Abstract: A refractory composition for use in contact with molten aluminum alloys containing a refractory aggregate, a binder and an additive for imparting aluminum resistance to the refractory composition, the additive comprising synthetic calcium fluoride containing aluminum borate aggregate consisting essentially of 10 to 50% by weight boron oxide, 10-50% by weight of aluminum oxide, and 25-75% by weight calcium flouride. The synthetic aggregate may be prepared by blending boric acid, aluminum oxide, and fluorspor and firing the resultant blend at a temperature above 800.degree. C. to form a synthetic aluminum borate having calcium fluoride contained in its insoluble structure.

Abstract: A high strength low density opaque shaped aluminum borate product is disclosed characterized by an MOR of at least 45,000 psi and a density of approximately 2.9 g/cm.sup.3. The shaped aluminum borate may be formed by reacting an aluminum oxide with a boron oxide at a temperature of at least 800.degree. C., grinding the reaction product, pressing the resulting particulate into a shaped form and sintering the shaped particulate at a temperature of from 800.degree. to 1400.degree. C. while maintaining the shaped particulate under a pressure of 2500 to 3500 psi.

Abstract: A ceramic material which comprises a composite of zirconia and O'-sialon or silicon oxynitride.The ceramic material may comprise a dispersion of zirconia in an O'-sialon matrix and such a dispersion is obtained when the amount of zirconia is from 5 to 30 volume percent, preferably 15 to 25 volume percent, based on the total volume of the composition.

Abstract: The invention relates to a sintered body of a ceramic composite material based on alumina, refractory hard phases and ZrO.sub.2, HfO.sub.2 and/or partially stabilized ZrO.sub.2 with a relative density of more than 98%. The sintered body according to the invention has chromium integrated in amounts corresponding to in all 1-20 weight % and ZrO.sub.2, HfO.sub.2 and/or partially stabilized ZrO.sub.2 present as 2-16 weight % with these latter phases present to more than 70% in the tetragonal crystal modification. Furthermore, the refractory hard constituents are present as particles with a grain size of less than 10 .mu.m and/or as whiskers or fibers with a diameter of less than 5 .mu.m and a length/diameter ratio of >10.

Abstract: A ceramics-based manufacturing material and a coating material are disclosed, both of which are used in high-temperature structures and applications. The ceramics-based manufacturing material may be used for building structural blocks or members, such as refractory bricks, that require the mechanical strength and thermal resistance when they are exposed to the high temperatures of 1,500.degree. C. or above. Those bricks made of the material disclosed provides the mechanical strength and heat resistance better than the conventional ones. The coating material may be used for forming a thermal resistant layer on metal or other material bases. Both materials have substantially the similar compositions, either of which may have the alternative use, such as the manufacturing material or the coating material. Simply adding an appropriate amount of water to either makes it a coating material. In either case, the requirements for the high temperature resistance and mechanical strength can be satisfied.

Abstract: An chrome-alumina refractory brick prepared by pressing and firing a mixture consisting essentially of about 15 to 90 percent by weight of a fused chrome-alumina grain, 5 to 25 percent by weight of chromic oxide, up to 30 percent by weight of a zirconia-containing grain, and the balance alumina.

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 refractory composition which is suitable for forming a sliding gate to be used at the bottom of a ladle or tundish is provided. The refractory composition comprises 10 to 30 parts by weight of an alumina-magnesia spinel material containing 40 to 70% by weight of Al.sub.2 O.sub.3, 25 to 60% by weight of MgO and 10% or less of impurities, and 70 to 90 parts by weight of a magnesia material containing at least 90% by weight of MgO, wherein the composition contains 10 to 25% by weight of Al.sub.2 O.sub.3 and 75 to 90% by weight of MgO. 1 to 10 parts by weight of Al.sub.2 O.sub.3 material may be further added together with the alumina-magnesia spinel material and the magnesia material, to form the refractory composition.

Abstract: Whisker-reinforced zirconia-mullite ceramic articles exhibiting excellent high-temperature modulus of rupture strength and good toughness are provided from batches comprising the free oxides ZrO.sub.2, SiO.sub.2 and Al.sub.2 O.sub.3 in combination with SiC whiskers for reinforcement. Due to the fine oxide particle sizes attainable and the fact that the mullite is formed in situ in the consolidation process, dense, whisker-reinforced mullite composite articles exhibiting excellent high-temperature strength and toughness may conveniently be obtained.

Abstract: Solid, transparent, non-vitreous, zirconia and zirconia-silica ceramic microspheres, useful as lens elements in retroreflective pavement markings. The microspheres are characterized by:(a) containing at least one additive metal oxide selected from alumina, magnesia, yttria and mixtures thereof;(b) an index of refraction greater than 1.6; and(c) being virtually free of cracks.These microspheres are formed by a sol-gel technique of extractive gelation (extracting carboxylic acid away from zirconyl carboxylate) of a sol in liquid medium such as hot peanut oil. The microspheres of this ceramic composition have been made with relatively large diameters, (e.g. 200-1000 micrometers) making them quite useful as lens elements in pavement marking sheet materials.

Abstract: A process for the production of a sinterable raw material powder to be used for the production of a partially stabilized ZrO.sub.2 sintered body or ceramic body containing 0 to 60 parts of alumina, and the process for the production of the sintered body or ceramic body using this powder.

Abstract: This invention is concerned with the production of a hard, tough, thermally conductive ceramic cutting tool insert consisting essentially of a zirconia alloy in a hard refractory ceramic insert. The ceramic cutting tool insert exhibits performance conducive to use in turning operations and/or milling operations.

Abstract: Toughening agents are produced by the application of high pressure, sufficient to transform a powder material into a denser high pressure polymorph. When the pressure is released, the high pressure phase is retrieved metastably at ambient conditions of pressure and temperature. The amount of high pressure phase retained at ambient conditions depends on the relative hydrostaticity of the pressurized environment and particle size of the powder. The high pressure phase is almost completely retained in a hydrostatic environment. One embodiment of the process of the present invention produces pressure transformation toughened zirconia comprising a high pressure phase having a symmetry no greater than tetragonal (defined as tetragonal II) dispersed within a matrix of a less dense monoclinic phase.

Abstract: A process for preparing a zirconia-alumina base composite ultra-fine powder is described, including the steps of: mixing an aluminum salt or an alumina hydrate with an aqueous zirconium oxychloride solution, with or without metal salt acting as a stabilizer; mixing urea or a substance capable of generating ammonia by hydrolysis with the resulting mixture; and allowing the mixture to react at a temperature of 140.degree. to 300.degree. C. and a pressure of 4 to 150 kg/cm.sup.2 in a high-temperature and -pressure vessel. The reaction product is further dried, calcined and crushed to obtain an ultra-fine powder.

Abstract: A silicon nitride sintered material for cutting tools comprising from about 3 to 10 wt % of partially stablized zirconium oxide, from about 1 to 5 wt % of aluminum oxide, and from about 1 to 10 wt % of yttrium oxide, the balance being silicon nitride, and the process for making the same.

Abstract: The present invention provides a fibre-strengthened ceramic formed body with improved mechanical strength, wherein it contains at least 15% by volume of zirconium dioxide, hafnium dioxide or zirconium dioxide/hafnium dioxide composition in the form of monoclinic crystals and an amount of inorganic fibres sufficient for increasing the strength, which is obtainable by hot pressing a mixture of ceramic matrix materials, at least 15% by volume of tetragonal zirconium dioxide, hafnium dioxide or zirconium dioxide/hafnium dioxide composition particles and the fibres at a temperature above the tetragonal.fwdarw.monoclinic transition temperature.The present invention also provides a process for the production of such a ceramic formed body.

Abstract: An improved thermal shock resistant and generally thermal resistant ceramic composition is disclosed. The ceramic composition is compounded of aluminum oxide as a primary constituent with additives in a preferred form comprising zirconium oxide plus manganese oxide or titanium oxide, or both, interacted by exposure to high temperature. The additives increase the thermal shock resistance of the fired ceramic composition, with retention of elevated temperature strength properties. The ceramic compositions are prepared as high density solid shapes or as porous structures. The solid shapes formed into machine components show improved resistance to rapid thermal excursions, differential thermal gradients and elevated temperatures. Open cell ceramic foams of the ceramic composition are useful for hot filters, such as for filtering molten metal as well as in reaction supporting applications, where such ceramic foam structures are subject to rapid temperature and pressure transients.

Abstract: A low thermal expansion ceramic composition having a predominant Al.sub.2 TiO.sub.5 phase along with zirconium titanate and zirconia phases. The final overall ceramic composition after firing has a low thermal expansion between 24.degree.-1000.degree. C. of not greater than 1.5.times.10.sup.-6 .degree. C..sup.-1 and a thermal stability in air such that (a) upon heating to 1200.degree. C. for at least 4 hours there is substantially no decomposition of the Al.sub.2 TiO.sub.5 phase to rutile or alumina as measured by X-ray diffraction, (b) physical growth after thermal cycling between 200.degree. and 1150.degree. C. for 300 cycles does not exceed 1.5%, and (c) the composition maintains a low average thermal expansion between 24.degree.-1000.degree. C. of not greater than 1.5.times.10.sup.-6 .degree. C..sup.-1 after the isothermal heating or cycling conditions. The composition is preferably made by forming a mixture of the equivalent of 50-90 volume percent Al.sub.2 TiO.sub.

Abstract: Alumina fiber modified by stabilized zirconia has improved strength and strength retention after high temperature exposure.

Abstract: A ceramic consisting essentially of from 1 to 15 percent of glass and 99 to 85 percent of a mixture of particulate Al.sub.2 O.sub.3 and particulate ZrO.sub.2 is disclosed. ZrO.sub.2 is present in a sufficient amount, usually from 1/4 to 6 percent based on the weight of the ZrO.sub.2 and Al.sub.2 O.sub.3, to strengthen the ceramic significantly, by comparison with an otherwise identical ceramic where the particulate ZrO.sub.2 is replaced either by the glass or by particulate Al.sub.2 O.sub.3. The glass constitutes a vitreous phase bonding the particulates into a dense, gas impervious structure, and can be a calcium magnesium silicate glass containing from 45 to 80 percent of SiO.sub.2, from 8 to 55 percent of CaO and MgO, and not more than 15 percent of Al.sub.2 O.sub.3.

Abstract: Disclosed is a 35 to 45 volume percent silicon carbide whisker reinforced ceramic composite containing alumina and from about 5 to 21 volume percent zirconia which is used to make hard cutting tools having excellent toughness and hardness. Also disclosed are methods of producing the same.

Abstract: The invention is based on the discovery that in a solid electrolyte galvanic sensor, e.g. an yttria-stablized zirconia body, it is not necessary, as has hitherto been believed, to eliminate all impurities to achieve the important performance characteristics of rapid response time, reduced susceptibility to aging, and improved reliability. It has now been found that these improvements can be obtained by reducing only the concentration of iron oxide (and any other variable valence oxides that sometimes occur) in the sample, and that it is unnecessary to lower the concentration of oxides of fixed valence elements, such as silicon, aluminum, magnesium, and the alkali and alkaline earth metals, many of which tend to occur frequently as impurities in ceramic materials. This inventive selective elimination of only the variable valence oxides saves substantial cost in manufacture without loss of the performance advantages mentioned above. Indeed, better mechanical properties are often obtained.

Abstract: Ceramic sintered mass having a mean grain size of no more than 3 microns of high toughness even at high temperatures is obtainable, the mass comprising 30-99.5% by weight of a component A as defined below and the balance being a component B as defined below:Component A: zirconia having a tetragonal and/or cubic system content of no less than 90% by weight, with the proviso that the tetragonal/cubic system ratio by weight is no less than 0.25, said zirconia including a stabilizer of Y.sub.2 O.sub.3, CaO, MgO, etc.Component B: one or more of borides, carbides and nitrides of Al, Si and an element in the groups 4a, 5a and 6a of the periodic table, and Al.sub.2 O.sub.3.The balance may incorporate a further component C, such as SiO.sub.2, Fe.sub.2 O.sub.3 and TiO.sub.2 and the like of no more than 3% by weight in the sintered mass.

Abstract: A sintered zirconia material containing at least 50 mol % tetragonal zirconia and 1.5-5 mol % yttria, from which carbon is substantially absent, the porosity of which is not greater than 0.6%, the pore size of which is not greater than 0.1 .mu.m and the pores of which exist mainly at triple points of zirconia grain boundaries. The sintered zirconia material can be obtained by sintering the raw material zirconia powder, the green body or the presintered material containing tetragonal zirconia and yttria in a required amount and in an oxidizing atmosphere, by hot isostatic pressing.The sintered material thus obtained has a high strength and high toughness, and particularly excellent properties for use under conditions of higher than 600.degree. C. and can be used as a material of various industrial machines or tools.

Abstract: Mold coatings that are relatively unreactive with titanium and titanium alloys during casting are prepared from zirconia or yttria sols, or mixtures thereof as a binder for a refractory such as zirconium oxide, yttrium oxide and mixtures thereof.

Abstract: A film magnetic slider which comprises a slider performing contact-start-stop actions on a recording medium and being provided with a film magnetic head device on the side end of the slider, at least the recording-medium-contacting part of the slider being made from a sintered material having a thermal conductivity of not more than 0.02 cal/cm.sec..degree.C. and an average crystal grain size of not more than 5 .mu.m has a good slidability on the recording medium and a good machinability and can improve the life of the recording medium.

Abstract: Alumina fibers whose surface is coated with zirconia to retain their identity in an alumina matrix when the mixture is sintered at temperatures needed to form a fully dense ceramic. The resulting fully dense ceramic composite shows the beneficial effects of such reinforcing fibers by having increased crack toughness.

Abstract: Preparation of a ceramic green body by hydrolyzing two groups of alkoxides to form a dispersion of their reaction product, concentrating the dispersion to a sediment without drying it, and admixing a binder solution, plasticizer and release agent with the sediment to make a ceramic slip formulation. The slip formulation is then cast as a ceramic green body. The proportions of alkoxides can be adjusted to produce a ceramic green body which is dielectric and useful for microcapacitors.

Abstract: A high zirconia fused refractory product consisting essentially of the following constituents analytically, on a weight basis:85 to 97% of ZrO.sub.2 ;0.05 to 3% of P.sub.2 O.sub.5 ;2 to 10% of SiO.sub.2 ;0.05 to 5% of B.sub.2 O.sub.3 ; andthe content of alkali metal oxides being less than 0.1%.

Abstract: A body of monolithic or composite partially stabilized zirconia is subjected to intense surface heating which raises the temperature of the exposed surface to 1100.degree. C.-1600.degree. C. without heating the interior of the body above 600.degree. C.-800.degree. C., and then the body is cooled. The heat treated body shows increased wear resistance and surface hardness as compared with an untreated body.

Abstract: A silicon nitride sintered body essentially consisting of compounds of Sr, Mg, Ce, Zr and Al in amounts of from 0.1 to 18% by weight when calculated as SrO, from 0.2 to 25% by weight when calculated as MgO, from 0.1 to 20% by weight when calculated as CeO.sub.2, from 0.1 to 15% by weight when calculated as ZrO.sub.2 and from 1 to 20% by weight when calculated as Al.sub.2 O.sub.3, respectively, and the balance being silicon nitride. A method of manufacturing the silicon nitride sintered body is also disclosed. The silicon nitride sintered body has a low thermal conductivity while high mechanical strength and high fracture toughness being maintained.

Abstract: A sintered body of zirconia ceramic comprising 74 to 87% by weight of ZrO.sub.2 and 26 to 13% by weight of CeO.sub.2, and 0.1 to 20% by weight of Al.sub.2 O.sub.3 and 99.9-80% by weight of ZrO.sub.2 --CeO.sub.2 in the form of tetragonal crystals with 20% by weight or less of monoclinic and/or cubic crystals, is excellent in mechanical strength, were resistance and thermal stability.

Abstract: A high strength metal working tool such as cutting tools and dies made of a zirconia-base sintered material comprising 50 to 98 weight percent of zirconia (ZrO.sub.2) containing 1.5 to 5 mol percent of yttira (Y.sub.2 O.sub.3) and 50 to 2 weight percent of alumina (Al.sub.2 O.sub.3) and/or spinel (MgAl.sub.2 O.sub.4) and having a three point bending strength of not less than 1700 MPa.

Abstract: Alumina-zirconia ceramic powders comprise from 10% to 25% by weight of zirconium oxide having specific crystalline phases and from 75% to 90% by weight of aluminum oxide having specific crystalline phases, and have an average particle size of no more than 1,000 .ANG.ngstroms and a two-phase structure wherein the zirconium oxide phase is dispersed in the aluminum oxide phase. A method of making such alumina-zirconia ceramic powders comprises the steps of suspending composite powders having a specific chemical composition and a specific average particle size in water to form a slurry, freeze-drying the slurry, and calcining the freeze-dried powder at atmospheric pressure in air at a temperature of from 800.degree. C. to 1,250.degree. C.

Abstract: The flexural strength and/or fracture toughness of SiC whisker-reinforced composites utilizing mullite or alumina as the matrix material for the composite are increased by the addition of zirconia in a monoclinic or tetragonal phase to the matrix. The zirconia addition also provides for a lower hot-pressing temperature and increases the flexural strength and/or fracture toughness of the SiC whisker-reinforced composites over SiC whisker-reinforced composites of the similar matrix materials reinforced with similar concentrations of SiC whiskers.

Abstract: A sliding nozzle plate enjoying outstanding stability to resist wear, spalling, corrosion, and particularly loss due to corrosion is produced by preparing a composition consisting of at least one refractory raw material selected from the group consisting of acidic and/or neutral refractory raw materials, carbon, metal powder, and 2 to 50% by weight, based on the total weight of the composition, of coarse and/or medium particles of an alumina-zirconia-titania mixture of 42 to 79.3% by weight of alumina, 20 to 40% by weight of zirconia, 0.5 to 16% by weight of titania, and the balance to make up 100% by weight and not more than 2% by weight of inevitably entrained elements. The composition is required to have a particle size distribution of 30 to 60% by weight of coarse and medium particles and the balance to make up 100% by weight of fine particles and/or fine powder. The composition is kneaded with a binder, molded in a prescribed shape, and subjected to firing in reducing atmosphere.

Abstract: Improved Si.sub.3 N.sub.4 /ZrO.sub.2 composite ceramics are described, having low thermal conductivity and which are substantially free of surface spalling and material degradation. Such composites are produced by incorporating an additive, e.g. MgO, CaO or Y.sub.2 O.sub.3, preferably Y.sub.2 O.sub.3, in suitable molar proporations based on ZrO.sub.2, and sintering the mixture with Si.sub.3 N.sub.4. In a preferred embodiment a powder mixture of 70% Si.sub.3 N.sub.4 and 30% ZrO.sub.2, by volume, and containing 6.6 mole percent Y.sub.2 O.sub.3 based on ZrO.sub.2, is formed and is sintered to produce a composite ceramic. The Y.sub.2 O.sub.3 is preferably pre-reacted with the ZrO.sub.2 to form a solid solution. A sintering aid, preferably Al.sub.2 O.sub.3, e.g. in an amount of about 2 to about 4%, by weight of the total mixture, can be added to permit production of the Si.sub.3 N.sub.4 /ZrO.sub.2 composite by pressureless sintering.

Abstract: Aluminous proppant media in the form of sintered bauxite spheres containing silica are improved in resistance to stress corrosion by inclusion of zirconia in the mix prior to firing in the amount of a silica to zirconia ratio of from 6/1 to 20/1.

Abstract: A refractory article for casting of liquid melts, especially steel, fabricated from a mixture of Al.sub.2 O.sub.3, graphite, a flux component, a synthetic resin binder and a metallic powder. The flux component contains a first flux with a melting point from 550.degree. to 900.degree. C. and a second flux that becomes active in the mixture in a temperature ranging from 1350.degree. and 1550.degree. C. The refractory article need not be heated before use, and the carbon contained therein, which determines the strength of the article, is retained for a much longer period during use, so that the article will have a long service life.

Abstract: The invention is an improvement in ledge tools in that the ledge, or cutting element, is made of alumina-base ceramic material.

Abstract: A method for manufacture of a high toughness sintered body, characterized by sintering a shaped body of a mixed powder consisting essentially of from 40 to 70% by weight of a first component of powdered ZrO.sub.2 containing at least one stabilizer selected from the group consisting of Y.sub.2 O.sub.3, CaO, and MgO and having an average particle diameter of not more than 1.mu. and from 30 to 60% by weight of a second component of powdered .alpha.-Al.sub.2 O.sub.3 having an average particle diameter of not more than 1 .mu.m, which mixed powder may also contain not more than 3% by weight of SiO.sub.2, not more than 0.5% by weight of Fe.sub.2 O.sub.3, or not more than 0.5% by weight of TiO.sub.2 in a combined proportion of not more than 3% by weight at a temperature in the range of from 1400.degree. C. to 1600.degree. C. under normal pressure thereby producing a sintered body wherein at least 90% by weight of ZrO.sub.

Abstract: A ceramic is fabricated by dispersing ceramic particles in a liquid, sedimenting the dispersion to remove large particles, and then changing its pH to flocculate the dispersed particles. The size distribution of the particles in each individual floc is similar to the size distribution of particles throughout the dispersion. The supernate is removed and the flocs are cast by centrifuging them into a mold. The cast flocs are dried and sintered to form the ceramic. To provide a multiphase ceramic, particles of two or more ceramics can be mixed together and flocced prior to centrifuging.

Abstract: A composition of matter comprises aluminium or aluminium alloy, such as LM 13, into which has been incorporated between 5 and 50% by volume of zirconia. The zirconia may be in the form of fibres or of powder. As compared with the aluminium alloy, this reduces the thermal conductivity and coefficient of expansion, and provides a material which has, particularly at elevated temperatures above 300.degree. C., improved tensile strength, compressive strength, and hardness and reduced elongation.

Abstract: A liquid transfer ball formed from sintered zirconium oxide particles which exhibits utility as the ball element of a ball pen writing instrument to transfer ink from an ink reservoir to a writing surface such as paper. The ball exhibits a porosity of less than 8% by volume and is immune to corrosive action of inks.

Abstract: Ceramic shaped articles are disclosed which are formed of dense, non-metallic, mechanically resistant materials and contain eutectic constituents consisting of zirconium oxide, hafnium oxide and at least one other high-melting oxide and mixtures thereof. The composition exhibits excellent hardness, wear properties and bending strength. A method for preparing the articles is also disclosed wherein the appropriate mixture in a hypoeutectic, eutectic, or hypereutectic ratio is heated to its melting point, poured into a preheated mold and cooled.

Abstract: A thermal spray powder comprising particles with a central core of a material selected from the group consisting of zirconium oxide, magnesium oxide, hafnium oxide, cerium oxide, yttrium oxide and combinations thereof. The core then has discrete aluminum particles and silicon dioxide homogeneously disposed in a binder deposited thereon to form the thermal spray powder which may be thermal sprayed to produce an abradable and erosion resistant coating.

Abstract: A flame spray ceramic powder is provided consisting essentially of about 10 to 50% alumina and the balance essentially zirconia. Preferably, the zirconia is stabilized. A method is disclosed for flame spraying the coating composition onto a metal substrate.

Abstract: A zirconia type sintered body consisting essentially of 50 to 98% by weight of zirconia (ZrO.sub.2) containing 1.5 to 5 mole % of yttria (Y.sub.2 O.sub.3) and 50 to 2% by weight of alumina (Al.sub.2 O.sub.3), spinal (MgAl.sub.2 O.sub.4) or mullite (3Al.sub.2 O.sub.3.2SiO.sub.2), and having a three-point bending strength of at least 1700 MPa is provided. This sintered body is prepared by a process wherein a powdery composition consisting essentially of 50 to 98% by weight of (a1) a powder of zirconia containing 1.5 to 5 mole % of yttria or (a2) a mixture comprising 1.5 to 5 mole % of a yttria powder and 95 to 98.5 mole % of a zirconia powder and 2 to 50% by weight of (b) a powder of an alumina type oxide selected from alumina, an alumina-magnesia type oxide, an alumina-silica type oxide, a mixture of alumina and magnesia and a mixture of alumina and silica is subjected to a hot isotactic pressing treatment under a pressure of at lesast 50 MPa at temperature of 1300.degree. C. to 1700.degree. C.

Abstract: A ceramic body of zirconium dioxide containing, if desired, aluminum oxide, nd partially stabilized with yttrium oxide and/or one or more rare earth oxides (e.g., cerium dioxide) and/or magnesium oxide and/or calcium oxide is partially stabilized with 0.5 to 5 mole-% of yttrium oxide and/or 5 to 12 mole-% of magnesium oxide and/or calcium oxide and/or cerium dioxide or one or more rare earth oxides, is 30 to 100% in the tetragonal lattice modification and has in the surface region a content of yttrium oxide, cerium dioxide, magnesium oxide, calcium oxide or rare earth oxide that is 1 to 20 mole-% higher than the average content, such that the body is coated with a thin, PSZ-like layer in a more highly stabilized tetragonal or with a layer that is predominantly in the cubic lattice form.

Abstract: The invention is a ceramic composition containing a new class of dispersant for hindering crack propagation by means of one or more energy-dissipative mechanisms. The composition is composed of a ceramic matrix with dispersed particles of a transformation-prone rare-earth niobate, tantalate or mixtures of these with each other and/or with a rare-earth vanadate. The dispersants, having a generic composition tRMO.sub.4, where R is a rare-earth element, B is Nb or Ta and O is oxygen, are mixed in powder form with a powder of the matrix ceramic and sintered to produce a ceramic form or body. The crack-hindering mechanisms operates to provide improved performance over a wide range of temperature and operating conditions.