.m. The silicon nitride ceramic sliding material preferably has a textural structure wherein the proportion of the total area of silicon nitride crystal grains of 0.1 to 10 .mu.m.sup.2 in area to the total area of all the silicon nitride crystal grains present in an arbitrary two-dimensional cross section is 30 to 90% and the proportion of the number of silicon nitride crystal grains of 2 to 10 in aspect ratio to the number of all the silicon nitride crystal grains present in that cross section is at least 20%. The material is produced by mixing a silicon nitride powder with a sintering aid powder, molding the resulting mixture, then heat-treating the resulting molded body in a nitrogen-containing atmosphere under reduced pressure at 1,000 to 1,500.degree. C.

Abstract: To provide a silicon nitride based sintered material having high strength and high hardness and superior in reliability, silicon nitride sintered material has a composition mainly composed of silicon nitride or Si--Al--O--N, and further comprises 0.5 to 3 wt % of a Mg component, calculated as MgO, and 3 to 10 wt % of a Yb component, calculated as Yb.sub.2 O.sub.3. As a secondary crystal phase, the material contains one or more of Yb.sub.2 Si.sub.3 N.sub.4 O.sub.3, Yb.sub.2 Si.sub.3 N.sub.2 O.sub.5 and Yb.sub.4 Si.sub.2 N.sub.2 O.sub.7. Silicon nitride or Si--Al--O--N comprises 20-50 vol % of needle-like crystals of the entire material.

Abstract: The present invention provides silicon nitride ceramics having high thermal conductivity and a method for production thereof. This invention relates to a method for producing a silicon nitride sintered body having a microstructure with silicon nitride crystals oriented uniaxially and exhibiting high thermal conductivity of 100 to 150 W/mK in the direction parallel to the orientation direction of the crystals, which comprises of preparing a slurry by mixing a mixed powder of a sintering auxiliary, beta-silicon nitride single crystals as seed crystals and a silicon nitride raw powder with a dispersing medium, forming the slurry by tape casting or extrusion forming, calcining the formed silicon nitride body with beta-silicon nitride single crystals oriented parallel to the casting plane to remove the organic components, densifying it by hot pressing and the like if required, and further annealing it at 1700 to 2000.degree. C. under the nitrogen pressure of 1 to 100 atmospheres.

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: Sintered reaction-bonded silicon nitride components, e.g., automotive components, are made by forming a powder mixture comprising silicon and oxide or oxide precursor additives. These additives comprise alumina and a calcium compound. The powder is formed into a preform, the silicon is reacted with nitrogen in a nitriding process to form silicon nitride, and the so-formed silicon nitride is sintered.

Abstract: The present invention relates to a silicon nitride sintered body having a remarkably increased strain-to-fracture, a low elasticity and high strength, characterized by consisting of a layered structure of alternating porous silicon nitride layers 1 to 1000 .mu.m thick with a porosity of 5 to 70 volume % and dense silicon nitride layers 1 to 1000 .mu.m thick with a porosity of less than 5 volume %, being layered as materials with optional tiers. In addition, this invention relates to a method for producing the silicon nitride sintered body as described above, which comprises of forming dense layers and porous layers by sheet casting or extrusion forming so as to prepare the layers to be capable of 1 to 1000 .mu.m thick after sintering, stacking them to obtain layered materials with optional tiers and sintering them at 1600.degree. to 2100 .degree. C. under a nitrogen atmosphere.

Abstract: In a process for producing a silicon nitride sintered material, a silicon nitride raw material powder selected from raw material powder lots such that the silicon nitride raw material powder has a dispersion .delta.N.beta..sub.1 of weight fraction of .beta.-silicon nitride, of 65% or less, is used. A process for producing a silicon nitride sintered material controls the firing conditions so that the raw material being fired gives, at any stage of firing, a dispersion .delta.N.beta..sub.2 of weight fraction of .beta.-silicon nitride, of 65% or less between the surface portion and the central portion. The first process allows for production of a silicon nitride sintered material having excellent properties in high-temperature strength, etc., at a high reproducibility and stability. The second process allows for production, of in any production batch, a silicon nitride sintered material very low in scattering of properties (e.g., density and strength) between the central portion and the surface portion.

Abstract: A process for the production of a silicon nitride sintered body which comprises heat-treating a stock of silicon nitride sintered body within a temperature range of from the temperature at which the internal friction of the stock exhibits a peculiar peak maximum minus 150.degree. C. to that plus 150.degree. C. A representative used in the process is one which is produced by mixing powdered silicon nitride with powdery sintering aids so as to give a powder mixture comprising 5 to 15% by weight (in terms of oxide) of at least one element selected from the group consisting of rare earth elements and aluminum, 0.5 to 5% by weight (in terms of oxide) of at least one element selected from the group consisting of Mg, Ti and Ca and the balance of Si.sub.3 N.sub.4, molding the powder mixture, and sintering the resulting compact in a nitrogen-containing atmosphere at 1500.degree. to 1700.degree. C.

Abstract: A silicon nitride ceramic of the present invention possesses excellent strength of the surface, including a silicon nitride and a rare earth oxide compound and being characterized in that the ratio of the transverse rupture strength, at a room temperature, of the fired surface used as a tensile surface to the transverse rupture strength, at a room temperature, of the worked surface used as a tensile surface subjected to the working so as to have the surface roughness of R.sub.MAX 0.8 .mu.m or less is 0.7 or more, and the strength ratio is satisfied even when any portion besides the fired surface is utilized as the tensile surface to be worked to have the surface roughness of R.sub.MAX 0.8 .mu.m or less. The present invention also provides a process for producing a silicon nitride ceramic including the steps of: (1) mixing .alpha.-Si.sub.3 N.sub.4 powder and .beta.-Si.sub.3 N.sub.4 powder to obtain a raw material powder so as to satisfy the formula indicated by 0.05.ltoreq..beta./.alpha.+.beta..ltoreq.0.

Abstract: A composite sintered body of silicon carbide and silicon nitride having a nano-composite structure in which fine SiC particles are dispersed in Si.sub.3 N.sub.4 particles and grain boundaries and fine Si.sub.3 N.sub.4 particles are dispersed in SiC particles is produced by (a) adding at least one sintering aid, boron and carbon to a mixed powder of silicon carbide and silicon nitride to form a green body, the sintering aid being (i) Al.sub.2 O.sub.3 or AlN and/or (ii) at least one oxide of an element selected from Groups 3A and 4A of the Periodic Table, and (b) sintering the green body by HIP or by a high-temperature normal sintering method.

Abstract: A high-porosity and high-strength porous silicon nitride body comprises columnar silicon nitride grains and an oxide bond phase containing 2 to 15 wt. %, in terms of oxide based on silicon nitride, of at least one rare earth element, and has an SiO.sub.2 /(SiO.sub.2 +rare earth element oxide) weight ratio of 0.012 to 0.65 and an average pore size of at most 3.5 .mu.m. The porous silicon nitride body is produced by compacting comprising a silicon nitride powder, 2 to 15 wt. %, in terms of oxide based on silicon nitride, of at least one rare earth element, and an organic binder while controlling the oxygen content and carbon content of said compact; and sintering said compact in an atmosphere comprising nitrogen at 1,650.degree. to 2,200.degree. C. to obtain a porous body having a three-dimensionally entangled structure made up of columnar silicon nitride grains and an oxide bond phase, and having an SiO.sub.2 /(SiO.sub.2 +rare earth element oxide) weight ratio of 0.012 to 0.65.

Abstract: There are provided a process for forming a silicon nitride sintered body, encompassing a sialon sintered body, by making much of the superplasticity of the sintered body intact as a simple material without formation thereof into a composite material, and a formed sintered body produced by the foregoing process. A silicon nitride sintered body (encompassing a sialon sintered body) having a relative density of at least 95% and a linear density of 120 to 250 in terms of the number of grains per 50 .mu.m in length in a two-dimensional cross section of the sintered body is formed through plastic deformation thereof at a strain rate of at most 10.sup.-1 /sec under a tensile or compressive pressure at a temperature of 1,300 to 1,700.degree. C. The formed sintered body has a degree of orientation of 5 to 80% as examined according to a method specified by Saltykov, a linear density of 80 to 200, and excellent mechanical properties especially at ordinary temperatures.

Abstract: A ceramic body comprising at least about 80 w/o silicon nitride and having a mean tensile strength of at least about 800 MPa.

Abstract: The invention reduces the time required for nitriding in the process of reaction sintering for production of a sintered body of silicon nitride, thereby improving productivity, and provides a sintered body of silicon nitride having sufficient compactness and high strength which can be produced by reaction sintering. The sintered body is Si.sub.3 N.sub.4 having an unpaired electron density of 10.sup.15 /cm.sup.3 to 10.sup.21 /cm.sup.3. The sintered body is produced through reaction sintering by using a Si powder having an unpaired electron density of 10.sup.15 -10.sup.20 /cm.sup.3, which is obtained by annealing a commercially available Si powder at temperatures of 300.degree. to 800.degree. C. in other than nitrogen atmosphere for 3-5 hours.

Abstract: A sintered silicon nitride-based body comprising 20% or less by weight of a grain boundary phase and the balance being a major phase of grains of silicon nitride and/or sialon, wherein the major phase contains a grain phase of a .beta.-Si.sub.3 N.sub.4 phase and/or a .beta.'-sialon phase, and a quantitative ratio of the grain phase of the .beta.-Si.sub.3 N.sub.4 phase and/or the .beta.'-sialon phase is in a range of 0.5 to 1.0 relative to the major phase; the grain boundary phase contains Re.sub.2 Si.sub.2 O.sub.7 (wherein Re represents a rare-earth element other than Er and Yb) as a first crystal component and at least one of ReSiNO.sub.2, Re.sub.3 Al.sub.5 O.sub.12, ReAlO.sub.3, and Si.sub.3 N.sub.4.Y.sub.2 O.sub.3 as a second crystal component; and a quantitative ratio of the first and second crystal components in the grain boundary phase to the grain phase of .beta.-Si.sub.3 N.sub.4 phase and/or the .beta.'-sialon phase ranges from 0.03 to 1.6.

Abstract: A method of making a shaped part of sintered silicon nitride is disclosed which includes preparing a mixture of Si.sub.3 N.sub.4 having a BET specific surface area in the range of from 2 to 15 m.sup.2 /g, having an O.sub.2 content of <1.5% by weight, a .beta.-form content of <2% by volume with finely divided Y.sub.2 O.sub.3, Al.sub.2 O.sub.3 or HfO.sub.2 and/or ZrO.sub.2, the total additive content being in the range of from 6 to 13% by weight, based on the total weight of the mixture, then mixing and milling mixture in a liquid dispersion medium, drying and agglomerating the suspension so produced, subsequently pressing, injection molding or redispersing and casting the agglomerated material obtained to make shaped parts, and finally sintering the shaped parts at temperatures between 1725.degree. and 1850.degree. C. under nitrogen for a period of up to 2 hours. The shaped parts produced according to the method have high mechanical strength and include at least 87% by weight Si.sub.3 N.sub.

Abstract: The invention aims to offer a method to manufacture a high-strength, high-reliability and low cost silicon nitride based sintered body which is not affected by the amount of metal impurities contained in the silicon nitride powder, without using high-purity silicon nitride powder, and can be sintered for a short sintering time. The invention uses silicon nitride and sintering aids, and the powder mixture containing 500-5000 ppm metal impurities is sintered at temperatures ranging from 1300.degree.-1900.degree. C., and under the conditions wherein the product of sintering temperature and sintering time ranges from 1.times.10.sup.5 to 10.times.10.sup.5 .degree. C. .multidot.seconds.

Abstract: Provided herein is a me silicon nitride based sintered body composed only of uniform, fine crystal grains, and improved in both strength and fracture toughness in the middle and low temperature ranges. The crystalline silicon nitride powder thus produced is composed of crystal grains whose longer-axis diameter is not more than 200 nm or an amorphous silicon nitride powder is used as material powder. According to the disclosed method, the silicon nitride powder is sintered at a temperature of 1200.degree. C. to 1400.degree. C. or sintered with a product of sintering temperature (.degree. C.) and sintering time (sec) below 600000 (.degree. C. sec) at a temperature of 1400.degree. C. to 1900.degree. C. By this method, a silicon nitride based sintered body in which the longer-axis diameter of silicon nitride and/or sialon crystals is not more than 200 nm is obtained.

Abstract: The specification describes a method for producing high density sintered silicon nitride (Si.sub.3 N.sub.4) having a relative density of at least 98%. In a first step, silicon nitride powder is compacted into a desired shape. It is then pre-sintered in a second step, generally, under normal pressure to obtain a presintered body having a relative density of at least 92%. In a third step, the presintered body is subjected to a hot isostatic pressing (HIP) in an inert gas atmosphere of 1500.degree.-2100.degree. C. and of nitrogen gas partial pressure of at least 500 atm. Since the presintering does not require any capsule, it is possible to produce high density sintered Si.sub.3 N.sub.4 of complex configurations. As a sintering aid, Y.sub.2 O.sub.3 --Al.sub.2 O.sub.3 --MgO system sintering aid is particularly effective. To improve the strength of sintered Si.sub.3 N.sub.4, it is effective to add a heat treatment step after the HIP and maintain the temperature of the sintered Si.sub.3 N.sub.4 above 500.degree. C.