Abstract: This invention relates generally to a novel method for removing metal from a formed self-supporting body. A self-supporting body is made by reactively infiltrating a molten parent metal into a bed or mass containing a boron donor material and a carbon donor material (e.g., boron carbide) and/or a boron donor material and a nitrogen donor material (e.g., boron nitride) and, optionally, one or more inert fillers. Once the self-supporting body is formed, it is then subjected to appropriate conditions which causes metallic constituent contained in the self-supporting body to be at least partially removed.

Abstract: In the present invention, there is described a setup for producing a self-supporting ceramic body or ceramic composite by the oxidation of a parent metal to form a polycrystalline ceramic material comprising the oxidation reaction product of said parent metal with an oxidant, including a vapor-phase oxidant, and optionally one or more metallic constituents dispersed throughout the polycrystalline ceramic material. The setup is used with a method which comprises the steps of providing at least a portion of said parent metal with a barrier means at least partially spaced from said parent metal for establishing at least one surface of the ceramic body, and heating said parent metal to a temperature above its melting point but below the melting point of the oxidation reaction product to form a body of molten metal. At that temperature, the molten metal is reacted with the oxidant, thus forming the oxidation reaction product.

Abstract: Compounds that satisfy the general formula A.sub.1-Y.sup.4+ A.sub.Y.sup.1+ A.sub.Y.sup.3+ V.sub.2-X E.sub.X O.sub.7 exhibit isotropic NTE behavior above a temperature of about 100.degree. C. Y is from about 0.0 to about 0.4, and more preferably is about 0.2. X is from about 0.6 to about 1.4, and is more preferably about 1. Particularly suitable NTE compounds have X about 1 and Y about 0. A.sup.4+ is selected from the group consisting of Hf, Zr, Zr.sub.a M.sub.b, Hf.sub.a M.sub.b and mixtures thereof wherein a plus b equals one and M is selected from the group consisting of Ti, Ce, Th, U, Mo, W, Pb, Sn, Ge and Si. More preferably, A.sup.4+ is selected from the group consisting of Hf and Zr. A.sup.1+ is selected from the group consisting of the alkali earth metals, A.sup.3+ is selected from the group consisting of the rare earth metals, and E is selected from the group consisting of P and As. The NTE materials may be incorporated into compositions such as epoxy and ceramic compositions.

Abstract: Moldable compositions comprising metallic powder or combination thereof with ceramic powder, mixed an organic binder are disclosed, at least a part of which comprises a synthetic resin component (A) having a heat deformation temperature of 130.degree. C. or higher. The component A may be used in combination with another component (B) having a melting point of 30.degree. C.-100.degree. C., with or without another thermoplastic component (C), having a heat deformation temperature of 13.degree. C. or less. Moldable compositions, comprising metallic and/or ceramic powder mixed with an organic binder comprising a secondary or tertiary amine (D), or combination thereof with a thermoplastic resin (E), are also disclosed.

Abstract: The present invention pertains to the use of a finely divided magnesium oxide micropowder for preparing ceramic masses and moldings.

Abstract: Disclosed is a phenol-formaldehyde resin binder for refractories, having from 0.05 to 0.6 methylol group on average per one phenolic constitutive unit and having a free phenol content of less than 5%. For producing refractory granules with the binder, a composition comprising carbon substances of 50% by weight or less in all and a balance of refractory substances is kneaded with the binder and water optionally along with a solvent having a boiling point of 200.degree. C. or higher, in a mixer as heated at 60.degree. to 130.degree. C. Optionally, the volatile content in the blended mix is adjusted to the shapable level. The process of using the binder is free from injury to human bodies and the danger of firing. The refractory granules may be shaped into refractory articles having a suitable gas-permeability stable against variation of the working environment. The refractory granules are suitable for shaping gas-blowing immersion nozzles having a suitable gas-permeability.

Abstract: A method of processing water-sensitive ceramic powders, particularly carbothermically produced aluminum nitride, whereby the ceramic powder is deagglomerated in a dry milling step with addition of an alkylamine which is liquid at room temperature is disclosed. The alkylamine is added in an amount sufficient to produce a monomolecular layer on the surface of the ceramic powder. The deagglomerated powder subsequently is vigorously stirred with a concentrated aqueous solution or dispersion of binder and rapidly and gently dried, preferably by freeze drying. Aluminum nitride powder prepared by this process can be further processed into shaped parts with a high thermal conductivity.

Abstract: High-packing silicon nitride powder having a tap density of at least about 0.9 g/cm.sup.3 is prepared by reacting a metallic silicon powder having a mean particle size of about 1 to 10 .mu.m, a BET specific surface area of about 1 to 5 m.sup.2 /g, and a purity of at least about 99% with nitrogen in a nitrogen atmosphere containing about 5 to 20% by volume of hydrogen at about 1,350 to 1,450.degree. C., and milling the resulting silicon nitride powder in a dry attritor. The powder is moldable into a compact having a density of at least about 1.70 g/cm.sup.3, from which a sintered part having improved dimensional precision and strength is obtained.

Abstract: Pressed parts based on pyrogenically produced titanium dioxide with the following physico-chemical characteristics:______________________________________ Outer diameter 0.8-15 mm BET surface according <1-20 m.sup.2 /g to DIN 66 131 Pore volume 0.01-0.29 cm.sup.3 /g Pore distribution no pores <10 nm at least 90% of the pores in a range of 10-80 nm Breaking strength 30-500 N/pressed part TiO.sub.2 phase rutile 100% Composition >99.5% TiO.sub.2 ______________________________________They are produced by mixing pyrogenically produced titanium dioxide with urea, graphite and water, compacting the mixture, optionally drying the resulting mass at 80.degree. C. to 120.degree. C. comminuting, subsequently extruding or tabletting to produce pressed parts and tempering the pressed parts at a temperature of 710.degree. C. to 1000.degree. C. for a period of 0.5 to 6 hours. The pressed parts can be used as catalyst or catalytic carrier.

Abstract: Submicron sized ceramic particles are produced by combining a ceramic precursor with an organic or carbonaceous carrier material, and exposing droplets of the mixture to a temperature sufficient to cause combustion of the organic material and subsequent vaporization and nucleation, or diffusion and oxidation, of the ceramic precursor to form pure, crystalline, uniform nanophase ceramic particles.

Abstract: A composition suitable for use as a binder of ceramic materials and a method for preparing a ceramic material which provides relatively greater green ceramic strength is disclosed. The improved binder contains a substantially hydrolyzed copolymer made from monomers having ester or amide functional groups, poly(vinyl amine), poly(vinyl formamide) or a copolymer of vinyl alcohol and vinyl amine. The binder is combined with an aqueous solution containing a ceramic powder to make a slurry, and the slurry is subsequently spray dried, pressed and heated to make a ceramic.

Abstract: High-packing silicon nitride powder is prepared by reacting metallic silicon powder having a mean particle size of 1 to 10 .mu.m and a purity of at least 99% directly with nitrogen for forming silicon nitride powder, milling the silicon nitride powder in a dry attritor until the tap density exceeds 0.9 g/cm.sup.3 and the content of particles having an aspect ratio of up to 3 exceeds 95% by weight, and further milling the silicon nitride powder in a wet attritor for finely dividing coarse particles having a particle size of at least 2 .mu.m. The silicon nitride powder has a tap density of at least 0.9 g/cm.sup.3 and a mean particle size of 0.4 to 0.6 .mu.m and contains at least 95% by weight of particles having an aspect ratio of up to 3 and up to 5% by weight of coarse particles having a particle size of at least 2 .mu.m. The powder is moldable into a high density compact, from which a sintered part having improved dimensional precision and strength is obtained.

Abstract: In the present invention, there is provided a method for producing a self-supporting ceramic or ceramic composite body by the oxidation of a parent metal to form a polycrystalline ceramic material comprising the oxidation reaction product of said parent metal with an oxidant, including a vapor-phase oxidant, and optionally one or more metallic constituents dispersed throughout the polycrystalline ceramic material. The method comprises the steps of providing at least a portion of said parent metal with a barrier means at least partially spaced from said parent metal for establishing at least one surface of the ceramic body, and heating said parent metal to a temperature above its melting point but below the melting point of the oxidation reaction product to form a body of molten metal. At that temperature, the molten metal is reacted with the oxidant, thus forming the oxidation reaction product.

Abstract: A process for producing a substantially non-explosive powder containing finely divided metallic particles suitable for being incorporated in a refractory mixture, comprising simultaneously grinding a mixture of pieces of metal with pieces of an inert refractory material to produce a premixture containing finely divided metallic particles and finely divided refractory particles which are intimately mixed together. The refractory particles are present in such particle sizes and quantities as ensure that the Minimum Explosible Concentration, as tested in a 20-L vessel with a chemical igniter, is greater than 100 gm/m.sup.3. The inert particles comprise at least 40% of the mixture, and preferably 50% to 75%. The invention also includes a premixed powder, produced by this process, especially as contained in drums or impermeable bags.

Abstract: A known relatively dense composite refractory material has a matrix of a refractory material and a dispersed phase in the form of particles of a ceramic material, each dispersed particle comprising an agglomerate of strongly bonded microcrystals, which exhibit strong thermal expansion anisotropy and do not crack spontaneously on cooling from about 1600.degree. C. to ambient temperature. The thermal shock resistance of this composite refractory material is improved by (a) ensuring that the matrix material comprises from 5 to 90 percent by volume of grains having a diameter in the range of from 15 micrometers to about 80 micrometers, and/or (b) including at least one thermal down-quench of from 50.degree. C. to 1500.degree. C. in the final cooling step in the production of the composite refractory material. Alumina is a typical matrix material, with monoclinic zirconia as the dispersed phase.

Abstract: An unsintered metal fiber burner is produced by mixing ceramic fibers with the metal fibers and binding the mixed metal-ceramic fibers together as a porous layer adherent to a foraminous support. By mixing ceramic fibers with metal fibers, the cost of a sintered metal fiber burner is reduced while the novel burner, because of the metal fiber therein, exhibits improved properties such as greater radiant efficiency, lower NO.sub.x emissions and increased durability.

Abstract: Compounds that satisfy the general formula A.sub.1-Y.sup.4+ A.sub.Y.sup.1+ A.sub.Y.sup.3+ V.sub.2-X P.sub.X O.sub.7 exhibit isotropic NTE behavior in the range of normal ambient temperatures. Y is from about 0.0 to about 0.4, and more preferably is about 0.2. X is from about 0.6 to about 1.4, and is more preferably about 1. Particularly suitable NTE compounds have X about 1 and Y about 0. A.sup.4+ is selected from the group consisting of Hf, Zr, Zr.sub.a M.sub.b, Hf.sub.a M.sub.b and mixtures thereof wherein a plus b equals one and M is selected from the group consisting of Ti, Ce, Th, U, Mo, Pt, Pb, Sn, Ge and Si. More preferably, A.sup.4+ is selected from the group consisting of Hf and Zr. A.sup.1+ is selected from the group consisting of the alkali earth metals, and A.sup.3+ is selected from the group consisting of the rare earth metals. Such NTE materials exhibit isotropic negative linear expansion at a temperature below about 100.degree. C.

Abstract: Novel self-supporting ceramic structures are produced by the oxidation reaction of a molten metal precursor with a vapor-phase oxidant to form an oxidation reaction product. The resulting ceramic material of the polycrystalline oxidation reaction product consists essentially of an oxidation reaction product and, optionally, one or more non-oxidized constituents of the metal precursor.

Abstract: There is disclosed a method for making a self-supporting ceramic composite article having a porous core bearing a dense surface layer formed integrally with said core. A preform comprises a filler material and parent metal distributed therethrough, wherein the volume percent of parent metal is sufficient to form a volume of oxidation reaction product exceeding the total volume available within said preform. The parent metal is melted and reacted with an oxidant to form an oxidation reaction product filling the spatial volume and leaving voids. The reaction is continued to further transport molten parent metal through the oxidation reaction product to at least one surface of the preform to form oxidation reaction product on said surface substantially free of voids thereby forming a relatively dense surface layer.

Abstract: A proteinaceous gelatin binder is used to make aqueous green ceramic compositions suitable for forming green ceramic tape by tape casting. Any known ceramic may be used. The tapes may be fired individual or as a laminate to produce sintered ceramic articles.

Abstract: Shaped, self-supporting ceramic bodies are produced by preparing a mold by applying a permeable, conformable material to a shape-defining surface of an expendable pattern. The permeable, conformable material, when set or stable, provides a mold with a shaped surface which is defined by, and is therefore substantially congruent to, the shape-defining surface. Upon heating, the material of the expendable pattern combusts or volatilizes and thus establishes the shaped cavity mold. A molten parent metal is then vaporized with a vapor-phase oxidant in such a manner as to form a ceramic body which grows into the mold cavity, and is shaped by it. The ceramic body is recovered from the mold having a shaped surface replicating the shape-defining surface of the expendable pattern.

Abstract: Ceramic oxide powders and a method for their preparation. Ceramic oxide powders are obtained using a flame process whereby two or more precursors of ceramic oxides are introduced into a counterflow diffusion flame burner wherein said precursors are converted into ceramic oxide powders. The morphology, particle size, and crystalline form of the ceramic oxide powders are determined by process conditions.

Abstract: A powdered admixture of a boron, carbon, nitrogen or silicon derivative of a first metal is combined with a source of a second metal and, optionally, a source of a third metal or an iron-group metal, subjected to densification conditions (heat and pressure), partially reacted and converted to a hard, wear resistant material. The wear resistant material contains an amount of the first metal derivative as well as a material of varying stoichiometry which is the partial reaction product of components of the powdered admixture. The material may also contain residual, unreacted portions of components other than the first metal derivative. Articles formed from this material can be useful as, for example, nozzles in abrasive or nonabrasive waterjet cutting machines and various parts of wire drawing apparatus.

Abstract: Ceramic binder for forming and processing ceramic ware, comprising a sol-gel of a mixture of highly charged metal hydroxy cations and one or more low charged metal hydroxy cations, which are able to form an aqueous sol.

Abstract: A non-magnetic substrate for use in a magnetic head, consists of the basic composition consisting of CoO and NiO or NiO, and (a) from 0.1 to 7% by weight of ZrO.sub.2 and HfO.sub.2 based on 100% of the basic composition, or (b) from 0.1 to 7% by weight of ZrO.sub.2, and from 0.1 to 2% by weight of Al.sub.2 O.sub.3. Cracking of the magnetic-layer structure is prevented.

Abstract: In ceramic welding processes, oxidising gas and a mixture of refractory and fuel powders are projected against a surface and the fuel is burnt to generate sufficient heat that the refractory powder becomes at least partially melted or softened and a cohesive refractory mass is progressively built up against that surface. In order to reduce any tendency for the weld mass to include a low-grade refractory phase and thus promote the refractoriness of that weld mass, the fuel powder is present in a proportion of not more than 15% by weight of the total mixture and includes at least two metals selected from aluminium, magnesium, chromium and zirconium, and in that at least the major part by weight of the refractory powder consists of one or more of magnesia, alumina and chromic oxide, and in that the molar proportions of silica and calcium oxide present in the refractory powder (if any) satisfy the following expression: molar concentration of SiO.sub.2 in % .ltoreq.0.

Abstract: The present invention provides a method of annealing optical glass layers, said method comprising the step of heating glass layers having an area greater than 0.01 cm.sup.2 to a temperature of between about 350 deg. C. and 1000 deg. C. in less than 10 minutes. The upper limit of the glass area that can be treated is limited only by the size of the quartz chamber. Current state-of-the-art chambers can accomodate glass areas of about 0.01 cm.sup.2 to about 324 cm.sup.2. According to another aspect of the invention, there is also provided an optical waveguide glass layer, treated according to the method of this invention, disposed on an integrated optical device.

Abstract: Improved fiber reinforced composites having near zero coefficients of thermal expansion are described. The improved composites include reinforcing fibers and matrix material in which gap structures which exist within the composite are filled with a bonding agent. The reinforcing fibers can be unidirectionally, bidirectionally or multidirectionally oriented within the matrix material and articles fabricated from the improved composite have reduced coefficients of thermal expansion in directions transverse to the orientations of the fibers. This improvement makes these improved composites useful for fabricating high energy laser mirror substrates.

Abstract: Novel, hot pressed metal-ceramic mixtures provide increased density, hardness, and flexural strength in comparison with pure densified ceramics.

Abstract: A powdered admixture of a boron, carbon, nitrogen or silicon derivative of a first metal is combined with a source of a second metal and, optionally, a source of a third metal or an iron-group metal, subjected to densification conditions (heat and pressure), partially reacted and converted to a hard, wear resistant material. The wear resistant material contains an amount of the first metal derivative as well as a material of varying stoichiometry which is the partial reaction product of components of the powdered admixture. The material may also contain residual, unreacted portions of components other than the first metal derivative. Articles formed from this material can be useful as, for example, nozzles in abrasive or nonabrasive waterjet cutting machines and various parts of wire drawing apparatus.

Abstract: A powdered admixture of a boron, carbon, nitrogen or silicon derivative of a first metal is combined with a source of a second metal and, optionally, a source of a third metal or an iron-group metal, subjected to densification conditions (heat and pressure), partially reacted and converted to a hard, wear resistant material. The wear resistant material contains an amount of the first metal derivative as well as a material of varying stoichiometry which is the partial reaction product of components of the powdered admixture The material may also contain residual, unreacted portions of components other than the first metal derivative. Articles formed from this material can be useful as, for example, nozzles in abrasive or nonabrasive waterjet cutting machines and various parts of wire drawing apparatus.

Abstract: Disclosed is a method of producing dense refractory products, comprising:(a) obtaining a quantity of exoergic material in powder form capable of sustaining a combustion synthesis reaction;(b) removing absorbed water vapor therefrom;(c) cold-pressing said material into a formed body;(d) plasma spraying said formed body with a molten exoergic material to form a coat thereon; and(e) igniting said exoergic coated formed body under an inert gas atmosphere and pressure to produce self-sustained combustion synthesis.Also disclosed are products produced by the method.

Abstract: The present invention provides an aluminum borate ceramic having a high porosity and a tightly controlled pore size distribution, while maintaining good mechanical strength. The ceramic body can be formed by decomposing boric acid-stabilized aluminum acetate to form an aluminum borate powder, and sintering the powder to form a ceramic body.

Abstract: The present invention relates to preparing refractory chromium-containing material and resides in local initiation of an exothermal reaction in a mixture of the following composition: a chromium-containing component, 8-20 mass % of a reducer selected from the group consisting of aluminium, magnesium, silicon, titanium, zirconium, or the alloys thereof, and 0.1-50 mass % of a filler, wherein as the filler use is made of periclase, sand, clay, refractory oxide, refractory scrap, wastes of blast-furnace processes, wastes of graphite or silicon carbide production, or an inorganic salt taken separately or in a mixture.

Abstract: This invention relates to a process for preparing a lithium containing ceramic article. The process provides a ceramic article that is substantially crack free and has as its principal crystalline phase a beta-eucryptite phase, a beta-spodumene phase, or a mixture thereof. The process comprises calcining a powder of a lithium-exchanged zeolite up to its collapse temperature for a time sufficient to collapse the zeolite framework and provide an amorphous powder. The amorphous powder is now formed into a shaped article and sintered at a temperature of about 700.degree. to about 1150.degree. C. for a time of about 1 to about 12 hours. The zeolites which can be used are those having a SiO.sub.2 Al.sub.2 O.sub.3 ratio of about 2 to about 8.5 and include zeolite B, zeolite ZK-19, zeolite W, phillipsite, hormotome, gismondine and mixtures thereof and have a sodium content less than about 1 weight percent. It is preferred that the lithium-exchanged zeolite have an average particle size of less than about 10 microns.

Abstract: Disclosed is a process for the preparation of multi-element metal oxide, high temperature superconductor precursor powder comprising spraying a homogenous solution of a multi-element metal salt solution mixed in a stoichiometric ratio corresponding to the desired superconducting composition into a horizontal tube-like furnace being heated to a temperature of 800.degree.-1000.degree. C., transporting resulting sprayed mist along the main axis of the furnace tube by the aid of hot air and collecting resultant finely divided metal oxide powder by the aid of a filter, whereby the resultant mixed metal oxide powder is a precursor for the preparation of a high temperature superconducting ceramic.

Abstract: This invention relates to the preparation of thermally stable, substantially polycrystalline silicon carbide ceramic fibers derived from a polycarbosilane resin. The unexpected thermal stability of these fibers is achieved by the incorporation of boron prior to ceramification.

Abstract: A method of producing shaped, self-supporting ceramic bodies includes preparing a mold by applying a permeable, conformable material to a shape-defining surface of an expendable pattern. The permeable, conformable material, when set or stable, provides a mold with a shaped surface which is defined by, and is therefore substantially congruent to, the shape-defining surface. Upon heating, the material of the expendable pattern combusts or volatilizes and thus establishes the shaped cavity mold. A molten parent metal is then vaporized with a vapor-phase oxidant in such a manner as to form a ceramic body which grows into the mold cavity, and is shaped by it. The ceramic body is recovered from the mold having a shaped surface replicating the shape-defining surface of the expandable pattern.

Abstract: A refractory coating composition, adapted to be applied to a substrate by spraying or gunning, comprising:from about 25 to about 40% by weight alumina;from about 15 to about 25% by weight ceramic fiber;from about 40 to about 60% by weight colloidal silica; andsufficient water to form an aqueous suspension thereof.

Abstract: A process for the production of a powder having a nanocrystalline structure from powders of at least two materials of the groups including metals, metallic compounds, and ceramic materials, in a composition which tends to develop an amorphous phase. The starting powders are subjected to high stresses of at least 12 G in a neutral or reducing atmosphere at about 20.degree. C. until there are no crystallites larger than about 10 nm.

Abstract: A porous filter for metal hot melt comprises ceramic aggregate particles bound by an inorganic binder. The aggregate particles contain not less than 50 wt % of particles with a shape factor in the range of 100 to 130 and the binder has needle-shaped crystals deposited on the surface thereof. By employing this filter, debris catching ability and initial impregnation of metal hot melt are highly improved.

Abstract: Improved inorganic ceramic papers comprising heterogeneous grades of ceramic fibers, namely small, high surface area fibers and at least one larger, lower surface area ceramic fiber are bonded into a matrix with the aid of an inorganic binder system having at least one metal oxide with an average particle size below 200 nm. Multiple different grades of inorganic ceramic fibers and small particle size inorganic binders impart good tensile strength and flexibility characteristics in the same sheet.

Abstract: A process for producing a dried particulate ceramic material in which a cake comprising a dispersion of at least 25% by volume of particulate ceramic material in a liquid medium is subjected to rapid drying. Also, a dried particulate ceramic material which may be dispersed in a liquid medium to form a dispersion containing at most only a small proportion of aggregates of the primary particles of the ceramic material.

Abstract: An aqueous plastic composition of an inorganic powder which per se has substantially no plasticity which comprises: the inorganic powder and a polysaccharide of natural origin.The molding and sintering of the plastic composition provide a sintered body of high mechanical strength and dimensional accuracy.

Abstract: A process for using nitride-containing aluminum dross residues to produce refractory products. The process involves mixing a dross residue which contains AlN, without prior conversion of the aluminum nitride in the dross to aluminum oxide or hydroxide, with a material comprising a metal oxide or a metal oxide precursor, and calcining the resulting mixture at a temperature suitable to produce a refractory product. During the calcination step, the AlN reacts with other components of the mixture. Since the reaction is exothermic, less heat is required for the calcination step than if a dross residue containing no AlN were used. The AlN can also reduce various contaminants (e.g. Fe.sub.2 O.sub.3, silicon and titanium) present in the metal oxide refractories, and so the invention can be used to produce conventional refractory products of improved purity and appearance. The process enables dross residues to be used for useful purposes rather than being discarded.

Abstract: There is disclosed a silicon nitride based sintered material which contains 0.1% to 20% by volume of zirconium oxide, 0.1% to 14% by volume of zirconium nitride, 3% to 15% by volume of a binder phase of an Mg-Si-O-N or Mg-Si-Zr-O-N system, and balance .beta.-silicon nitride. The sintered material may include an oxide layer of an average thickness of 10 to 1,000 .mu.m in a surface thereof and having a zirconium oxide concentration increasing toward the surface thereof. A process specifically adapted to manufacture the above sintered material is also disclosed.

Abstract: A heat resistant, low expansion phosphate compound and sintered bodies thereof, having a composition of RZr.sub.4 P.sub.6 O.sub.24 (R is one or more cations of IIa group in the periodic table, such as Ba, Sr and Ca): an average thermal expansion coefficient between room temperature and 1,400.degree. C. of -10.about.+10.times.10.sup.-7 /.degree.C.; and having a high temperature type crystalline structure having R3c symmetry at room temperature. The sintered body of the invention can be manufactured by mixing and shaping starting materials, firing the resulting shaped body at 1,400.degree. C..about.1,700.degree. C. to provide a sintered body with a composition of RZr.sub.4 P.sub.6 O.sub.24 and then, keeping the obtained sintered body at a high temperature of not lower than a temperature of phase transition between a high temperature type and a low temperature type crystalline structure, followed by quenching.

Abstract: A silicon nitride powder prepared by nitriding a metallic silicon powder and having the following physical characteristics (1) to (3):(1) the oxygen content in the form of a solid solution is at most 0.5% by weight,(2) the specific surface area is from 6 to 16 m.sup.2 /g, and(3) the content of fine powder of at most 0.2 .mu.m is at most 7% by volume.

Abstract: Compositions having the nominal formula Bi.sub.2 Sr.sub.3-x Y.sub.x Cu.sub.2 O.sub.8+y wherein x is from about 0.05 to about 0.45 and y is from about 0 to about 1 are superconducting.

Abstract: Silicon aluminum oxynitride materials having high hardness and high density are formed by pressureless sintering of silicon nitride, yttrium oxide and aluminum nitride. The materials contain at least 75 weight percent of alpha prime phase sialon.