Abstract: An Al.sub.2 O.sub.3 -TiC sintered product comprising Al.sub.2 O.sub.3 as a main component and containing TiC in an amount of from 20 to 40% by weight, wherein the average particle diameter of Al.sub.2 O.sub.3 particles in the sintered product is larger by 5 to 50% than the average particle diameter of TiC particles, the average particle diameter of the sintered product as a whole is not larger than 1 .mu.m, the average particle diameter of TiC particles is not larger than 0.9 .mu.m, and the total amount of the grain boundary phases other than Al.sub.2 O.sub.3 and TiC is not larger than 1.0% by weight. The Al.sub.2 O.sub.3 -TiC sintered product can be used as a substrate 1 for a magnetic head, and has portions such as grooves 4 and stepped portions formed in the surface of the air bearing surface 2 of the slider by being irradiated with ions. The sintered product exhibits excellent surface quality after machined by being irradiated with ions and can be machined at an increased rate.

Abstract: An aqueous alumina dispersion prepared from high quality, submicrometer alumina powder, suitable for manufacturing fine ceramic products, is disclosed. The sub-micrometer alumina particles have a surface area of 2.5 to 50 m.sup.2 per gram of the alumina particles. There are three components in the dispersion: sub-micrometer alumina particles (10 to 68 percent based on weight of the colloidal dispersion), semicarbazide hydrochloride derivative (0.1 to 5 percent based on the weight of the alumina particles), and water (the balance).

Abstract: A method of making a .beta.-alumina compound which is a polyaluminate of the general formula M.sub.y O.multidot.xAl.sub.2 O.sub.3 in which M is a metal selected from monovalent metals and divalent metals, y=2 when M is a monovalent metal, y=1 when M is a divalent metal and x=4-12 comprises forming a green precursor of the 62 -alumina compound by mixing together particulate aluminium metal and a reagent compound comprising an oxide of the metal M or a precursor thereof. The mixture is heated to 800.degree.-1150.degree. C. in an oxidizing environment to cause oxidation of at least part of the aluminium. Further heating then takes place to 1150.degree.-1350.degree. C. in said environment to cause the oxidized aluminium and oxide of the metal M to react to form the .beta.-alumina compound.

Abstract: The invention relates to a densely sintered tabular ceramic part of aluminum oxide having improved thermal shock resistance, which possesses a fine porosity of at most 10% by volume, does not contain inclusions having a diameter of .gtoreq.70 .mu.m within the ceramic microstructure and is not destroyed on immersion in a molten metal bath having a temperature of at least 350.degree. C. The invention also relates to a process for producing such a shaped part.

Abstract: Binders for ceramic products are provided which are crosslinkable and impart improved tensile strength to ceramic green bodies. The binders are particularly useful in tape-casting processes for the manufacture of thin ceramic sheets which are used as substrates for electronic packaging.

Abstract: An alumina based ceramic fiber having submicron sized alpha alumina crystals and a density of at least 95% theoretical is obtained from a sol-gel process.

Abstract: A monolithic refractory powder mixture containing from 2 to 3 wt % of spheroidized refractory particles having a mean particle size of at most 30 .mu.m of at least one member selected from the group consisting of alumina cement, alumina, titania, bauxite, diaspore, mullite, aluminous shale, chamotte, pyrophyllite, sillimanite, andrewsite, silica rock, chromite, spinel, magnesia, zirconia, zircon, chromia, silicon nitride, aluminum nitride, silicon carbide, boron carbide, zirconium boride and titanium boride, and having a cone flow value of at least 180 mm when a refractory mixture having the powder mixture kneaded by an addition of 6 parts by weight of water per 100 parts by weight of the powder mixture, is cast into a cone-shaped mold with a dimension of 70 mm.o slashed.-100 mm.o slashed..times.60 mm and left to stand for 60 seconds without exerting vibration after removing the cone-shaped mold.

Abstract: A ceramic composition comprising a polycrystalline alumina matrix having titanium carbide whiskers distributed therein. The composition comprises 50 to 90 volume percent high purity alumina, 10 to 50 volume percent single crystal titanium carbide whiskers, and up to 3 volume percent being the residue of sintering aids.

Abstract: A method of forming a ceramic having a smooth ceramic surface and an assembly for forming ceramics having a flat and smooth ceramic surface are disclosed. A greenware precursor is disposed between a greenware base and a greenware cover. A frame is disposed between the greenware base and greenware cover for limiting compression of the greenware article to an amount which allows formation of a smooth ceramic surface during densification of the greenware precursor. The greenware base, greenware cover and greenware precursor are densified to cause the greenware precursor to form a ceramic having a smooth ceramic surface.

Abstract: A high temperature superconducting system comprising M--R--Tl--Sr--Cu--O wherein: M is at least one compound selected from the group consisting of Hg, Pb, K, and Al; and R represents rare earth metals. In one embodiment, a composition forms a 93K superconducting phase having the composition: M--R--Tl--Sr--Cu--O wherein: M is selected from the group consisting of Hg and Al; and R is a rare earth metal. In another embodiment, the composition comprises M--R--Tl--Sr--Cu--O wherein: M is selected from the group of Pb and/or K; and R is a rare earth metal.

Abstract: Novel aluminum phosphates, in particular amorphous aluminum phosphate powders having a BET specific surface no greater than 25 m.sup.2 /g, well suited as binders/hardeners or for the production of ceramic shaped articles, are prepared by reacting at least one aluminum compound, e.g., an aluminum oxide, hydroxide or oxyhydroxide, with phosphoric acid or an aluminum phosphate, e.g., an acid aluminum orthophosphate, in a liquid reaction medium devoid of inorganic acid anions other than of phosphoric acid, and then spray- or freeze-drying the suspension thus obtained.

Abstract: A method of producing a self-supporting ceramic composite body having therein at least one cavity which inversely replicates the geometry of a positive mold of parent metal. The method includes embedding the mold of parent metal within a conformable bed of filler to provide therein a cavity shaped and filled by the mold. The assembly is heated to melt the parent metal mold, e.g., an aluminum parent metal mold, and contacted with an oxidant to oxidize the molten parent metal to form a polycrystalline material which grows through the surrounding bed of filler, the molten metal being drawn through the growing polycrystalline material to be oxidized at the interface between the oxidant and previously formed oxidation reaction product whereby the cavity formerly filled by the mold of parent metal is eventually evacuated of the metal. There remains behind a cavity whose shape inversely replicates the original shape of the mold.

Abstract: Alumina-based abrasive grain comprising rare earth oxide and calcium oxide and/or strontium oxide, and a method of making the same. The abrasive grain is useful in abrasive articles, such as coated abrasives, three-dimensional, low density abrasives, and bonded abrasives.

Abstract: A novel ceramic composite material consisting of single crystal .alpha.-Al.sub.2 O.sub.3 and polycrystal Y.sub.3 Al.sub.5 O.sub.12 and a ceramic composite material consisting of polycrystal .alpha.-Al.sub.2 O.sub.3 and polycrystal Y.sub.3 Al.sub.5 O.sub.12, each having a high mechanical strength and creep behavior particularly at high temperature are provided.

Abstract: Transparent, polycrystalline garnet bodies having desirable properties for use as laser material, luminescent x-ray scintillator materials and other uses are produced by mixing a chloride source solution of the desired cations with a basic ammonium solution to produce a precipitate having a substantially uniform composition which can be further processed to provide the desired transparent body. This precipitate is separated from the solution, dried, thermally decomposed at a temperature in the range from 700.degree. to 1,000.degree. C., pressed to form a compact, isostatically pressed at up to 60,000 psi to provide a green, unsintered compact having a density in the vicinity of 55% of theoretic density. That green compact is then sintered in oxygen at a temperature between 1,400.degree. and 1,700.degree. C. to produce the desired transparent body. Alternatively, the compact may be sintered in oxygen at temperatures in the range from about 1,400.degree. to about 1,600.degree. C.

Abstract: A ceramic composite contains one spinel phase and one or more than one oxides phases. The composite is derived from the mixtures of two oxides, A.sub.2 O.sub.3 and BO, with different molar ratio, in which A and B are metallic ions of three and two valences respectively. The oxides are heated at a high temperature to form a composite containing a spinel and residual oxides. The formed spinel and residual oxides also undergo densification under high temperature. After the treatment at high temperature, not only the spinel is formed but also the composite is densified. The performance of the composite is superior in its strength, toughness and high-temperature stability.

Abstract: The reactant manifolds and corners of a molten carbonate fuel cell stack are sealed with particulate lithium aluminate members which are sufficiently porous so as to resist significant electrolyte migration therethrough. The seal members which are disposed in vertical planes of the stack are preferentially formed from lithium aluminate grains which are bonded together by a silica-free glass binder. The seal members which are disposed in horizontal planes in the stack are preferably formed from lithium aluminate grains which are bonded together by surface hydrolysis. Alumina-clad stainless steel labyrinth seal members are associated with each of the horizontal seal members to inhibit electrolyte migration from the cell electrolyte matrices to the vertical seal members.

Abstract: A ceramic composition for thermistor exhibiting stable resistance values over a wide temperature range and capable of being used for a prolonged time. The composition is represented by (M.sup.1 M.sup.2 O.sub.3).sub.1-x .multidot.(M.sup.1 AlO.sub.3).sub.x, wherein M.sup.1 is an element selected from the elements of the group 3A of the International Periodic Table excluding La and M.sup.2 is an element of the groups 4A, 5A, 6A, 7A and 8 of the International Periodic Table, and wherein the mixing ratio between an electrically conductive substance stable at elevated temperatures and an insulating substance stable at elevated temperatures, may be adjusted. A thermistor formed of the composition is superior in high-temperature stability and can be used over a broad temperature range because its resistance value can be selected to an optimum value.

Abstract: The present invention provides a process for the production of a K- or Rb-.beta."- or -.beta.-aluminum oxide powder preparation, wherein a cubic densely packed aluminum oxide (.gamma.-aluminum oxide) or a precursor thereof is subjected to attrition together with a doping material or a precursor thereof, the so obtained mixture is calcined in an oxygen-containing atmosphere, potassium oxide or rubidium oxide or a precursor of these compounds is added to the calcination product obtained, the mixture is subjected to attrition and then calcined in an oxygen-containing atmosphere at a temperature greater than 900.degree. C. The present invention also provides a process for the production of a ceramic formed body in which a powder obtained by the above process is converted by attrition, isostatic pressing and sintering into a ceramic formed body. Such a ceramic formed body can be used as an ion conductor.

Abstract: The invention relates to the thermal barriers, to a process and material for their production, and to their application. Thermal barriers consist of a material comprising at least one refractory oxide with low thermal diffusivity and at least one quasicrystalline aluminum alloy, the proportion of which represents from 2-30% by volume. They can be produced by deposition of a mixture of refractory oxide and of quasicrystalline alloy in vapor phase, or from a mixture of refractory oxide and quasicrystalline aluminum alloy in the molten state, or else by deposition onto the support to be protected with the aid of an oxygen-gas torch fed with material using a flexible cord which contains the refractory oxide and the quasicrystalline alloy. The applications include the protection of components of aircraft or motor vehicle engines, of aeronautical or aerospace components, of chemical reactors or of electrical households appliances.

Abstract: A light weight ceramic armor providing complete ballistic protection agai penetration from projectiles of caliber 0.30 and 7.62 mm. armor piercing and ball projectiles, and consisting of a composite having a hard frangible facing the principle ingredient of which is a refractory oxide selected from the group consisting of magnesium oxide and aluminum oxide, bonded to a reinforced plastic back-up such as laminated fiber glass. This composite has an area density of approximately 12 pounds per square foot and provides approximately 1.7 times the ballistic protection as compared to standard steel armor of equal area density.

Abstract: A ceramic adhesive comprises a ceramic matrix formed from a mixture of a metallic oxide and an alkali silicate in water, and silicon carbide whiskers dispersed within the ceramic matrix. Further, a ceramic adhesive comprises a ceramic matrix formed from a mixture of magnesium oxide in the range of about 50% to about 80% by weight and sodium silicate in water in the range of about 50% to about 20% by weight, and silicon carbide whiskers dispersed within said ceramic matrix, the whiskers being in the range of about 3% to about 25% by weight of the ceramic matrix. A ceramic adhesive of the present invention is particularly useful in mounting and bonding in-cylinder sensors to steel internal engine parts.

Abstract: A slurry for joining metallic or ceramic surfaces or for coating metallic or ceramic and refractory surfaces, comprising a liquid suspending medium and at least two constituents in particulate form suspended in the medium, the constituents being so selected and proportioned as to undergo combustion synthesis when ignited. A method for coating or joining metallic or ceramic surfaces comprises applying such a slurry to a surface to be coated or to surfaces to be joined, and igniting the slurry to cause combustion synthesis.

Abstract: High zirconia fused cast refractories which include as chemical components of refractories in weight %, 85 through 91% of ZrO.sub.2, 7.0 through 11.2% of SiO.sub.2, 0.85 through 3.0% of Al.sub.2 O.sub.3, 0.05 through 1.0% of P.sub.2 O.sub.5, 0.05 through 1.0% of B.sub.2 O.sub.3 and 0.01 through 0.12% of a summed amount of K.sub.2 O and Na.sub.2 O, wherein the weight % of K.sub.2 O is not smaller than the weight % of Na.sub.2 O.

Abstract: The invention relates to nano-composite powders of alumina and metal constituted of grains of micronic size. Each grain comprises a compact matrix of alumina of a specific surface area less than 5 m.sup.2 /g, in which are dispersed crystallites of transition metals of alloys of these metals, of sizes less than 50 nm. The powder according to the invention may be produced starting with a precursor comprised of a mixed carboxylic salt of aluminum and one or more transition metals. The powders according to the invention permit producing by sintering cermets of alumina/metal benefitting from greatly improved mechanical and thermo-mechanical properties.

Abstract: A substantially non-explosive mixed powder containing finely divided metallic particles suitable for being incorporated in a refractory mixture, intimately mixed together with inert refractory particles. 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 80%. The invention also includes a premixed powder, of the metallic and refractory powder, especially as contained in a shipping container in drums or impermeable bags. Due to the presence of the refractory powder, the mixed powder can be shipped without the precautions usually needed for shipping finely divided metal powders.

Abstract: A method for producing alumina-silicon carbide ceramic powders by in situ production of silicon carbide particles by introducing a pyrolyzable carbon source, preferably a gaseous hydrocarbon, into a reactor containing an alumino-silicate, pyrolyzing the pyrolyzable carbon source to form carbon particles in situ, wherein the carbon particles are capable of reacting with a silicate in the alumino-silicate to form carbide products, and then reacting the silicate and the carbon particles in situ at an effective temperature, preferably at least 1450.degree. C. and more preferably at least 1500.degree. C., for a sufficient time to transform the alumino-silicate and the pyrolyzable carbon source into the composite ceramic powder having alumina (Al.sub.2 O.sub.3) and silicon carbide (SiC) as major phases.

Abstract: A sol-gel process of producing durable alpha alumina-based ceramic particularly useful as abrasive grain from alpha alumina monohydrate is improved by the addition of a nucleating agent. Improved abrasive products containing the durable ceramic abrasive grains are also provided.

Abstract: A solid state process for the bulk conversion of a dense polycrystalline ceramic body to a single crystal body has been accomplished by heating the polycrystalline material to a temperature above one-half of the melting temperature of the material but below the melting point of the material. As the process is a solid state process, no melting of the ceramic body is necessary to convert it to a single crystal. The process has been used to convert a dense polycrystalline alumina body (PCA) containing less than 100 wppm of magnesia to sapphire (single crystal alumina) by heating the PCA to temperatures above 1100.degree. C. but below 2050.degree. C., the melting point of alumina.

Abstract: A process for production of a fine alpha-alumina powder having a specific surface area of not smaller than 10 m.sup.2 /g and superior polishing characteristics is provided, the process comprising heat-treating a mixture of gamma-alumina powder and silica at a temperature at which gamma-alumina is converted to alpha-alumina in the presence of silica, wherein the mixture contains not more than about 10 wt % of silica, based on the weight of the gamma-alumina.

Abstract: Ceramic foams in which the open cells are connected by a three-dimensional, substantially continuous ceramic matrix formed of interconnected hollow ligaments, are made from an open-cell, reticulated precursor metal, i.e. a metal foam. The precursor metal first is treated so as to allow a support coating to form thereon, and thereafter the coated precursor is heated above the melting point of the metal in the presence of an oxidant to form an oxidation reaction product.

Abstract: The sol-gel process for forming dense alumina based cermics or dense ceramics with alumina as a sintering additive, the process comprising the steps of: preparing polymeric alumina sol by hydrolysis of Al (O--iBu)3 with a strong acid; preparing the ceramic dispersion in the alumina sol; gelling the dispersion; drying the gel dispersion to form a solid; calcining the solid; and sintering the calcined solid.

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: There is provided a method for producing a self-supporting ceramic composite comprising (1) a ceramic matrix obtained by oxidation of an aluminum zinc alloy to form a polycrystalline oxidation reaction product of the metal with an oxidant, and (2) one or more fillers embedded by the matrix. The metal alloy and permeable mass of filler having at least one defined surface boundary are oriented relative to each other so that formation of the oxidation reaction product will occur into said mass of filler and in a direction towards said defined surface boundary. On heating the metal to a first temperature above its melting point but below the melting point of said oxidation reaction product to form a body of molten parent metal, the molten metal reacts with said oxidant to form said oxidation reaction product which infiltrates said mass of filler to said defined surface boundary.

Abstract: A sintered high-toughness alumina-based composite body comprises a plate- or rod-like, corundum or alumina-based compound structure and another structure having a fine granular corundum structure and containing inevitable impurities. A sintered high-toughness alumina-based composite can be produced by mixing a crystal-growth-promoting additive with a first portion of alumina powder to prepare a mix A, mixing a crystal-growth-inhibiting additive with a second portion of alumina powder to prepare a mix B, granulating at least one of the mix A and the mix B into granules, mixing the mix A and the mix B into a mix C, forming tile mix C into a green body, and then firing the green body, whereby crystals of the corundum or alumina-based compound in the mix A are allowed to grow.

Abstract: Al.sub.2 O.sub.3 -Er.sub.2 O.sub.3 ceramic abrasive grains comprising a second phase consisting of aluminum oxides and erbium oxides in the form of reaction products surrounding a first phase and the first phase exclusive of the second phase and substantially consisting of alpha alumina only, the size of the crystal grain consisting of two phases being below 1 micron, which are obtained by a sol-gel process wherein erbium precursor is incorporated before sintering in an amount of 0.05-0.4 wt % in a form of Er.sub.2 O.sub.3, which is suitable for lapping composition, grinding wheel, grinding disc and coated abrasive articles.

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

Abstract: Ceramic moldings composed of aluminum oxide which have a proportion of intercrystalline fracture of more than 50%, an average pore radius of more than 4 .mu.m and a porosity of more than 2%, are obtained by:a) grinding aluminum oxide which is at least 99.5% pure and has an average primary crystal size of 1 to 4 .mu.m to an average fragment size of 2 to 7 .mu.m,b) adding a source of magnesium oxide, silicon oxide and calcium oxide in amounts such that the magnesium oxide content is 0.2 to 2.5%, the silicon dioxide content is 1 to 6% and the calcium oxide content is 0.1 to 2.5%, in each case with respect to the amount of Al.sub.2 O.sub.3,c) shaping a green compact andd) sintering.

Abstract: The present invention provides an aluminium titanate ceramic composed of, as main crystalline phases, 60-85% of an aluminum titanate phase, 10-25% of a rutile phase, 2-10% of a corundum phase and 2-10% of a mullite phase, wherein the amount of vitreous phase is 5% or less. The aluminum titanate ceramic is superior in both heat cycle durability and casted property.

Abstract: A dense, self-sintered silicon carbide/carbon-graphite composite material and a process for producing the composite material is disclosed. The composite material comprises a silicon carbide matrix, between 2 and 30 percent by weight carbon-graphite, and small amounts of sintering aids such as boron and free carbon. The silicon carbide has an average grain size between 2 and 15 .mu.m, and the carbon-graphite has an average grain size between 10 and 75 .mu.m, the average grain size of the carbon-graphite being greater than the average grain size of the silicon carbide. The composite material has a density of at least 80 percent of theoretical density as determined by the rule of mixtures for a composite material. This density is achieved with minimal microcracking at a high graphite loading with large graphite particles. The composite material exhibits good lubricity and wear characteristics, resulting in improved tribological performance.

Abstract: Electrical heating elements and related articles having oxidation resistance at high temperatures, produced by a method involving micropyretic synthesis. A composition subjected to micropyretic synthesis includes a filler material, a reactive system capable of undergoing micropyretic synthesis, and (optionally) a plasticizer or extrusion agent. The method of preparation of articles includes slurry techniques, plastic extrusion, slip casting, or coating.

Abstract: There is now provided an oxide-based, preferably aluminum oxide based, matrix with 5-50, preferably 10-40% by volume of homogeneously dispersed whiskers based upon nitrides, carbides and/or borides of metals from group IVB (Ti,Zr,Hf) and/or VB (V,Nb,Ta) of the periodic system or solid solutions thereof and 1-20, preferably 3-8% by volume of particulate additions with a size <500 nm, preferably <200 nm, based upon carbides, nitrides and/or borides of metals from group IVB (Ti,Zr,Hf) and/or VB (V,Nb,Ta) of the periodic system or solid solutions thereof. The nanosize particulate additions are predominantly present inside the matrix grains and not in the grain boundaries.

Abstract: There is now provided a ceramic cutting tool material comprising a ceramic, preferably aluminum oxide based, matrix with 5-50%, preferably 10-40%, by volume of homogeneously dispersed SiC-whiskers and 1-20%, preferably 3-8%, by volume of particulate additions with a size <500 nm, preferably <200 nm, based upon carbides and/or nitrides and/or borides of metals from group VB (V,Nb,Ta) in the periodic system or solid solutions thereof. The nanosize particulate additions are predominantly present inside the matrix grains and not in the grain boundaries.

Abstract: A substantially amorphous, aluminum-containing oxide having the composition Al.sub.1-x-y1-y2 Bi.sub.x M.sub.1y1 O.sub.z (wherein x is defined by 0.0001.ltoreq.x.ltoreq.0.10, M.sub.1 is at least one selected from Si, P, B, Sb, Se, Te, Sn, Zn, In, Cr, Nb, Sc, Y, Sr, Ba, Ca, Na, Li, Mg, Mn, W, Ti, Zr, Hf, Be and rare earth metals, M.sub.2 is at least one selected from Fe, Ni, Co, Rh, Ru, Re, Cu and Pb, y1 is defined by 0.ltoreq.y1.ltoreq.0.1, y2 is defined by 0.ltoreq.y2.ltoreq.0.01, z is defined by 1.2.ltoreq.z.ltoreq.1.5, and x, y1, y2 and z are each an atomic ratio); an aluminum-containing metal composition containing the above oxide and Al and/or Bi in a metallic state; a process for producing the above oxide or the above metal composition; and a molded article formed from the above oxide or the above metal composition. The above oxide or the above metal composition is useful as an electronic part, a catalyst, and the like.

Abstract: A granular material which includes an inorganic substrate and a ceramic coating shows improved adhesion to bituminous surfaces, decreased alkalinity, and, when formulated as a three coated algae-resistant granule, exhibits improved algae-resistance over previously known granules. The ceramic coating comprises the reaction product of an alkali metal silicate and an aluminosilicate, the ceramic coating further including a borate compound and zinc oxide having a particle size less than about 0.13 micrometer. It has been found that the use of a borate compound and zinc oxide having the stated particle size allows the granules to be adhered to a substrate for longer periods of time, thus producing a surface which retains its original color for a longer period of time. Methods of producing such ceramic-coated granular materials, and composite sheets including the granules are also presented.

Abstract: Hydrogen fluoride-resistant articles are disclosed which have HF contact surfaces consisting essentially of sintered, single phase, polycrystalline, solid solution alumina and magnesia ceramic. The ceramic has a magnesia content equal to or less than the solubility limit of magnesia in alumina at the sintering temperature for the ceramic. Also disclosed are processes using such surfaces as HF contact surfaces.

Abstract: An improved sintered ceramic core is used in a mold during the casting of a reactive metal. Prior to sintering, the core contains ceramic material which includes yttrium aluminate and alumina (Al.sub.2 O.sub.3). It is preferred to have the ceramic material contain between 10% and 40% yttrium aluminate. Prior to sintering, the yttrium aluminate has a mean particle size of less than 20 microns and, preferably, less than 10 microns. Particularly advantageous results has been obtained by using yttrium aluminate having a mean particle size, prior to sintering, of approximately 3 microns. It is contemplated that the ceramic material will be utilized to form other articles, such as a mold, filter, or liner for a ladle, which are exposed to reactive metals during casting.

Abstract: The invention concerns self-supporting ceramic structures, including ceramic composite structures embedding a filler, and methods of making them. The ceramic structures comprise a polycrystalline material made by oxidation of a body of molten parent metal with an oxidant. The polycrystalline material has a first region substrate surmounted by a terminal region stratum which is integral with the first region. The terminal region stratum which is harder and of denser, finer crystalline structure than the first region substrate and is formed in a reaction stage subsequent to the reaction stage in which the first region of polycrystalline material is formed. Growth of the first stage is attained by by attenuating or interrupting the transport of molten parent metal to the first region under conditions which nonetheless leave or maintain therein enough oxidizable molten parent metal to form the polycrystalline material of the terminal region.

Abstract: The present invention relates to a ceramic cutting insert containing whiskers for chip forming machining of steel and having improved mechanical, thermal and wear properties. The insert comprises besides the oxide-based matrix 5-50% by volume, preferably 10-40% by volume, of homogeneously dispersed whiskers of carbides, nitrides and/or borides of titanium and/or zirconium and, where applicable, solid solutions thereof. A part of the whiskers may be replaced by whiskers of silicon carbide. The properties of the composite material can be further modified by coating the whisker material with thin layers. The whiskers reinforced cutting material shows an improved toughness behaviour and resistance to thermal crack formation without having a negative influence on the wear resistance to any appreciable extent.

Abstract: Transparent ceramic armor consisting of a light weight composite formed by tilizing a face plate of transparent aluminum oxide or transparent magnesium oxide with a back-up plate of transparent plastic and the two plates bonded together with a transparent adhesive. This composite on test affords complete ballistic protection against 0.30 AP M2 projectiles at 0.degree. obliquity with a muzzle velocity of 2770 ft. per sec.