Silica flour, made by grinding sand, is used in paints, as a facing for sand molds, and for making flooring blocks. Silver bond silica is water-floated silica flour of 98.5% SiO 2 , ground to 325 mesh. In zinc and lead paints it gives a hard surface. Pulverized silica, made from crushed quartz, is used to replace tripoli as an abrasive. Ultrafine silica, a white powder having spherical particles of 157 to 984 in (4 to 25 m), is made by burning silicon tetrachloride. It is used in rubber compounding, as a grease thickener, and as a flatting agent in paints. Aerosil, of Cabot Corp., is this material. Silica pow- der, of Praxair Inc., is a white, amorphous powder with maximum particle size of 1,969 nin (50 nm). Other natural amorphous silicas come in an average particle size of 59 in (1.5 m) with no particles larger than 394 in (10 m). Quso, of Philadelphia Quartz Co., is a soft, white powder with small particles, 394 to 787 nin (10 to 20 nm). It is used in cosmetics and paper coatings and as an anticaking agent in pharmaceuticals. As a filler in plastics, it gives a plasticizing action that aids extrusion. These fine silicas are also marketed as dust-free agglomerate particles which disperse easily in solution to the discrete hydrophyllic particle. Arc silica, of PPG Industries, used as a flat- ting agent in clear lacquers, is produced directly from silica sand in an arc furnace at 5432°F (3000°C). It has crystals of 0.59 in (0.015 m) agglomerated into translucent grains, 79 to 118 in (2 to 3 m). Valron, of Du Pont, originally called Estersil, is ester-coated silica powder of 0.3- to 0.4-in (8- to 10-mm) particle size, for use as a filler in silicone rubbers, printing inks, and plastics. Ludex, of the same company, is another colloidal silica with the fine particles nega- tively charged by the incorporation of a small amount of alkali. It forms a sol, or high-concentration solution, without gelling. Min-U- Sil, of Pennsylvania Glass Sand Corp., for making molded ceramics, has tiny crystalline particles. Syton, of Monsanto, is a water disper- sion of colloidal silica for treating textiles. Translucent silica particles deposited on the fibers increase the coefficient of friction, giving uni- formly high-strength yarns. A polymer-impregnated silica, Polysil, produced by Westinghouse, has twice the dielectric strength of porcelain as well as better strength. It is also cheaper to make, and its composition can be tailored to meet specific environmental and operating conditions. Silica aerogel is a fine, white, semitransparent silica powder, the grains of which have a honeycomb structure, giving extreme lightness. It has a density of 2.5 lb/ft 3 (40 kg/m 3 ) and is used as an insulating material in the walls of refrigerators, as a filler in molding plastics, as a flatting agent in paints, as a bodying agent in printing inks, and as a reinforcement for rubber. It is produced by treating sand with caustic soda to form sodium silicate and then treating with sulfuric acid to form a jellylike material called silica gel, which is washed and ground 840 SILICA 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 to a fine, dry powder. It is also called synthetic silica. Syloid is this material. It is a fluffy, white powder with a pH of 7.2. Silica hydrogel is a colorless, translucent, semisolid hydrated silica of composition SiO 2 и xH 2 O, bulking about 44 lb/ft 3 (705 kg/m 3 ). It contains 28% solids and 72 water. It becomes fluid by mixing with water and regels on standing. It is used for paper and textile coatings, ointments, and water suspensions of silica. Hi-Sil, of PPG Industries, and Santocel, of Monsanto, are silica gels. Mertone WB-2, of the same company, is silica gel used as a coating material for blueprint papers to deepen the blue and increase legibility. When silica gel is used as a pigment, the vehicle surrounds the irregular particle formation, producing greater rigidity and hardness of paint surface than when a smooth pigment is used. For insulation use, the thermal conductivity of silica gel powder is given as 0.1 Btu/(h и ft 2 и °F [0.57 W/(m 2 и K)] at Ϫ115°F (Ϫ81°C). Silicon monoxide, SiO, does not occur naturally but is made by reducing silica with carbon in the electric furnace and condensing the vapor out of contact with air. It is lighter than silica, having a specific gravity of 2.24, and is less soluble in acid. It is brown powder valued as a pigment for oil painting, as it takes up a higher percentage of oil than ochres or red lead. It combines chemically with the oil. Monox is a trade name for silicon monoxide. Fumed silica is a fine, translucent powder of the simple amorphous silica formula made by calcining ethyl silicate. It is used instead of carbon black in rubber compounding to make light-colored products, and to coagulate oil slicks on water so that they can be burned off. It is often called white carbon, but the “white carbon black” of Cabot Corp. called Cab-O-Sil, used for rubber, is a silica powder made from silicon tetrachloride. Cab-O-Sil EH5, a fumed colloidal form, is used as a thickener in resin coatings. The thermal expansion of amorphous fused silica is only about one-eighth that of alumina. Refractory ceramic parts made from it can be heated to 2000°F (1093°C) and cooled rapidly to subzero temperatures with- out fracture. QLF silicon oxide, of Airco Coating Technology, is a vapor-deposited barrier coating for resistance to oxygen and moisture in paperboard/polyethylene laminate products. SILICON. A metallic element, symbol Si, used chiefly in its combined forms. Pure silicon metal is used in transistors, rectifiers, and elec- tronic devices. It is a semiconductor and is superior to germanium for transistors, as it withstands temperatures to 300°F (149°C) and will carry more power. Rectifiers made with silicon instead of selenium can be smaller and will withstand higher temperatures. Its melting point when pure is about 2615°F (1434°C), but it readily dissolves in molten metals. It is never found free in nature, but combined with oxygen, it forms silica, SiO 2 , one of the most common substances in SILIICON 841 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 earth. Silicon can be obtained in three modifications. Amorphous silicon is a brown powder with a specific gravity of 2.35. It is fusible and dissolves in molten metals. When heated in air, it burns to form silica. Graphitoidal silicon consists of black, glistening spangles and is not easily oxidized and is not attacked by the common acids, but is soluble in alkalies. Crystalline silicon is obtained in dark, steel-gray globules or crystals or six-sided pyramids of specific gravity 2.4. It is less reactive than the amorphous form, but is attacked by boiling water. All these forms are obtainable by chemical reduction. High-quality crystalline silicon is the most efficient material for pho- tovoltaic cells used to generate electricity from sunlight. Amorphous silicon films are also used and are less costly, but the cells are less effi- cient because the atoms are random. Silicon is an important con- stituent of commercial metals. Molding sands are largely silica, and silicon carbides are used as abrasives. Commercial silicon is sold in the graphitoidal flake form, or as ferrosilicon, and silicon-copper. The latter forms are employed for adding silicon to iron and steels. Commercial refined silicon contains 97% pure silicon and less than 1 iron. It is used for adding silicon to aluminum alloys and for fluxing copper alloys. High-purity silicon metal, 99.95% pure, made in an arc furnace, is too expensive for common uses, but is employed for elec- tronic devices and in making silicones. For electronic use, silicon must have extremely high purity, and the pure metal is a nonconductor with a resistivity of 118,000 ⍀иin (300,000 ⍀иcm). For semiconductor use it is “doped” with other atoms, yielding electron activity for con- ducting current. Epitaxial silicon is higher purified silicon doped with exact amounts of impurities added to the crystal to give desired electronic properties. Thus, silicon doped with boron has resistivities in grades from 394 to 3,940 ⍀иin (1,000 to 10,000 ⍀иcm). Silicon ribbon of Westinghouse, for semiconductors, consists of dendritic sili- con crystals grown into thin continuous sheets 0.5 in (1.3 cm) wide, thus eliminating the need to saw slices from ingots. Pure single-crys- tal silicon ribbon of Dow Chemical is as thin as 49 in (1.25 m) and is made as a membrane formed by surface tension between two growing dendritic crystals. Float-zoned single-crystal silicon is 100 times purer than semiconductor-grade silicon. It is used in wafer form for laser and infrared detectors in guided bombs and missiles and for high-power switching devices, such as thyristors. Silicon does not possess a metallic-type lattice structure and, like antimony, is a semimetal and lacks plasticity, but is more akin to the diamond in structure. Because of its feeble electronegative nature, it has a greater tendency to form compounds with nonmetals than with metals. Silicon forms silicon hybrids of general formula Si x H 2x+2 , 842 SILIICON 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 similar to the paraffin hydrocarbons, but they are very unstable and ignite in air. But a mixture of ferrosilicon and sodium hydroxide, called hydrogenite, which yields hydrogen gas when water is added, is used for filling balloons. Silicon, like carbon, has a valence of 4 and links readily to carbon in SiC chain formations. The SiC bond acts as the CᎏC bond of organic chemistry, but silicon does not enter into animal or plant structures. SILICON BRONZE. A family of wrought copper-base alloys (C64700 to C66100) and one cast copper alloy (C87200), the wrought alloys con- taining from 0.4 to 0.8% silicon (C64700) to 2.8 to 4.0 silicon (C65600), and the cast alloy 1.0 to 5.0, along with other elements, usually lead, iron, and zinc. Other alloying elements may include manganese, alu- minum, tin, nickel, chromium, and phosphorus. The most well-known alloys are probably silicon bronze C65100, or low-silicon bronze B, and silicon bronze C65500, or high-silicon bronze A, as they were formerly called. As these names imply, they differ mainly in silicon content: 0.8 to 2.0% and 2.8 to 3.8, respectively, although the latter alloy also may contain as much as 0.6 nickel. C87200 contains at least 89% copper, 1.5 silicon, and as much as 5 zinc, 2.5 iron, 1.5 aluminum, 1.5 manganese, 1 tin, and 0.5 lead. Regardless of alloying ingredients, copper content is typically 90% or greater. Both of the common wrought alloys are quite ductile in the annealed condition, C65500 being somewhat more ductile than C65100, and both can be appreciably strengthened by cold working. Annealed, tensile yield strengths are on the order of 15,000 to 25,000 lb/in 2 (103 to 172 MPa) depending on mill form, with ulti- mate tensile strengths to about 60,000 lb/in 2 (414 MPa) and elonga- tions of 50 to 60%. Cold working can increase yield strength to as much as 70,000 lb/in 2 (483 MPa). Electrical conductivity is 12% for C65100 and 7 for C65500 relative to copper, and thermal conductiv- ity is 33 Btu/(ft и h и °F) [57 W/(m и K)] and 21 Btu/(ft и h и °F) [(36 W/m и K)], respectively. The alloys are used for hydraulic-fluid lines in aircraft, heat-exchanger tubing, marine hardware, bearing plates, and various fasteners. Silicon bronze C87200, which is suitable for centrifugal, invest- ment, and sand-, plaster-, and permanent-mold casting, also has been known by the trade names Everdur, Herculoy, and Navy Tombasil. Typical as-sand-cast tensile properties are 55,000 lb/in 2 (379 MPa) ultimate strength, 25,000 lb/in 2 (172 MPa) yield strength, and 30% elongation. Brinell hardness is 85, electrical conductivity 6%, and, relative to free-cutting brass, machinability is 40%. Uses include pump and valve parts, marine fittings, and bearings. SILICON BRONZE 843 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 SILICON CARBIDE. A bluish-black, crystalline, artificial mineral of composition SiC having a Knoop hardness of 2,500. It is used as an abrasive as loose powder, coated abrasive cloth and paper, wheels, and hones. It withstands temperatures to its decomposing point of 4175°F (2301°C) and is valued as a refractory. It retains its strength at high temperatures and has low thermal expansion, and its heat conductivity is 10 times that of fireclay. It is used for butterfly valves that control the flow of hot blasts through the tuyeres of blast fur- naces, and for high-pressure, high-temperature mechanical seals in polymer-processing reactors. Silicon-carbide particulates are used as reinforcements in aluminum-alloy composites, and silicon-carbide fibers and whiskers serve as reinforcements in emerging metal-matrix and ceramic-matrix composites. The material is also a potential matrix material for composites. Fibers are used to strengthen and toughen glass ceramics. Thermal-insulation blankets of spacecraft, which can withstand repeated exposure to tempera- tures as high as 3632°F (2000°C), comprise layers of silicon-carbide and aluminoborosilicate fabrics, and silicon-carbide thread is used to stitch the fabrics. The material also holds promise for integrated cir- cuits able to withstand higher temperatures than silicon-based ICs and for mirrors of superior mechanical, thermal, and optical proper- ties in space systems, solar collectors, and astronomical telescopes. Silicon carbide is made by fusing sand and coke at a temperature above 4000°F (2204°C). It can also be made from polymer precursors and by vapor-phase reactions. One such precursor, developed at Rensselaer Polytechnic Institute, is hydridopolycarbosilane. When it is heated to 1832°F (1000°C), 90% of the polymer converts to the carbide. Silicon carbide can also be made from wood or sawdust. The Glenn Research Center of the National Aeronautics and Space Administration reports that parts formed to net shape are pyrolyzed at 1800°F (982°C) and infiltrated with molten silicon or silicon alloys. Unlike aluminum oxide, the crystals of silicon carbide are large, and they are crushed to make the small grains used as abrasives. They are harder than aluminum oxide, and as they fracture less eas- ily, they are more suited for grinding hard cast irons and ceramics. The standard grain sizes are usually from 100 to 1,000 mesh. The crystalline powder in grain sizes from 60 to 240 mesh is also used in lightning arrestors. Carborundum, of Standard Oil Engineered Materials Co., Crystolon, of Norton Co., and Carbolon, of Exolon Co. of Canada Ltd., are trade names for silicon carbide. Many other trade names are used, such as Carborite, Carbolox, Carbolite, Carbobrant, Storalon, Sterbon, and Natalon. Ferrocarbo is a silicon carbide of Carborundum Co. in briquettes for adding to the iron cupola charge. It breaks down in the cupola above 2000°F 844 SILICON CARBIDE 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 (1093°C) to form nascent carbon and silicon for adding to the iron and also for deoxidizing. It produces more-uniform iron castings. Alsimag 539 is a fine-grained silicon carbide in the form of molded parts for brazing fixtures and furniture for kilns for high-temperature sinter- ing. The siliconized graphites produced by Pure Carbon Co., named Purebide, are graphite materials with surfaces chemically converted to silicon carbide. They have the wear resistance of silicon carbide, but retain some of the lubricity of graphite. Cost savings are achieved by machining graphite into intricate shapes before conver- sion, and subsequently impregnating parts to control leakage or mod- ify strength and/or wear properties. When used as a refractory in the form of blocks or shapes, silicon carbide may be ceramic-bonded or self-bonded by recrystallization. A standard silicon carbide brick has about 90% SiC, with up to 8 silica. The specific gravity is about 3.2. It has very high resistance to spalling. The thermal conductivity is about the same as that of mul- lite, and the coefficient of expansion is about 2.6 ϫ 10 Ϫ6 /°F (4.7 ϫ 10 Ϫ6 /K). Carbex is a silicon carbide firebrick of General Refractories Co. Refrax silicon carbide of Carborundum Co. is bonded with silicon nitride. It is used for hot-spray nozzles, for heat- resistant parts, and for lining electrolytic cells for smelting alu- minum. Silicon carbide KT, of the same company, is molded without a binder. It has 96.5% SiC with about 2.5 silica. The specific gravity is about 3.1, and it is impermeable to gases. Parts made by pressing or extruding and then sintering have a flexural strength of 24,000 lb/in 2 (165 MPa) and compressive strength of 150,000 lb/in 2 (1,034 MPa). The Knoop hardness is 2,740. It is made in rods, tubes, and molded shapes, and the rough crystal surface can be diamond-ground to a smooth, close tolerance. The operating temperature in inert atmo- spheres is to 4000°F (2204°C) and in oxidizing atmospheres to 3000°F (1649°C). For reactor parts, it has a low neutron-capture cross section and high radiation stability. The thermal conductivity is 2.5 times that of stainless steel. Crystolon R of Norton Co. is a stabilized sili- con carbide bonded by recrystallization. It has a specific gravity of 2.5, a tensile strength of 5,500 lb/in 2 (38 MPa), compressive strength of 25,000 lb/in 2 (172 MPa), and Knoop hardness of 2,500. The porosity is 21%. It is for parts subject to temperatures to 4200°F (2316°C), and it withstands high thermal shock. Crystolon C is a self-bonding sili- con carbide for coating molded graphite parts to give high wear and erosion resistance. The coatings, 0.003 to 0.020 in (0.008 to 0.051 cm) thick, produced by high-temperature chemical reaction, form an inte- gral part of the graphite surface. Vitropore filter candles, of Pall Corp., are made from rigid silicon carbide and are used to recover particulates from hot gas streams. They are especially effective in SILICON CARBIDE 845 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 recovering catalysts from fluid-catalytic-cracking processes. Diasil, of Crestel Pty of Australia, comprises low-value, crushed diamond dust in silicon carbide and is used for cutting, drilling, and grinding ceramics. For humidity protection of integrated circuits, Dow Corning and National Semiconductor developed a dual thin-film coating for appli- cation prior to plastic encasement. A silicon dioxide layer smooths circuit topology, then a silicon carbide layer serves as a barrier against moisture and activated ion impurities. Silicon carbide foam is a lightweight material made of self-bonded silicon carbide foamed into shapes. The low-density foam has a density of 17 lb/ft 3 (272 kg/m 3 ), a porosity of 90%, and tensile and compressive strengths of 30 lb/in 2 (0.2 MPa). The high-density foam of 33 lb/ft 3 (529 kg/m 3 ) has a tensile strength of 85 lb/in 2 (0.6 MPa) and compressive strength of 750 lb/in 2 (5 MPa). Its porosity is 80%. It is inert to hot chemicals and can be machined. Silicon carbide crystals are used for semiconductors at tempera- tures above 650°F (343°C). As the cathode of electronic tubes instead of a hot-wire cathode, the crystals take less power and need no warm-up. In the silicon carbide crystal, both the silicon and the crys- talline carbon have the covalent bond in which each atom has four near neighbors and is bonded to each of these with two electrons sym- metrically placed between the atoms; but since there is an electroneg- ative difference between silicon and carbon, there is some ionic bonding which results in a lesser mobility for lattice scattering. The silicon carbide semiconductor crystals of Westinghouse have less than 1 part of impurities to 10 million, and the junction is made by diffus- ing aluminum atoms into the crystal at a temperature of 3900°F (2149°C), making a p-type junction. Silicon carbide fiber is one of the most important fibers for high- temperature use. It has high strength and modulus and withstands temperatures even under oxidizing conditions up to 3272°F (1800°C), though the fibers show some deterioration in tensile strength and modulus properties at temperatures above 2192°F (1200°C). It has advantages over carbon fibers for some uses, having greater resis- tance to oxidation at high temperatures, superior compressive strength, and greater electrical resistance. SCS silicon-carbide fibers, of Textron Specialty Materials, maintain strength at tempera- tures over 2500°F (1371°C) and are useful as reinforcements for ceramic-matrix composites. There are two commercial processes for making continuous silicon carbide fibers: (1) by coating silicon carbide on either a tungsten or a carbon filament by vapor deposition to produce a large filament [3,937 to 5,906 in (100 to 150 m) in diameter], or (2) by melt-spinning an 846 SILICON CARBIDE 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 organic polymer containing silicon atoms as a precursor fiber followed by heating at an elevated temperature to produce a small filament [394 to 1,181 in (10 to 30 m) in diameter]. Fibers from the two processes differ considerably, but both are used commercially. Silicon carbide whiskers as small as 276 in (7 m) in diameter can be made by a number of different processes. Although these whiskers have the disadvantage in some applications of not being in continuous-filament form, they can be made with higher tensile strength and modulus values than continuous silicon carbide filament. SILICON CAST IRON. An acid-resistant cast iron containing a high percentage of silicon. When the amount of silicon in cast iron is above 10%, there is a notable increase in corrosion and acid resistance. The acid resistance is obtained from the compound Fe 3 Si, which contains 14.5% silicon. The usual amount of silicon in acid-resistant castings is from 12 to 15%. The alloy casts well but is hard and cannot be machined. These castings usually contain 0.75 to 0.85% carbon. Lesser amounts decrease acid resistance. Too much carbon also sepa- rates out as graphite in silicon irons, causing faulty castings. Increasing the content of silicon in iron reduces the melting point pro- gressively from 2786°F (1530°C) for pure iron to 2282°F (1250°C) for iron containing 23% silicon. A 14 to 14.5% silicon iron has a silvery- white structure, a compressive strength of about 70,000 lb/in 2 (483 MPa), and Brinell hardness 299 to 350, and it is resistant to hot sul- furic acid, nitric acid, and organic acids. Silicon irons are very wear-resistant and are valued for pump parts and for parts for chemi- cal machinery. They are marketed under many trade names. Duriron, of Duriron Co., contains 14.5% silicon and 1 carbon and manganese. The tensile strength is 16,000 lb/in 2 (110 MPa) and den- sity 0.253 lb/in 3 (7,003 kg/m 3 ). SILICON-COPPER. An alloy of silicon and copper used for adding sili- con to copper, brass, or bronze, also employed as a deoxidizer of cop- per and for making hard copper. Silicon alloys in almost any proportion with copper, and is the best commercial hardener of cop- per. A 50–50 alloy of silicon and copper is hard, extremely brittle, and black. A 10% silicon, 90 copper alloy is as brittle as glass; in this pro- portion silicon copper is used for making the addition to molten cop- per to produce hard, sound copper-alloy castings of high strength. The resulting alloy is easy to cast in the foundry and does not dross. Silicon-copper grades in 5, 10, 15, and 20% silicon are also marketed, being usually sold in slabs notched for breaking into small sections for adding to the melt. A 10% silicon-copper melts at 1500°F (816°C); a 20% alloy melts at 1152°F (623°C). SILICON-COPPER 847 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 SILICON-MANGANESE. An alloy employed for adding manganese to steel and as a deoxidizer and scavenger of steel. It usually contains 65 to 70% manganese and 12 to 25 silicon. It is graded according to the amount of carbon, generally 1, 2, and 2.5%. For making steels low in carbon and high in manganese, silicomanganese is more suitable than ferromanganese. A reverse alloy, called manganese-silicon, contains 73 to 78% silicon and 20 to 25 manganese, with 1.5 maxi- mum iron and 0.25 maximum carbon. It is used for adding man- ganese and silicon to metals without the addition of iron. Still another alloy is called ferromanganese-silicon, containing 20 to 25% manganese, about 50 silicon, and 25 to 30 iron, with only about 0.50 or less carbon. This alloy has a low melting point, giving ready solubility in the metal. Silicon-spiegel is an alloy of silicon and manganese with iron employed for making additions of silicon and manganese to open- hearth steels, and also for adding manganese to cast iron in the cupola. A typical analysis gives 25 to 30% manganese, 7 to 8 silicon, and 2 to 3 carbon. Both the silicon and manganese act as strong deox- idizers, forming a thin, fusible slag, making clean steel. SILICON NITRIDE. Si 3 N 4 is a hard, lightweight, heat- and creep-resis- tant polycrystalline ceramic having low coefficients of friction and thermal expansion and good resistance to corrosion and thermal shock. Powder, the starting stock for parts production, is commonly made by the nitridation of metallic silicon. Other methods include gas-phase ammonolysis of silicon tetrachloride, carbothermic reduc- tion of silicon dioxide, and thermal decomposition of silicon diimide. In Japan, the Isuzu Ceramic Research Institute begins with silicon powder containing by weight as much as 2% iron and up to 5 alu- mina, tantalum oxide, and yttria. The mixture is evenly dispersed, put into a mold and heated in a nitrogen atmosphere at 9-bar pres- sure and stepped temperatures of 2552 to 3362°F (1400 to 1850°C) for 3 days, forming Si 3 N 4 . Parts are usually made by reaction bonding without sintering or hot-pressing and liquid-phase sintering. Reaction bonding involves reacting a consolidated and shaped mass of pure silicon powder with nitrogen at high temperature. Resulting parts, commonly designated reaction-bonded silicon nitride (RBSN), are 15 to 20% porous, thus only moderate in strength, but essentially shrink-free, thus quite accurate as formed. Hot-pressing powder, using powder with sintering additives, followed by sintering results in parts commonly designated hot-pressed silicon nitride (HPSN). These are nearly full-density parts of more-robust mechanical performance. Density ranges from 0.111 to 0.122 lb/in 3 (3,072 to 3,377 kg/m 3 ), and the coeffi- 848 SILICON MANGANESE 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 cient of thermal expansion is 1.67 ϫ 10 Ϫ6 to 2.17 ϫ 10 Ϫ6 /°F (3 ϫ 10 Ϫ6 to 3.9 ϫ 10 Ϫ6 /K). Tensile modulus ranges from 36 ϫ 10 6 to 47 ϫ 10 6 lb/in 2 (248,000 to 324,000 MPa), and the flexural strength is 65,200 to 159,500 lb/in 2 (450 to 1,100 MPa). At 2552°F (1400°C), the modulus ranges from 25.4 ϫ 10 6 to 36.2 ϫ 10 6 lb/in 2 (175,000 to 250,000 MPa), with the flexural strength as high as 87,000 lb/in 2 (600 MPa). Noralide, of Norton Co., is an HPSN used for ball and roller bear- ings. Such bearings, used in machine-tool spindles and instruments, are noted for their light weight, low friction, and good wear and fatigue resistance. Other silicon nitride applications include valves, seals, and cutting tools. Ceralloy 147, of Ceradyne, Inc., is a cast sili- con nitride material for check-valve balls and mechanical seals. Its key features are resistance to abrasion, oxidation, corrosion, and ther- mal shock. Ceralloy 147-3 Needlelok is toughened by interlocking, needlelike grains. It has a Vickers hardness of 1,600, a tensile strength of 113,000 lb/in 2 (780 MPa), and a fracture toughness of 5,600 (lb/in 2 ) и ͙in ෆ (6.2 MPa и ͙m ෆ ), and it is used for oil-drilling applications. Roydazide, of Materials Research Corp., is for coatings as well as parts production. Silicon nitride auto-engine valves made by cold isostatic pressing at Hoechst CeramTec in Germany have demonstrated 2 to 6% fuel sav- ings over metal valves, while reducing nitrous oxide and carbon monox- ide emissions. At Japan’s Agency of Industrial Science and Technology, a 17,076-Btu/min (300-kW) ceramic turbine using Si 3 N 4 in the high-temperature sections attained 29% thermal efficiency in a 39-h test compared with 15 to 20% for conventional turbines by allowing gas inlet temperatures of 2192°F (1200°C) rather than 1652°F (900°C) or less for the conventional. Crystalline silicon nitride applied by chemical vapor deposition can protect carbon-carbon composites from oxidation at temperatures as high as 3200°F (1760°C) for up to 5 h. Silicon nitride fibers have been made by reacting silicon oxide and nitrogen in the presence of a reducing agent in an electrical- resistance furnace at 2552°F (1400°C). Discontinuous fibers are used as reinforcements in composites for specialty aircraft and elec- trical parts, and in radomes (microwave windows). Whiskers have been made by the reaction of nitrogen and a mixture of silicon and silica. For the emerging ceramic-matrix composites, silicon nitride is a potential matrix and reinforcement material. As of 2000, the silicon nitride in use was beta silicon nitride. The long, thin rods of bonded beta-silicon nitride crystals account for its high strength and toughness. At that time a new form—alpha silicon nitride—was discovered by researchers at the University of Pennsylvania in work sponsored by Air Force Office of Scientific Research. Having a similar but slightly more complicated structure SILICON NITRIDE 849 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 [...]... electronic applications, is produced in several forms Amorphous powder is made by chemical reduction and comes in particle sizes of 35 to 591 in (0.9 to 15 m) Powder made electrolytically is in dendritic crystals with particle sizes from 394 to 7,874 in (10 to 200 m) Atomized powder has spherical particles Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright... to the Terms of Use as given at the website Materials, Their Properties and Uses 852 SILICONES heat resistance than organic resins, have higher dielectric strength, and are highly water-resistant Like organic plastics, they can be compounded with plasticizers, fillers, and pigments They are usually cured by heat Because of the quartzlike structure, molded parts have exceptional thermal stability Their... All rights reserved Any use is subject to the Terms of Use as given at the website Materials, Their Properties and Uses SILVER 857 and may be as fine as 400 mesh Silver-clad powder for electric contacts is a copper powder coated with silver to economize on silver Silver flake is in the form of laminar platelets and is particularly useful for conductive and reflective coatings and circuitry The tiny,... gold, and platinum Silver plating is sometimes done with a silver-tin alloy containing 20 to 40 parts silver and the remainder tin It gives a plate having the appearance of silver but with better wear resistance Silver plates have good reflectivity at high wavelengths, but reflectivity falls off at about 13, 780 nin (350 nm), and is zero at 118,110 nin (3,000 nm), so that it is not used for heat reflectors... point of 130 0°F (704°C) It contains 15% silver, 80 copper, and 5 phosphorus Lap joints brazed with Sil-Fos have a tensile strength of 30,000 lb/in2 (207 MPa) The phosphorus in the alloy acts as a deoxidizer, and the solder requires little or no flux It is used for brazing brass, bronze, and nickel alloys The grade made by this company under the name of Easy solder contains 65% silver, melts at 132 5°F... screening smokes, or smoke screens, or they may be toxic and called blanketing clouds There are two types of smokes: those forming solid or liquid particles and those forming fogs or mists by chemical reaction White smokes, which do not have light-absorbing particles, such as carbon, are formed by chemical reaction and have the best opacity or screening action The first naval smoke screens were made... 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 SOAP 865 unless a phosphate is added Many industrial cleansers, therefore, may be balanced combinations of soaps, synthetic detergents, phosphates, or alkalies, designed for particular purposes About half of all soap is made with tallow, 25% with coconut oil, and the remainder... when used in soluble oils in the metal industry Zinc oxide, benzoic acid, and other materials are used in facial soaps with the idea of aiding complexion Excessive alkalinity in soaps dries and irritates the skin, but hand grit soap usually has 2 to 5% alkaline salts such as borax or soda ash and 10 to 25% abrasive materials Softer hand soap may contain marble flour Silicate of soda, used as a filler,... (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 SOLDER 873 A common solder is called half-and-half, or plumbers’ solder, and is composed of equal parts of lead and tin It melts at 360°F (182°C) The density is 0.318 lb/in3 (8,802 kg/m3), the tensile strength is 5,500 lb/in2 (38 MPa),... solder is the best quality of plumbers’ solder, containing 63 to 66% tin and the balance lead The earliest solders were the Roman solders called argentarium, containing equal parts of tin and lead, and tertiarium, containing 1 part tin and 2 lead Both alloys are still in use, and throughout early industrial times tertiarium was known as tinman’s solder Good-quality solders for electrical joints should . white, amorphous powder with maximum particle size of 1,969 nin (50 nm). Other natural amorphous silicas come in an average particle size of 59 in (1.5 m) with no particles larger than 394 in (10. particle sizes of 35 to 591 in (0.9 to 15 m). Powder made electrolytically is in dendritic crystals with particle sizes from 394 to 7,874 in (10 to 200 m). Atomized powder has spherical particles 856. 0.4-in (8- to 10-mm) particle size, for use as a filler in silicone rubbers, printing inks, and plastics. Ludex, of the same company, is another colloidal silica with the fine particles nega- tively