Abstract: This invention relates to processes for preparing ceramic articles which are especially suited for electronic applications. The process involves taking a shaped article which has been formed from a magnesium exchanged zeolite powder, the zeolite selected from the group consisting of philipsite, harmotome, gismondine, zeolite B, zeolite ZK-19 and zeolite W, and sintering it at a temperature of about 1,000.degree. C. to 1,350.degree. C. for about 1 to about 6 hours. The magnesium exchanged zeolite has a SiO.sub.2 /Al.sub.2 O.sub.3 ratio of about 2.3 to about 2.8 and a sodium content less than 0.5 weight percent. The ceramic article that is formed has a substantially crystalline cordierite phase and has a density of at least 90% of its theoretical density. A preferred process involves calcining the magnesium exchanged zeolite powder at a temperature of about 600.degree.-800.degree. C. to collapse the zeolite framework and give upon sintering a cordierite ceramic article which is substantially crack free.

Abstract: A method of producing self-supporting ceramic or ceramic composite structures comprising (i) a polycrystalline oxidation reaction product formed upon oxidation of a body of molten parent metal with an oxidant, and (ii) interconnected porosity at least partially accessible from one or more surfaces of the ceramic or ceramic composite body. A second polycrystalline ceramic material is incorporated into the porosity of the ceramic or ceramic composite body to modify or contribute to its properties.

Abstract: Sinterable raw material product for ceramics based on aluminum titanate, consisting essentially of particles having a core/shell structure with a core of an oxide, oxide hydrate or hydroxide of ether of aluminum or titanium on which are precipitated, as a shell, sparingly soluble compounds of the other aluminum or titanium not used as the core matrial, with the molar ratio of titanium to aluminum of from 1:0.1 to 1:30, which in addition to the precipitated compounds of aluminum or titanium contains additional sparingly soluble compounds of elements in a quantity of from 0.1 to 65% by weight, calculated as oxide of the element and based on the total quantity are useful in fabricating sintered bodies for high temperature environments which include internal combustion engine parts, tubes for transporting liquid metals, catalysts carriers and so forth.

Abstract: Ceramic materials to be insert-cast are disclosed, which each contain not less than 65% by volume of aluminum titanate as a crystalline phase, and have an average particle diameter of crystals thereof being not less than 10 .mu.m, Young's modulus of 50 to 2,000 kgf/mm.sup.2, compression strength of 5 to 40 kgf/mm.sup.2, and porosity of 5 to 35%. Ceramic port liners are also disclosed, which are free from cracking due to compression force during insert-casting, peeling-off during use, and facilitate insert-casting. To attain this, a reinforcement which meets either one or both of requirements that differences in coefficient of thermal expansion at 800.degree. C. and Young's modulus between the reinforcement and a material constituting the port liner body are in a range of .+-.0.1% and in a range of .+-.1,000 kgf/mm.sup.2, respectively, is filled into a depressed portion at an outer peripheral surface of the port liner body to form an integrated structure with a flat or swelled surface.

Abstract: Disclosed is a high strength aluminum borate ceramic matrix composite product and a method of making the same which comprises providing a slurry of aluminum oxide, boron oxide and organic or aqueous binder, the aluminum oxide and boron oxide capable of reacting to form aluminum borate. The slurry is introduced to a body, e.g., web of ceramic fibers, to provide an infiltrated web. After removing liquid and organic binder from the infiltrated web, it is sintered to react the aluminum oxide and boron oxide to form a ceramic matrix composite comprised of aluminum borate and said web of ceramic fibers. The reaction causes a volume expansion which aids in filling or removal of pores or voids resulting from the removal of organic binder.

Abstract: A moldable refractory composition containing from about 42 to about 83% by weight of a liquid vehicle, such as water; from about 13 to 50% by weight of ceramic fiber; from about 0.5 to 7% by weight of an inorganic binder derived from an inorganic colloidal dispersion having active hydroxyl groups capable of reacting with hydroxyl groups of the ceramic fiber; and from about 0.5 to 5% by weight of a high molecular weight organic resin which serves multiple functions including tackifier of the wet composition, cohesiveness of the wet composition, appropriate rheology of the wet composition to provide shelf life and a wide range of applications and in dry composition to provide green strength. Also described is the method of manufacture for the subject refractory moldable composition.

Abstract: A self-supporting ceramic composite body produced by a method body which comprises preparing a polycrystalline material as the oxidation reaction product of a parent metal with a vapor-phase oxidant, comminuting the resulting material to a particulate, forming a permeable mass of said particulate as filler, and infiltrating said particulate with an oxidation reaction product of a parent metal with a vapor-phase oxidant, thereby forming said ceramic composite body.

Abstract: In a method for producing ceramic body by oxidation of a parent metal having a graded microstructure characterized by a plurality of zones differing from each other in one or more properties by altering the process conditions during formation of said ceramic body such that a zone of the oxidation reaction product formed posterior to said altering has one or more properties different from a zone of the oxidation reaction product formed anterior to said altering.

Abstract: A pigment useful for coloring building materials such as bricks is a heat-stable isometric iron oxide brown pigment of .gamma.-Fe.sub.2 O.sub.3 structure which has a silicon content, expresed as SiO.sub.2, of 0.1 to 12% and an Al content, expressed as Al.sub.2 O.sub.3, of 0.02 to 5%.

Abstract: A method for making composite mullite/cordierite ceramics comprises the steps of:preparing a mullite-intensive sol by mixing alumina and silica sols together at an Al.sub.2 O.sub.3 /SiO.sub.2 molar ratio of 1.37-1.76,preparing a cordierite-intensive sol by mixing alumina, silica and magnesia sols together,gelating a mixture of the mullite- and cordierite-intensive sols obtained at a weight ratio of 80:20-20:80calcinating the thus obtained gel at 1200.degree.-1400.degree. C., andcompacting and sintering the thus calcinated material at 1300.degree.-1450.degree. C.

Abstract: A process for producing mineral fibers and the fibers thus produced are disclosed. The process involves forming a melt comprising an alumina-containing residue from a metal melting operation and one or more mineral raw materials suitable for forming mineral fibers, dividing the melt into streams and cooling the streams to produce the fibers. The residue from the metal melting operation acts as an inexpensive, substantially non-polluting source of alumina which can be used to increase the alumina content of the fibers and thus improve their properties, or which can be used as a replacement for more expensive or less desirable sources of alumina.

Abstract: Ceramic insulation has a mat of intersecting, discrete ceramic fibers bonded with a sol-gel glass binder. A fabric-reinforced glass coating is bonded to at least one surface of the mat. The insulation is prepared by forming a slurry of ceramic fibers, molding the slurry to form a soft felt mat, drying the mat, and incrementally introducing the binder into the mat with a multiple-impregnation technique, which controls shrinkage of the ceramic fiber mat. The fabric-reinforced glass coating is formed by applying a glass fiber cloth to a surface of the ceramic fiber mat and coating the same with a powdered glass. The powdered glass is melted and cooled.The process provides a layering technique that permits formation of a continuous fibrous structure having layers that impart distinct characteristics at desired regions within the structure.

Abstract: A process for preparing monoclinic celsian from AlF.sub.3, Al.sub.2 O.sub.3, BaCO.sub.3, and fused SiO.sub.2 powders by heating an intimate mixture of the powders (1) at from about 700.degree. to 900.degree. C. to form topaz and then (2) at a temperature as low as 900.degree. C. to produce monoclinic celsian. The reactions take place in an atmosphere of the gases generated by the reactions.

Abstract: Insulating lightweight refractory materials which are resistant to attack by molten metals, particularly molten aluminum and its alloys and compositions used to form such materials. The materials are settable compositions which comprise a mixture of ceramic fibres, wollastonite powder, milled and/or screened vermiculite (optional), aqueous colloidal silica having a solids content of about 5-25% and preferably 12-15% by weight, and unmilled vermiculite. The weight ratio of the ceramic fibers to the wollastonite powder to the milled and/or screened vermiculite (when present) is 0.8-1.2:1.5-2.5:0.25-0.75, respectively. The amount of the unmilled vermiculite is up to 50% by weight of the total weight of the other solid ingredients. The composition optionally contains carbon fibres, metal fibres or inorganic fibres as reinforcements. The composition can be cast to form shaped products or used as a joining material or as a "face-off" material to protect an underlying article.

Abstract: A lightweight oil and gas well proppant made by simultaneously mixing and compacting a milled calcined kaolin clay powder to form green pellets and then drying, screening and sintering the pellets to form proppant pellets having a specific gravity of 3.0 or less and a conductivity of at least 4,200 millidarci-feet and preferably at least 5,100 md-ft as measured by the Stim-Lab method after 50 hours at 8,000 psi and 275.degree. F. in the presence of deoxygenated aqueous 2% solution of KCl.

Abstract: Fused cast refractory moldings having a random microstructure, which are near in size and configuration to the desired final shape, and process and apparatus used in their manufacture are described. The process includes rapid melting of the refractory material followed by controlled rapid cooling. Laminated composite fused cast refractories may be produced.

Abstract: A sintered body of tin oxide is made by forming a finely divided mixture containing at least about 0.2 weight percent ZnO, at least about 0.2 weight percent SiO.sub.2, up to about 0.5 weight percent Al.sub.2 O.sub.3, balance pure SnO.sub.2, with the sum of the proportions of ZnO and SiO.sub.2 being less than about 2 weight percent. The mixture is compacted and heated to a sintering temperature. The tin oxide may be doped with antimony.

Abstract: A process for treating spent potlining from the electrolytic smelting of aluminum in cryolite includes incinerating the potlining to combust carbonaceous material to form an ash at a temperature low enough to maintain low fluorine vapor pressures, admixing siliceous material with the potlining either before of after the ash-forming stage, and heating the ash and siliceous material to form a glassy residue.The residue formed by the process of the present invention produces a spent potlining suitable for landfill characterized by a low leachability of fluorine in water.

Abstract: Cordierite compositions having increased porosity and improved thermal expansion characteristics are disclosed. The cordierite compositions comprise from about 0.025 to about 1.5 percent by weight germanium dioxide and exhibit reduced CTE. The cordierite compositions are made by heating a mixture of kaolin, talc, alumina, kyanite and germanium dioxide to temperatures of between 1350.degree. and 1475.degree.C. The cordierite compositions are preferably made from a mixture which includes a calcined material, such as calcined talc, so that the mixture is more easily processed and the resulting cordierite compositions are more porous, and thus, more easily coated.

Abstract: This invention relates generally to a novel method of preparing self-supporting bodies and to the novel products made thereby. In its more specific aspects, this invention relates to a method of producing self-supporting bodies comprising one or more boron-containing compounds, e.g., a boride or a boride and a carbide, by reacting, in one embodiment, a powdered parent metal, in molten form, with a bed or mass comprising a boron carbide material and, optionally, one or more inert fillers, to form the body. In another embodiment, both of a powdered parent metal and a body or pool of molten parent metal are induced to react with a bed or mass comprising a boron carbide material, and, optionally, one or more inert fillers.

Abstract: This invention relates to a method for producing a self-supporting ceramic structure comprising an oxidation reaction product of a parent metal and a vapor-phase oxidant characterized by an altered microstructure attributable to the addition of one or more process modifiers relative to substantially the same oxidation reaction product produced without a process modifier.

Abstract: A method of producing self-supporting ceramic composite bodies of desired shape by infiltrating a permeable self supporting preform with polycrystalline matrix material comprising an oxidation reaction product obtained by oxidation of a parent metal precursor, such as aluminum, and optionally containing therein metallic constituents. The composite body is formed by contacting a zone of a permeable self supporting preform, having at least one defined surface boundary spaced from said contacting zone, with a body of molten metal which is reacted with a suitable vapor-phase oxidant to form an oxidation reaction product.

Abstract: There is disclosed a method for producing a self-supporting ceramic body by oxidation of a molten precursor metal with a vapor-phase oxidant to form an oxidation reaction product and inducing a molten flux comprising said molten precursor metal through said oxidation reaction product. A second metal is incorporated into said molten flux during the oxidation reaction. The resulting ceramic body includes sufficient second metal such that one or more properties of said ceramic body are at least partially affected by the presence and properties of said second metal.

Abstract: A process for the production of a precursor which is a polymeric material comprising at least one metallic or non-metallic element, oxygen and carbon and from which a ceramic material, e.g. a carbide, nitride, boride, or silicide, may be produced by pyrolysis, which process comprises reacting(1) a first reactant which comprises a compound or compounds of at least one metallic or non-metallic element having two or more groups reactive with hydroxyl groups, and(2) a second reactant which comprises at least one organic compound having two or more hydroxyl groups,said reaction being effected in a liquid medium in which the reactants are soluble and/or dispersible and in which the polymeric material which is produced by the reaction is insoluble or in which the polymeric material may be caused to be insoluble, precipitating the polymeric material in the liquid medium in particulate form, and recovering the polymeric material from the liquid medium in particulate form.

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 molted 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 method of producing ceramic composites of Al.sub.2 O.sub.3 reinforced by shaped SiC particles preferably shaped as fine particles (random), platelets, whiskers or fibres by in situ production of SiC particles by heating a mixture of carbon particles of the desired shape with silicates of Al.sub.2 O.sub.3 to a temperature above 1500.degree. C., convert the silicates and carbon to Al.sub.2 O.sub.3 and SiC to produce in situ SiC particles of the desired shape and provide a ceramic powder that may be densified by techniques such as hot pressing, isostatic pressing or sintering.

Abstract: This invention relates to materials produced by diluting in a solvent a platinum or rhodium catalyzed preceramic mixture of a hydrogen silsesquioxane resin and a metal oxide precursor selected from the group consisting of an aluminum alkoxide, a titanium alkoxide, and a zirconium alkoxide. The preceramic mixture solvent solution is applied to a substrate and ceramified by heating. One or more ceramic coatings containing silicon carbon, silicon nitrogen, or silicon carbon nitrogen can be applied over the ceramified SiO.sub.2 /metal oxide coating. A CVD or PECVD top coating can be applied for further protection. The invention is particularly useful for coating electronic devices.

Abstract: A ceramic sintered body having a Young's Modulus of not less than 1,600 kg/mm.sup.2 produced by sintering 1 to 10 weight % of magnesium oxide, 0.5 to 10 weight % of silicon oxide, the remainder being substantially aluminum titanate.

Abstract: Multilayered ceramic substrates having Cu electrode patterns in or on ceramic-glass insulating layers which consist essentially of Al.sub.2 O.sub.3, SiO.sub.2, B.sub.2 O.sub.3, Na.sub.2 O, K.sub.2 O, CaO, MgO and PbO. The methods for manufacturing the substrate comprises thermally treating a laminate of alternately superimposing ceramic-glass insulating layers and CuO-based electrode layers of desired patterns in air or in a molecular oxygen-containing atmosphere to eliminate organic binders from the laminates by burning out, reducing the CuO into metallic Cu at low temperatures in an atmosphere containing hydrogen, and firing the thus reduced laminate in an inert gas such as nitrogen. The firing is effected at 850.degree. to 950.degree. C. The multilayered ceramic substrate may also be obtained by forming ceramic-glass insulating layers and CuO-based electrode layers alternately on a sintered ceramic support, followed by the thermal treatment, reduction and firing set forth above.

Abstract: The present invention relates to a novel method of manufacturing a composite body, such as a ZrB.sub.2 --ZrC--Z composite body, by utilizing a post-treatment technique. Moreover, the invention relates to novel products made according to the process. The novel process modifies at least a portion of a composite body by exposing said body to a source of second metal.

Abstract: A process for preparing monoclinic celsian from topaz and BaCO.sub.3, pows by heating an intimate mixture of the powders at a temperature of from 900.degree. C. to less than 1590.degree. C. in an atmosphere of the gases generated by the monoclinic celsian formation reaction itself.

Abstract: A low thermal conductivity, high strength refractory castable composition with high abrasion resistance consisting essentially of about 55 to 80% by weight amorphous silica, about 5 to 25% by weight of a calcined alumino-silicate aggregate having a density of about 30 to 70 pcf and a particle size of about -10 to +65 mesh, about 5 to 40% by weight of calcined fireclay fines, about 1 to 10% by weight of a flow aid for particle packing, and about 5 to 25% by weight of a calcium aluminate cement.

Abstract: Fused AZS grain refractory compositions suitable for making ceramically or chemically bonded refractory articles, and the articles so made, are disclosed. The refractory compositions consist essentially of (a) 40-85 wt. % fused AZS grain, and (b) 15-50 wt. % of at least one constituent selected from the group consisting of (i) 10-20 wt. % reactive alumina and (ii) 0-45 wt. % chromic oxide.

Abstract: Thin flakes can be made from a sol of metal oxides by a method analogous to blowing soap bubbles, preferably by directing a laminar flow of air through a narrow, annular orifice. The bubbles can be dried and broken into fragments which are fired to produce refractory flakes that can be incorporated into protective coatings. The resulting coatings can be pearlescent while also affording good resistance to abrasion and to corrosive materials.

Abstract: This invention relates to processes for preparing ceramic articles which are especially suited for electronic applications. The process involves taking a shaped article which has been formed from a magnesium exchanged zeolite powder, the zeolite selected from the group consistig of phillipsite, harmotome, gismondine, zeolite B, zeolite ZK-19 and zeolite W, and sintering it at a temperature of about 1,000.degree. to 1,350.degree. C. for about 1 to about 6 hours. The magnesium exchanged zeolite has a SiO.sub.2 /Al.sub.2 O.sub.3 ratio of about 2.3 to about 2.8 and a sodium content less than 0.5 weight percent. The ceramic article that is formed has a substantially crystalline cordierite phase and has a density of at least 90% of its theoretical density. A preferred process involves calcining the magnesium exchanged zeolite powder at a temperature of about 600.degree.-800.degree. C. to collapse the zeolite framework and give upon sintering a cordierite ceramic article which is substantially crack free.

Abstract: A lightweight oil and gas well proppant made by simultaneously mixing and compacting a mixture of kaolin clay which has been calcined at a temperature low enough to prevent the formation of mullite and crystobalities to an LOI of 12 or less when tested at 1400.degree. C., and amorphous to microcrystalline silica both of which have been milled to an average agglomerated particle size of 7 microns or less to form green pellets, and then drying, screening and sintering the pellets to form proppant pellets having a specific gravity of 2.7 or less, the proppant having a conductivity of at least 3,000 millidarci-feet as measured by the StimLab Technique after 50 hours at 8,000 psi and 275.degree. F., in the presence of deoxygenated aqueous 2% solution of KCl using sandstone shims.

Abstract: An alumina porous body which comprises coarse alumina particles as a filler and SiO.sub.2, said alumina and SiO.sub.2 forming an Al.sub.2 O.sub.3 -SiO.sub.2 compound (mullite) on the surface of the coarse alumina particles through the reaction between them that takes place at the time of firing, said compound binding said coarse alumina particles, forming pores between them. The invention also relates to a process for producing an alumina porous body which comprises mixing coarse alumina particles with SiO.sub.2, molding the mixture, and firing the molding at a temperature not higher than 1700.degree. C., thereby sintering the coarse alumina particles.

Abstract: A ceramic composition, comprises a fired product of a starting material mixture containing 10% by weight to 70% by weight of silicon dioxide powder added to mullite powder fired at 1500.degree. C. to 1650.degree. C.

Abstract: Hydrogel-bound aggregate lightweight building materials, such as blocks for use in replacement of lightweight concrete or extruded clay blocks, prepared by expanding and drying a foamable composition containing precursors for an alkali metal aluminosilicate hydrogel, fine grain particulate aggregates, and a viscosity-reducing agent sufficient to result in a starting slurry composition viscosity of less than 40,000 cps at a solids content of 70% by weight or greater.

Abstract: Cutting tools are disclosed which are comprised of composite bodies comprising a ceramic matrix reinforced by ceramic whiskers. The ceramic matrix may be alumina or silicon nitride, and may contain toughening components. The whiskers are preferably silicon carbide, but may be other known ceramic whiskers. Whisker content in the composite is 2-40%, with higher contents generally used for tools when the expected service involves interrupted cutting and lower contents generally used for continuous cutting tools.

Abstract: A mullite-alumina composite sintered body composed of from 75 wt % to 85 wt % Al.sub.2 O.sub.3 balance SiO.sub.2, consisting of two crystalline phases, mullite and .alpha.-phase alumina, and being free from glass phase, wherein both of the average diameters of mullite grains and .alpha.-phase alumina grains are not more than 1.0 .mu.m, the content of grains having the longitudinal-length of not less than 2.5 .mu.m is 1% or less in the observation of a cross section of said sintered body, and the porosity of said sintered body is 1% or less.The sintered body of the present invention is produced by a process comprising the steps of preparing a starting powdery material composed of from 75 wt % to 85 wt % Al.sub.2 O.sub.3 balance SiO.sub.2 and containing amorphous phase from 65 wt % to 90 wt %, wherein each particle of said starting powdery material contains both Al.sub.2 O.sub.3 and SiO.sub.2, and sintering said starting powdery material at a temperature in the range from 1500.degree. C. to 1650.degree. C.

Abstract: The present invention relates to a method for producing a protective layer on a ceramic or a ceramic composite body. Stated more particularly, by subjecting a ceramic or a ceramic composite body being interconnected residual metal therein to a particular atmosphere, a protective layer can be formed from the interconnected metal. Such a layer can be protective, especially in corrosion environments which include various gaseous or solid species containing sodium and silicon, such as those found in glass tanks.

Abstract: The present invention provides a process for treating spent potlining from the electrolytic smelting of aluminum in cryolite including burning the spent potlining to form an ash, mixing with a siliceous material either before or after the ash-forming step, and heating to form a residue suitable for landfill. The ash and siliceous material are mixed in a specified mole ratio of at least about 1.4 silicon to sodium. The process further includes cooling the residue rapidly.The residue formed by the process of the present invention produces a spent potlining suitable for landfill characterized by a low leachability of fluorine in water.

Abstract: Microcrystalline alpha-alumina based ceramic articles comprising at least 60% alumina by weight in which substantially all the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites with an average crystallite size less than 0.5 micrometer and a density greater than 90% theoretical are disclosed. Ceramic articles particularly useful as high modulus refractory fibers, among other shaped bodies such as beads, flakes, coatings, and shaped or randomly-shaped abrasive particles, are produced from a unique sol-gel process wherein hydroxy iron polymers are utilized to nucleate the alpha alumina transformation. An inherent advantage of the unique process disclosed is the resulting fine grained microstructure which is essential if a ceramic article such as an alpha alumina fiber is to have reasonable strength.

Abstract: A process for the production of a refractory compound, e.g. a carbide or nitride, of a metallic or non-metallic element, by reacting a mixture of a compound of the metallic or non-metallic element having at least two groups reactive with hydroxyl groups and an organic compound having at least two hydroxyl groups to produce an oxygen-containing polymeric product, and pyrolysing the polymeric product, e.g. in an inert atmosphere to produce a carbide or in an atmosphere of reactive nitrogen compound to produce a nitride, in which the reaction mixture contains an aluminium compound containing at least one group reactive with hydroxyl groups.The presence of the aluminium compound in the reaction mixture leads to an increase in the proportion of carbon in the product initially produced by pyrolysis, and to a higher purity in the refractory compound which is ultimately produced.

Abstract: A process in which (1) AlF.sub.3 and SiO.sub.2 or AlF.sub.3, SiO.sub.2, and Al.sub.2 O.sub.3 powders are formed into a green body of a desired shape and size; (2) the green body is heated at 700.degree. C. to 950.degree. C. in an anhydrous SiF.sub.4 atmosphere to form barlike topaz crystals; and then (3) heated in an anhydrous SiF.sub.4 atmosphere at about 1150.degree. C. to 1700.degree. C. to convert the barlike topaz crystals to needlelike single crystal mullite whiskers which form a porous, rigid felt structure. The felt has the same shape as the green body with about 1.5 or less percent change in linear dimensions. The felt can be used as preforms for ceramic-matrix or metal-matrix composites or by itself as thermal insulation.

Abstract: A settable liquid system for refractories comprises a gelable alkoxide such as ethyl silicate, water to hydrolyze the alkoxide and a mutual solvent for the alkoxide water and any catalyst. The system further includes a solvent for the alkoxide only.

Abstract: This invention relates to sintered ceramic materials in which the densification during sintering takes place with a liquid phase preferably based on silicon nitride. During sintering such materials are often embedded in a powder of inert material such as BN, etc. The invention resides in the fact that by embedding the material to be sintered in a protective powder with a composition similar to that of the intergranular phase, a surface zone with a composition and/or structure different from that of the core can be obtained.

Abstract: A ceramic munitions projectile, particularly useful for practice or target munitions is provided. The projectile has a tensile strength greater than about 250 MPa, a critical stress intensity factor greater than about 6 MPam.sup.1/2, and a Weibull modulus greater than about 10. Preferably the projectile is frangible.

Abstract: High-quality ceramic bodies suitable for use as a substrate of electronic devices can be prepared by sintering, at an outstandingly low temperature of 1000.degree. C. or below, a binary powder mixture composed of 30-50% by weight of a non-glassy phase of aluminum oxide and 70-50% by weight of a glassy phase having a quaternary composition composed of silicon dioxide, boron oxide, aluminum oxide and one or more of alkaline earth metal oxides, of which at least 60% by weight is strontium oxide, each constituent being formulated in a specified weight fraction. The ceramic body is particularly advantageous over conventional ones, along with the high mechanical strengths and low dielectric constant, in respect of the resistance against migration of metals therethrough when the ceramic body is in contact with metal-made parts such as electrodes.