Materials Handbook 15th ed - G. Brady_ H. Clauser_ J. Vaccari (McGraw-Hill_ 2002) WW Part 9 ppsx

for marine engine oil call for 15 to 20% blown, refined rapeseed or peanut oil. This lubricating oil has a flash point of 350°F (177°C). Steam cylinder oil has 5 to 10% fatty acid vegetable oils, and the flash point is 450°F (232°C). Absorbed oil is a name of a combina- tion oil of E. F. Houghton & Co. which acts as both film and lubri- cant. Amlo is a trade name of a mineral oil refined wax-free, used for low-temperature lubrication. The silicones are now often used to replace lubricating oils for very high and very low temperature con- ditions, but in general the lubricating value is not high. Antioxidants used in oils to reduce oxidation and minimize sludging and acid formation are usually tin compounds such as tin dioxide, tin tetraphenyl, and tin ricinoleate. Tin dust alone also has an inhibitory action. Detergents are compounded in lubricating oils for internal combustion engines in order to prevent and break down carbon and sludge deposits. High percentages of animal or vegetable oils may be added to lubricating oils for use on textile machinery. They are called stainless oils for this purpose, since such oils wash out of the textile more easily than mineral oils do. They also give lower coefficients of friction. The high lubricating qualities of the vegetable oils without the disadvantage of gumming can be obtained with mineral oils by the addi- tion of an oiliness agent such as cetyl piperidine ricinoleate. The EP lubricants (extreme pressure) for heavy-duty gear lubrication are made with a high-quality oil compounded with a lead-sulfonated soap. For extreme high pressure and high temperatures where oils and greases oxidize, molybdenum disulfide, MoS 2 , is used alone or mixed with oils or silicones. It is a fine, black powder, available in particle sizes as small as 30 ␮in (0.75 ␮m), which adheres strongly to metal surfaces, gives a low coefficient of friction, and permits opera- tion up to 750°F (399°C), but it has an acid reaction and is corrosive to metals. MoS 2 resembles graphite but is twice as dense. The sulfur attaches itself with a weaker electron bond on one side than the other, forming laminal plates or scales in the molecular structure which tend to split off and give the sliding or lubrication action. MoS 2 may be used as a filler in nylon gears and bearings to reduce friction. It also increases the flexural strength of the plastic. MoS 2 , code- posited with and infiltrated into titanium nitride at Oak Ridge National Laboratory, can serve as a self-lubricating composite coating for engine and other moving parts. Molysulfide, of Climax Molybdenum, M o S 2 . Tungsten disulfide is also used as a lubricant in the same way as molybdenum disulfide. The electron bond of sulfur to tungsten is stronger than that to molybdenum, and it is thus more stable at high temperatures. The tungsten disulfide of GTE Corp. is a crystalline, gray-black powder with particle size from 39 to 79 ␮in (1 to 2 ␮m). 560 LUBRICATING OILS 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 Liqui-Moly, of Lockrey Co., and Molykote are molybdenum disulfide lubricants. Dry-film lubricants are usually graphite or molybdenum sulfide in a resin or volatile solution. They are sprayed on the bearing surface, and the evaporation of the solvent leaves an adherent thin film on the bearing. Polytetrafluoroethylene, which resists tem- peratures up to 500°F (260°C), is a dry-film lubricant. It is also used as an additive to lubricating oils. Krytox perfluoropolyether lubricant, from Du Pont, is like Teflon in many ways, resists heat to at least 450°F (232°C) and is used on ball bearings. Selenium disulfide, SeS 2 , will retain its lubricating qualities at temperatures to 2000°F (1093°C) and is useful for lubrication under vacuum because of its low emission of gas. Other materials used as dry lubricants are tantalum disulfide, TaS 2 , tantalum diselenide, TaSe 2 , titanium ditelluride, TiTe 2 , and zirconium diselenide, ZrSe 2 . Hydraulic fluids for the operation of presses must lubricate as well as carry the pressure. They are mostly mineral oils, but chemicals are used where high temperatures are encountered, such as in die- casting machines. Lindol HF-X, of Hoechst Celanese Corp., is a flame-resistant hydraulic fluid with a tricresyl phosphate base. Skydrol, of Monsanto Chemical Co., for aircraft hydraulic systems, is an oily ester produced from petroleum gas. The ignition point is 1050°F (566°C), and it operates at temperatures as low as Ϫ40°F (Ϫ40°C). The Fluorolube oils of Hooker Chemical are polymers of trifluorovinyl chloride fractionated to provide grades from a color- less, low-viscosity oil to an opaque, heavy grease. They have high lubricating values, are resistant to acids and alkalies, and have an operating range from 572°F (300°C) down to very low subzero temperatures. Hydraulic fluid QF-6-7009, of Dow Chemical USA, for closed systems operating from Ϫ25 to 550°F (Ϫ32 to 288°C), is a diphenyl didodecyl silane. Refrigeration oils, for lubricating refrigerating machinery, are mineral oils refined to remove all mois- ture and wax. Ansul oil, of Ansul Chemical Co., is an oil of this class which remains stable at temperatures as low as Ϫ70°F (Ϫ57°F). Hydrolube HP-5046, of Union Carbide, is a water-glycol hydraulic fluid that can be used at pressures up to 5,000 lb/in 2 (34 MPa). It has a pour point of Ϫ81°F (Ϫ63°C) and a viscosity index of 170, and it can be used over a wide temperature range with minimal effect on the bulk fluid viscosity. Environmentally acceptable hydraulic fluids are being used increasingly in agricultural equipment and other environ- mentally sensitive applications. These fluids, such as Mobil Oil’s EAL 224H, are highly biodegradable and relatively nontoxic to animal and fish life. Fluid life compares favorably with conventional hydraulic LUBRICATING OILS 561 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 fluids, and they are compatible with seal and hose materials used with mineral oils. The nature of the bearing metals often has an effect upon the action of the lubricating oil. In highly alloyed metals, some elements act as catalyzers to oxidize the oil, or the acids or moisture in the oils may act to break down the metal. In lead-bearing metals, free magnesium causes disintegration of the lead in contact with moisture. The alkali- lead metals also tend to dissolve in contact with animal or fish oils. Normally, however, none of the white bearing metals are attacked by the animal and vegetable oils used for lubrication unless there are perceptible amounts of a freely oxidizing element present. Graphite adds to the effectiveness of a lubricating oil and can be held in suspen- sion with a tannin. Graphite lubricants are used where continuous lubrication is difficult, for running in, for springs, or for bearings where heavy films are desired. The Dag Lubricants and Dag Dispersants of Acheson Colloids Co. comprise a large group of lubricants, lubricant coatings, and mold partings consisting of graphite or molybdenum sulfide in oils, resins, or solvents, usually applied by spray. Glydag is a solution of 10% graphite in glycerin, Castordag is a graphite in castor oil, Glydag B is graphite in butylene glycol, and Dag Dispersion 223 is molybdenum disulfide in an epoxy resin. Neolube, of Huron Industries, is graphite in alcohol. With these, the carrier liquid evaporates, leaving a film of graphite on the bearing. Polyphenyl ether lubricants are highly radiation-resistant. They lubricate after absorbing gamma-ray doses that solidify mineral oils. They are used as specialty lubricants under extreme high-tempera- ture conditions. There are five principal types of synthetic lubricants: polyal- phaolefins (PAOs), polyglycols, polyol esters, diesters, and phosphate esters, the PAOs being the most widely used in the United States. Compared with mineral oils or petroleum-based lubricants, the synthetics can operate over a wider temperature range [Ϫ100 to 550°F (Ϫ73 to 288°C)], reduce friction better, and are more durable. They may also reduce the risk of fire in high-tempera- ture applications. Phosphate esters containing 8 to 12% phosphorus are inherently fire-resistant. Triaryl phosphate esters have flash points from 460 to 485°F (238 to 251°C), compared with 300 to 350°F (149 to 177°C) for mineral oils. Their autoignition tempera- tures are between 950 and 1050°F (510 and 566°C), compared with 500 and 700°F (260 and 371°C) for the oils. However, the synthetics are far more costly. Tricresyl phosphate ester, once widely used, has lost appeal due to its neurotoxicity. New synthesis routes have been developed, however, to create other triaryl phosphate esters that are safer. Two such synthetics of Akzo Chemicals are isopropyl 562 LUBRICATING OILS 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 phenyl phosphates and t-butyl phenyl phosphates. Durad- 620B, of FMC Corp., is a triaryl phosphate ester of superior hydrolytic and oxidative stability. LUMINOUS PIGMENTS. Pigments used in paints to make surfaces visi- ble in the dark and in coatings for electronic purposes. They are used for signs, watch and instrument hands, airfield markings, and sig- nals. They are of two general classes. The permanent ones are the radioactive paints, which give off light without activation, and the phosphorescent paints, or fluorescent paints, which require acti- vation from an outside source of light. The radioactive paints contain a radioactive element that emits alpha and beta rays which strike the phosphors and produce visible light. Radium, sometimes used for paints for watch hands, gives a greenish-blue light, but it emits dan- gerous gamma rays. Also, the intense alpha rays of radium destroy the phosphors quickly, reducing the light. Strontium 90 gives a yellow- green light and has a long half-life of 25 years, but it emits both beta and gamma rays and is dangerous. Tritium paints, with a tritium isotope and a phosphor in the resin-solvent paint base, have a half-life of 12.5 years and require no shielding. The self-luminous phosphors for clock and instrument dials contain tritium, which gives off beta rays with only low secondary emission so that the glass or plastic covering is sufficient shielding. Other materials used are krypton 85, with a half-life of 10.27 years, promethium 147, with a half-life of 2.36 years, and thallium 204, with a half- life of 2.7 years. Fluorescent paints depend upon the ability of the chemical to absorb energy from light and to emit it again in the form of photons of light. This variety usually has a base of calcium, strontium, or barium sul- fide with traces of other metal salts to improve luminosity, and the vehicle contains a moistureproof gum or oil. Temporary luminous paints may be visible for long periods after the activating light is with- drawn. A paint activated by 5-min exposure to sunlight may absorb sufficient energy for 24 h of luminosity. Luminous wall paints used for operating rooms to eliminate shadows are made by mixing small amounts of zinc or cadmium sulfide into ordinary paints. After being activated with ultraviolet rays, they will give off light for 1.5 h. Phosphorescent paints are lower in cost than radioactive paints and may be obtained in various colors. In general, the yellow and orange phosphorescent pigments are combinations of zinc and cadmium sulfides, the green is zinc sulfide, and the violet and blue pigments are combinations of calcium and strontium sulfides. They are mar- keted in powder form to be stirred into the paint or ink vehicle, since mixing by grinding lowers the phosphorescence. The natural LUMINOUS PIGMENTS 563 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 minerals are not used, as the pigments must be of a high degree of purity, as little as a millionth part of iron, cobalt, or nickel killing the luminosity of zinc sulfide. These phosphorescent pigments are called phosphors, but technically they are incomplete phosphors; and cop- per, silver, or manganese is coprecipitated with the sulfide as an acti- vator or to change the color of the emitted light. The metals that are used as activators are called phosphorogens, and their atoms dif- fuse into the lattice of the sulfide. For fluorescent screens the phos- phors must have a rapid rate of extinguishment so that there will be no time lag in the appearance of the events. For television, electron microscope, and radar screens, the phosphors must cease to flow 0.02 s after withdrawal of excitation. They must also be of very minute particle size so as not to give a blurred image. For a white television screen, mixtures of blue zinc sulfide with silver and yellow zinc-beryl- lium silicates are used. For color television the screen is completely covered with a mixture of various colored phosphors, especially rare- earth metal combinations. For scintillation counters for gamma-ray- detection phosphors, the pulses should be of longer duration, and for this purpose crystals of cadmium or cadmium tungstate are used. Fluorescent fabrics for signal flags and luminescent clothing are impregnated with fluorescent chemicals which can be activated by an ultraviolet light that is not seen with the eye. Some fluorescent paints contain a small amount of luminous pigment to increase the vividness of the color by absorbing the ultraviolet light and emitting it as visible color. Fluorescein, made from phthalic anhydride and resorcinol, has the property of fluorescence in a solvent. Since cellulose acetate will keep it in a permanently solvent state, acetate rayon is used as the carrier fabric. Signal panels are distinguishable from a plane at great heights even through a haze, and at night they give a brilliant glow when activated with ultraviolet rays. Fluorescent paints for signs may have a white undercoat to reflect the light passing through the semitransparent pigment. In passing through the color pigments the shorter violet and blue wavelengths are changed to orange, red, and yellow hues, and the reflected visible light is greater than the original light. Uranine, the sodium salt of fluorescein, is used by fliers to mark spots in the ocean. One pound (0.45 kg) of uranine will cover 1 acre (4,047 m 2 ) of water to a bril- liant, yellowish green easily seen from the air. One part of uranine is detectable in 16ϫ10 6 parts of water. Luminous plastic for air- craft markings is coated on the inside with radioactive material to give visibility in the dark. The fluorescent pigments almost always consist of particles of a colorless resin containing a color-fluorescing dye. Two well-known dyes are Potomac Yellow and Alberta Yellow from Day-Glo Color 564 LUMINOUS PIGMENTS 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 Corp. BASF AG makes a series under the trade name Rhodamine; Sandoz Chemical markets Xylene Red B; and Bayer produces Macrolex Fluorescent Yellow 10GN. The pigment matrix is usually a mixed amino resin consisting of toluenesulfonamide, melamine, and formaldehyde resins. The fluorescent plastic of Rohm & Haas Co. is acrylic sheet containing a fluorescent dye. Lettering or designs cut from the sheet will glow brightly in the dark after exposure to light. It is used for direction signs and decorative panels. Spot-Lite Glo is a phosphorescent frit for incorporating into ceramics for luminous signs. It contains a zinc sulfide that is stable at high heats and has a long afterglow. Whitening agents, optical whiteners, or brightening agents, used to increase the whiteness of paper and textiles, are fluorescent materials that convert some of the ultraviolet of sunlight to visible light. The materials are colorless, but the additional light supplied is blue, and it neutralizes yellow discolorations and enhances the white- ness. They were first developed in Germany and called blankophors. Ultrasan, the first of the German blankophors, was a 1,3,5-triazine derivative. The M.D.A.C., of Carlisle Chemical Corp., is a methyl diethyl aminocoumarin of empirical formula C 14 H 17 O 2 N. It comes in tan-colored granules melting at 158°F (70°C), soluble in water and in acid solutions. It gives a bright-blue fluorescence in daylight and adds whiteness to fabrics and makes colors more vivid. As little as 0.001% added to soaps, detergents, or starches is effective for wool and syn- thetic fibers, but it is not suitable for cotton. It is also used to overcome yellow casts in varnishes and plastics, and in oils and waxes. Solium, of Lever Bros., used in detergents, is a whitener of this type. The DAS triazine, triazinyl diaminostilbene disulfonic acid, used with naphthyl triazole, is effective for cotton and rayon. Luminous materials also occur in nature as organic materials, with bioluminescence thought to be a form of chemiluminescence. Fireflies, bacteria, glow worms, and some luminous fish are capable of this feat. It occurs by the mixing of two substances present in the organism; one is luciferin, which oxidizes the second, an enzyme known as luciferase. The reaction produces an excited form of luciferase, which emits light when it returns to its normal state. LUTES. Adhesive substances, usually of earthy composition, deriving the name from the Latin lutum, meaning “mud.” A clay cement was used by the Romans for cementing iron posts into stone. Although lutes often contain a high percentage of silica sand or clays, the active ingredient is usually sulfur. They may also contain other reactive ingredients such as lead monoxide or magnesium compounds. Plumber’s lutes are used for pipe joints and seams and for coating LUTES 565 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 pipes to withstand high temperatures. Plaster of paris mixed with a weak glue will withstand a dull-red heat. Fat lute is pipe clay mixed with linseed oil. Spence’s metal is the name of an old lute for pipe jointing. It was made by introducing iron disulfide, zinc blende, and galena into melted sulfur. It melts at 320°F (160°C) and expands on cooling. It makes a good cast joint which is resistant to water, acids, and alkalies. It is not a metal, but is a mixture of sulfur with metallic oxides. Sulfur cements, or lutes, usually have fillers of silica or carbon to improve the strength. They are poured at about 235°F (113°C). They form a class of acid-proof cements used for ceramic pipe connections. Modern lutes for very high heat resistance do not contain elemental sulfur. Industrial lutes are used for sealing in wires and connections in electrical apparatus, and are compounded to give good bonding to ceramics and metals. A lute cement for adhering knife blades to handles is composed of magnesium acid sulfates, calcined magnesia, with fine silica or powder. The term sealant generally refers to a wide range of mineral-filled plastics formulated with a high proportion of filler for application by troweling or air gun. MADDER. Formerly the most important dyestuff with the exception of indigo. It is now largely replaced by the synthetic mauve dye alizarin. It was grown on a large scale in France and the Near East and was known by its Arabic name alizari and by the name Turkey red. Madder is the ground root of the plant Rubia tinctorum, which has been stored for a time to develop the coloring matter, the orange- red alizarin, C 14 H 18 O 4 , which is a dihydroxyanthraquinone, a powder melting at 552°F (289°C). It occurs in a madder root as the glucoside, ruberythric acid, C 26 H 28 O 14 , but is now made synthetically from anthracene. Its alkaline solution is used with mordants to give madder lakes. With aluminum and tin it gives madder red, with calcium it gives blue, and with iron it gives violet-black. Purpurin, C 14 H 18 O 5 , is also obtained from madder, but is now made synthetically. Madder gives fast colors. MAGNESIA. A fine, white powder of magnesium oxide, MgO, obtained by calcining magnesite or dolomite and refining chemi- cally. It is used in pharmaceuticals, in cosmetics, in rubbers as a scorch-resistant filler, in soaps, and in ceramics. It requires 6.5 tons (5.9 metric tons) of dolomite to yield 1 ton (0.9 metric tons) of pure magnesia powder. Particle size of the powder is 19.7 ␮in (0.5 ␮m). For chemical uses it is 99.7% minimum purity with no more than 0.06% iron oxide and 0.08 calcium oxide, and the magnesia for elec- tronic parts has a maximum of 0.03% iron oxide and 0.0025 boron. This powder is converted from magnesium hydroxide. Maglite, of 566 MADDER 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 Whittaker, Clark & Daniels, Inc., used for rubbers, is produced from seawater. Magox magnesia, of Basic Chemicals, is 98% pure MgO extracted from seawater. It comes in particle sizes to 325 mesh in high- and low-activity grades for rubber, textile, and chem- ical uses. A very pure magnesia is also produced by reducing mag- nesium nitrate. Magnesia ceramic parts, such as crucibles and refractory parts, are generally made from magnesia that is usually electrically fused and crushed from the large cubic crystals. The crystals have ductil- ity and can be bent. The particle size and shape are easily con- trolled in the crushing to fit the needs of the molded article. Pressed and sintered parts have a melting point of about 5070°F (2765°C) and can be employed to 4172°F (2300°C) in oxidizing atmospheres or to 3092°F (1700°C) in reducing atmospheres. The material is inert to molten steels and to basic slags. Magnafrax 0340, of Carborundum Co., is magnesia in the form of plates, tubes, bars, and disks. The material has a specific gravity of 3.3 and a thermal conductivity twice that of alumina. Its vitreous structure gives it about the same characteristics as a single crystal for elec- tronic purposes. Magnorite, of Norton Co., is fused magnesia in granular crystals with a melting point of 5072°F (2800°C), used for making ceramic parts and for sheathing electric heating elements. K-Grain magnesia, of Kaiser Aluminum and Chemical Corp., is 98% magnesia, containing no more than 0.4 silica. The magnesia ceramic, of Corning Inc., is 99.8% pure. The cast, pressed, or extruded parts when high-fired have a fine-grained, dense struc- ture with practically no shrinkage and a flexural strength of 15,500 lb/in 2 (107 MPa). MAGNESITE. A white to bluish-gray mineral used in the manufac- ture of bricks for basic refractory furnace linings and as an ore of magnesium. The ground, burned magnesite is a light powder, shaped into bricks at high pressure and baked in kilns. Magnesite is a magnesium carbonate, MgCo 3 , with some iron carbonate and ferric oxide. Magnesite releases carbon dioxide on heating and forms magnesia, MgO. When heated further, it forms a crystalline structure known as periclase, which has a melting point of 5070°F (3076°C) and specific gravity of 3.58. The mineral periclase occurs in nature but is rare. A crystalline form is called breunnerite. The fused magnesia made in the arc furnace is actually synthetic peri- clase. The synthetic material is in transparent crystals up to 2 in (5 cm), which are crushed to powder for thermal insulation and for making refractory parts. Magnesite in compact, earthy form or granular masses has a vitreous luster, and the color may be white, MAGNESITE 567 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 gray, yellow, or brown. Mohs hardness is 3.5 to 4.5, and the specific gravity is about 3.1. The U.S. production of crude magnesite is in Nevada, Washington, and California. The product known as dead-burned magnesite is in the form of dense particles used for refractories. It is produced by calcining mag- nesite at 2642 to 2732°F (1450 to 1500°C). Caustic magnesite is a product resulting from calcination at 1292 to 2192°F (700 to 1200°C), which leaves from 2 to 7% carbon dioxide in the material and gives sufficient cementing properties for use as a refractory cement. Beluchistan magnesite has 95 to 98% MgCO 3 , with 0.5 to 1 iron oxide. Manchurian dead-burned magnesite has 90.9% magnesia with 4 silica, and some iron oxide and alumina. Magnesite for use in producing magnesium metal should have at least 40% MgO, with not over 4.5 CaO and 2 FeO. Brucite, a nat- ural hydrated magnesium oxide found in Ontario, contains a higher percentage of magnesia than ordinary magnesite and is used for furnace linings. Austrian magnesite has from 4 to 9% iron oxide, which gives it the property of fritting together more readily. Magnesite is a valued refractory material for crucibles, furnace brick and linings, and high-temperature electrical insulation because of its basic character, chemical resistance, high softening point, and high electrical resistance. Its chief disadvantage is its low resistance to heat shock. Magnesite brick and refractory prod- ucts are marketed under a variety of trade names, such as Ritex, of General Refractories Co., and Ramix. It is also used as a covering for hot piping. The German artificial stone called Kunststein is magnesite. MAGNESIUM. A silvery-white metal, symbol Mg, which is the lightest metal that is stable under ordinary conditions and produced in quantity. One of its chief uses is as an alloying element in aluminum, zinc, lead, and other nonferrous alloys. It is also used for cathodic protection of other metals from corrosion. It is the sixth most abun- dant element, and it was originally called magnium by Sir Humphry Davy. Specific gravity is 1.74, melting point 1202°F (650°C), boiling point about 2030°F (1110°C), and electrical conduc- tivity about 40% that of copper. Ultimate tensile strengths are about 13,000 lb/in 2 (90 MPa) as cast, at least 23,000 lb/in 2 (159 MPa) for annealed sheet, and 26,000 lb/in 2 (179 MPa) for hard-rolled sheet, with corresponding elongations of about 4, 10, and 15%. The strength is somewhat higher in the forged metal. Magnesium has a close- packed hexagonal structure that makes it difficult to roll cold, and its narrow plastic range requires close control in forging. Repeated reheating causes grain growth. Sheet is usually formed at 300 to 568 MAGNESIUM 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 400°F (150 to 200°C). It is the easiest of the metals to machine. Its heat conductivity is about half that of aluminum, and it has high damping capacity. Electrolytic magnesium is usually 99.8% pure, and the metal made by the ferrosilicon-hydrogen reduction process may be 99.95% pure. Magnesium develops a corrosion-inhibiting film upon exposure to clean atmospheres and freshwater, but that film breaks down in the presence of chlorides, sulfates, and other media, necessitating corro- sion protection in many applications. Many protective treatments have been developed for this purpose. It is also rapidly attacked by mineral acids, except chromic and hydrofluoric acids, but is resis- tant to dilute alkalies; aliphatic and aromatic hydrocarbons; certain alcohols; and dry bromine, chlorine, and fluorine gases. Anodizing magnesium improves its corrosion resistance. Magnesium is valued chiefly for parts where light weight is needed. It is a major constituent in many aluminum alloys, and very light alloys have been made by alloying magnesium with lithium. Photoengraving plates made of commercially pure magnesium, or of slightly alloyed metal, are easier to etch than zinc, lighter in weight, and resistant to wear. It has also been used as a facing and shielding material in building construction; the light weight of mag- nesium gives high coverage, 1 lb (0.45 kg) of 0.005-in (0.013-cm) sheet covering 22.2 ft 2 (2 m 2 ). The pure metal ignites easily, and even when it is alloyed with other metals, the fine chips must be guarded against fire. In alloying, it cannot be mixed directly into molten metals because of flashing, but is used in the form of master alloys. The metal is not very fluid just above its melting point, and casting is done at temperatures considerably above the melting point so that there is danger of burning and formation of oxides. A small amount of beryllium added to magnesium alloys reduces the tendency of the molten metal to oxidize and burn. The solubility of beryllium in magnesium is only about 0.05%. As little as 0.001% lithium also reduces fire risk in melting and working the metal. Molten magnesium decomposes water so that green-sand molds cannot be used, as explosive hydrogen gas is liberated. For the same reason, water sprays cannot be used to extin- guish magnesium fires. The affinity of magnesium for oxygen, how- ever, makes the metal a good deoxidizer in the casting of other metals. Magnesium is produced commercially by the electrolysis of a fused chloride, or fluoride obtained either from brine or from a min- eral ore, or it can be vaporized from some ores. Much of the magne- sium produced in the United States is from brine wells of Michigan, whose brine contains 3% MgCl 2 , and from seawater. From seawater the magnesium hydroxide is precipitated, filtered, and treated with MAGNESIUM 569 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 [...]... heat-treated); T5 (artificially aged); T6 (solution heat-treated and artificially aged); and T8 (solution heat-treated, cold-worked, and artificially aged) Thus AZ91C-T6 is the designation for an alloy containing 8.7% aluminum and 0.7 zinc as the major alloying elements The letter C indicates that it is the third such alloy to be standardized, and, in this case, it is in the solution heat-treated MAGNESIUM... 300°F (1 49 C) Melamine-urea-formaldehyde resin with a lignin extender is used as an adhesive for water-resistant plywood Phenol-modified melamine-formaldehyde resin solution is used for laminating fibrous materials Highly translucent melamineformaldehyde resin is used for molding high-gloss buttons Methylolmelamine, made by alkylating a melamine-formaldehyde resin with methyl alcohol, is used for shrinkproofing... 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 576 MAGNETIC MATERIALS MAGNETIC MATERIALS Metallic and ceramic materials that become magnetized when placed in a magnetic field All magnetic materials can be classified into two broad... manganese are used as sound-damping alloys for thrust collars for jackhammers and other power tools Electrolytic manganese can be produced from low-grade ores by electrochemical methods and is 99 .9% pure The material produced from high-grade ores is designated electromanganese It comes in chips about 0.0625 in (0.16 cm) thick in sizes larger than 1 in (2.54 cm) square It is at least 99 .97 % pure, 150... ( 192 kg/m3) Hydrated magnesium carbonate is a fine, white powder called magnesia alba levis, slightly soluble in water, and used in medicine MAGNESIUM CARBONATE A colorless to white, bitter-tasting material occurring in sparkling, needle-shaped crystals of composition MgSO 4 и 7H 2 O The natural mineral is called epsomite, from Epsom Spa, Surrey, England In medicine it is called epsom salt It is used... 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 METALLIC MATERIALS 593 much as 15% can be used in poultry feed without producing a fishy taste in the eggs Most edible oil is hydrogenated and blended in margarines and shortenings... to nonferrous alloys, is marketed in crushed form containing 95 to 98 % manganese, 2 to 3 maximum iron, 1 maximum silicon, and 0.25 maximum carbon, but for the controlled addition of manganese to nonferrous metals and to high-grade steels, high purity, 99 .9% plus, electrolytic manganese metal is now used Manganese metal has very high sound-absorbing properties, and copper-manganese alloys with high percentages... used for 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 586 MANGANESE STEEL air-hardening and oil-hardening cold-work tool steels The original Hadfield manganese steel made in 1883 contained... to 2.5 It is mined in various parts of Europe, Australia, Brazil, Argentina, Ghana, Cuba, India, Canada, and the United States It is valued for glass manufacture, and when used as a decolorizer for glass, pyrolusite has been called glassmakers’ soap MANGANESE ORES Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies... gravity from 4.5 to 4 .9 Ferrimag, of Crucible Steel Co., and Cromag are ceramic magnets Strontium car- 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 MAGNETIC MATERIALS 5 79 bonate is superior . for signs may have a white undercoat to reflect the light passing through the semitransparent pigment. In passing through the color pigments the shorter violet and blue wavelengths are changed to. fabricated); O (annealed); H1 0 and H1 1 (slightly strain- hardened); H2 3, H2 4, and H2 6 (strain-hardened and partially annealed); T4 (solution heat-treated); T5 (artificially aged); T6 (solu- tion heat-treated. tiny magnets MAGNETIC MATERIALS 577 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any