Key Ceramic Materials

Amblygonite

Natural fluophosphate of aluminum and lithium. The least expensive source of alumina phosphate and highest lithia-containing lithium mineral. Active flux: useful in low-temperature bodies and porcelain enamels. Promotes opacity in glass dinnerware.

Andalusite (Al₂O₃ .SiO₂)

Contains Al₂O₃ and SiO₂ in theoretical weight ratio of 62.9% and 37.1% (as sillimanite and kyanite). Typically makes up to 40% of refractory and whiteware products. Widely used in refractories: brick and monolithics. Forms mullite upon heatup, with volume increase < 4%. Andalusite refractories are used mainly in the iron and steel industry in blast furnace troughs and stove checkers, pouring ladles and electric furnace roofs. Used for frits for ceramic glazes.

Anhydrite (CaSO₄)

Natural calcium sulfate. Found as layers in gypsum and halite deposits. Harder than gypsum and lacks water of crystallization. Can be made to set selectively with special chemical accelerators such as alum.

Apatite

Natural calcium phosphate. Substitute for bone ash in some translucent whiteware bodies. Used in the manufacture of opal glass.

Baddeleyite

Composite of natural zirconium oxide, hydrated zirconium oxide and zirconium silicate. Excellent refractory. Ingredient of low-expansion bodies.

Ball Clay

Clay containing kaolinite, lignite and organic colloids that promote plasticity. Can be easily flocculated or deflocculated through adsorption of ions from electrolytes, giving a wide range of viscosities in ball clay slurries or slips. Important raw material in ceramics for achieving plasticity, bonding strength and refractoriness. Useful as an auxiliary flux. Bonds nonplastic material such as special refractories high in prefired grog or calcined material. Fine-grained ball clays are used to decorate bricks and tiles. The plasticity allows formation of ball clay containing ware by variety of methods, including jiggering, extrusion, pressing and casting.

Baryte (BaSO4)

Bauxite

Primarily aluminum hydroxide, with impurities containing oxides of iron, titanium etc. The principal source of alumina. Used directly in the calcined form for producing abrasives, refractories and other ceramic materials. For refractory purposes, a calcined bauxite of high alumina content, controlled iron and low loss on ignition is required, with low alkali preferred. Used in rotary kilns for the manufacture of Portland cement, dolomite and lime. Used in combustion chamber linings for boilers and furnaces where the ash is highly corrosive to brick. Used for the manufacture of quick-hardening special high-alumina cement. Bauxite abrasives are prepared by fusion of a mixture of calcined bauxite, coke and iron turnings in electric arc furnace. Crushed, ground and separated into various grit sizes to produce grinding wheels, abrasive stones, cloths and papers, and grinding and polishing powders.

Bentonite

A hydrous, clay-like, silicate of alumina, derived from volcanic ash with trilayered clay mineral montmorillonite (Al2O35SiO27H2O) as main constituent. Used as plasticizer in electrical porcelain bodies, increases dry and fired strengths and reduces absorption. Additive in high temperature cements, mortars and plastic refractories. In porcelain enamels, bentonite is used as a suspending agent.

Beryl (3BeO^.Al₂O₃)

Silicate of beryllium and aluminum. Used in spark plug porcelain for high electrical resistance, even at elevated temperatures. Improves dielectric strength, lowers firing shrinkage, increases impact resistance and transverse strength and improves resistance to thermal shock. Active flux used in high-temperature electrical porcelain and crucible bodies. Forms an eutectic with feldspar. When substituted for feldspar, hardens glaze. Beryl glazes are highly fluid and of are of shorter firing range. Improper design may lead to excessive crystallization of cristobalite and mullite. In borate glasses gives high coefficient of thermal expansion, high permeability to UV rays. Inhalation of particles of any BeO compound should be avoided due to their toxicity.

Clay

A mixture of particles of hydrated silicates of aluminum, e.g. kaolinite, Al₂O₃^.2SiO₂^.2H₂O, and montmorillonite, (Mg,Ca)O^.Al₂O₃^.5SiO₂^.H₂O, of various sizes and properties. Typically contains both plastic and non-pastic fractions, and organics. Nonplastic portion consists of altered and unaltered rock particles e.g. quartz, micas, feldspar. Organic matter is crucial to clay properties, e.g. plasticity. Typical clay minerals have microscopic plate-like structures, giving enhanced plasticity (formability) when wetted with water. Hardens when dried. Forms ceramic bond when fired. Substantially shrinks during drying and firing. High content of fine particles (<1 micron) is responsible for clay plasticity, influences drying performance, drying shrinkage, warping, and tensile, transverse and bonding strength after firing. Ball clays and china clays (kaolin) are important in the pottery industry.

Kaolin (Al₂O₃^.2SiO₂^.2H₂O, China Clay)

White-burning clays formed by weathering of feldspathic rocks, granites, etc. Secondary (sedimentary) kaolins are formed by weathering, then transported and redeposited elsewhere. Widely used in the refractory, sanitaryware, paper and elastomeric industries. Due to high purity kaolin has high fusion point and is most refractory of all clays.

Diatomite (Diatomaceous Earth)

Highly siliceous mineral with closed cells and high porosity, hence low density and low thermal conductivity. Used for insulating bricks.

Dolomite ( CaMg(CO₃)₂ )

Intermediate between limestone (CaCO₃) and magnesite (MgCO₃). Calcines at 900^oC (CO₂ is expelled). Glass plants use dolomitic quicklime which becomes dolomitic hydrate upon addition of 20% water. Raw dolomite is dry-milled and air-floated to uniform fineness for pottery applications. Dolomite adds luster to ware, is a powerful fluxing agent, fines glass quicker than other lime-sources and increases modulus of rupture of glass. Dolomite can replace most lime fluxes in pottery bodies and glazes. Used as auxiliary in clays with variable amounts of alkaline earths. Acts as stabilizing flux and tends to lower and widen firing range.

Feldspar

Found as microcline (K₂O^. Al₂O₃^.6SiO₂), albite (Na₂O^.Al₂O₃^.6SiO₂) and anorthite (CaO^.Al₂O₃^.2SiO₂). Used as flux for porcelain bodies. Decreases plasticity of unburned ceramic bodies. At elevated temperature feldspar melts and dissolves clay and then flint particles. Used in glazes for fluxing action, where potash feldspar is more desirable over soda feldspar because it dissolves silica more readily and makes durable glaze. Used in porcelain enamels, where introduces alumina (with relatively high thermal expansion for fitting purposes. Feldspar increases enamel’s viscosity and resistance to corrosion.

Fluorspar

Fluorite. CaF₂. Used as opacifier and flux for enamels an opal glasses. Decreases coefficent of thermal expansion of enamel. Used as addition to glazes to prevent crazing. Used in optical glassess due to low index of refraction and small dispersion. In whiteware bodies, acts as auxiliary flux in promoting decreased porosity or lower firing temperatures. Small amounts effective in vitreous and semivitreous sanitaryware and electrical porcelain bodies.

Halloysite (Al₂O₃^. 2SiO₂ ^.xH₂O)

Aluminum silicate, resembling kaolinite, but higher in water content. Used in both refractories and whiteware. Used in dinnerware for its unique firing properties.

Nepheline (K₂O^. 3Na₂O ^. 4Al₂O₃^.9SiO₂)

Higher in alkali and alumina, lower in silica than feldspars. Crystallizes from magma, instead of soda feldspar, due to insufficient supply of silica

Nepheline Syenite

Composed of nepheline, potash feldspar, soda feldspar and other minor minerals. Used as substitution for potash feldspar to lower firing temperature of whitewares. The resulting fired vitreous ware helps to lower fuel and refractory costs and speed up firing cycles. Substitution of nepheline syenite for potash feldspar in wall tile bodies lowers absorption and moisture expansion, increases shrinkage and mechanical strength. Floor tile bodies show less variation in thermal expansion with differences in thermal treatment than corresponding feldspar bodies. In electrical porcelain, substitution of nepheline syenite for potash feldspar increases firing range, strength, decreases absorption and increases shrinkage at lower firing temperature. Promotes state of compression in glazes and reduces crazing.

Potash (K₂O)

Additive to lower viscosity of glasses and glazes (in addition Na₂O). Excess potash may cause peeling and crazing. In hydroxide or carbonate form, important deflocculating agent. Used to prepare casting slips, glaze slips, to purify clay; to reduce plasticity of excessively plastic clays.

Pyrophyllite (Al₂O₃^.4SiO₂ ^.H₂O)

Hydrous aluminum silicate, similar to talc (magnesium silicate). Used in manufacture of refractory products: fire bricks, castables, plastic and gunning mixes. Expands upon heating and thus counteracts shrinkage of plastic fraction of mix, keeping refractory volume constant. Provides good spalltion and slag resistance. Used in electrical insulator bodies

Rutile

Mineral containing mainly TiO₂. The principal source of chemically pure titania, and titanium. Stain in pottery. Substitute for titania pigments. Colorant for glass and ceramics. Constituent in welding rods coating.

Sillimanite (Al₂O₃^.SiO₂)

Mineral with same composition as andalusite and kyanite. Upon heating to 1545^oC, decomposes mullite and silica. Further heating to 1810^oC, beaks it up into corundum and glass.

Talc (3MgO^.SiO₂^.H₂O)

Soft, platy hydrous magnesium silicate. Used in tile bodies, kiln furniture and electrical porcelains. Used to synthesize cordierite (formed from 44% pure talc, 41% plastic kaolin and alumina), a silicate of very low coefficient of thermal expansion, for use in kiln furniture and automotive catalysts supports. Used as flux for high alumina ceramics, sanitaryware and dinnerware. Low-cost source of magnesium. Helps to produce less porous bodies at lower firing temperatures.

Wollastonite (CaSiO₃)

Provides reduced drying and firing shrinkage, higher strength and thermal shock resistane, faster firing, easy pressing, better bonding, and superior electrical properties to bodies, glazes, porcelain enamels and frits. Makes brighter and smoother glazes, better low-loss dielectric bodies; good flux for stronger welding rod coatings. Excellent material for semivitreous bodies. Applications include glazed porous ceramics, dinnerware, ovenware, artware, structural clay products, sanitaryware, abrasives, refractories, electrical porcelains, spark plugs, frits and investment castings.

Zeolite

Variety of hydrous silicates analogous in composition to feldspars. Act as ion-exchangers. Include various natural or synthesized silicates of similar structure used especially to treat water and as absorbents and catalysts.

Alumina

Along with silica, the most widely utilised ceramic. Produced from bauxites (impure aluminum hydroxides) through Bayer process. Available in powder form in very wide range of sizes, from fine (sub-micron) sinterable powders, to mm size grinding grits, and in fibrous and single-crystal form. Component of enamels, glazes and glasses. Chemically stable against most environments except hydrofluoric acid and some molten salts. Excellent refractory. Sets upon hydration if produced in the special form of re-hydratable alumina cement (more commonly in the form of calcium aluminate cement). Hard and stiff ceramic, widely used for wear parts, abrasives, IC substrates, insulators, seals, armor plates,

Aluminum Titanate (Al₂O₃^.TiO₂)

Known for low stiffness and low thermal expansion coefficient, which combined give high thermal shock resistance. Shows expansion hysteresis loop due to internal fractures caused by anisotropy of expansion coefficients. Fired aluminum titanate is easy to machine. Thermal shock-resistant applications include catalytic converter and diesel engine components.

Antimony Oxide

Component of leadless white enamels (opacifier) on cast iron and sheet steel (recently replaced largely by titanium oxide). In pottery used as yellow stain. In glass oxdizes iron to ferritic state and thus leads to de-coloration.

Barium Ferrite

The major component of low-loss ceramic magnets (ferrites), which exhibit both high magnetic permeability and electric resistivity. Synthesized trough calcining barium carbonate and iron oxide, followed by solid-state diffusion and reaction to form the ferrite.

Barium Titanate

Synthesized trough calcining barium carbonate and titanium oxide, followed by solid-state diffusion and reaction to form the titanate. Due to very high relative dielectric constant (several thousands) used as capacitors. Usually stabilised with zirconates or other titanates to achieve less variation of the dielectric constant with temperature. As piezoelectric, used for ultrasonic generators and sensors, for application in sonars, ultrasonic cleaners, accelerometers etc.

Beryllium Oxide

Toxic if in powdered form. As a sintered body, has the highest thermal conductivity of all ceramics. As it is also a good dielectric, it is used as a substrate for high-power IC, heat sinks, microwave tube parts, etc. Non-wettable by many molten metals and slags, leading to corrosion resistance.

Bismuth Oxide

Component of optical glasses for high durability and refractive index. Flux for silver paints. Replaces lead oxide flux in glazes for consumer products.

Calcium Titanate

Similar to barium titanate, synthesized trough calcining calcium carbonate and titanium oxide, followed by solid-state diffusion and reaction to form the titanate. Due to very high relative dielectric constant (several thousands) used for capacitors. Usually stabilised with zirconates or other titanates to achieve less variation of the dielectric constant with temperature. As piezoelectric, used for ultrasonic generators and sensors, for application in sonars, ultrasonic cleaners, accelerometers etc.

Calcium Oxide (Lime)

Basic refractory oxide, very sensitive to hydration. As an additive, e.g. in glass batches, enamels or pottery, used in the form of "whiting", i.e. calcium carbonate (limestone) with some impurity of magnesium carbonate (forming together dolomite). Used in construction as marble (crystallised limestone)

Chromium Oxide

Additive to glasses, glazes and enamels to obtain green color. Used for wear resistant parts (sintered or hot pressed) or coatings (thermal sprayed). Component of refractory linings.

Germanium Oxide

As additive in glass provides high refractive index. Used in manufacturing of glass fibers for fiber optics, optic glass for lenses and night-vision instrumentation.

Hafnium Oxide

Similar to zirconium oxide, found as impurity in zirconium ores. Super-refractory (MP 2,800^oC), used for specialized crucibles etc. Stabilized with CaO to avoid damaging phase transformations during thermal cycling.

Iron Oxide

Main component of ferrites, MeFe₂O₄, ceramic magnets with spinel structure. For applications in electronics and data storage (tapes, disks). In glass and pottery iron oxide impurities give the usually undesirable dark brown colour. Thus, its content in clays is closely monitored and determines quality of clay.

Lead Oxide

Additive in optical glases to increase the refractive index. In glazes gives superior brilliance, lustre and smoothness, together with chemical and mechanical resistance. Preferably converted to lead silicate to minimise leaching of lead from glaze. Used for enamels on cast irons for acid resistance. Used in large amounts (40-50%) for enamels on aluminum, to provide low viscosity at temperatures around 400^oC.

Lead Titanate

Additive to batium titanate to enhance piezoelectricity. In solid solution with lead zirconate gives lead zirconate titanate (PZT) ceramics, one of the best piezoelectrics and ferroelectrics.

Lithium Oxide

Flux for glasses with low thermal expansion coefficient. Component of glass-ceramics, allows very high thermal shock resistance. Allows transmission of ultraviolet light if in large amount in glass. Component of pottery and electrical porcelain glazes and enamels.

Magnesium Oxide

Basic refractory material for metals processing, primarily steel. Used for specialised crucibles for metals handling and thermocouple shields.

Silicon Oxide

Along with alumina, the most widely utilised ceramic. Although three basic crystalline forms are found (quartz, tridmite, crystobalite), the largest amounts of silica are found in reacted form in alumino-silicates. In pure form obtained from quartz sands. Frequently occurs in glassy form, e.g. in window glass, optic fibers. The glassy form is preferable in any ceramic experiencing periodic temperature variations due to large strains accompanying crystalline phase transformations. Glassy silica has very low thermal expansion coefficient, whereas the crystalline forms is at least ten times larger. Therefore, glassy silica is thermal shock resistant, whereas the crystalline silica is not. Fused silica (glassy) refractories are widely used in glass tanks, coke furnaces and open hearth furnaces.

Thorium Oxide

The highest-melting point oxide (3,200C). Used for super-refractory crucibles for metal handling (non-wettable by metals). Used in electronics industry for cathodes for magnetron vacuum tubes (combined with Mo into a cermet).

Tin Oxide

Opacifier for glazes. Provides pink color in enamels and glazes.

Titanium Oxide

The strongest white pigment known, used for paints. Opacifier for glass enamels on metal sheet, precipitates in the form of anatase from super-saturated glass. Rutile form of TiO2,having a moderately high dielectric constant (~90) is used for capacitors.

Cordierite

2MgO^.2Al₂O₃^.5SiO₂, a very low thermal expansion alumino-silicate, with the resulting large thermal shock resistance. Low dielectric loss ceramic, used for electric insulators for AC, for low and high-temperatures.

Calcium Aluminate Cement

Hydrates in contact with water much like Portland cement. Designed for use as binders in monolithic (castable) refractories. Binder selection is primarily based on refractory concrete’s required service temperature, extended by increasing alumina and lowering iron contents. Cement colors range from white for high purity to darker for low-purity grades.

Forsterite (2MgO^.SiO₂)

Synthetic magnesium silicate used extensively in electronic ceramic formulations and ceramic metal seals because of its high CTE, comparable to that of some metals.

Hydroxyapatite (Ca(PO₄)₃OH)

Complex calcium phosphate mineral, chief structural element of vertebrate bone. Important bioceramic. Many bioceramics (including glass, glass-ceramics and ceramics) develop a thin hydroxycarbonate-apatite (HCA) surface layer upon exposure to body fluids. Collagen fibrils incorporated within this growing inorganic mineral layer produce mechanically strong bond between the implant and the host tissue, to result in bioactive fixation.

Magnesium Phosphate (Mg₂P₂O₈)

Replaces tin oxide in raw, leadless sanitaryware glazes, for aesthetic value. Works well both in low-alkali and high-alkali glazes.

Mullite (3Al₂O₃^.2SiO₂)

Occurs in most ceramic products containing alumina and silica. Very refractory, breaks up into corundum and liquid silica at 1810^oC. Sintered and electrofused synthetic mullites are used in kiln furniture and refractories for glass and steel industries. Resistant to spalling and deformation under load. Has high strength due to interlocking of long, needle-like crystals, growth of which is promoted by presence of impurities. Mullite body with short, interlocking crystals is stable againat load-induced deformation at high temperatures.

Sodium Phosphate (Na₄P₂O₇)

Efficient suspending and dispersing agent for grease, dirt, clay, and other insoluble materials. Thinning agent in clay slips. Deflocculant for glazes and in purification of clays. Removes iron from clays by washing. Efficient water conditioning agent; treats hard water.

Sodium Silicate (Na₂O ^.xSiO₂)

Synthesized by melting sand and soda ash in reverberatory furnace. Na₂O:SiO₂ ratio changes from1:6 for alkaline grades to 1:3.5 for most siliceous kind. More alkaline sodium silicates (e.g. metasilicate, Na₂O ^.SiO₂) are used in detergents. Effective for cleaning metal prior to enameling. Used extensively as deflocculant. Used in enamels for aluminum. Used for bonding lightweight insulating brick made from vermiculite or perlite, together with calcium carbonate. Used in dry clay type bonding mortars, mixed with water just before use. Dry hydrated silicates used with chrome ore formulations for gunning mixes used in patching linings in hot furnaces. Gives greater green strength and greater fired strength in air-set refractory specialties.

Spinel (MgO^.Al₂O₃)

Formed by solid-state interaction of magnesia and alumina. Excellent refractory, highly resistant to attack by slags, glass. High-purity spinel is chemically-derived by co-precipitation of magnesium and aluminum complex sulfates followed by calcination to form oxide compound. Ceramic powders thus prepared can be hot pressed into transparent window materials with exceptional IR transmission range. Member of spinel structural group of general formula XY₂O₄. Ferrospinels are either magnetic (related to inverse structure) or nonmagnetic (related to normal structure). Available as fused spinel for special refractory applications.

Spodumene

Lithium alumino-silicate Li₂O^.Al₂O₃^.4SiO₂ . The principal source of lithium oxide flux for glazes, glasses and porcelains.

Strontium Titanate (SrTiO₃)

High relative dielectric constant material (225-250). Can be dry pressed or slip cast, fired to vitrification at about 1200^oC. Used by itself or combined with barium titanate for capacitors and other electronic components requiring high dielectric constant.

Superconducting Ceramics

Conducts electricity with zero resistance. Includes YBa₂Cu₃O₇ (known as 1-2-3 compound due to ratio of cations) superconducting below 93K. Other cuprate superconducting systems include Bi-Sr-Ca-Cu-O phases. Bi₂O₃ is helpful in processing due to minimum volatility since it melts below the sintering temperature allowing for liquid-phase sintering. The superconducting properties are highly process-dependent since grain boundaries are detrimental for conduction. Greatest reproducibility of results was achieved in single-crystals formed using a single-crystal SrTiO₃ as epitaxy substrate. Recent system with high Tc=125K include Tl-Ba-Ca-Cu-O phases, but are more process-sensitive and chemically unstable than 1-2-3 material. Also, contains extremely toxic thallium oxide. Main application in medical field, in nuclear magnetic scanners used to examine soft tissue without surgery. Photovoltaic substances interfaced with superconductor act as signal detectors (e.g. IR devices) sensible to minute electrical fields.

Boron Carbide (B₄C)

Light, strong, very hard ceramic. High hardness and strength-weight ratio makes B₄C especially attractive for armor and aerospace applications. Usually hot pressed, but high-temperature (2200^oC) pressureless sintering is possible. Best properties when pure fine powder is densified without additives. Pressureless sintering to high density is possible using ultrafine powder, with carbon additives. Boron carbide-based cermets and metal or ceramic matrix composites (Al/B₄C, Mg/B₄C, Ti/B₄C, TiB₂/B₄C) have unique properties and specialized applications. As abrasive, B₄C is used for fine polishing and ultrasonic grinding and drilling. However, the tendency to oxidize at working temperatures precludes use in bonded abrasive wheels.

Chromium Carbide (Cr₂₃C₆, Cr₇C₃, Cr₃C₂)

Available as finished cermet products bonded with nickel, or as a powder. Formed by standard powder metallurgy techniques (cold pressing and sintering). Reaches high hardness and excellent surface finish (bright, high reflectivity and optical flatness) appropriate for precision gage blocks. Structural applications include bearings, seals, valve seats and orifices. Used a cermet powder for thermal sprayed coatings.

Silicon Carbide (SiC)

Hard, high thermal conductivity; high strength at elevated temperatures, semiconductor. Oxidizes very slowly in air, due to formation of a protective layer of silica. Resistant to acids, but reacts with fused caustic, halogens and some metal oxides at high temperatures. Super-refractory, used as setter tile and kiln furniture, muffles, retorts and condensors, skid rails, hot cyclone liners, rocket nozzles, and combustion chambers, and mechanical shaft seals. Electrical uses include lightning arrestors, heating elements, nonlinear resistors. SiC refractories are classified on basis of bonds used: dense materials contain 85-99% SiC, clay-bonded contain 75-80% SiC, semisilicon carbides still lower in SiC content. Added to plastic fireclays, SiC imparts high thermal emissivity and conductivity to refractory. Used in refractory cements for laying SiC brick or shapes, ramming or patching linings, and washes. Used in the manufacture of grinding wheels and coated abrasives. Manufactured as fibers or whiskers for reinforcement of ceramic composites.

Titanium Carbide (TiC)

Very hard, refractory material, known for its high wear-resistance and thermal shock resistance. Used for bearings, nozzles, cutting tools, wear parts. Available as high-purity or technical grade, depending on carbon content. Used as cermet reinforcement, for components such as jet engine blades and cemented carbide tool bits. Electrical conductor especially at high temperatures.

Aluminum Nitride (AlN)

Known for very high thermal conductivity. Hydrolyzes on contact with moisture, stable against acids. Major applications include thermally conductive substrates and heat sinks for semiconductors, automotive and transit power modules, mobile communications and multichip modules.

Boron Nitride (BN)

Highly refractory material with physical and chemical properties similar to carbon. Graphite-like (g-BN), wurzite (w-BN) and zinc blende (z-BN) are polymorphs of BN corresponding to graphite (hexagonal) and diamond (cubic) structures. All forms are good electrical insulators and thermal conductors, chemically inert in most environments, resisting attack by mineral acids or wetting by glasses, slags and molten oxides; cryolite and fused salts; and most molten metals including aluminum. Hexagonal BN powders are used as mold release agents, high temperature lubricants, and additives in oils, rubbers and epoxies to improve thermal conductance of electrical compounds. Powders also used in metal- and ceramic-matrix composites to improve thermal shock and modify wetting characteristics. Uses include crucibles, parts for chemical and vacuum equipment, metal casting fixtures, boron sources for semiconductor processing and transistor processing and transistor mounts. Cubic BN is second hardest material, after diamond. Used for high-performance tool bits and in special grinding applications. BN tooling typically outlasts alumina and carbide tooling and preferred in applications where diamond not appropriate, e.g. grinding of ferrous metals.

Silicon Nitride (Si₃N₄)

Tough high-temperature ceramic due fibrous grain structure (beta form). Excellent corrosion and oxidation resistance over wide temperature range. Used in molten-metal-contacting parts, wear surfaces, special electrical insulator components and metal forming dies. Possible application in gas turbine and heat engine components, as well as antifriction bearing members. Available as Reaction Bonded Silicon Nitride (RBSN), through nitridation of silicon powder. Although RBSN is porous (10-20% pores), it is an attractive form of silicon nirdide exhibiting near sero processing shrinkage and stable behaviour at elevated temperatures.

Sialon

Silicon-aluminum oxynitride, synthesized by reacting Si₃N₄, Al₂O₃ and AlN, usually with some liquid-phase additives, such as yttrium oxide or MgO, CaO. Sialons are used as bearing materials in systems which are lubrication-free and require wear resistance and light weight. Widespread use as cutting tools. Other uses include rocket nozzles and orbital-welder gas shrouds.

Titanium Boride (TiB₂)

Very hard, electrically conductive ceramic with oxidation resistance to 1500^oC. Known for chemical resistance against molten aluminum and cryolite. Densified as cermet (with Ni additives) or hot pressed as pure ceramic. Proposed applications include cutting tools, electrodes, armor plates, wear parts.

Antimony Sulfide (Sb₂S₃)

Used in glass batches to achieve cloudy amber or ruby glass; in opal glasses; in enamel batches. Antimony – antimony sulfide enhances adherence of white enamel to steel.

Arsenic Oxide (As₂O₃)

Used as decolorizing agent, through oxidizing effect of As₂O₃ on ferrous ion, adding to color stability and increasing brilliancy. Reduces purple color to faint color of manganous ion. Used as opacifier in glazes; in enamels, however its toxicity limits applications to special products, e.g. jewelry.

Binders

Increase green-strength ceramics, enabling handling and machining. Desirable binder imparts high strength; is nonabrasive; free of noncombustible residual material; burns out readily at low temperatures; does not stick to die parts or pick up atmospheric moisture; readily dispersible as solution or emulsion. Keeps final product cost low. Include clays, natural gums, pitch, asphalt, alginates, glues, thermoplastic resins, silicates dextrin , waxes , starches lignosulfonates or lignin, microcrystalline cellulose and cellulose derivatives. Polymers, such polyvinyl alcohol (PVA) or polyvinyl butyral (PVB) are used as binders for advanced ceramics.

Cerium Oxide (CeO₂)

Use in medical tubing glass for UV protection and in color TV face plates for antibrowning. Used in optical filters to reduce UV haze and for UV protection in pink ophthalmic glass. Used in gamma radiation shielding glasses and as major constituent in glass polishing compounds. Used to stabilize alumina in alpha phase. Used as opacifier for special effects in tile industry; as replacement for tin oxide in porcelain enamels.

Citric Acid (C₆H₈O₇)

Used for rust and scale removal in metal cleaning formulations, e.g. before porcelain enameling. Dispersant for alumina.

Cobalt Oxide (Co₂O₃ ,CoO)

Coloring agent in glass, pottery and enamel, providing blue color. Used to enhance adherence of enamel coating to metal substrate. Improves quality of enamel and decreases pinholing. Usually mixed and calcined with alumina and lime, and with lead for very soft underglazes.

Copper Carbonate (CuCO₃ . Cu(OH)₂)

Introduces copper colors into glazes, especially for subtle shades under reducing conditions. High silica glass, gives copper blue; blue glaze obtained with varying amounts of copper carbonate; compound non-volatile.

Copper Oxide (Cu₂O, CuO)

Cuprous oxide (Cu2O): cubic red crystals insoluble in water, soluble in HCl, NH₄Cl and NH₄OH. Cupric oxide or black copper oxide (CuO) – insoluble in water, soluble in acids and NH₄OH. Cupric oxide is preferred in glazes, giving wide range of colors. Cuprous oxide produces blue or green glass.

Deflocculants (Dispersants)

Added to mixture of ceramics and solvent (e.g. water) to increase fluidity. Usually hydroxides of Na+, K+, NH₄+, or salts that hydrolyze to bases (e.g. sodium carbonate or sodium silicate) or alkali salts of organic materials (e.g. pyrogallic acid, tannic acid, humic acid, starch). Sodium salts of polyphosphate glasses are efficient deflocculants, providing very fluid slips at relatively low pH and high solids content.

Lubricants

Facilitate flow in low-plasticity materials during formation of dense compacts under pressure. Especially useful in dry pressing. Proper lubrication of die and powders to be pressed equalizes pressure in pressed component. Lubricants reduce friction between particles and die surfaces, enhancing density, lowering forming pressures and easing ejection. Include alginates, camphor, alcohols, kerosene-lard oil, lignosulfonates, methyl cellulose, mineral oils, polyvinyl acetate, polyvinyl alcohol, starches, dispersed stearates, stearic acid and stearates, wax emulsions, solid waxes.

Manganese Oxide (MnO)

Used in ferromagnetic ferrites as primary constituent of zinc-manganese type. A major constituent of computer memory core ferrites.

Polyethylene Glycols

Non-volatile liquids and solids. Dissolve in water to form transparent solutions; also soluble in many organic solvents. Used as components of ceramic slips and glazes for manufacture of porcelain and other vitreous coatings. Improve adhesion of coatings sprayed on ceramic surface.

Sodium Carbonate (Na2CO3 , soda ash)

Used as fluxing ingredient in glass industry. Very active enamel flux, raises thermal expansion coefficient. Used as deflocculant in clay-water systems, improves workability, gives greater green and dry strength and less cracking. Reacts with massive lignite in ball clays to produce very soluble and highly effective organic dispersing agent.

Barium Carbonate (BaCO₃)

Used in manufacture of optical glass. Important ingredient in crown and flint optical glasses. Corrosive to glass refractories. In enamels, acts as flux, having lowest melting point of all alkaline earths. Improves strength, elasticity and resistance to organic acids. In leadless cast iron enamels, active flux used in sanitaryware, giving better luster and harder surface to finish. In pottery bodies, imparts better translucency. Prevents formation of scum and efflorescence in brick, tile, masonry cement, terra cotta and sewer pipe by precipitating out barium sulfate from soluble sulfates; Reduces dielectric loss in fired ware e.g. steatites, forsterites. Produces maximum flux density in hard-core permanent magnets. Component of barium titanates for electronic applications.

Barium Aluminate (3BaO^.Al₂O₃)

Used in glass batches as source of BaO in finished product. Specific compositions used for cathode coatings in vacuum tubes.

Bone Ash (~4Ca₃(PO4)₂ ^.CaCO₃)

In enamels, used as accessory opacifier. Used in glazes to produce opacity. In pottery, used in making of bone china, resulting in superior translucency and whiteness. Small amounts of bone ash in chinaware body increase fluxing action of feldspar. As opacifier in production of opal glass.

Cryolite (Na₃AlF₆)

Powerful flux with relatively low melting point. Excellent solvent due to strong reaction with SiO₂, Al₂O₃, and CaO. Bath component in electrolytic recovery of aluminum from Al₂O₃ . Fluxing power used to accelerate melting of clear glass batches, and as a source of sodium and aluminum. Used for decolorizing of glass due to formation of iron-fluorine complexes. Used in white cover-coat formulations for enamels. Included in jewelry enamel and ground-coat formulations. Used in opal glass and enamels. Efficient medium for introduction of fluorides to glass batches. Mineralizer for dental cement, quartzite, alumina, mullite; auxiliary flux for whiteware bodies; special glazes. In light bulbs used to prevent or retard blackening by tungsten. Used as filler for abrasive wheels, especially resin- and rubber-bonded types; flux coatings for welding rods.

Flint (SiO₂)

Black, gray or brown cryptocrystalline variety of quartz (dark color probably due to carbonaceous matter impurities). Calcined and ground flint is used in pottery to reduce shrinkage in drying and firing and to give body rigidity. Employed in manufacture of whiteware, e.g. fine earthenware, bone china and porcelain. Flint body, compared to other mineral silicas, gives superior transparency to hotel china body.

Flux

Material that lowers melting temperature of another system. Fluxing substances may occur as natural impurities in raw material (e.g. alkali content of clay will flux the clay) or fluxes can be separate raw materials. Typically compounds of alkali metals and alkaline-earths metals (for low-loss dielectrics). Lead and boron compounds are important fluxes for glasses, glazes and enamels. Premelted glasses or frits are used to flux clay or other bodies. Term flux also designates low melting glass used in decorating glass products or overglaze for clay ware.

Frit

Fused combination of oxides usually including silica. Used for glazing to develop more uniform coating that fires at lower temperature. Used with clay and electrolytes for coating steel, aluminum, cast iron and other metals; porcelain enamel coat used on major household appliances, sanitaryware.
Used as component for bonding grinding wheels, body flux to lower vitrification temperatures, flux for glass-decorating enamels. Used as mold lubricant in continuous casting of steel and metal extrusion.

Glass Enamel

Fine powder mix of low melting flux and calcined ceramic pigment, designed for deposition as vitrifiable coating on glass. The thermal expansion coefficient of enamel should be close (and smaller) to that of the substrate. Enamels are usually compounded for maximum acid, alkali and detergent resistance. Special enamels are used on Pyrex and low-coefficient glass. Applications include: containers, dinnerware, drinking ware, lighting goods, building panels, chalk boards and signs.

Glazes

A silicate mixture fused onto surface of ceramic body. Produces hard, glassy coating with low solubility except in strong acids or bases, impermeable to gases and liquids. Usually has highly reflective, glossy surface. By dispersing selected crystals in glaze, matte finish, opacity or color can be obtained. Design glaze to "fit" given ceramic body, in terms of processing temperature, maturity, thermal expansion, viscosity and mechanical strength.

Grog

Calcined fireclay, usually produced from new and used refractory rejects (firebrick, shapes, pottery and other burned ware). Special grog types, included in the formulation, improve physical properties of stoneware, saggers, fireclay, sanitaryware, refractories, high temperature porcelain, and other ceramics.

Gypsum (CaSO₄^. 0.5H₂O)

Calcined gypsum, prepared by heating and partially dehydrating gypsum dihydrate, CaSO4 2H2O. Rehydration brings back dihydrate, accompanied by heat up, expansion and finally "setting" to solid mass. Additive to portland cement to control early setting. Used as additives to glazes, supplying neutral, slightly soluble calcium and sulfate sulfur. Combined with soda ash, used in glass batching to replace portion of salt cake. Used for model making, low-density insulation provides green strength to mixtures of clays, nonplastic refractories and organics. Used for slip-casting molds for wide variety of ceramics products.

Lead Carbonate (2PbCO₃^.Pb(OH)₂)

Constituent of glazes, enamels and glasses. Preferred for whiteware, earthenware, and vitreous tile to other lead compounds. Presence of free lead and minor iron is detrimental, as it may cause pinholing or discoloration of the fired glaze.

Lithium Carbonate (Li₂CO₃)

Precursor of lithia flux in enamel smelter batch. Resulting enamel has smoother surface and increased gloss. Used in glass for TV tubes. In aluminum refinery baths helps to lower bath temperature and save energy in electrolysis; also, scavenges fluoride ions, minimizing effluent problem. In dinnerware glazes, used as frit component of leadless glazes.

Magnesium Carbonate (MgCO₃)

Used in production of fused MgO, additive in refractory applications, to improve high-temperature corrosion resistance to molten metal slag; as insulating powder in manufacture of sheathed heating elements. Used as flocculant for clay, improving and stabilizing set and suspension characteristics. Influences fusibility in terra-cotta glazes and acts as strong opacifying agent in enamels used for stoneware. Acts as secondary opacifier in some frits and also affects color. Introduced into glass batches to allow lower annealing temperature, higher melting rate, improved working properties, lower tendency toward devitrification.