Barium titanate crystals are used to replace quartz for electronic use. Ethylenediamine tartrate crystals may be used to replace quartz for telephone and sonar work. Quartz is harder than most minerals, being Mohs 7, and the crushed material is much used for abrasive purposes. Finely ground quartz is also used as a filler, and powdered quartz is employed as a flux in melting metals. When quartz is fused, it loses its crystalline structure and becomes a silica glass with a specific gravity of 2.2, compressive strength 210,000 lb/in 2 (1,448 MPa), tensile strength 4,000 lb/in 2 (28 MPa), Mohs hardness 5, and dielectric strength 410 V/mil (16 ϫ 10 6 V/m). The chemical formula of this material is some- times given as SiO 3 , but is really SiO 2 repeated in a lattice structure but different from that of quartz crystal. Fused quartz, or quartz glass, is used for bulbs, optical glass, crucibles, and tubes and rods in furnaces. Its softening and working temperature is about 3040°F (1671°C), and it fuses at 3193°F (1755°C). The translucent material, made from sand, has a specific gravity of 2.7, with much lower strength. It withstands rapid changes of temperature without breaking. Fused quartz made from rock crystal is transparent to vis- ible light, while fused silica is normally translucent or opaque. Vitreosil is fused quartz, containing 99.8% silica. It comes opaque, translucent, and transparent. It transmits ultraviolet and short wavelengths, has high electrical resistance, and has a coefficient of expansion about one-seventeenth that of ordinary glass. Quartz tubing for electronic use comes in round, square, hexagonal, and other shapes. The softening point is 3033°F (1667°C). Tubing as small as 0.003 in (0.008 cm), produced by Monsanto Co., is flexible and as strong as steel. Quartz fiber originally was made by extruding the molten quartz through a stream of high-pressure hot air which produced a fluffy mass of fine fibers of random lengths. Quartz fibers are now made with many differing compositions and methods of manufacture. Fibers used for wool or mat have a diameter of 39 to 591 in (1 to 15 m). Those used for continuous filament may be as small as 0.0035 in (0.009 cm). Astroquartz and Astroquartz II fiber, of JPS Glass and Industrial Fabrics, are 99.95% fused silica. The specific gravity is 2.2, tensile strength 870,000 lb/in 2 (6000 MPa), elastic modulus 10 ϫ 10 6 lb/in 2 (69,000 MPa), the dielectric strength 3.78, and the thermal expansion almost zero. It is an excellent electrical insulator. It is insoluble in water, nonhygroscopic, and resistant to halogens and most common acids but not hydrofluoric or hot phosphoric. It should not be used in strong alkali concentrations. It is used in high-temperature composites, radome and antenna applications, high-speed printed-circuit boards, and insulation blankets. 770 QUARTZ Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Materials, Their Properties and Uses Quartz yarn made from these filaments is used for weaving into tape and fabric. Quartz paper, or ceramic paper, developed by the Naval Surface Weapons Center and used to replace mica for electrical insulation, is made from quartz fiber by mixing with bentonite and sheeting on a papermaking machine. It has high dielectric strength and withstands temperatures to 3000°F (1649°C). Micro quartz is felted, fine quartz fibers for insulation. The felted material has a den- sity of 3 lb/ft 3 (48 kg/m 3 ) and is capable of service temperatures to 2000°F (1093°C). Since quartz crystallizes more slowly than many other minerals, the natural crystals may include other minerals which were crys- tallized previously. Sagenite is a form of crystalline quartz con- taining hairlike crystals crossing in a netlike manner. A variety of fibered quartz with a pale-amethyst color which shows deep red by transmitted light, found in Russia and Colorado, is called onegite. Rutilated quartz is clear quartz penetrated by rutile crystals. A smoky, dark quartz of this type is the Venushair stone. Aventurine is a form of quartz crystal containing the inclusion in the form of flakes or spangles. It comes from the Ural Mountains and from India and is prized for gems. For costume jewelry it is made synthetically in great quantities under the name of gold- stone by melting the inclusions into quartz glass. Amethyst, topaz, and many other gemstones are quartz. The golden-yellow topaz of Mexico and Brazil is a type of quartz called citrine. The yellow variety called imperial topaz in Brazil is rare, but yellow-brown stones are common. Pink topaz is also rare, but can be made by heating yellow-brown stones with a risk of breaking. Inferior-colored amethysts may also be made into yellow or orange citrine by heating. The rose quartz of South Dakota is prized in the beautiful rose color, but in the large deposits the shades may run from milky white through pale pink to deep rose-red. The best stones are used for gems, as are also the translucent pink crystals from Maine. Other grades are cut into vases, ornaments, and archi- tectural facings. Chalcedony is a cryptocrystalline quartz with a waxy luster deposited in rock veins from colloidal solution, or in concentric rings on rocks. Its fibers are biaxial instead of the uniax- ial of quartz. The chalcedony of South Dakota known as beckite fluoresces under ultraviolet light. Chalcedony was an ancient gem- stone and was used for intaglios and seals and for figurines and vases. Some chalcedony from New Mexico and Arizona is stained and cut for costume jewelry. Chrysoprase is a translucent, apple- green variety of cryptocrystalline quartz colored with hydrated nickel silicate found in Silesia. It is highly valued for mural decora- tions and as a gemstone. QUARTZ 771 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Materials, Their Properties and Uses The so-called massive topaz used as a refractory material instead of kyanite is not true topaz or quartz. The massive topaz mined in North Carolina contains about 50% Al 2 O 3 and 40 SiO 2 , with iron oxide. When calcined for refractory use, it has the same composition as kyanite. The topaz from the wolframite mines of São Paulo, Brazil, used for refractories, has a high alumina content and a high fluorine content. The purer crystals have a melting point of 3416°F (1880°C). The quartz known as cristobalite, used as a refractory, differs from ordinary quartz only in crystal structure. It has a melting point of 3140°F (1725°C). Jasper is a variety of quartz colored red with iron oxide. It is cut and polished as an orna- mental building stone. Egyptian jasper is brown with dark zones. In ancient times many of the gemstones were silica stones, and the Athiaenon stone from Cyprus was jasper of bright colors. The jasper iron ore of Michigan has an iron content of about 33% with less silica than taconite, making it easier to crush, but concentra- tion must be done by flotation, which is more expensive than the magnetic separation of taconite. Quartzite is a rock composed of quartz grains cemented together by silica. It is firm and compact and breaks with uneven, splintery fractures. Most of the quartzites used are made up of angular grains of quartz and are white or light in color with a glistening appearance. It often resembles marble, but is harder and does not effervesce in acid. Quartzite is employed for making silica brick, abrasives, and siliceous linings for tube mills. It is also rather widely used as a structural stone and as a broken stone for roads. It is found as a widely distributed common rock. Medina quartzite, from Pennsylvania, contains 97.8% silica. The melting point is about 3092°F (1700°C). QUASSIA. Also known as bitterwood. The wood of the Jamaica quassia tree, Picroena excelsa, and of the Surinam quassia, Quassia amara, of the West Indies and northern South America. The Jamaica quassia is a large tree, sometimes called bitter ash because the leaves resemble those of the common ash. The wood is yellow, light, dense, and tough. It is odorless, but has an intensively bitter taste. The wood is imported mostly as chips for the production of the extract which is used in medicine as a bitter tonic, and in insec- ticides. It is also used as an ingredient in stock-feed tonics for cattle. In tropical countries the wood is valued for furniture, as it is resistant to insects. The wood of the Surinam quassia is darker in color, heav- ier, and harder, but has similar properties. Quassin, extracted from quassia, is used to denature alcohol. 772 QUASSIA Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Materials, Their Properties and Uses QUEBRACHO. The wood of the quebracho colorado, or red que- bracho, tree, Aspidospera quebracho, found only along the west bank of the Parana and Paraguay rivers in Argentina and Paraguay. It contains about 24% tannin. The wood is exceedingly hard and has a brownish-red color, often spotted and stained almost black. Quebracho is valued as a firewood in Argentina, and is used for crossties and posts, but is too brittle for structural work. It takes a fine polish and is very durable, carvings of this wood being in perfect condition after 300 years. The density is 78 lb/ft 3 (1,250 kg/m 3 ). Quebracho extract, from the wood, is a hard, resinous, brownish-black, and extremely bitter solid containing 62% soluble tannins. One and one-tenth ton (1 metric ton) of wood yields about 551 lb (250 kg) of solid extract. The liquid extract contains 25 to 35% tannin. It is employed in tanning leather and is rapid-acting, but is seldom used alone, as it makes a dark leather. It is mixed with alum and salt, or with chestnut extract. Some extract is used in boiler compounds, but one of the larger uses has been for the treatment of oil-well-drilling muds. Aerosol Q, of American Cyanamid Co., is powdered quebracho and an organic colloid for oil-well muds. White quebracho, Schinopois lorentsii, is a smaller tree than the red quebracho, growing over a wider area of Argentina, Brazil, and Paraguay. It produces a similar tannin. Some urunday extract is produced in Argentina for export instead of quebracho. The urunday wood is red and very hard, but not as brittle as quebracho, and is valued for cabinetwork. The tannin from the wood is similar to quebracho extract. RADIOACTIVE METALS. Metallic elements which emit radiations that are capable of penetrating matter opaque to ordinary light. They give out light and appear luminous, also having an effect on photographic plates. The metal radium is the most radioactive of all the natural elements, and was much used for luminous paints for the hands of watches and instrument pointers. Because of the emission of danger- ous gamma rays, however, it has been replaced for this purpose by radioactive isotopes of other metals. These isotopes, such as cobalt 60, used as a source of gamma rays, and krypton 85, for beta rays, are marketed selectively. Radioactive metals are used in medicine, for luminous paints, for ionization, for breaking particle bonds in pow- dering minerals, for polymerization and other chemical reactions, and for various electronic applications. The metals which are naturally radioactive, such as uranium and thorium, all have high atomic weights. The radiating power is atomic and is unaffected in combinations. Radium and other radioactive metals are changing substances. Radium gives out three types of RADIOACTIVE METALS 773 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Materials, Their Properties and Uses rays; some of the other elements give out only one or two. The mea- sure of the rate of radioactivity is the curie, which is the equivalent of the radioactivity of 0.0022 lb (1 g). Each radioactive metal has a definite breakdown period, mea- sured in half-life. Actinium, which is element 89, has a half-life of 21.7 years. It emits alpha particles to decay to actinium K, which is the radioactive isotope of francium, and then emits beta particles. Radioactive metals break down successively into other elements. By comparison of changing atomic weights, it has been deduced that the metal lead is the ultimate product, and uranium the parent metal under existing stability conditions. But heavier metals, now no longer stable under present conditions, have been produced syn- thetically, notably plutonium. The heavy element 103 was first pro- duced in 1961 and named lawrencium in honor of the inventor of the cyclotron. Not all radiation produces radioactive materials, and by controlled radiation useful elements may be introduced into alloys in a manner not possible by metallurgy. The crystal lattice of an alloy can be expanded, or atoms displaced in the lattice, thus altering the properties of the alloy. In like manner, the molecules of plastics may be cross-linked or otherwise modified by the applica- tion of radiation. For example, ethylene bottles may be irradiated after blowing to give higher strength and stiffness. Radioactive iso- topes are also used widely in chemistry and in medicine and as sources of electric power. RADIUM. The best-known radioactive metal, symbol Ra, scattered in minute quantities throughout almost all classes of rocks, but com- mercially obtainable only from the uranium ores monazite, carnotite, and uraninite. It is a breakdown product, and it disinte- grates with a half-life of 1,590 years. The metal is white, but it tar- nishes rapidly in air. The melting point is about 1292°F (700°C). It was discovered in 1898 by Curie, and the original source was from the pitchblende of the Sudetenland area of Austria after extraction of thorium oxide, but most of the present supply comes from the carnotite of Zaire and from the pitchblende of western Canada. One gram of radium and 7,800 lb (3,538 kg) of uranium are obtained from 370 tons (336 metric tons) of pitchblende. The ratio of radium to uranium in any uranium ore is about 1:3,000,000. Radium is mar- keted in the form of bromides or sulfate in tubes and is extremely radioactive in these forms. In a given interval of time, a definite proportion of the atoms break up with the expulsion of ␣, ß, and ␥ rays. When an alpha particle is emitted from radium, the atom from which it is emitted becomes a new substance, the inert gas radon, or element 86, with a half-life of 774 RADIUM Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Materials, Their Properties and Uses 3.82 days. During its short life, it is a definite elemental gas, but it deposits as three isotopes in solid particles, decaying through polo- nium to lead. Radium is most widely known for its use in therapeutic medicine. It is also used for inspecting metal castings for flaws. Radium-beryllium powder is marketed for use as a neutron source. RAMIE. A fiber used for cordage and for various kinds of coarse fab- rics, obtained from the plant Urtica nivea, of temperate climates, and U. tenacissima, of tropical climates. The former plant has leaves white on the underside, and the latter has leaves all green. The name rhea is used in India to designate the latter species. It is also grown in China, Egypt, Brazil, and Florida. The plants grow in tall, slender stalks like hemp and belong to the nettle family. The bast fibers underneath the bark are used, but are more difficult to sepa- rate than hemp fiber owing to the insolubility of the adhesive gums. The fibers are 8 times stronger than cotton, 4 times stronger than flax, and nearly 3 times stronger than hemp. They are fine and white and are as silky as jute. They are not very flexible and are not in general suitable for weaving, but their high wet strength, absorbent qualities, and resistance to mildew make the fibers suit- able for warp yarns in wool and rayon fabrics. The yarn is used also for strong, wear-resistant canvas for such products as fire hose. The fiber is valued for marine gland packings and for twine. The compo- sition is almost pure cellulose, and the tow and waste are used for making cigarette paper. China grass is the hand-cleaned but not degummed fiber. It is stiff and greenish yellow. Grass cloth is woven fabric made in China from ramie. Swatow grass cloth, imported into the United States, is made of ramie fibers in parallel strands, not twisted into yarns. RAPE OIL. Also known as rapeseed oil, colza oil, and recently canbra oil. An oil obtained from seeds of the mustard family, Cruciferae. The genus Brassica, a form of turnip, species of which are referred to as B. campestris, B. rapa, B. napus, and B. hirta, is grown in India, Pakistan, Europe, and Canada. Rapeseed is one of the principal oil seeds of the world. It is widely used as an edible oil, for making factice, and for mixing with lubricating and cutting oils and for quenching oils. The seeds are very small, with 1 oz (28 g) having as many as 40,000 seeds. The seeds contain 40% oil. The edi- ble oil is cold-pressed and refined with caustic soda. The burning and lubricating oils are refined with sulfuric acid. The refined oil has a pungent, mustardlike odor that can be removed by deodoriza- tion. The iodine value is about 100, the specific gravity 0.915, and RAPE OIL 775 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Materials, Their Properties and Uses the flash point 455°F (235°C). The oil contains palmitic, oleic, linoleic, and stearic acids and 43 to 50% of the typical acid, erucic acid, also called brassidic acid, C 21 H 41 COOH. It has a melting point of 93°F (34°C). It occurs also in grape seed oil. For edible oils, the erucic acid is reduced, generally to less than 5%; the high-erucic-acid oils are used industrially as lubricant additives. Genetic variants with no erucic acid have also been made. Edible low-erucic-acid canola oils for food applications are made by Agro Ingredients, Inc. Colza oil is a rape oil extracted from French seed, used to mix with mineral oils to make cutting oils. The name colza now refers to any refined rape oil. Chinese colza oil, from B. campestris chinoleifera, contains the mustard volatile oil. The spe- cific gravity is 0.91, saponification value 174, and iodine number 100.3. From 15 to 20% of blown rapeseed oil is mixed with mineral oil for lubricating marine engines. Crambe seed oil, from Crambe abyssinica, an Asiatic mustard, contains 55 to 60% erucic acid. The erucic can be broken down to perlargonic acid used as a substitute for dibasic acids such as azelaic and brassylic acids. Cameline oil, called also dodder oil and German sesame oil, has the same uses as rape oil. It is from the plant Camelina sativa grown in central Europe. The seeds contain 35% oil which contains oleic and palmitic acids and erucic acid. The seed itself is high in mineral and protein content and is used in birdseed mixtures. RAPID PROTOTYPING MATERIALS. Materials used primarily to rapidly create precise models of prototype parts using computer-based systems and computer-aided-design data. They are also used to make tools and limited quantities of parts. Several systems are laser-based. Stereolithography, of 3D Systems, Inc., involves sequential curing of a liquid photopolymer on a descending platform by an ultraviolet laser beam. Two such polymers are Ciba Geigy’s Cibatool 5170 epoxy for use with helium-cadmium lasers and Cibatool 5180 for use with argon lasers. Exactomer resins, of Allied Signal, use vinyl ethers and cationic photoinitiators to start polymerization. DTM Corp. uses a low-power CO 2 laser beam to trace part outlines in a thin layer of powder and to sinter the pow- der particles. Again, layer upon layer of material is built up on a descending platform until the model is completed. Materials, called Laserite, include investment-casting wax, nylon, and polycar- bonate. This system can also be used to form iron-matrix-compos- ite tools. In this case, thermoplastic-coated carbon-steel powder particles are tacked in place and transferred to a furnace where the coating is burned off and the powder sintered to a porous shape, and the shape infiltrated with copper. A similar laser is used by Helisys 776 RAPID PROTOTYPING MATERIALS Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Materials, Their Properties and Uses Inc. in what is called laminated object manufacturing. Here the laser cuts thin paper or film, dispensed on a roll, to the part outline, and the cut pieces are deposited on a descending table until the model is completed. The materials are heat-activated, adhesive-coated, bleached kraft paper or polyester film in various colors. The paper results in a model resembling wood. The film creates water-resistant models. In fused deposition modeling, by Stratasys, Inc., a thermoplastic or wax filament from a spool is heated, extruded, and deposited in thin layers onto a base by a robot-held dispensing head. The model is built from the base up. The materials, which include machinable wax, investment-casting wax, Plastic P200 polyolefin, and nylonlike Plastic P300 and Plastic P301, are heated just sufficiently to flow, and solidify instantly upon deposition. Acrylonitrile-butadiene- styrene parts, having a tensile strength of 3,000 lb/in 2 (21 MPa), and polyester parts also have been made. A robotic extrusion system developed by IBM accepts thermoplastic pellets, including an elas- tomer and a machinable nylonlike material. In solid ground modeling, by Cubital Ltd. (Israel) and Cubital America, successive layers of a liquid photopolymer are exposed and cured by an ultraviolet lamp through a glass mask generated ionographically using toner and rep- resenting part cross sections. The exposed resin is then removed, and the cavity filled with water-soluble wax. The layer is cooled and milled to accurate thickness, and the next layer is formed. When all the layers have been built up, the wax is dissolved, leaving the model shape. Direct shell production casting, developed at the Massachusetts Institute of Technology and marketed by Soligen Technology Inc., is based on three-dimensional printing. This system bypasses the modeling stage and is used directly to make metal-infiltrated, ceramic-matrix-composite cores and molds for casting parts. A jet, similar to an ink jet but using a colloidal silica binder, sprays successive patterns of the part shape onto alumina powder, which is compacted between powder charges. When the final layer is formed, the partially consolidated shape is removed, the binder burned off, and the shape sintered and infiltrated with metal. Aluminum and stainless-steel parts have been cast using molds and cores made in this way. RARE-EARTH METALS. A group of trivalent metallic elements that occur together. They are also called rare earths, because of the diffi- culty of extracting them, not because of their rarity. They include ele- ments 57 through 71, from lanthanum to luterium, and yttrium, element 39, and thorium, element 90, because these are also together in monazite, the chief ore. The cerium metals are a group RARE-EARTH METALS 777 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Materials, Their Properties and Uses of rare-earth metals consisting of elements with atomic numbers 57 through 63, including the metal cerium. This group is also referred to as the light rare earths. The metal ytterbium (atomic number 70) also may be included in this group because of its light weight. Thorium is separated by a relatively easy process, and the others remain grouped as the cerium metals, to be extracted as metals or compounds for special purposes justifying high costs. The separate metals are regularly marketed in pellets and in 325-mesh powder of 99.9% purity for pyrophoric and electronic uses, and as oxides of 99.9% purity. Cerium metal has an iron-gray color, is only slightly harder than lead, and is malleable. It has a specific gravity of 6.77 and a melting point of 1480°F (804°C). Cerium-based pigments are being considered as alternatives to cadmium pigments for coloring plastics because of the toxicity of cadmium. After extraction of the thorium oxide from monazite, the chief rare- earth ore, the residual matter is reduced by converting the oxides to chlorides and then removing the metals by electrolysis. The product obtained is an alloy containing about 50% cerium together with lan- thanum, didymium, and the other rare-earth metals. It is usually called mischmetal, the German name for mixed metal, and its origi- nal use was for making pyrophoric alloys. Cerium standard alloy of Cerium Metals Corp. is a mischmetal containing 50 to 55% cerium, 22 to 25 lanthanum, 15 to 17 neodymium, and the balance a mixture of yttrium, terbium, illinium, praseodymium, and samarium, with 0.5 to 0.8 iron. Mischmetal is used in making aluminum alloys and in some steels and irons. In cast iron it opposes graphitization and produces a mal- leable iron. It removes the sulfur and the oxides and completely degasifies steel. In stainless steel it is used as a precipitation-harden- ing agent. An important use of mischmetal is in magnesium alloys for castings. From 3 to 4% of mischmetal is used with 0.2 to 0.6 zirco- nium, both of which refine the grain and give sound castings of com- plex shapes. The cerium metals also add heat resistance to magnesium castings. Ceria, cerium oxide, or ceric oxide, CeO 2 , is a pale-yellow, heavy powder of specific gravity 7.65, used in coloring ceramics and glass for producing distortion-free optical glass. It is used also for de-colorizing crystal glass, but when the glass contains titania, it pro- duces a canary-yellow color. Cerious oxide, Ce 2 O 3 , is a greenish powder of specific gravity 7.0 and refractive index 2.19. About 3% of the oxide in glass makes the glass completely absorbent to ultraviolet rays. It is also an excellent opacifier for ceramics. Cerium fluoride, CeF 3 , is used in arc carbons to increase brilliance. Cerious nitrate, Ce(No 3 ) 3 и 6H 2 O, is a red, crystalline powder used in gas-mantle man- 778 RARE-EARTH METALS Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Materials, Their Properties and Uses ufacture. Cerium salts are used for coloring glass. Ceric titanate, Ce(TiO 3 ) 2 , gives a golden-yellow color, and ceric molybdate gives a blue color. Neodymium has a specific gravity of 7.01 and a melting point of 1875°F (1024°C). It is used in magnesium alloys to increase strength at elevated temperatures and is used in some glasses to reduce glare. Neodymium glass, containing small amounts of neodymium oxide, is used for color television filter plates since it transmits 90% of the blue, green, and red light rays and no more than 10% of the yellow. It thus produces truer colors and sharper contrasts in the pictures and decreases the tendency toward gray tones. Neodymium is also a dopant for yttrium-aluminum-garnet, or YAG, lasers as well as for glass lasers. Praseodymium has a specific gravity of 6.77 and a melt- ing point of 1715°F (935°C). Lanthanum is a white metal, malleable and ductile, with a specific gravity of 6.16, and melts at 1688°F (919°C). Like the other cerium metals, it oxidizes easily in air and is easily soluble in acids. Lanthanum oxide, La 2 O 3 , is a white powder used for absorbing gases in vacuum tubes. Lanthanum boride, LaB 6 , is a crystalline powder used as an electron emitter for maintaining a constant, active cathode surface. It has high electrical conductivity. Didymium is not an element, but is a mixture of rare earths with- out cerium. It averages 45% La 2 O 3 ; 38 neodymium oxide, Nd 2 O 3 ; 11 praseodymium oxide, Pr 6 O 11 ; 4 samarium oxide, Sm 2 O 3 ; and other oxides. It is really the basic material from which the rare metals are produced. In glass it gives a neutral gray color, and it is used in glass for welders’ goggles, as it absorbs yellow light and reduces glare and eye fatigue. It is available as didymium carbonate, a pink powder soluble in acids; as didymium oxide, a brown acid-soluble powder; and as didymium chloride in pink lumps soluble in water and in acids. Dysprosium has a specific gravity of 8.56 and a melting point of 2700°F (1482°C). Its corrosion resistance is higher than that of other cerium metals. It also has good neutron-absorption ability, with a neutron cross section of 1,100 barns. The metal is paramagnetic. It is used in nuclear reactor control rods, in magnetic alloys, and in fer- rites for microwave use. It is also used in mercury-vapor lamps. With argon gas in the arc area, it balances the color spectrum and gives a higher light output. Samarium has a higher neutron cross section, 5,500 barns, and is used for neutron absorption in reactors. Samarium has a specific gravity of 7.54 and a melting point of 1925°F (1052°C). Terbium has a melting point of 2473°F (1356°C) and is used as a phosphor, as a catalyst, and in alloys with dysprosium and iron for magnetostrictive devices or with cobalt for magneto-optic storage devices. RARE-EARTH METALS 779 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Materials, Their Properties and Uses [...]... plasma-sprayed, or consolidated by powder metallurgy The materials have exceptional wear and corrosion resistance properties in corrosive media and in air up to 2000°F (1093°C) Typical applications are in pumps, valves, bearings, seals, and other parts for chemical process equipment Also, the materials are suited for marine and saltwater applications and for parts subject to wear in atomic energy plants REFRIGERANTS... strength of the brick is 12, 500 lb/in2 (85 MPa) This type of material can be made only in simple shapes, but is also made into rolls for roller-type furnaces Refrax FS is fused silica bonded with silicon nitride It is used for formed parts up to 23 in (58 cm) in diameter for such applications as brazing fixtures, and has dimensional stability and thermal shock resistance to 2250°F (123 2°C) Silfrax is in... powder bonded to itself by recrystallization under heat and pressure In general, parts made from them do not have binders or contain only a small percentage of stabilizing binder The intermetallic compounds, or intermetals, are marketed regularly as powders of particle size from 150 to 325 mesh for pressing into mechanical parts or for plasma-arc deposition as refractory coatings, and the powders are... and pressures for parts manufacturing However, adapting a process developed at the Georgia Institute of Technology, Advanced Engineered Materials uses magnesium or aluminum powder mixed with titanium oxide and boron oxide Ignition of the mixture initiates reaction of the oxides at temperatures above 3632°F, leaving residual magnesium oxide that can be leached out and submicrometer particles of titanium... they are lightweight and have high strength Sintered parts resist oxidation to 3000°F (1649°C) Molybdenum disilicide, MoSi2, has a crystalline structure in tetragonal prisms, a Knoop hardness of 1,240, and excellent oxidation resistance up to at least 2 912 F (1600°C) It is a potential candidate for high-temperature composites for aircraft-turbine parts The decomposition point is above 3398°F (1870°C)... (1300°C), and retains a low creep rate at this temperature and a compressive stress of 17,400 lb/in2 (120 MPa) Developed at Ames Laboratory of the U.S Department of Energy, it is made by arc melting the three elemental constituents, and can be ground into powder, pressed into shapes, and inert sintered at 2 912 to 3272°F (1600 to 1800°C) Tungsten disilicide, WSi2, is not as hard and not as resistant to oxidation... synthetic materials are much used To manufacture refractory products, powders of the raw materials are mixed and usually dry-pressed to form the desired shape REFRACTORIES Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Materials, ... are viewed as possible replacements for HCFCs and CFCs Allied Signal’s Genetron AZ-50 is an azeotropic mixture of HFC -125 and HFC-143a, and Du Pont’s Suva HP 62 is a blend of HFC -125 , HFC-134a (CF3CH2F), and HFC-143a Suva Blend-MP is a blend of HFC-152a (CHF2CH3), HCFC-22, and HCFC -124 Historically, resins is the term applied to an important group of substances obtained as gums from trees or manufactured... McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Materials, Their Properties and Uses 792 REFRACTORIES in the molten aluminum Phosphate-bonded refractories having at least 50% alumina content, relatively low density, and 3 to 5-in (76- to 127 -mm) thickness are used to thermally insulate steel ducts and bypass stacks of incinerators The silica... temperatures to 2200°F (120 4°C) Foamsil, of Pittsburgh Corning Corp., is this material Pinite, from Nevada, is a secondary material derived from the alteration of feldspar and other rocks, and it is used for kiln linings in cement plants It is a hydrous silicate of alumina and potash, and the massive material resembles steatite It will bond alone as clay does and has low shrinkage At 2057°F ( 1125 °C), the mineral . protein content and is used in birdseed mixtures. RAPID PROTOTYPING MATERIALS. Materials used primarily to rapidly create precise models of prototype parts using computer-based systems and computer-aided-design. trace part outlines in a thin layer of powder and to sinter the pow- der particles. Again, layer upon layer of material is built up on a descending platform until the model is completed. Materials, . has a half-life of 21.7 years. It emits alpha particles to decay to actinium K, which is the radioactive isotope of francium, and then emits beta particles. Radioactive metals break down successively