Abstract: A composite sintered body contains a silicon phase which is a main phase, a cordierite phase, and an amorphous phase containing Si. Further, the volume resistivity thereof at a room temperature is not lower than 0.1 ?·cm and not higher than 2.5 ?·cm.

Abstract: The invention relates to a granulated powder intended, in particular, for the production of ceramic sintered parts, said powder having the following chemical weight composition, based on dry matter, namely: at least 1% of a first binder having a glass transition temperature less than or equal to 25° C.; 0-4% of an additional binder having a glass transition temperature greater than 25° C.; 0-4% of a temporary additive different from the first binder and the additional binder, the total content of the first binder, the additional binder and the temporary additive being less than 9%; 0-15% of an additive for sintering the ceramic material; at least 2% impurities; and the remainder comprising a ceramic material, and optionally an agent for stabilizing said ceramic material, to make up 100%. According to the invention, the median diameter D50 of the powder is between 80 and 130 ?m, the percentile D99.5 is less than 500 ?m and the relative density of the granules is between 30% and 60%.

Abstract: A method of making disposable adobe dinnerware articles includes providing extracted clay with inclusions removed, preparing the clay to a predetermined consistency, and combining the clay with a filler to create an adobe mixture. The method can also include adding an additive, testing the humidity level of the adobe mixture and adjusting the humidity of the adobe mixture when the humidity is not within a predetermined humidity range, and preheating a mold. The method can also include adding the adobe mixture to the mold, and pressing the adobe mixture in the mold and heating the mold in a series of production stages to form a molded adobe tableware product.

Abstract: The present disclosure relates to cordierite-forming batch materials and methods of using the same, and in particular batch materials for forming porous cordierite bodies suitable for treating engine emissions. The batch materials include sources of magnesium, alumina, silica, and high BET specific surface area raw kaolin clay. In some embodiments, the BET specific surface area of the raw kaolin clay is greater than 22 m2/g. In other embodiments, the BET specific surface area of the raw kaolin clay is greater than 13 m2/g, and the source of magnesium oxide and the source of non-kaolin clay source of silica both have relatively coarse particle size.

Abstract: The invention provides novel binder, slurry and dry mix compositions for use in the production of investment casting moulds. These compositions comprise water insoluble fibers and significant amounts of uncalcined clay. The compositions display favourable separation characteristics and short drying times. The moulds formed using the compositions have a favourable green strength and conform closely to the wax pattern on which the mould is coated. Also provided are methods of producing the compositions, methods of investment casting mould production utilising the compositions and investment casting coating shells produced using the compositions of the invention.

Abstract: An alumina-based sintered body for a spark plug having enhanced mechanical strength and a method of manufacturing the same, as well as a spark plug having the alumina-based sintered body for a spark plug and a method of manufacturing the same.

Abstract: To provide a long-life refractory capable of maintaining durability under severe conditions. The castable refractory comprises a mixture containing at least one of 2 to 10 mass % of silicon carbide and 3 to 10 mass % of chamotte, as an auxiliary raw material, and a binder material, with the remaining balance being one or more main raw materials selected from corundum, mullite, bauxite, chamotte, talc and silica, and is used in an environment exposed to an alkali component-containing hot gas atmosphere. In an alkali component-containing gas atmosphere at a high temperature (750° C. or more), silicon carbide and/or chamotte are vitrified to a thickness of 1 mm or less in the surface layer of the refractory to prevent the alkali component-containing gas from intruding inside of the refractory.

Abstract: A method of producing cordierite ceramic where the degree of stacking faults and the particle diameter of kaolinite used as a component of a cordierite-forming raw material are appropriately adjusted so that microcracks having an average width of 0.3 ?m or more are introduced into the resulting cordierite ceramic to produce a high-quality cordierite ceramic that includes a cordierite crystal oriented in a specific direction and has a porosity of 25% or more and a coefficient of thermal expansion of 0.30×10?6/° C. or less.

Abstract: The present invention relates to a method of producing a ceramic material comprising the steps of; a) mixing a first clay composition silica and a silicate mineral with a second clay composition; and b) firing the mixed clay composition from step a)to form a ceramic product. The present invention also relates to an engobe clay composition, sanitary ware and methods of productions thereof.

Abstract: The invention relates to an improvement in tourmaline known as a functional ore. In particular, the invention provides a composite having a novel formation in which a far infrared radiation emitting property and others among tourmaline's properties are effectively exploited, a novel process for producing the composite, and composite materials to be used therefore.

Abstract: This invention relates to a process for producing a free radical control agent of the structural formula: wherein Z is selected from the group consisting of wherein R1 is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl; wherein R2 is an alkoxy group of 1 to 8 carbon atoms or a cycloalkoxy group of 5 to 8 carbon atoms; wherein Alk is a divalent hydrocarbon of 1 to 18 carbon atoms; and wherein Y represents a functional group that is capable of activating a vinylic carbon toward free radical addition; said process comprising the steps of (1) reacting a mercaptosilane of the structural formula: Z-Alk-SH with carbon disulfide in the presence of a phase transfer catalyst and an alkali metal hydroxide to produce a trithiocarbonate salt; and (2) reacting the trithiocarbonate salt with a halogen containing compound of the structural formula X-Y to produce the free radical control agent, wherein X represents a halogen atom.

Abstract: The use of a three-component water-soluble polymer comprising 5–90% by weight of a component a), preferably of the maleic acid, fumaric acid or itaconic acid type, 5–90% by weight of a component b) essentially from the group consisting of 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid and vinylphosphonic acid, and 5–90% by weight of a component c) comprising acrylic acid, methacrylic acid, acrylamide or methacrylamide, as fluidizer for refractory compositions comprising alumina cement is described. The copolymer, which has a preferred molecular weight Mw of <50,000, can also be combined with further quality-improving additives such as silica, lime or soda and further customary additives for refractory compositions.

Abstract: Methods and compositions are provided for making low temperature sintering ceramic bodies that have very low thermal expansion and low porosity.

Abstract: Methods and compositions are provided for making low temperature sintering ceramic bodies that have very low thermal expansion and low porosity.

Abstract: Ceramics containing 80 wt % or greater of alumina (Al2O3), with Mn, Ti, Fe, Si, Ca and Mg, with Mn—Al spinel (MnO·Al2O3) crystals and anorthite crystals (CaO·Al2O3·2SiO2) generated by calcination, and having a volume resistivity of 1×1011 &OHgr;·cm or less. The ceramics contains a combined weight of 2-11 wt % or greater of Mn, Ti and Fe as the oxides, 0.5 wt % or greater of Mn as manganese dioxide (MnO2 ), 0.5 wt % or greater of Ti as titanium oxide (TiO2), and 0.

Abstract: A raw material with a high content of aluminum oxide has the following composition, in weight-percent, based on dry weight: 1 Al2O3  50-80% MgO   2-15% SiO2   1-15% CaO 0.5-20% Fe2O3 0.5-2% Na2O 0.5-2% Al (metallic) 0.1-2% AlN 0.1-1% K2O 0.1-1.5% F 0.1-2% Cl 0.1-0.

Abstract: An economical and environment-friendly process for the synthesis of anionic clays with carbonate and/or hydroxide anions as the charge-balancing interlayer species is disclosed. The process involves reacting a slurry comprising an aluminum source and a magnesium source, the aluminum source comprising two types of aluminum-containing compounds, preferably aluminum trihydrate and/or thermally treated calcined aluminum trihydrate. There is no necessity to wash or filter the product. It can be spray dried directly to form microspheres or can be extruded to form shaped bodies. The product can be combined with other ingredients in the manufacture of catalysts, absorbents, pharmaceuticals, cosmetics, detergents, and other commodity products.

Abstract: An improved lightweight and highly permeable proppant composition for use in increasing the productivity of a gas or oil well. The proppant composition includes equal amounts by weight of uncalcined bauxite, uncalcined shale and quartz, held together with a binder formed of wollastonite and talc in an amount of less than 10% by weight of the composition. The proppant composition has an alumina content of less than 25% by weight of the composition and a silica content of over 45% by weight of the composition.

Abstract: A dry refractory composition having superior insulating value. The dry refractory composition also may have excellent resistance to molten metals and slags. The composition includes filler lightweight material, which may be selected from perlite, vermiculite, expanded shale, expanded fireclay, expanded alumina silica hollow spheres, bubble alumina, sintered porous alumina, alumina spinel insulating aggregate, calcium alumina insulating aggregate, expanded mulllite, cordierite, and anorthite, and matrix material, which may be selected from calcined alumina, fused alumina, sintered magnesia, fused magnesia, silica fume, fused silica, silicon carbide, boron carbide, titanium diboride, zirconium boride, boron nitride, aluminum nitride, silicon nitride, Sialon, titanium oxide, barium sulfate, zircon, a sillimanite group mineral, pyrophyllite, fireclay, carbon, and calcium fluoride.

Abstract: An economical and environment-friendly process for the synthesis of anionic clays with carbonate and/or hydroxide anions as the charge-balancing interlayer species is disclosed. The process involves reacting a slurry including an aluminum source and a magnesium source, the aluminum source including two types of aluminum-containing compounds, preferably aluminum trihydrate and/or thermally treated calcined aluminum trihydrate. There is no necessity to wash or filter the product. It can be spray dried directly to form microspheres or it can be extruded to form shaped bodies. The product can be combined with other ingredients in the manufacture of catalysts, absorbents, pharmaceuticals, cosmetics, detergents, and other commodity products.

Abstract: A device serves to seal the tap hole 10 of a tiltable converter with a sealing plug 8. The sealing plug 8 is characterised in particular by the composition of its material. Plastics material, preferably polystyrene foam in the shape of balls, serves therein, among other things, as material for the sealing plug 8. This gives the sealing plug 8 a considerably lower weight and above all guarantees more favourable deformation properties. The addition of the plastics material causes the sealing plug to melt or evaporate more quickly on impact by liquid steel, thus resulting in simpler and more precise handling of a converter.

Abstract: A ceramic particulate material which comprises particles having an irregular three dimensional surface profile having jagged projections and a median particle diameter of 200 micrometers or less, the particles being fractals produced by comminution of foamed ceramic material. The material may be such that in a sphere of rotation of the particle, from 30% to 80% of the volume of the sphere is void, the remainder being continuous solid material. The material may be produced by a process which includes providing a suspension of ceramic forming particles e.g., of an aluminosilicate such as clay, in a liquid medium; incorporating a gas in the liquid medium before or after formation of the suspension therein to produce a foamed suspension; extruding the foamed suspension; optionally drying the extrudate formed thereby; calcining the extrudate; and comminuting the calcined material, e.g. by crushing. The material may be used as a substitute for diatomite.

Abstract: This invention concerns a process for the reliable avoidance of slag contamination of the converter tapping steel by flush slag. In accordance with the invention a plastic, workable stopper made of fire-proof material containing silicic and oxidic components as well as suitable binding agents is used for this purpose. The stopper is introduced so far into the tapping channel with the help of a setting device that its front surface, terminated with a funnel-shaped compression plate, almost aligns flushly with the interior side of the converter, and it fills in the diameter of the tapping channel as a result of being compressed, creating such a plane that the flush slag occurring during tipping of the converter is reliably directed past the tapping channel. Stopper systems used up to now had the disadvantage that age-dependent enlargements of the tapping channel had a detrimental effect on the functioning of the stopper.

Abstract: Beta-spodumene bodies and method of preparing the bodies that involves providing a uniform plastic batch of inorganic raw materials, organic binder, and vehicle, wherein the inorganic raw materials are composed of, in percent by weight, about 75% to 95% minerals, and about 5% to 25% glass. The batch is formed into a green body that is fired to produce a body composed substantially of beta-spodumene, and having a thermal expansion coefficient of <10.times.10.sup.-7 /.degree.C.(0-800.degree. C.), and a strength of .gtoreq.4 Ksi.

Abstract: The present invention is directed to an insulating coating for refractory articles, adapted to be applied by spraying or gunning, which is easy to apply, cost effective, eliminates the potential health hazards associated with ceramic fiber paper, and which imparts sufficient insulating properties to the refractory article in high temperature environments. More particularly, the present invention is directed to an insulating coating and a method of preparing the insulating coating wherein the coating composition is comprised of about 25% to about 75% by weight of lightweight aggregate, up to about 25% to about 75% by weight of binder, up to 0.5% by weight of organic fiber, up to about 15% by weight of an additive to improve green strength, and up to about 5% by weight of a foaming agent.

Abstract: A composition suitable for admixture with refractory grains to make a refractory monolithic formulation, consisting essentially of:2 to 10 parts by weight of activated alumina;0.25 to 1.0 parts by weight of an additive material which comprises at least one of an alumino-silicate-phosphate compound; a resin derived from an aldehyde and either an amine or an aromatic hydroxy compound; cellulose; polyethylene glycol(s); and methoxy polyethylene glycols;0 to 50 parts by weight of fine alumina;0 to 10 parts by weight of fine silica;0 to 1 parts by weight of a dispersant; and0 to 1 part by weight calcium aluminate cement.

Abstract: An object of the present invention is to provide a glassy sintered body and to effectively reuse scrapped glass.The glassy sintered body of the present invention is made by preparing a raw material of the body by adding ceramic clay to glass as a main element so as to adjust the amount of water and kneading the glass and the clay, forming the raw material into a prescribed form, and sintering the formed material.

Abstract: A synthetic clay for ceramics is formed of 30-65 wt % of amorphous silica, 30-65 wt % of alumina trihydrate, and 2-20 wt % of at least one element selected from a group consisting of sepiolite, palygorskite, and bentonite. The clay may have a slurry form, partially dehydrated form, or mass or dry powder. The synthetic clay is comparable or even superior to natural clay in plasticity, water retentivity and capability of forming water film. The synthetic lay is useful for ceramic industry or pottery.

Abstract: A ceramic kiln-fired product which comprises glass, fly ash, and a clay binder. Further provided is a method for preparing raw material suitable for forming a shaped, kiln-fired, ceramic product. The method comprises mixing glass, fly ash, and a clay binder with from about 10 wt. % to about 15 wt. % water, on a dry weight basis, to form an aqueous mixture, separating the aqueous mixture using a mesh of from about 10 to about 12 screen into first and second portions, the first portion comprising the aqueous mixture which does not pass through the mesh and the second portion comprising the aqueous mixture which passes through the mesh, and drying the second portion until the moisture content of the second portion is less than about 0.5 wt. % to form the raw material. The present invention also provides a tile glazing formulation which may be used with the ceramic product of the present invention, as well as a method of using the formulation. The glazing formulation comprises, on a dry weight basis, about 70 wt.

Abstract: A refractory mix for forming high strength, low thermal conductivity refractory shapes comprising from about 40 to 75% by weight of at least one dense refractory aggregate, about 10 to 30% by weight of a bonding agent, and about 5 to 25% by weight of hollow ceramic microspheres having a diameter of about 1 to 350 microns.

Abstract: A lime-free silicon carbide based refractory containing about 87 wt.% silicon carbide sized -10 mesh, about 5 wt.% alumina sized -325 mesh, about 3 wt.% silica sub-micron size, and about 5 wt.% alkaliphosphate modified alumino-silicate binder. This material finds particular applicability in the construction of cast shapes and troughs for non-ferrous metal production and as a refractory lining for boiler tubes.

Abstract: An isocyanate-reactive composition having a plurality of isocyanate-reactive groups comprising:(i) at least one polyol having a number average molecular weight of from 2000 to 12,000;(ii) at least one low molecular weight polyol, including water, immiscible in said high molecular weight compound and having a molecular weight in the range of 18-500; and(iii) a compatibilizing amount of an amidine compound of the Formula (1) ##STR1## wherein each of R.sup.1 to R.sup.4 represent H or, independently or together, an organic radical selected from:(a) alkyl radicals having 1 to 25 carbon atoms;(b) cyclo alkyl radicals having 5 to 25 carbon atoms;(c) aralkyl and/or aryl radicals having 6 to 18 carbon atoms, and(d) polymeric chains containing hetero atoms selected from polyether, polythioether, polyester, polycarbonate and polyacetal chains.The amidine improves the stability of compositions comprising high and low molecular weight polyols.

Abstract: An improved gunning composition for use in the steel industry includes between 60-75% by weight of a refractory base material, 10-20% by weight of silicon carbide, 7-15% by weight of ball clay, 4-8% by weight of a silica binder material, and, optionally, 5-10% by weight of a graphite material. The silica binder replaces binders composed of petroleum pitch or clay. The silica binder causes the composition to have (1) better adhesion, (2) less cracking, (3) improved strength, and (4) increased resistance to oxidation, corrosion and erosion.

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: There is disclosed a porous inorganic material, suitable for use as a support material for biological macromolecules, comprising substantially spherical particles of an aluminosilicate ceramic material, any internal cavities present in a particle occupying no more than 10% of the volume of the particle, each particle having a diameter in the range of from 5 micrometers to 5 millimeters and consisting predominantly of an open three-dimensional matrix of needles of the ceramic material each of which needles has a length in the range of from 2 to 20 micrometers and a width in the range of from about 0.2 to 2 micrometers, the ceramic needles defining between them interconnecting pores of width of from 0.1 to 5 micrometers. Also disclosed is a method of preparing such a porous inorganic material.

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: There is disclosed a porous inorganic material suitable for use as a support for immobilizing biological macromolecules and which comprises a 3-dimensional network of defect aluminium-silicon spinel, said network defining an interconnecting array of pores predominantly in the size range of from 100 to 1000 .ANG..A process for preparing the porous inorganic material is also disclosed.

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: A porous cordierite ceramic and a process for making the same are provided by the present invention. Preferably, the ceramic material includes at least about 95 percent cordierite in the crystal phase, a porosity of at least about 30 volume percent, a crush load strength of at least about 6 pounds, and a thermal conductivity of less than about 5 watts/meter-.degree.K. The method of producing a porous cordierite ceramic includes (a) combining alumina, clay, talc, a pore-forming material and preferably free silica; (b) adding binder, water and other additives; and (c) shaping the mixture to form a green body. The green body is thereafter fired to form a sintered ceramic body. The porous cordierite is useful in a heat source retainer.

Abstract: A thermal storage brick for use with thermal storage heaters comprised of predetermined amounts of crushed taconite pellets, clay and talc. The ingredients are formed into a brick shape under approximately 4000 p.s.i. and are fired at approximately 2150.degree. F. and are allowed to soak for approximately five hours.

Abstract: High strength porcelain having an unglazed bending strength of greater than 1,400 kg/cm.sup.2 and consisting essentially of 22-85% by weight of SiO.sub.2, 10-73% by weight of Al.sub.2 O.sub.3, and 1.5-6.5% by weight of K.sub.2 O and/or Na.sub.2 O. The porcelain has a total degree of crystallinity of more than 40% by weight, and a crystalline grain size of not greater than 20 .mu.m, and it is free from defects of larger than 40 .mu.m. The porcelain is produced by pulverizing a starting material mixture of quartz-feldspar-alumina system so that 85-95% by weight of particles thereof have a grain size of not greater than 10 .mu.m, calcining the mixture, adding clay-mineral material therein, pulverizing so that the clay-mineral-added mixture contains less than 85% by weight of particles with a grain size of not greater than 10 .mu.m, forming, drying, and firing at 1,100.degree.-1,400.degree. C.

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: A refractory composition characterized by abrasion resistance and low thermal conductivity comprising about 40 to about 96 weight percent amorphous silica, about 2 to about 50 weight percent -65 mesh calcined refractory aggregate having a density of at least about 140 lb/ft.sup.3 and about 2 to about 40 weight percent calcium aluminate cement.

Abstract: This invention is an improved heat storage means in the form of a high density masonry product for storing large amounts of heat in a relatively small area. This is accomplished through a special manufacturing process utilizing specific selected materials.

Abstract: A means for producing nitride bonded refractory shapes, in situ, by mixing an aluminum metal powder, relatively pure silica, crude clay and a refractory aggregate. The mixes are pressed into shapes and burned at elevated temperatures in a nitriding atmosphere to form the bond.

Abstract: A method for producing a high porosity ceramic material characterized by the steps of: (1) wetting a finely divided, non-crystalline, amorphous silica with a wetting agent; (2) combining the wetted silica with a ceramic slip to produce a mixture; and (3) removing the majority of the wetting agent to produce a solid, low-density, highly porous bisque. The bisque if preferably partially covered with an impermeable coating, and an aromatic fluid is applied to an exposed surface of the bisque for absorption into the body of the bisque.

Abstract: A composition for coating the refractory liners of ladles and troughs for pouring and/or conveying molten metals comprising an aqueous dispersion containing finely divided zirconia, a colloidal silica, finely divided mica, finely divided zircon, finely divided bentonite and, optionally, an inert coloring agent. The coating composition is capable of re-bonding fractured liners and the resulting coating prolongs the effective life of the liner and exhibits superior reflectivity, causing the molten metal to retain its heat which facilitates better pouring.

Abstract: A process for the production of construction material comprising the steps of:1. heating soil to a temperature sufficient to destroy substantially the property of the soil to swell with changing levels of moisture without causing any of the soil constituents to melt, which temperature will normally lie between 500.degree. and 750.degree. C. depending upon the soil type,2. adding to the soil, either before or after the heating step, iron oxide in a finely divided form, to form a mixture and3. introducing into, or creating within, the mixture a solution of sodium silicate, such as by adding an aqueous solution of sodium silicate to the mixture or by adding to the mixture a strong solution of sodium hydroxide and a silica source.The construction material formed by the process, and articles formed thereform, form part of the invention.

Abstract: A composition for coating the molding surfaces of molds for casting metal parts comprising an aqueous dispersion containing finely divided zirconia, a colloidal silica composition, finely divided mica, finely divided zircon, finely divided bentonite and, optionally, an inert coloring agent. While capable of protecting the molding surfaces against high temperature molten metal and producing castings having substantially defect-free surfaces, the coating composition provides cleaner castings by partially attaching to the casting and spalling off as the casting cools.

Abstract: A monolithic refractory composition including from about 63% to about 90% by weight high purity Al.sub.2 O.sub.3 ; from about 2% to 8% by weight crystalline silica having a particle size of -200 mesh; from about 2% to 6% by weight high purity Cr.sub.2 O.sub.3 ; from about 1% to 8% by weight high purity kaolin clay having a particle size of -10.mu. (micron); and from about 5% to 15% by weight phosphate binder. About 1-5% water may be substituted for Al.sub.2 O.sub.3. Preferably, the high purity Al.sub.2 O.sub.3 is a mixture of tabular alumina and calcined alumina and the phosphate binder is H.sub.3 PO.sub.4.