Abstract: A ceramic product comprising both carbon and nitrogen and a method for its production are provided. The product is formed in a reactor having a chamber defined therein which is divided into a combustion zone and a reaction zone. A combustible mixture is injected into the combustion zone in a direction generally toward the reaction zone, and is accordingly combusted in the combustion zone to produce hot combustion products. At least one reactant containing carbon, nitrogen and an additional component (i.e. silicon) is injected at the boundary between the zones into the reactor chamber so as to flow with the hot combustion products into the reaction zone and react to form the ceramic product.

Abstract: A process for coating powders with ultrafine particles of silicon, silicon oxide, silicon nitride or alloys thereof, entailing:a) introducing a reactant gas into a bed of core powders, thereby uniformly suspending the core powders in the reactant gas,b) entraining the uniformly suspended core powders into a chemical vapor deposition (CVD) reactor,c) selectively forming ultrafine particles of silicon, silicon oxide, silicon nitride or alloys thereof in the gas phase by homogeneous deposition of the reactant gas, while minimizing core powder growth by CVD at surfaces of suspended core powders, andd) coating the core powders with the ultrafine particles of silicon, silicon oxide, silicon nitride or alloys thereof, by introducing hot inert gas into the uniformly suspended core powders in the reactant gas.

Abstract: A method of making a polysilazane comprising forming a reaction medium comprising at least one halomonosilane, an ammonium compound, and an organic solvent for said at least one halomonosilane, carrying out the reaction between said at least one halomonosilane and said ammonium compound in the absence of any catalyst, oxygen, and moisture at atmospheric pressure and at a temperature of about -80.degree. C. to 50.degree. C. for a time sufficient to form said polysilazane, and separating said polysilazane from said reaction medium.

Abstract: A method is disclosed for preparing and recovering metal nitrides from their ferrometal alloys and nickel metal alloys. Exemplary steps of the process involve niobium nitride prepared from ferroniobium alloys (FeNb) which are first hydrided to provide a friable, comminutable product which is then nitrided under conditions which form distinct phases of iron nitride and niobium nitride respectively.

Abstract: A process is disclosed for producing sintering active silicon nitride powders with low oxygen content by wet grinding a silicon nitride starting material, leaching the ground suspension with fluorine-free mineral acid, and separating off the purified silicon nitride powder.

Abstract: Silicon diimide having a carbon content of at most 0.5% by weight and a chlorine content of at most 20 ppm is prepared by reacting ammonia with organyl amino silane at 50.degree.-300.degree. C. at elevated pressure and is useful as an intermediate for high grade silicon nitride.

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: This invention relates to a novel method of, and means for, directing energy through Si.sub.2 HSb.sub.2 in such a manner that normal energy parameters can be exceeded. The principal object of the invention is to provide the means for more efficient radiant energy power systems to be constructed. For example, this invention can be applied to construct more efficient rocket propulsion systems.Si.sub.2 HSb.sub.2 has a crystalline structure with a regular pattern of electron deficiencies which physicists call "holes" in the lattice. Energy can be radiated at the top of the compound and be accelerated as it passes through to a new higher velocity as it expelled out the bottom of the compound. This is accomplished by applying electrical potentials to the sides of the compound which rectify the "holes" in the lattice. The electrical potentials applied to the sides of the compound can be varied to allow the radiated energy output to be directed in the x,y plane.

Abstract: A method of producing a composite ceramic powder is provided herein. A precursor product powder is first produced in a reactor from at least one carbide-forming reactant by heating the reactant(s) by means of combustion of a fuel, and the precursor product powder as collected from the reactor is heated in a nitrogen-containing atmosphere to produce a final product comprising a carbide compound as well as a nitride compound.

Abstract: An apparatus and methods are provided for producing ceramic products in a reactor so as to minimize deposits therein. The reactor has a chamber defined therein which is divided into a combustion zone, into which a combustible mixture is injected, and a reaction zone in which the ceramic product is produced from at least one reactant injected into the chamber at the boundary between the zones. At least a portion of the wall defining the reaction zone is surrounded by at least one passageway through which coolant fluid is passed during ceramic production. Either carbide product or nitride product can be produced in the reaction zone according to the invention.

Abstract: To prepare silicon nitride having a crystallite size of 40 to 60 nm and a specific surface area according to BET of 21 to 40 m.sup.2 /g, amorphous silicon nitride or amorphous silicon nitridoimide is brought into surface contact with gas containing water vapor or water-containing solvents and the amorphous silicon nitride or amorphous silicon nitridoimide thus surface-contacted is heated under a nitrogen atmosphere at a heating rate of at least 1.degree. C./minute to above the crystallization temperature of .alpha.-silicon nitride, which is above 1100.degree. C.

Abstract: The present invention relates to high performance ceramics and methods for their production using supercritical temperatures and supercritical pressures. Furthermore, the present invention relates to high performance ceramics for use in the automobile industry.

Abstract: To prepare spherical amorphous silicon nitride (Si.sub.3 N.sub.4), a silicon halide and ammonia are reacted in the vapor phase in the absence of water or water vapor in a vertically arranged reaction container, a silicon halide/ammonia reaction product being formed. In this reaction, a silicon halide/inert gas mixture is passed into the lower part of the reaction container and ammonia is passed into its upper part, the ratio of SiHal.sub.4 :NH.sub.3 being 1:(5.8 to 6.6). By establishing a stationary state, the reaction takes place only in the central part of the reaction container. After the silicon halide/ammonia reaction product has been removed from the reaction container, it is heated to temperatures of 950.degree. to 1150.degree. C. in an atmosphere containing ammonia.

Abstract: Silicon nitride powder is produced in two steps, by supplying metallic silicon powder to a fluidized bed composed of silicon nitride and nitrogen or ammonia gas where primary nitriding reaction is effected until the silicon powder is nitrided to an amount of at least 50% and transferring the nitrided product from the fluidized bed into a moving bed where secondary nitriding reaction is effected for nitriding the unreacted silicon with nitrogen or ammonia gas. This method is adapted for manufacture on a commercial scale because the silicon nitride powder thus obtained is consistent and has a very high degree of nitriding and a minimal variation in quality.

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 method and apparatus are provided for producing a product comprising a nitride compound, such as for example silicon nitride. A reactor is provided which has a chamber defined therein which is divided into a combustion zone and a reaction zone. A combustible mixture is injected into the combustion zone in a direction generally toward the reaction zone, and is accordingly combusted in the combustion zone. At least one reactant is injected at the boundary between the zones into the reactor chamber in a direction generally parallel to the longitudinal axis of the chamber so as to react to form raw product comprising the nitride compound. According to another aspect, a raw product powder as produced by the reactor comprises silicon nitride as the nitride compound and further comprises elemental silicon.

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 process for making metal oxides including niobium or tantalum oxides from ferro and nickel alloys containing these metals involving the multiple steps of hydriding the ferro or nickel alloy selected, under conditions of suitable temperature and pressure to render the alloys friable, subdividing the hydrided product into selected particle sizes, then nitriding with a nitrogen-containing gas at elevated temperatures above 500.degree. C. to form the alloy constituent nitrides, thereafter leaching the nitrides formed with aqueous acid to separate the formed ferro or nickel nitride from the acid soluble nitrides from the acid insoluble nitrides, calcining the acid insoluble nitrides with oxygen-containing gas under conditions suitable for the formation of the metal oxide of the acid soluble nitride.

Abstract: A method and apparatus are provided for producing a product comprising a nitride compound, such as for example silicon nitride. A reactor is provided which has a chamber defined therein which is divided into a combustion zone and a reaction zone. A combustible mixture is injected into the combustion zone in a direction generally toward the reaction zone, and is accordingly combusted in the combustion zone. At least one reactant is injected at the boundary between the zones into the reactor chamber in a direction generally parallel to the longitudinal axis of the chamber so as to react to from raw product comprising the nitride compound. According to another aspect, a raw product powder as produced by the reactor comprises silicon nitride as the nitride compound and further comprises elemental silicon.

Abstract: The invention relates to a process for the production of silicon ceramic whiskers and silicon ceramic powder from silicon fluoride and ammonia or a hydrocarbon, at an elevated temperature. According to the invention, the hydrocarbon or ammonia (4) is decomposed separately at a high temperature into reactive carbon or nitrogen and hydrogen, whereafter the carbon or nitrogen radical thus obtained is further in a gas phase contacted with reactive silicon formed therein from silicon difluoride, in order to deposit finely-divided silicon nitride or silicon carbide out from the gas phase.

Abstract: A method and apparatus are provided for producing a product comprising a nitride compound, such as for example silicon nitride. A reactor is provided which has a chamber defined therein which is divided into a combustion zone and a reaction zone. A combustible mixture is injected into the combustion zone and accordingly combusted to form hot combustion products. At least one reactant (i.e. silane) is injected at the boundary between the zones so as to be carried into the reaction zone by the combustion products and react to form raw product comprising the nitride compound. The raw product can be purified by subsequent processing to remove oxygen and convert by-products to the desired nitride compound. The product of the invention has a low level of impurities and is made up of primarily submicron, highly uniform particles. This makes the product particularly useful for fabrication of sintered ceramic parts.

Abstract: Method and apparatus are provided for collecting reaction product solids entrained in a gaseous outflow from a reaction situs, wherein the gaseous outflow includes a condensable vapor. A condensate is formed of the condensable vapor on static mixer surfaces within a static mixer heat exchanger. The entrained reaction product solids are captured in the condensate which can be collected for further processing, such as return to the reaction situs. In production of silicon imide, optionally integrated into a production process for making silicon nitride caramic, wherein reactant feed gas comprising silicon halide and substantially inert carrier gas is reacted with liquid ammonia in a reaction vessel, silicon imide reaction product solids entrained in a gaseous outflow comprising residual carrier gas and vaporized ammonia can be captured by forming a condensate of the ammonia vapor on static mixer surfaces of a static mixer heat exchanger.

Abstract: An aluminum nitride-based sintered product can be produced at a relatively low heating temperature by mixing at least 20% by weight of ultrafine aluminum powder having an average size of not exceeding 0.5 .mu.m with other powdery raw material, compression molding the resultant powdery mixture, and heating the molded article under a nitrogen atmosphere at a heating temperature ranging from 600.degree. to 800.degree. C. to nitride the ultrafine aluminum powder, whereupon the heat of nitridation is utilized to sinter the molded article.

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 process for nitriding materials containing silicon to form a silicon nitride material predominantly in the alpha phase is disclosed which includes nitriding the silicon-containing material by subjecting it to a nitriding atmosphere containing at least nitrogen gas in combination with at least one other nitriding gas while keeping the composition of the nitriding atmosphere substantially constant by maintaining a substantially constant partial pressure of nitrogen gas during the nitriding, even though nitrogen is being consumed during the nitriding step to form the silicon nitride.

Abstract: In the method of heat-treating a silicon nitride sintered body which was produced from silicon nitride powder and sintering aid powder in order to provide it with an increased crystallinity, the silicon nitride sintered body is heat-treated in a non-oxidizing atmosphere under conditions such that the silicon nitride sintered body is embedded in at least one selected from the group consisting of powders of W, Mo, Ta, Re and carbides thereof.

Abstract: A process for preparing an alpha-phase silicon nitride material and thereafter converting to non-densified beta-phase silicon nitride material includes comminuting a slurry including a mixture of silicon powder and water to form non-oxidized surfaces on the silicon powder and to allow chemical reaction between the silicon and water, reducing the water content of the reacted slurry to a degree sufficient to form a resultant dry mass, nitriding the dry mass by exposure to a nitriding gas including at least nitrogen to form a mass of alpha-phase silicon nitride, and converting the resultant silicon nitride mass at a conversion temperature of from about 1450.degree. C. to about 2100.degree. C. to convert the silicon nitride from an alpha-phase material to a non-densified beta phase silicon nitride material.

Abstract: A low temperature process is described for forming a coating or powder comprising one or more metals or metal compounds by first reacting one or more metal reactants with a halide-containing reactant to form one or more reactive intermediates capable of reacting, disproportionating, or decomposing to form a coating or powder comprising the one or more metal reactants. When one or more metal compounds are formed, either as powders or as coatings, a third reactant may be injected into a second reaction zone in the reactor to contact the one or more reactive intermediates formed in the first reaction zone to thereby form one or more metal compounds such as metal nitrides, carbides, oxides, borides, or mixtures of same.

Abstract: The invention relates to the production of a new ceramic composite material containing molybdenum disilicide in the form of 20-60 .mu.m grains.The method involves preparation of an exothermic mixture containing silicon, molybdenum (VI) oxide, aluminium and molybdenum with the following ratio of the components (wt %):______________________________________ silicon 29-38 molybdenum (VI) oxide 7-42 aluminium 3-16 molybdenum 13-52 ______________________________________its heat treatment in a combustion mode, followed by compaction of the obtained combustion products by way of at least two-stage compression with a degree of deformation from 0.75 to 0.90 at each stage, at a temperature within 1500.degree. to 1900.degree. C.

Abstract: Preceramic polysilazanes which (1) are composed of silicon, nitrogen, and hydrogen, (2) can be isolated and redissolved in common organic solvents, and (3) are capable of providing a high ceramic yield when pyrolyzed are prepared by reacting a mixture of one molar proportion of a tetrahalosilane, preferably tetrachlorosilane, and at least 4.5 molar proportions of a dihalosilane, preferably dichlorosilane, in an organic solvent. Ceramics obtained from the polysilazanes are nanoporous, amorphous silicon nitride ceramics having high purity.

Abstract: A method is described for producing silicon carbide particles using solar energy. The method is efficient and avoids the need for use of electrical energy to heat the reactants. Finely divided silica and carbon are admixed and placed in a solar-heated reaction chamber for a time sufficient to cause a reaction between the ingredients to form silicon carbide of very small particle size. No grinding of silicon carbide is required to obtain small particles. The method may be carried out as a batch process or as a continuous process.

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: The process of this invention for preparing oxynitride ceramic fibers comprises spinning a viscous sol obtained by the hydrolysis of a feed mainly consisting of metal alkoxides, steam-treating the gel fibers, and firing the steam-treated gel fibers in a stream of ammonia and is commercially useful for the production of oxynitride fibers with excellent hardness, strength, modulus of elasticity, heat resistance, and corrosion resistance.

Abstract: The present invention provides a process for the production of silicon nitride by the reaction of silicon and nitrogen, wherein, in one reaction step, silicon powder is reacted with nitrogen which continuously rotates at a temperature of from 1000.degree. to 1800.degree. C. and at a pressure of from 1.01 to 1.8 bar up to a nitrogen content of 1 to 39.5% by weight.The present invention also provides a silicon nitride produced by this process wherein it is obtained in porous form and has the following properties.a) grain size of 0.1 to 20 mm.b) nitrogen content of 1 to 39.5% by weight,c) oxygen content of 1%,d) ratio of .alpha.:.beta.-phase of 1:9 to 9:1.

Abstract: Ternary CaO-TiO.sub.2 -SiO.sub.2 compositions are discussed. These compositions are useful as sintering aids for silicon nitride sintering. Use of these ternary compositions allows silicon nitride to be effectively sintered at lower temperatures than when conventional yttria sintering aids are used.

Abstract: A process for producing a refractory material having the form TB.sub.o, e.g. zirconium nitride (ZrN), includes a first step of mixing a first salt having the form TX.sub.n, e.g. zirconium tetrachloride (ZrCl.sub.4) and a second salt having the form A.sub.m B, e.g. lithium nitride (Li.sub.3 N) in a ratio of n/m in a container. The process also includes a second step of igniting the mixture of the first and second salts, e.g. ZrCl.sub.4 and Li.sub.3 N, whereby the refractory material, e.g. ZrN, is produced along with byproducts having forms nAX and (n/m-o)B, e.g. 4LiCl and (1/6)N.sub.2, respectively. The process further includes a third step of separating the refractory material from the byproducts by solvent extraction. The stoichiometric ratio of the second salt to the first salt is n/m, e.g. 4/3. T is selected from the group consisting of transition metals, e.g. zirconium, and tetrelides, i.e. carbon, silicon, germanium, tin and lead.

Abstract: A system for manufacturing fine-grained SiO powder includes means for heating a mixture of an SiO.sub.2 containing material and an Si and/or C containing material for generating SiO vapor, and for condensing the generated SiO vapor from a gaseous state in the presence of non-oxidizing gas and under substantially low pressure. Preferably, vacuum is maintained at the position where thermal reaction generates SiO vapor. Non-oxidizing gas serves for transferring vapor-state SiO and/or fine-grained SiO powder to an SiO collection chamber. This successfully prevents the SiO from being accumulated within a transfer pipe or duct and thus prevents the pipe or duct from being blocked. Furthermore, substantially low pressure (vacuum) atmosphere encourages SiO vapor generation from the reagent mixture and thus permits a lower heating temperature to cause SiO vapor generation.

Abstract: A high purity and high strength inorganic silicon nitride continuous fiber substantially composed of Si and N with excellent properties can be provided. A method of producing the fiber is also disclosed.

Abstract: Superconductive structures and a method of forming the same wherein an assembled mass (12) of superconductive particles, or of a mixture of superconductive particles and particles having other properties, are formed into a desired confined configuration and consolidated into a rigid useful unitized body through shock-wave treatment performed at relatively lower temperatures.

Abstract: The invention relates to novel polysilazanes, the preparation thereof, the further processing thereof to form silicon nitride-containing ceramic material, and this material itself. In order to prepare the polysilazanes, dialkylaminoorganyldichlorosilanes of the formula RSiCL.sub.2 --NR'R' are reacted with ammonia. The polysilazanes can then be pyrolyzed to form silicon nitride-containing ceramic material. The polysilazanes according to the invention dissolve in customary aprotic solvents.

Abstract: A process for producing silicon carbide platelets and the platelets so produced. The process comprises reacting particles of a non-graphitizable form of hard carbon containing 0.5-1.5% by weight of aluminum and at least 0.2% by weight of iron (preferably anthracite coal, most preferably Pennsylvania anthracite), with silica or a silica precursor at a temperature in the range of 1900.degree.-2100.degree. C. under an inert atmosphere. If the carbon contains 0.2-1.0% by weight of iron, 0.1-10% by weight of boron, relative to the weight of SiO.sub.2, is added (if not already present). The carbon is in the form of particles of less than 50.mu. and the silica or precursor is preferably in the form of particles of less than about 1 .mu.. The weight ratio of silica to carbon is greater than 1.67:1. The resulting platelets are substantially unagglomerated and preferably of a size of less than 50.mu. with an aspect ratio greater than 5. The platelets can be used as reinforcements for ceramic and metal matrix materials.

Abstract: The process of preparing silicon nitride is improved by reacting silicon-oxygen compounds and a carbon-containing material in an ammonia or ammonia/nitrogen atmosphere at 1300.degree. to 1600.degree. C.

Abstract: Silicon nitride powder is prepared by continuously supplying metallic silicon powder to a first fluidized bed which is composed of silicon nitride powder and a non-oxidizing reaction gas containing nitrogen or ammonia gas and maintained at 1,000.degree. to 1,400.degree. C. where primary nitriding reaction takes place, and continuously withdrawing the nitride product from the first fluidized bed and supplying it to a second fluidized bed of similar composition where secondary nitriding reaction takes place for nitriding the unreacted metallic silicon powder.

Abstract: Silicon nitride powder having a total oxygen content of less than 1.8% by weight and an isoelectric point in 0.001M aqueous KNO.sub.3 solution of below pH 4 is prepared by calcining Si.sub.3 N.sub.4 powder having an oxygen content of 0.4% by weight or less in an oxygen containing atmosphere at temperatures between 700.degree. and 1200.degree. C. for 15 to 90 minutes or by grinding such as Si.sub.3 N.sub.4 powder in water, lower alcohol or a water/alcohol mixture for 15 to 120 minutes.

Abstract: A method of producing a silicon nitride sintered body which comprises using an amorphous Si.sub.3 N.sub.4 powder having a mean particle size of 5 to 50 nm, a nitrogen content of 30 to 39 wt. %, an oxygen content of 1 to 10 wt. %, the sum of the nitrogen content and the oxygen content being 38 to 42 wt. % and an unavoidable impurities content of less than 500 ppm as the raw material to form a molded body, sealing the molded body in a capsule and treating it with HIP in the range of 1000.degree. to 1800.degree. C. and 1000 to 2000 atm until the density becomes 3.1 to 3.4 g/cm.sup.3. In the method of the invention, active surface energy of silicon nitride powder is utilized as the driving force for sintering due to using a super fine powder. The super fine powder improves sintering ability by uniform mixing. The sintering ability is further improved by substituting a suitable amount of the nitrogen in the silicon nitride with oxygen.

Abstract: A sintered body of silicon nitride with high density, strength, toughness, and hardness, which can be used for a structural part of an engine, etc. The sintered body of the invention includes 80 to 94 wt % Si.sub.3 N.sub.4, 2 to 10 wt % Mg compound calculated in MgO equivlent, and 2 to 10 wt % Y compound calculated in Y.sub.2 O.sub.3 equivalent. The Si.sub.3 N.sub.4 contains 5 to 40% .alpha.-phase. The sintered body is manufactured in the following steps: (a) mixing powdery Si.sub.3 N.sub.4 with a Mg compound and a Y compound in the above proportions, and then molding the mixture in which the Si.sub.3 N.sub.4 powder contains 80% or more .alpha.-phase and its grains are 1 .mu.m or less in diameter on average; (b) performing primary sintering at 1,600.degree. C. or less in an atmospher of nitrogen or of an inert gas at 20 atm or less; and (c) performing secondary sintering at 1,400.degree. to 1,600.degree. C. in an atmosphere of nitrogen or of an inert gas at 300 atm or more.

Abstract: A processing for producing silicon carbide whiskers in which a source of silica is mixed with a residual oil or crude petroleum and the resultant mixture is heated in a substantially nonoxidizing atmosphere at temperature sufficiently high to carbonize the residual oil or crude petroleum, thereby forming an intimate mixture of carbon and silica. The intimate mixture is then heated in a nonoxidizing atmosphere in the presence of a seeding component comprising an element selected from the group consisting of boron, the rare earths, Group IA, Group IB, Group VB, Group VIB, Group VIIB and Group VIII of the Periodic Table of Elements at temperatures sufficiently high to induce the reaction between carbon and silica to form silicon carbide. The resultant silicon carbide product will contain a relatively high concentration of silicon carbide whiskers.

Abstract: The invention relates to preparing refractory inorganic compounds, particularly, to methods of preparing silicon nitride with a high a -phase content.The method of preparing silicon nitride with a high .alpha.-phase content is accomplished by means of self-propagating high-temperature synthesis. The method includes contacting the charge containing a silicon-reagent with an additive in a nitrating medium. The silicon-reagent is metallic silicon and at least one ammonium halide is used as an additive in the amount of 1-60% of the mass of metallic silicon. The synthesis is carried out at a pressure of 4-30 MPa.

Abstract: Si.sub.3 N.sub.4 powders having a total oxygen content of less than 1.8% by weight with the proportion of surface oxygen content of more than 65% of the total oxygen content, and having a fluorine content of less than 35 ppm are prepared by annealing Si.sub.3 N.sub.4 powders having a total oxygen content of less than or equal to 0.4% by weight in an oxygen-containing atmosphere at temperatures of 700.degree. C. to 1200.degree. C. for 15 to 90 minutes or by grinding Si.sub.3 N.sub.4 powders having a total oxygen content of less than or equal to 0.4% by weight in water, alcohol or aqueous alcohol 15 to 120 minutes.

Abstract: A method for the production of a nitride of zirconium, hafnium, silicon, germanium, tin, lead, boron, aluminium, gallium, indium or thallium either alone or as mixtures is claimed. Ammonia and a halide of at least one of these elements are heated by means of a direct electric current plasma in a non-oxidizing gas in a reactor in which recirculation is induced such that the defined recirculation ratio is greater than 2.5 and preferably greater than 4.0. Any titanium halide present shall be less then 40% by weight of mixed halides.