Materials Handbook 15th ed - G. Brady_ H. Clauser_ J. Vaccari (McGraw-Hill_ 2002) WW Part 13 doc

called Cab-O-Sil, used for rubber, is a silica powder made from silicon tetrachloride.. Thelatter forms are employed for adding silicon to iron and steels.Commercial refined silicon cont

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% SiO2, 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 isused 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 silicascome in an average particle size of 59
in (1.5
m) with no particleslarger 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 actionthat aids extrusion These fine silicas are also marketed as dust-freeagglomerate 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 particlesdeposited 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 asbetter strength It is also cheaper to make, and its composition can betailored 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/ft3 (40 kg/m3) and is used as an insulatingmaterial 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 areinforcement for rubber It is produced by treating sand with causticsoda to form sodium silicate and then treating with sulfuric acid to

form a jellylike material called silica gel, which is washed and ground

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

SiO2 xH2O, bulking about 44 lb/ft3(705 kg/m3) It contains 28% solidsand 72 water It becomes fluid by mixing with water and regels onstanding 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 theblue and increase legibility When silica gel is used as a pigment, thevehicle surrounds the irregular particle formation, producing greaterrigidity and hardness of paint surface than when a smooth pigment isused For insulation use, the thermal conductivity of silica gel powder

is given as 0.1 Btu/(h ft2 °F [0.57 W/(m2 K)] at 115°F (81°C)

Silicon monoxide, SiO, does not occur naturally but is made by

reducing silica with carbon in the electric furnace and condensing thevapor out of contact with air It is lighter than silica, having a specificgravity 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 calciningethyl 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 Thethermal expansion of amorphous fused silica is only about one-eighththat 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 combinedforms Pure silicon metal is used in transistors, rectifiers, and elec-tronic devices It is a semiconductor and is superior to germanium fortransistors, as it withstands temperatures to 300°F (149°C) and willcarry more power Rectifiers made with silicon instead of seleniumcan be smaller and will withstand higher temperatures Its meltingpoint when pure is about 2615°F (1434°C), but it readily dissolves inmolten metals It is never found free in nature, but combined withoxygen, it forms silica, SiO2, one of the most common substances in

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 gravity2.4 It is less reactive than the amorphous form, but is attacked byboiling 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 Amorphoussilicon 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, andsilicon carbides are used as abrasives Commercial silicon is sold inthe graphitoidal flake form, or as ferrosilicon, and silicon-copper Thelatter forms are employed for adding silicon to iron and steels.Commercial refined silicon contains 97% pure silicon and less than 1iron It is used for adding silicon to aluminum alloys and for fluxingcopper alloys High-purity silicon metal, 99.95% pure, made in an arcfurnace, is too expensive for common uses, but is employed for elec-tronic devices and in making silicones For electronic use, silicon musthave extremely high purity, and the pure metal is a nonconductorwith a resistivity of 118,000   in (300,000   cm) For semiconductoruse 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 desiredelectronic properties Thus, silicon doped with boron has resistivities

in grades from 394 to 3,940   in (1,000 to 10,000   cm) Silicon

ribbon of Westinghouse, for semiconductors, consists of dendritic

sili-con crystals grown into thin sili-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 twogrowing dendritic crystals Float-zoned single-crystal silicon is 100times purer than semiconductor-grade silicon It is used in wafer formfor laser and infrared detectors in guided bombs and missiles and forhigh-power switching devices, such as thyristors

Silicon does not possess a metallic-type lattice structure and, likeantimony, is a semimetal and lacks plasticity, but is more akin to thediamond in structure Because of its feeble electronegative nature, ithas a greater tendency to form compounds with nonmetals than with

metals Silicon forms silicon hybrids of general formula SixH2x+2,

similar to the paraffin hydrocarbons, but they are very unstable andignite 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 andlinks readily to carbon in SiC chain formations The SiC bond acts asthe CC bond of organic chemistry, but silicon does not enter intoanimal 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 siliconcontent: 0.8 to 2.0% and 2.8 to 3.8, respectively, although the latteralloy also may contain as much as 0.6 nickel C87200 contains at least89% 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 theannealed condition, C65500 being somewhat more ductile thanC65100, and both can be appreciably strengthened by cold working.Annealed, tensile yield strengths are on the order of 15,000 to25,000 lb/in2 (103 to 172 MPa) depending on mill form, with ulti-mate tensile strengths to about 60,000 lb/in2(414 MPa) and elonga-tions of 50 to 60% Cold working can increase yield strength to asmuch as 70,000 lb/in2 (483 MPa) Electrical conductivity is 12% forC65100 and 7 for C65500 relative to copper, and thermal conductiv-ity is 33 Btu/(ft h  °F) [57 W/(m  K)] and 21 Btu/(ft  h  °F) [(36W/m 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/in2

(379 MPa) ultimate strength, 25,000 lb/in2(172 MPa) yield strength,and 30% elongation Brinell hardness is 85, electrical conductivity6%, and, relative to free-cutting brass, machinability is 40% Usesinclude pump and valve parts, marine fittings, and bearings

SILICON CARBIDE. A bluish-black, crystalline, artificial mineral ofcomposition SiC having a Knoop hardness of 2,500 It is used as anabrasive as loose powder, coated abrasive cloth and paper, wheels,and hones It withstands temperatures to its decomposing point of4175°F (2301°C) and is valued as a refractory It retains its strength

at high temperatures and has low thermal expansion, and its heatconductivity is 10 times that of fireclay It is used for butterfly valvesthat control the flow of hot blasts through the tuyeres of blast fur-naces, and for high-pressure, high-temperature mechanical seals inpolymer-processing reactors Silicon-carbide particulates are used asreinforcements in aluminum-alloy composites, and silicon-carbidefibers and whiskers serve as reinforcements in emerging metal-matrix and ceramic-matrix composites The material is also apotential matrix material for composites Fibers are used tostrengthen and toughen glass ceramics Thermal-insulation blankets

of spacecraft, which can withstand repeated exposure to tures as high as 3632°F (2000°C), comprise layers of silicon-carbideand aluminoborosilicate fabrics, and silicon-carbide thread is used tostitch the fabrics The material also holds promise for integrated cir-cuits able to withstand higher temperatures than silicon-based ICsand 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 temperatureabove 4000°F (2204°C) It can also be made from polymer precursorsand by vapor-phase reactions One such precursor, developed at

tempera-Rensselaer Polytechnic Institute, is hydridopolycarbosilane When

it is heated to 1832°F (1000°C), 90% of the polymer converts to thecarbide Silicon carbide can also be made from wood or sawdust TheGlenn Research Center of the National Aeronautics and SpaceAdministration 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 Thecrystalline 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 theiron cupola charge It breaks down in the cupola above 2000°F

(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 siliconcarbide, but retain some of the lubricity of graphite Cost savings areachieved 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, siliconcarbide may be ceramic-bonded or self-bonded by recrystallization Astandard silicon carbide brick has about 90% SiC, with up to 8 silica.The specific gravity is about 3.2 It has very high resistance tospalling The thermal conductivity is about the same as that of mul-lite, and the coefficient of expansion is about 2.6  106/°F (4.7 

106/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 resistant parts, and for lining electrolytic cells for smelting alu-

heat-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 isabout 3.1, and it is impermeable to gases Parts made by pressing orextruding and then sintering have a flexural strength of 24,000 lb/in2

(165 MPa) and compressive strength of 150,000 lb/in2 (1,034 MPa).The Knoop hardness is 2,740 It is made in rods, tubes, and moldedshapes, and the rough crystal surface can be diamond-ground to asmooth, 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 sectionand 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 of2.5, a tensile strength of 5,500 lb/in2 (38 MPa), compressive strength

of 25,000 lb/in2(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 anderosion 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 recoverparticulates from hot gas streams They are especially effective in

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 grindingceramics

For humidity protection of integrated circuits, Dow Corning andNational 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 barrieragainst moisture and activated ion impurities

Silicon carbide foam is a lightweight material made of

self-bonded silicon carbide foamed into shapes The low-density foamhas a density of 17 lb/ft3 (272 kg/m3), a porosity of 90%, and tensileand compressive strengths of 30 lb/in2 (0.2 MPa) The high-densityfoam of 33 lb/ft3 (529 kg/m3) has a tensile strength of 85 lb/in2 (0.6MPa) and compressive strength of 750 lb/in2 (5 MPa) Its porosity is80% 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 fournear 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 ionicbonding which results in a lesser mobility for lattice scattering Thesilicon carbide semiconductor crystals of Westinghouse have less than

1 part of impurities to 10 million, and the junction is made by ing aluminum atoms into the crystal at a temperature of 3900°F

diffus-(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 withstandstemperatures even under oxidizing conditions up to 3272°F (1800°C),though the fibers show some deterioration in tensile strength andmodulus properties at temperatures above 2192°F (1200°C) It hasadvantages 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 tures over 2500°F (1371°C) and are useful as reinforcements forceramic-matrix composites

tempera-There are two commercial processes for making continuous siliconcarbide fibers: (1) by coating silicon carbide on either a tungsten or acarbon 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

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 twoprocesses differ considerably, but both are used commercially

Silicon carbide whiskers as small as 276
in (7
m) in diametercan be made by a number of different processes Although thesewhiskers have the disadvantage in some applications of not being incontinuous-filament form, they can be made with higher tensilestrength 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 above10%, there is a notable increase in corrosion and acid resistance Theacid resistance is obtained from the compound Fe3Si, which contains14.5% silicon The usual amount of silicon in acid-resistant castings isfrom 12 to 15% The alloy casts well but is hard and cannot bemachined 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/in2 (483MPa), 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/in2 (110 MPa) and sity 0.253 lb/in3(7,003 kg/m3)

den-SILICON-COPPER. An alloy of silicon and copper used for adding con to copper, brass, or bronze, also employed as a deoxidizer of cop-per and for making hard copper Silicon alloys in almost anyproportion with copper, and is the best commercial hardener of cop-per A 50–50 alloy of silicon and copper is hard, extremely brittle, andblack 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 Theresulting 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 sectionsfor adding to the melt A 10% silicon-copper melts at 1500°F (816°C);

sili-a 20% sili-alloy melts sili-at 1152°F (623°C)

SILICON-MANGANESE. An alloy employed for adding manganese tosteel 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 theamount of carbon, generally 1, 2, and 2.5% For making steels low incarbon 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 mum iron and 0.25 maximum carbon It is used for adding man-ganese and silicon to metals without the addition of iron Still

maxi-another alloy is called ferromanganese-silicon, containing 20 to

25% manganese, about 50 silicon, and 25 to 30 iron, with only about0.50 or less carbon This alloy has a low melting point, giving readysolubility in the metal

Silicon-spiegel is an alloy of silicon and manganese with iron

employed for making additions of silicon and manganese to hearth steels, and also for adding manganese to cast iron in thecupola 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

open-SILICON NITRIDE. Si3N4is a hard, lightweight, heat- and tant polycrystalline ceramic having low coefficients of friction andthermal expansion and good resistance to corrosion and thermalshock Powder, the starting stock for parts production, is commonlymade by the nitridation of metallic silicon Other methods includegas-phase ammonolysis of silicon tetrachloride, carbothermic reduc-tion of silicon dioxide, and thermal decomposition of silicon diimide

creep-resis-In Japan, the Isuzu Ceramic Research creep-resis-Institute begins with siliconpowder 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 Si3N4

Parts are usually made by reaction bonding without sintering orhot-pressing and liquid-phase sintering Reaction bonding involvesreacting a consolidated and shaped mass of pure silicon powder withnitrogen 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, thusquite accurate as formed Hot-pressing powder, using powder withsintering 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 Densityranges from 0.111 to 0.122 lb/in3(3,072 to 3,377 kg/m3), and the coeffi-

cient of thermal expansion is 1.67  106to 2.17  106/°F (3  106

to 3.9  106/K) Tensile modulus ranges from 36  106 to 47  106

lb/in2(248,000 to 324,000 MPa), and the flexural strength is 65,200 to159,500 lb/in2 (450 to 1,100 MPa) At 2552°F (1400°C), the modulusranges from 25.4  106 to 36.2  106lb/in2(175,000 to 250,000 MPa),with the flexural strength as high as 87,000 lb/in2(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 andfatigue 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 Itskey 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 tensilestrength of 113,000 lb/in2 (780 MPa), and a fracture toughness of5,600 (lb/in2) 兹in苶 (6.2 MPa  兹m苶), 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 atHoechst 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 Si3N4 in the high-temperature sections attained 29% thermal efficiency in a 39-htest compared with 15 to 20% for conventional turbines by allowing gasinlet temperatures of 2192°F (1200°C) rather than 1652°F (900°C) orless for the conventional Crystalline silicon nitride applied by chemicalvapor 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 resistance furnace at 2552°F (1400°C) Discontinuous fibers areused as reinforcements in composites for specialty aircraft and elec-trical parts, and in radomes (microwave windows) Whiskers havebeen made by the reaction of nitrogen and a mixture of silicon andsilica For the emerging ceramic-matrix composites, silicon nitride

electrical-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 ScientificResearch Having a similar but slightly more complicated structure

than the beta type, it combines strength, toughness, and hardnesssuperior to all other engineering ceramics on the market at the time,but it is less stable However, it can slowly convert to the beta type athigh temperature, with the newly grown crystals consuming theunstable matrix and forming long rods much like the crystals in geo-logical formations On the other hand, starting with beta siliconnitride mixed with additives, the new crystals also form long rods andcreate the same toughening effect This new form of the ceramic is40% harder than the beta type and equivalent to silicon carbide, thehardest commercial abrasive currently in use Potential uses includeaircraft bearings, cutting tools, engine valves, and other applications.

SILICON STEEL. All grades of steel contain some silicon, and mostcontain from 0.10 to 0.35% as a residual of the silicon used as a deoxi-dizer But from 3 to 5% silicon is sometimes added to increase themagnetic permeability, and larger amounts are added to obtain wear-resisting or acid-resisting properties Silicon deoxidizes steel,and up to 1.75% increases the elastic limit and impact resistancewithout loss of ductility Silicon steels within this range are used forstructural purposes and for springs, giving a tensile strength of about75,000 lb/in2 (517 MPa) and 25% elongation A common low-siliconstructural steel contains up to 0.35% silicon and 0.20 to 0.40 carbon,

but the structural silicon steels are ordinarily silicon-manganese

steel, with the manganese above 0.50% Low-carbon steels used as

structural steels are made by careful control of carbon, manganese,

and silicon and with special mill heat treatment LT-75, of Lukens

Steel, contains 0.2% carbon, up to 1.35 manganese, and 0.3 silicon.The tensile strength is 90,000 lb/in2 (621 MPa), with elongation of24% European silicon structural steels contain 0.80% or more silicon,with manganese above 0.50, and very low carbon The silicon alone is

a graphitizer and, to be most effective, needs the assistance of ganese or other carbide-forming elements It is useful in high-strength, low-alloy steels and has a wide range of utility whenused in alloy steels Considerable addition of silicon above 1.75%increases the hardness and the corrosion resistance, but reduces theductility and makes the steel brittle The lower grades can be rolled,however, and silicon-steel sheet is used for electric transformer lami-nations Silicon forms a chemical combination with the metal, form-ing an iron silicide

man-The value of silicon steel as a transformer steel was discovered by

Hadfield in 1883 Silicon increases the electrical resistivity anddecreases the hysteresis loss, making silicon steel valuable for mag-

netic circuits where alternating current is used Electrical steel, or

electric sheet, is sheet steel for armatures and transformers, in

ious grades from 1 to 4.5% silicon Hipersil is a high-permeability icon steel, and Cubex is a silicon steel containing 3% silicon which

sil-has been processed so that each cubic crystal of the steel structure isoriented with the faces symmetric, giving alignment in four directionsinstead of the normal two The steel is easily magnetized across aswell as along the sheet In transformers it lowers energy losses, andalso gives greater flexibility in designing shapes One silicon iron isdouble-oriented, with the cubic crystals of the iron in exact alignment

in all directions with the sides of the cubes parallel to the sides andends of the sheets It gives high permeability with low induction loss

Relay steel, used for relays and magnets, contains 0.5 to 2.75%

sili-con Orthosil is silicon steel sheet, 0.004 in (0.010 cm) thick, for trical laminations NK Super E-core, of NKK Corp of Japan, is a

elec-6.5% silicon electrical steel in which about half of the silicon is fused into the sheet after cold rolling

dif-Several cold-work steels and shock-resisting tool steels

tain 1 to 2.25% silicon Of the cold-work air-hardening type, A10 tains 1.25% silicon Of the cold-work oil-hardening type, O6 contains1% silicon And of the shock-resisting type, S2 contains 1%; S4 andS5, 2%; and S6, 2.25%

con-SILICONES. A group of resinlike materials in which silicon takes theplace of carbon of the organic synthetic resins Silicon is quadrivalent,like carbon But while carbon also has a valence of 2, silicon has onlyone valence of 4, and the angles of molecular formation are different.The two elements also differ in electronegativity, and silicon is an

amphoteric element, having both acid and basic properties The

molecular formation of the silicones varies from that of the common

plastics, and they are designated as inorganic plastics as distinct from the organic plastics made with carbon.

In the long-chain organic synthetic resins, the carbon atoms repeatthemselves, attaching on two sides to other carbon atoms, while in thesilicones the silicon atom alternates with an oxygen atom so that the

silicon atoms are not tied to each other The simple silane formed by

silicon and hydrogen corresponding to methane, CH4, is also a gas, as

is methane, and has the formula SiH4 But, in general, the silicones donot have the SiH radicals, but contain CH radicals as in the organicplastics Basically, silicon is treated with methyl chloride and a cata-lyst to produce a gas mixture of silanes, (CH3)x(SiCl)4x After condens-ing, three silanes are fractioned, methyl chlorosilane, dimethyldichlorosilane, and trimethyl trichlorosilane These are the common

building blocks of the siloxane chains, and by hydrolyzing them cyclic

linear polymers can be produced with acid or alkali catalysts to give

fluids, resins, and rubbers Silicone resins have, in general, more

heat resistance than organic resins, have higher dielectric strength,and are highly water-resistant Like organic plastics, they can be com-pounded with plasticizers, fillers, and pigments They are usuallycured by heat Because of the quartzlike structure, molded parts haveexceptional thermal stability Their maximum continuous-use servicetemperature is about 500°F (260°C) Special grades exceed this and go

as high as 700 to 900°F (371 to 482°C) Their heat-deflection ture for 265 lb/in2 (1.8 MPa) is 900°F (482°C) Their moisture absorp-tion is low, and resistance to petroleum products and acids is good.Nonreinforced silicones have only moderate tensile and impactstrength, but fillers and reinforcements provide substantial improve-ment Because silicones are high in cost, they are premium plasticsand are generally limited to critical or high-performance products such

tempera-as high-temperature components in the aircraft, aerospace, and tronic fields

elec-A great variety of molecular combinations are available in the cone polymers, giving resins of varying characteristics, and those hav-

sili-ing CH radicals with silicon bonds are termed organosilicon

polymers Silicon tetramethyl, Si(CH3)4, is a liquid boiling at 79°F

(26°C) Trichlorosilane, HSiCl3, is also called silicochloroform,

and it corresponds in formation to chloroform By replacing the

hydro-gen atom of this compound with an alkyl group, the

alkylchlorosi-lanes are made which have high adhesion to metals and are used in

enamels Methyl chlorosilane, (CH3)2SiCl2, is a liquid used forwaterproofing ceramic electrical insulators The material reacts withthe moisture in the ceramic, forming a water-repellent coating ofmethyl silicone resin and leaving a residue of hydrochloric acid which

is washed off

Silicone insulating varnishes will withstand continuous operating

temperatures at 350°F (177°C) or higher Silicone enamels and

paints are more resistant to chemicals than most organic plastics,and when pigmented with mineral pigments, they withstand temper-atures up to 1000°F (538°C) For lubricants the liquid silicones arecompounded with graphite or metallic soaps and operate between

50 and 500°F (46 and 260°C) The silicone liquids are stable attheir boiling points, between 750 and 800°F (399 and 427°C), andhave low vapor pressures, so that they are also used for hydraulic flu-

ids and heat-transfer media Silicone oils, used for lubrication and

as insulating and hydraulic fluids, are methyl silicone polymers Theyretain a stable viscosity at both high and low temperatures Ashydraulic fluids, they permit smaller systems to operate at highertemperatures In general, silicone oils are poor lubricants comparedwith petroleum oils, but they are used at high temperatures, 302 to392°F (150 to 200°C), low speeds, and low loads

Silicone resins are blended with alkyd resins for use in outside

paints, usually modified with a drying oil Silicone-alkyd resins are

also used for baked finishes, combining the adhesiveness and

flexibil-ity of the alkyd with the heat resistance of the silicone A phenyl

ethyl silicone is used for impregnating glass-fiber cloth for electrical

insulation, and it has about double the insulating value of ordinaryvarnished cloth

Silicone rubber is usually a long-chain dimethyl silicone which

will flow under heat and pressure, but can be vulcanized by cross-linking the linear chains Basically, it consists of alternate sili-con and oxygen atoms with two methyl groups attached to each sili-con atom The tensile strength is 300 lb/in2(2 MPa), but with fillers it

is raised to 600 lb/in2 (4 MPa) It is usually compounded with silicaand pigments It is odorless and tasteless, is resistant to most chemi-cals but not to strong acids and alkalies, resists heat to 500°F(260°C), and remains flexible to 70°F (57°C) The dielectricstrength is 500 V/mil (20  106V/m) Silicone adhesive sealants havesimilar advantages and bond well to various metals and nonmetallics.Ordinary silicone rubber has the molecular group H CH2 Si 

CH2 H in a repeating chain connected with oxygen linkages, but in

the nitrile-silicone rubber one of the end hydrogens of every fourth

group in the repeating chain is replaced by a C:N radical These polarnitrile groups give a low affinity for oils, and the rubber does notswell with oils and solvents It retains strength and flexibility at tem-peratures from 100°F (73°C) to above 500°F (260°C) and is usedfor such products as gaskets and chemical hose As lubricants, sili-cones retain a nearly constant viscosity at varying temperatures

Fluorosilicones have fluoroalkyd groups substituted for some of the

methyl groups attached to the siloxane polymer of dimethyl silicone.They are fluids, greases, and rubbers, incompatible with petroleumoils and insoluble in most solvents The greases are the fluids thick-ened with lithium soap, or with a mineral filler

SILK. The fibrous material in which the silkworm, or larva of the moth

Bombyx mori, envelops itself before passing into the chrysalis state Silk

is closely allied to cellulose and resembles wool in structure, but unlikewool, it contains no sulfur The natural silk is covered with a wax or silkglue which is removed by scouring in manufacture, leaving the glossy

fibroin, or raw-silk fiber The fibroin consists largely of the amino acid alanine, CH3CH(NH2)CO2H, which can be synthesized from pyruvic

acid Silk fabrics are used mostly for fine garments, but are also

val-ued for military powder bags because they burn without a sooty residue.The fiber is unwound from the cocoon and spun into threads Eachcocoon has from 2,000 to 3,000 yd (1,829 to 2,743 m) of thread The chief

silk-producing countries are China, Japan, India, Italy, and France.

Floss silk is a soft silk yarn practically without twist, or is the loose

waste silk produced by the worm when beginning to spin its cocoon

Hard silk is thrown silk from which the gum has not been discharged Soft silk is thrown silk yarn, degummed, dyed or undyed Souple silk

is dyed skein silk from which little gum has been discharged It is

firmer but is less lustrous Organizine silk is from the best grade of cocoons Marabout silk, used for making imitation feathers, is a white silk, twisted and dyed without discharging the gum Silk waste is silk

other than that reeled from the cocoon It includes cocoons not fit forreeling, partly unwound cocoons, broken filaments, mill waste, and dis-

carded noils It is used in the spun-silk yarn industry Noils consist of

the short, staple knotty combings

In China the cultivation of the silkworm is claimed to date back to

2640 B.C Silk was first woven in Rome about 50 B.C The eggs of the

silkworm were smuggled into Europe in the year 552 Sericulture,

or silkworm culture, is a highly developed industry The larvae, whichhave voracious appetites, are fed on mulberry leaves for 24 days, afterwhich they complete their cocoons in 3 to 4 days In 7 to 70 days theseare heated to kill the chrysalis to prevent bursting of the shell The

reeling is done by hand and by machine Wild silk is from a night

peacock moth which does not feed on the mulberry It is coarser and

stronger, but darker in color and less lustrous Tussah silk is a ety of wild silk from South China and India Charka silk is raw silk produced in Bengal on native hand-reeling machines Byssus silk is

vari-a long fiber from vari-a mussel of Svari-ardinivari-a vari-and Corsicvari-a which spins thethread to attach itself to rocks The fiber is golden brown, soft, lus-trous, and elastic, and not dissolved by acids or alkalies It was for-merly used for fine garments but is no longer obtained commercially

Canton silk is soft and fluffy, but is greenish and lacks firmness It

is from B textor and is used for weft yarns and in crepes The silk

grown in India and known as Indian silk is the finest of all silks

with fibers 0.0004 in (0.0016 cm) compared with 0.001 in (0.003 cm)for Japanese silk Before World War II Japan produced most of thesilk of the world from a cultivated moth of the tussah variety,

Antheria yama mai Shantung silk is from a tussah moth, A pernyi,

which feeds on oak leaves

The fabric called shantung is a rough-textured, plain-woven silk

with irregular fillings It is heavier and more bumpy than pongee

Grosgrain is a heavy, close-woven, corded fabric of silk It is used for

tapestry and in narrow widths for ribbons China silk, or habutai, is

an unweighted, all-silk fabric of close, firm, but uneven texture woven

of low-quality, unthrown raw silk in the gum, but it is also imitated

with textiles with a silk warp and a rayon filling The lightweight

grades of 3, 3.5, and 4 momme, or 371, 317, and 273 ft2/lb (76, 65, and

56 m2/kg), are classified as sheer fabrics and are used for impregnatedfabrics for umbrellas, raincoats, and hospital sheetings Unimpregnatedhabutai is used for curtains, lampshades, handkerchiefs, and caps.Heavyweight habutai of 12 momme [53 ft2/lb (18 m2/kg)] is used for

parachutes Pongee is a rough-textured, plain-woven, silk fabric with

irregular filling yarns It is made in natural color or dyed and, like

China silk, has a gummy feel Bolting cloth, for screening flour, is a

fine, strong, silk fabric The yarn is a fine-thread, hard-twist tramthrown in the gum from high-quality raw silk The fabric has a linoweave with two warp threads swiveled around the weft It comes invarious meshes, the finest having 166 to 200 threads/linear inch (65 to

79 threads/linear cm) It is produced on handlooms in Switzerland and

France Cartridge cloth is a thin, strong fabric for powder bags for

large-caliber guns It is made of silk waste and noils The silk is sumed in the explosion without leaving residues that would cause pre-mature explosion of the subsequent charge It also does not deteriorate

con-in storage con-in contact with the powder

The kente cloth of Ghana is a silk fabric of fine weave in delicate

col-ors, hand-woven in long, narrow strips which are sewn together to make

a pattern Satin is a heavy silk fabric with a close twill weave in which

the fine warp threads appear on the surface and the weft threads arecovered up by the peculiar twill Common satin is of eight-leaf twill, theweft intersecting and binding down the warp at every eighth pick, but

16 to 20 twills are also made In the best satins a fine quality of silk is

used It was originally called zayton, derived from the Arab name of

the Chinese trading post where the fabric was produced Varieties ofimitation satin are made with a cotton weft Satins are dyed to manycolors and much used for linings and trimmings

Qiana, of Du Pont, originally called Fiber Y, produces synthetic resin fabrics with the feel and drape of silk They are resilient and

take dyes readily The fiber is a polyamide based on an alicyclic

diamine A-Tell is a Japanese textile fiber of great silkiness It is a

polyethylene oxybenzoate, the molecule having both ester and etherlinkages Another Japanese fiber is 50% polyvinyl chloride and 50

polyvinyl alcohol Called Cordelan, it produces fabrics with the feel

of wool

SILVER. A white metal, symbol Ag, very malleable and ductile, andclassified with the precious metals It occurs in the native state, andalso combined with sulfur and chlorine Copper, lead, and zinc oresfrequently contain silver; about 70% of the production of silver is aby-product of the refining of these metals Mexico and the UnitedStates produce more than half of the silver of the world Canada,

Peru, and Bolivia are also important producers Although nearly 90%

of the silver produced in Arizona comes from copper ores, most of thatproduced in California is a by-product of gold quartz mining Silver isthe whitest of all the metals and takes a high polish, but easily tar-nishes in air because of the formation of a silver sulfide It has thehighest electrical and heat conductivity: 108% IACS relative to 100%for the copper standard and about 244 Btu/(ft h  °F) [422 W/(m  K)],respectively Cold work reduces conductivity slightly The specificgravity is 10.7, and the melting point is 1764°F (962°C) When heatedabove the boiling point (3925°F, 2163°C), it passes off as a greenvapor It is soluble in nitric acid and in hot sulfuric acid The tensilestrength of cast silver is 41,000 lb/in2(283 MPa), with a Brinell hard-ness of 59 The metal is marketed on a troy-ounce value

Since silver is a very soft metal, it is not normally used industrially

in its pure state, but is alloyed with a hardener, usually copper

Sterling silver is the name given to a standard high-grade alloy

con-taining a minimum of 925 parts in 1,000 of silver It is used for thebest tableware, jewelry, and electrical contacts This alloy of 7.5% cop-per work-hardens and requires annealing between roll passes Silvercan also be hardened by alloying with other elements The old alloy

silanca contained small amounts of zinc and antimony, but the name

sterling silver is applied only to the specific silver-copper alloy.

The standard types of commercial silver are fine silver, sterling

sil-ver, and coin silver Fine silver is at least 99.9% pure and is used for

plating, making chemicals, and for parts produced by powder

metal-lurgy Coin silver is usually an alloy of 90% silver and 10 copper, but

when actually used for coins, the composition and weight of the coinare designated by law Silver and gold are the only two metals which

fulfill all the requirements for coinage The so-called coins made

from other metals are really official tokens, corresponding to papermoney, and are not true coins Coin silver has a Vickers hardness of

148 compared with a hardness of 76 for hard-rolled pure silver It isalso used for silverware, ornaments, plating; for alloying with gold;and for electric contacts When about 2.5% of the copper in coin silver

is replaced by aluminum, the alloys can be age-hardened to Vickers

190 Silver is not an industrial metal in the ordinary sense It derivesits coinage value from its intrinsic aesthetic value for jewelry andplate, and in all civilized countries silver is a controlled metal

Silver powder, 99.9% purity, for use in coatings, integrated

cir-cuits, and other electrical and electronic applications, is produced inseveral forms Amorphous powder is made by chemical reduction andcomes in particle sizes of 35 to 591
in (0.9 to 15
m) Powder madeelectrolytically is in dendritic crystals with particle sizes from 394 to7,874
in (10 to 200
m) Atomized powder has spherical particles

and may be as fine as 400 mesh Silver-clad powder for electric

con-tacts 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,flat plates are deposited in overlapping layers permitting a metalweight saving of as much as 30% without reduction in electrical prop-

erties Nickel-coated silver powder, for contacts and other parts

made by powder metallurgy, comes in grades with 0.25, 0.5, 1, and 2%nickel by weight

The porous silver of the Pall Corp comes in sheets in standard

porosity grades from 79 to 2,165
in (2 to 55
m) It is used for

chemi-cal filtering Doré metal used for jewelry is silver containing some

gold, but the material known as doré metal, obtained as a by-product

in the production of selenium from copper slimes, is a mixture of silver,

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 reflectiv-ity 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 Silvar, of Texas

Instruments, is a silver and nickel-iron composite made by infiltratingsilver into a porous preform of the alloy It is intended for heat-sinkand thermal management applications in electronics

Silver-clad sheet, made of a cheaper nonferrous sheet with a

coat-ing of silver rolled on, is used for food processcoat-ing equipment It isresistant to organic acids but not to products containing sulfur

Silver-clad steel, used for machinery bearings, shims, and

reflec-tors, is made with pure silver bonded to the billet of steel and thenrolled For bearings, the silver is 0.010 to 0.35 in (0.025 to 0.889 cm)thick, but for reflectors the silver is only 0.001 to 0.003 in (0.003 to

0.008 cm) thick The silver-clad stainless steel of American

Cladmetals Co is stainless-steel sheet with a thin layer of silverrolled on one side for electrical conductivity

Silver iodide is a pale-yellow powder of composition AgI, best

known for its use as a nucleating agent and for seeding rain clouds

Silver nitrate, formerly known as lunar caustic, is a colorless,

crystalline, poisonous, and corrosive material of composition AgNO3

It is used for silvering mirrors, for silver plating, in indelible inks, inmedicine, and for making other silver chemicals The high-puritymaterial is made by dissolving silver in nitric acid, evaporating thesolution and crystallizing the nitrate, then redissolving the crystals indistilled water and recrystallizing It is an active oxidizing agent

Silver chloride, AgCl, is a white, granular powder used in

silver-plating solutions This salt of silver and other halogen compounds of

silver, especially silver bromide, AgBr, are used for photographic

plates and films The image cast on the plate by the lens breaks downthe atomic structure of the compound in proportion to the intensity oflight waves received and time of exposure Electrons gather on thepositive lower side of the bromide grains, causing the formation ofblack threads of silver when the film is placed in a developing solu-

tion of ferrous oxalate, FeC2O4, or other reducing chemical Thecomparative values, or tones, in the picture come from the differentcolor wavelengths in the white light and the different intensities ofincoming waves Measured in seconds, the action of violet light, theshortest wavelength, on the compound is more than 40 times greaterthan the action of the long wavelength of red light To prevent furtheraction by light, the film is transferred to a fixing bath of sodium thio-sulfate which dissolves out the unreduced silver bromide

VerdeFilm, developed by Xerox Corp for commercial printing,

requires only electrostatic sensitizing prior to use and no silver halide

or chemical developers Its use avoids wastewater disposal problemsassociated with developers, fixers, and solubilized silver salts

Silver chloride crystals in sizes up to 10 lb (4.5 kg) are grown

synthetically The crystals are cubic and can be heated and pressedinto sheets The specific gravity is 5.56, index of refraction 2.071, andmelting point 851°F (455°C) They are slightly soluble in water andsoluble in alkalies The crystals transmit more than 80% of the wave-lengths from 1,969 to 7,874
in (50 to 200
m) Cerargyrite, some-

times called horn silver, an ore of silver, found in the upper zone of

silver veins in Nevada, Colorado, Idaho, Peru, Chile, and Mexico, is asilver chloride containing theoretically 75.3% silver, with sometimessome mercury The Mohs hardness is 2.3 and specific gravity 5.8 It ismassive, resembling wax, with a pearl-gray color

Silver sulfide, Ag2S, is a gray-black, heavy powder used for ing in metal work It changes its crystal structure at about 355°F(179°C), with a drop in electrical resistivity, and is also used for

inlay-self-resetting circuit breakers Silver potassium cyanide,

KAg(CN)2, is a white, crystalline, poisonous solid used for

silver-plat-ing solutions Silver tungstate, Ag2WO4, silver manganate,

AgMnO4, and other silver compounds are produced in high-puritygrades for electronic and chemical uses

SILVER SOLDER. High-melting-point solder employed for solderingjoints where more than ordinary strength and, sometimes, electrical

conductivity are required Most silver solders are copper-zinc

braz-ing alloys with the addition of silver They may contain from 9 to

80% silver, and the color varies from brass yellow to silver white.Cadmium may also be added to lower the melting point Silver sol-

ders do not necessarily contain zinc, and may be alloys of silver andcopper in proportions arranged to obtain the desired melting pointand strength A silver solder with a relatively low melting point con-tains 65% silver, 20 copper, and 15 zinc It melts at 1280°F (693°C),has a tensile strength of 64,800 lb/in2(447 MPa), and elongation 34%.The electrical conductivity is 21% that of pure copper A solder melt-ing at 1400°F (760°C) contains 20% silver, 45 copper, and 35 zinc.

ASTM silver solder No 3 is this solder with 5% cadmium replacing

an equal amount of the zinc It is a general-purpose solder ASTM

sil-ver solder No 5 contains 50% silsil-ver, 34 copper, and 16 zinc It melts

at 1280°F (693°C) and is used for soldering electrical work and eration equipment

refrig-Any tin present in silver solders makes them brittle; lead and ironmake the solders difficult to work Silver solders are malleable andductile and have high strength They are also corrosion-resistant andare especially valuable for use in food machinery and apparatuswhere lead is objectionable Small additions of lithium to silver sol-ders increase fluidity and wetting properties, especially for brazing

stainless steels or titanium Sil-Fos, of Handy & Harmon, is a

phos-phor-silver brazing solder with a melting point of 1300°F (704°C) Itcontains 15% silver, 80 copper, and 5 phosphorus Lap joints brazedwith Sil-Fos have a tensile strength of 30,000 lb/in2 (207 MPa) Thephosphorus in the alloy acts as a deoxidizer, and the solder requireslittle 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 1325°F (718°C), and is a color match for

sterling silver TL silver solder of the same company has only 9%

silver and melts at 1600°F (871°C) It is brass yellow in color and is

used for brazing nonferrous metals Sterling silver solder, for

braz-ing sterlbraz-ing silver, contains 92.8% silver, 7 copper, and 0.2 lithium.Flow temperature is 1650°F (899°C)

A lead-silver solder recommended by Indium Corp of America to

replace tin solder contains 96% lead, 3 silver, and 1 indium It melts

at 590°F (310°C), spreads better than ordinary lead-silver solders,and gives a joint strength of 4,970 lb/in2(34 MPa) Silver-palladium

alloys for high-temperature brazing contain from 5 to 30%

palla-dium With 30%, the melting point is about 2250°F (1232°C) Thesealloys have exceptional melting and flow qualities and are used inelectronic and spacecraft applications

SISAL. The hard, strong, light-yellow to reddish fibers from the large

leaves of the sisal plant, Agave sisalana, and the henequen plant, A fourcroydes, employed for making rope, cordage, and sacking About

80% of all binder twine is normally made from sisal, but sisal ropes

have only 75% of the strength of Manila rope and are not as resistant

to moisture Sisal is a tropical plant, and grows best in semiaridregions The agave plant is native to Mexico, but most of the sisalcomes from Haiti, east Africa, and Indonesia The retting, separation,and washing of the fiber are done by machine, and less than 5% of the

weight of the leaf results in good fiber Mexican sisal is classified in

seven grades from the Superior white fiber 41 in (105 cm) in length to

Grade C-1, short-spotted fiber 24 in (60 cm) in length Yucatan sisal,

or henequen, is from the henequen plant and is reddish, stiffer, and

coarser, and is used for binder twine The Indian word henequen

means knife, from the knifelike leaves The plant is more drought-resistant than sisal Henequen also comes from Indonesia as

the spotted or reddish grades of sisal Maguey, or cantala, is from

the leaves of A cantala of India, the Philippines, and Indonesia It is

used principally for binder twine The fibers are white, brilliant, stiff,and lightweight The fibers are not as strong as sisal, but have a bet-

ter appearance and greater suppleness Zapupe fiber, of Mexico, is

from A zapupe The fiber is similar to sisal, finer and softer than

henequen Salvador sisal, of El Savador, is from A letonae The

leaves are more slender than those of Mexican sisal, and the fiber issofter and finer It is used for cordage and fabrics

The fibers of sisal are not as long or as strong as those of Manilahemp, and they swell when wet, but they are soft and are preferred

for binder twine either alone or mixed with Manila hemp Sisal fiber

is also used instead of hair in cement plasters for walls and in

lami-nated plastics Corolite is a molded plastic made with a mat of sisal fibers so as to give equal strength in all directions Agave fibers

from other varieties of the plant are used for various purposes,

notably tampico, from A rigida, which yields a stiff, hard, but pliant

fiber employed for circular power brushes, and istle, a similar stiff

brush fiber from several plants Tampico is valued for polishingwheels, as the fibers hold the grease buffing compositions, and it is

not brittle but abrades with flexibility Jaumave istle is from A.

funkiana of Mexico It yields long, uniform fibers finer than tampico.

Lechuguilla is a type of istle from A lechuguilla.

There are at least 50 species of agave in Mexico and the ern United States which yield valuable by-products in addition tofiber From some varieties saponin is obtained as a by-product From

southwest-a number of thick-lesouthwest-aved species the buds southwest-are cut off, lesouthwest-aving southwest-a csouthwest-avity

from which juice exudes This juice is fermented to produce pulque, a

liquor with a ciderlike taste containing about 7% alcohol The juice

contains a sugar, agavose, C12H22O11, which is used in medicine as a

laxative and diuretic Agava, of Agava Products, Inc., is a

dark-brown, viscous liquid extracted from the leaves of agave plants, used

as a water conditioner for boiler-water treatment It is a complex ture of sapogenines, enzymes, chlorophyllin, and polysaccharides.

mix-A fine strong fiber is obtained from the long leaves of the

pineap-ple, Ananus comosus, native to tropical America The plant is grown

chiefly for its fruit, known in South America under its Carib name

ananá and marketed widely as canned fruit and juice, preserves, and

confections Pineapple concentrate is also sold as a flavor

enhancer, as much as 10% being added to apricot, cherry, or otherfruit juices without altering the original flavor For fiber productionthe plants are spaced widely for leaf development and are harvestedbefore the leaves are fully mature The retted fibers are long, white,and of fine texture and may be woven into water-resistant fabrics

The very delicate and expensive piña cloth of the Philippines is made from pineapple fiber The fabrics of Taiwan are usually

coarser and harder

SLAG. The molten material that is drawn from the surface of iron inthe blast furnace Slag is formed from the earthy materials in the oreand from the flux Slags are produced in the melting of other metals,but iron blast-furnace slag is usually meant by the term Slag is used

in cements and concrete, for roofing, and as a ballast for roads andrailways Finely crushed slag is used in agriculture for neutralizing

acid soils Blast-furnace slag is one of the lightest concrete

aggre-gates available It has a porous structure and, when crushed, is lar It is also crushed and used for making pozzuolana and othercements Slag contains about 32% silica, 14 alumina, 47 lime, 2 mag-nesia, and small amounts of other elements It is crushed, screened,

angu-and graded for marketing Crushed slag weighs 1,900 to 2,100 lb/yd3

(1,127 to 1,245 kg/m3), or is about 30% lighter than gravel

Honey-comb slag weighs only about 30 lb/ft3(481 kg/m3) The finestgrade of commercial slag is from 0.1875 in (0.48 cm) to dust; the

run-of-crusher slag is from 4 in (10 cm) to dust Basic phosphate

slag, a by-product in the manufacture of steel from phosphatic ores,

is finely ground and sold for fertilizer It contains not less than 12%phosphoric oxide, P2O5, and is known in Europe as Thomas slag.

Foamed slag is a name used in England for honeycomb slag used for

making lightweight, heat-insulating blocks A superphosphate cement

is made in Belgium from a mixture of basic slag, slaked lime, andgypsum

SLATE. A shale having a straight cleavage Most shales are of mentary origin, and their cleavage was the result of heavy or long-continued pressure In some cases slates have been formed by theconsolidation of volcanic ashes The slaty cleavage does not usually

coincide with the original stratification Slate is of various colors:black, gray, green, and reddish It is used for electric panels, chalk-boards, slate pencils, tabletops, roofing shingles, floor tiles, and treads.

The terms flagstone and cleftstone are given to large, flat sections of

slate used for paving, but the names are also applied to blue stones cut for this purpose Slate is quarried in large blocks, and thenslabbed and split The chief slate-producing states are Pennsylvania,

sand-Vermont, Virginia, New York, and Maine Roofing slates vary in size

from 12 by 6 in (30 by 15 cm) to 24 by 14 in (61 by 36 cm), and from0.125 to 0.75 in (0.32 to 1.91 cm) in thickness, and are usually of theharder varieties The roofing slate from coal beds is black, fine-grained, and breaks into brittle thin sheets It does not have thehardness or weather resistance of true slate As late as 1915 morethan 85% of all slate mined was used for roofing, but the tonnage now

used for this purpose is small Ribbon slate, with streaks of hard

material, is inferior for all purposes Lime impurities can be detected

by the application of dilute hydrochloric acid to the edges and noting ifrapid effervescence occurs Iron is a detriment to slates for electricpurposes The average compressive strength of slate is 15,000 lb/in2

(103 MPa) and the density 175 lb/ft3 (2,804 kg/m3) Slate granules are small, graded chips used for surfacing prepared roofing Slate

flour is ground slate, largely a by-product of granule production It is

used in linoleum, caulking compounds, and asphalt surfacing

mix-tures Slate lime is an intimate mixture of finely divided, calcined

slate and lime, about 60% by weight lime to 40 slate It is employed formaking porous concrete for insulating partition walls The processconsists in adding a mixture of slate lime and powdered aluminum,zinc, or magnesium to the cement The gas generated on the addition

of water makes the cement porous

SMOKE AGENTS. Chemicals used in warfare to produce an obscuringcloud of fog to hide movements Smokes may be harmless and are

then called 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 ical reaction and have the best opacity or screening action The firstnaval smoke screens were made by limiting the admission of air tothe fuel in the boilers, and the first Army smoke pots containedmixtures of pitch, tallow, saltpeter, and gunpowder The British

chem-smoke candles contained 40% potassium nitrate, 29 pitch, 14

sul-fur, 8 borax, and 9 coal dust They gave a brown smoke, but onethat lifted too easily

Fog or military screening may be made by spraying an oil mixtureinto the air at high velocity The microscopic droplets produce an

impenetrable fog which remains for a long period White

phospho-rus gives a dense, white smoke, called WP smoke, by burning to the

pentoxide and changing to phosphoric acid in the moisture of the air

Its vapor is toxic Smoke from red phosphorus is known as RP

smoke Sulfuric trioxide, SO3, is an effective smoke producer inhumid air It is a mobile, colorless liquid vaporizing at 113°F (45°C) toform dense, white clouds with an irritating effect The French

opacite is tin tetrachloride, or stannic chloride, SnCl4, a liquidthat fumes in air When hydrated, it becomes the crystalline pentahy-drate, SnCl4 5H2O The smoke is not dense, but it is corrosive and it

penetrates gas masks Sulfuryl chloride, SO2Cl2, is a liquid thatdecomposes on contact with the air into sulfuric and hydrochloric

acids FS smoke is made with a mixture of chlorosulfonic acid and sulfur trioxide Silicon tetrachloride, SiCl4, is a colorless liquidthat boils at 140°F (60°C), and fumes in the air, forming a densecloud Mixed with ammonia vapor, it resembles a natural fog The

heavy mineral known as amang, separated from Malayan tin ore, containing ilmenite and zircon, is used in smoke screens Titanium

tetrachloride, TiCl4, is a colorless to reddish liquid boiling at 277°F(136°C) It is used for smoke screens and for skywriting from air-

planes In most air it forms dense, white fumes of titanic acid,

H2TiO3, and hydrogen chloride The commercial liquid contains about25% titanium by weight

A common smoke for airplanes is oleum It is a mixture of sulfur trioxide in sulfuric acid, which forms fuming sulfuric acid, or pyro-

sulfuric acid, H2S2O7 The dense liquid is squirted in the exhaust

manifold Zinc smoke is made with mixtures of zinc dust or zinc oxide with various chemicals to form clouds HC smoke is zinc chlo-

ride with an oxidizing agent to burn up residual carbon so that the

smoke will be gray and not black Signal smoke is colored smoke

used for ship distress signals and for aviation marking signals Theyare mixtures of a fuel, an oxidizing agent, a dye, and sometimes acooling agent to regulate the rate of burning and to prevent decompo-sition of the dye Unmistakable colors are used so that the signalsmay be distinguished from fires, and the dyes are mainlyanthraquinone derivates, together with mixtures of azo, azine, anddiphenyl-methane compounds

SNAKESKINS. The snakeskins employed for fancy leathers are in eral the skins of large, tropical snakes which are notable for thebeauty or oddity of their markings Snakeskins for shoe-upperleathers, belts, and handbags are glazed like kid and calfskin after

tanning Small cuttings are used for inlaying on novelties The leather

is very thin, but is remarkably durable and is vegetable-tanned and

finished in natural colors, or is dyed Python skins are used for ladies’ shoes Regal python skins from Borneo, the Philippines, and

the Malay Peninsula sometimes measure 30 ft (9 m) in length andhave characteristic checked markings Diamond-backed rattlesnakesare raised on snake farms in the United States The meat is canned asfood, and the skins are tanned into leather Only the back is used forleather, as the belly is colorless

SOAP. A cleansing compound produced by saponifying oils, fats, orgrease with an alkali When caustic soda is added to fat, glycerin sep-

arates out, leaving sodium oleate, Na(C17H33O2), which is soap Butsince oils and fats are mixtures of various acid glycerides, the soapsmade directly from vegetable and animal oils may be mixtures of

oleates, palmitates, linoleates, and laurates Soap oils in general,

however, are those oils which have greater proportions of nearly rated fatty acids, since the unsaturated fractions tend to oxidize toform aldehydes, ketones, or other acids, and turn rancid If an excess

satu-of alkali is used, the soap will contain free alkali; and the greater theproportion of the free alkali, the coarser is the action of the soap.ASTM standards for milled toilet soap permit only 0.17% free alkali.Soap makers now employ refined and bleached oils, which are thenhydrolyzed into fatty acids and glycerol prior to saponification withcaustic This allows the fatty acids to be distilled, resulting in a more

stable product Sodium soaps are always harder than potassium

soaps with the same fat or oil Hard sodium soaps are used for chips,

powders, and toilet soaps Soft, caustic potash soaps are the liquid,soft, and semisoft pastes Mixtures of the two are also used Soaps are

made by either the boiled process or the cold process Chip soap is

made by pouring the hot soap onto a cooled revolving cylinder fromwhich the soap is scraped in the form of chips or ribbons which are

then dried to reduce the moisture content from 30 to 10% Soap

flakes are made by passing chips through milling rollers to make

thin, polished, easily soluble flakes

Powdered soap is made from chips by further reducing the

mois-ture and grinding Milled soaps are made from chips by adding color

and perfumes to the dried chips and then passing through milling

rollers and finally pressing in molds Toilet soaps are made in this

way Soap is used widely in industrial processing, and much of theproduction has consisted of chips, flakes, powdered, granulated, andscouring powders Soaps have definite limitations of use They areunstable in acid solutions and may form insoluble salts In hardwaters they may form insoluble soaps of calcium or magnesium

unless a phosphate is added Many industrial cleansers, therefore,may be balanced combinations of soaps, synthetic detergents, phos-phates, or alkalies, designed for particular purposes.

About half of all soap is made with tallow, 25% with coconut oil,and the remainder with palm oil, greases, fish oils, olive oil, soybeanoil, or mixtures A typical soap contains 80% mixed oils and 20coconut oil, with not over 0.2 free alkali Auxiliary ingredients areused in soap to improve the color, for perfuming, as an astringent, orfor abrasive or harsh cleaning purposes Phenol or cresylic acid com-

pounds are used in antiseptic soap The soft soaps and liquid soaps

of USP grade have a therapeutic value and may be sold under tradenames

Solvents are added to industrial soaps for scouring textiles or whenused in soluble oils in the metal industry Zinc oxide, benzoic acid, andother materials are used in facial soaps with the idea of aiding com-plexion 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, also irritates the

skin Face soaps, or toilet soaps, contain coloring agents, stabilizers, and perfuming agents For special purposes, cosmetic soaps contain medications Deodorant soaps contain antibacterial chemicals, such

as triclosan, which inhibit the production of bacteria on the skin.

Experts disagree on whether antibacterial ingredients are harmful to

the skin Some, such as Dove, are a blend of detergents and soap.

Castile soap is a semitransparent soap made with olive oil Marseilles soap and Venetian soap are names for castile soap with

olive oil and soda Ordinary soft soaps used as bases for toilet soap aremade with mixtures of linseed oil and olive oil Linseed oil, however,gives a disagreeable odor Soybean oil, corn oil, and peanut oil are alsoused, although peanut oil, unless the arachidic acid is removed, makes

a hard soap Tall oil soaps are sodium soaps made from the fatty

acids of tall oil They are inferior to sodium oleate in detergency, butsuperior to sodium rosinate Many toilet soaps contain excess

unsaponified oil, fatty acid, or lanolin and are known as superfatted.

Saddle soap is any soap used for cleaning leather goods which has

the property of filling and smoothing the leather as well as cleaning.The original saddle soaps were made of palm oil, rosin, and lye, withglycerin and beeswax added Oils for the best soaps are of the nondry-

ing type High-grade soft soap for industrial use is made with

coconut or palm kernel oil with caustic potash But soft soap in pasteform is generally made of low-titer oils with caustic soda, usually lin-seed, soybean, or corn oil The lauric acid of coconut oil gives thecoconut-oil soaps their characteristic of profuse lathering, but lauric

acid affects some skins by causing itching, and soaps with highcoconut-oil content and low titer are also likely to break down in hotwater and wash ineffectively Palm-kernel oil develops free acids, andupon aging the soap acquires the odor of the oil Palm oil produces acrumbly soap It does not lather freely, but is mild to the skin Oliveoil is slow-lathering, but has good cleansing powers It is often used intextile soaps Cottonseed oil is used in some laundry soaps, but devel-ops yellow spots in the soap Corn oil with potash makes a mild softsoap Soybean oil also makes a soft soap Rosin is used to make yellow

laundry soaps ASTM standards for bar soap permit up to 25% rosin.

Sulfonated oils do not give as good cleansing action as straight oils,but are used in shampoos where it is desirable to have some oil orgreasiness Blending of various oils is necessary to obtain a balance ofdesired characteristics in a soap Hand soaps may be made with

trisodium phosphate or with disodium phosphate, or sodium

perbo-rate, NaBO3 H2O, known as perborin, all of which are crystalline substances which are dissolved in water solution Soap powder is

granular soap made in a vacuum chamber or by other special

processes It usually contains 15 to 20% soap and the balance sodium

carbonate Scouring powder is an intimate mixture of soap powder and an insoluble abrasive such as pumice Floating soaps are made light by blowing air through them while in the vats Soapless sham-

poos and tooth powders contain saponin or chemical detergents Liquid soaps are made by saponification with potassium and ammo-

nium hydroxide, or triethanolamine, to produce more-soluble

prod-ucts The floating soaps, such as Ivory from Procter & Gamble Co.,

are made by injecting air into the molten soap

SOAPSTONE. A massive variety of impure talc employed for tric panels, gas-jet trips, stove linings, tank linings, and as an abra-sive It can be cut easily and becomes very hard when heatedbecause of the loss of its combined water The waste product fromthe cutting of soapstone is ground and used for the same purposes

elec-as talc powder Steatite is a melec-assive stone rich in talc that can be

cut readily, while soapstone may be low in talc When free of ironoxide and other impurities, block steatite is used for making spacerinsulators for electronic tubes and for special electrical insulators

Block steatite suitable for electrical insulation is mined in

Montana, India, and Sardinia Steatite is also ground and moldedinto insulators It can be purified of iron and other metallic impuri-ties by electrolytic osmosis When fluxed with alkaline earthsinstead of feldspar, the molded steatite ceramics have a low lossfactor at high frequencies, and have good electrical properties athigh temperatures The white-burning refractory steatite of the

Red Sea coast of Egypt averages 60% silica and 30.5 magnesia, with

1 iron oxide and 1.5 CaO

Alberene stone, quarried in Virginia, is blue-gray The

medium-hard varieties are used for building trim and for chemical laboratorytables and sinks, and the hard varieties are employed for stair treadsand flooring Alberene stone marketed by the Alberene Stone Corp as

a basic refractory substitute for chrome or magnesite for medium

temperatures has a fusion point of 2400°F (1316°C) Virginia

green-stone is a gray-green soapgreen-stone resistant to weathering, used as a

building stone Talc crayons for marking steel are sticks of

soap-stone

SODA ASH The common name for anhydrous sodium carbonate,

Na2CO3, which is the most important industrial alkali It is a white, lumpy material which loses any water of crystallization whenheated For household use in hydrous crystallized form, Na2CO310H2O, it is called washing soda, soda crystals, or sal soda, as distinct from baking soda, which is sodium hydrogen carbonate,

grayish-or sodium bicarbonate, NaHCO3 Sal soda contains more than 60%water Another grade, with one molecule of water, Na2CO3 H2O, isthe standard product for scouring solutions Federal specificationscall for this product to have a total alkalinity not less than 49.7%

Na2O Commercial high-quality soda ash contains 99% minimum

Na2CO3, or 58 minimum Na2O It varies in size of particle and in bulkdensity, being marketed as extra-light, light, and dense The extra-light has a density of 23 lb/ft3(368 kg/m3) and the dense has a density

of 63 lb/ft3 (1,009 kg/m3) Laundry soda is soda ash mixed with

sodium bicarbonate, with 39 to 43% Na2O Modified sodas, used for

cleansing where a mild detergent is required, are mixtures of sodiumcarbonate and sodium bicarbonate They are used in both industrial

and household cleaners Tanners’ alkali, used in processing fine leathers, and textile soda, used in fine wool and cotton textiles, are modified sodas Flour bland, used by the milling industry in making

free-flowing, self-raising food flours, is a mixture of sodium ate and tricalcium phosphate

bicarbon-Soda ash is made by the Solvay process, which consists of treating asolution of common salt with ammonia and with carbon dioxide and

calcining the resulting filter cake of sodium bicarbonate to make light

soda ash Dense soda ash is then made by adding water and

recal-cining Soda ash is less expensive than caustic soda and is used forcleansing, for softening water, in glass as a flux and to prevent fog-ging, in the wood-pulp industry, for refining oils, in soapmaking, and

for the treating of ores Caustic ash, a strong cleaner for metal

scour-ing and for paint removal, is a mixture of about 70% caustic soda and

30 soda ash Flake alkali, of PPG Industries, contains 71% caustic

soda and 29 soda ash Soda ash is also used as a flux in melting iron toincrease the fluxing action of the limestone, as it will carry off 11% sul-

fur in the slag Soda briquettes, used for desulfurizing iron, are

made of soda ash formed into pellets with a hydrocarbon bond

Hennig purifier is soda ash combined with other steel-purifying

agents made into pellets

The natural hydrous sodium carbonate of Egypt and Libya is called

nitron Natural soda ash is obtained in Wyoming from beds 5 to 10 ft

(1.5 to 3.0 m) thick located 1,200 ft (366 m) underground, which tain 47% Na2CO3 and 36 NaHCO3, designated as trona, Na2CO3NaHCO3 2H2O By calcination the excess CO2 is driven off, yieldingsoda ash The salt brine of Owens Lake, California, is an importantsource of soda ash The brine, which contains 10.5% Na2CO3 and 2.5

con-sodium borate decahydrate, is concentrated and treated to

precip-itate the trona The Salt Lake area of Utah is a source of trona Soda

ash and sodium carbonate may be sold under trade names Purite is

a sodium carbonate Tronacarb is an industrial grade, and

Tronalight, as the name suggests, is a light soda ash Both products

are made by Kerr-McGee Chemical Corp

SODIUM. A metallic element, symbol Na and atomic weight 23, ring naturally only in the form of its salts The most important min-eral containing sodium is the chloride, NaCl, which is common salt Italso occurs as the nitrate, Chile saltpeter, as a borate in borax, and as

occur-a fluoride occur-and occur-a sulfoccur-ate When pure, sodium is silvery white occur-and tile, and it melts at 208°F (97.8°C) and boils at 1620°F (882°C) Thespecific gravity is 0.97 It can be obtained in metallic form by the elec-trolysis of salt When exposed to the air, it oxidizes rapidly, and itmust therefore be kept in airtight containers It has a high affinity foroxygen, and it decomposes water violently It also combines directlywith the halogens, and is a good reducing agent for the metal chlo-rides Sodium is one of the best conductors of electricity and heat The

duc-element has five isotopes, and sodium 24, made by neutron

irradia-tion of ordinary sodium, is radioactive It has a half-life of 15 h and

decays to stable magnesium 24 with the emission of one beta

parti-cle and two gamma rays per atom

The metal is a powerful desulfurizer of iron and steel even in

com-bination For this purpose it may be used in the form of soda-ash

pellets or in alloys Desulfurizing alloys for brasses and bronzes

are sodium-tin, with 95% tin and 5 sodium, or sodium-copper.

Sodium-lead, used for adding sodium to alloys, contains 10% sodium

and is marketed as small, spheroidal shot It is also marketed as

sodium marbles, which are spheres of pure sodium up to 1 in (2.54

cm) in diameter coated with oil to reduce handling hazards Sodium

bricks contain 50% sodium metal powder dispersed in a paraffin

binder They can be handled in air and are a source of active sodium.Sodium in combination with potassium is used as a heat-exchangefluid in reactors and high-temperature processing equipment

A sodium-potassium alloy, containing 56% sodium and 44

potas-sium, has a melting point of 66°F (19°C) and a boiling point of 1517°F

(825°C) It is a silvery, mobile liquid High-surface sodium is

sodium metal absorbed on common salt, alumina, or activated carbon

to give a large surface area for use in the reduction of metals or inhydrocarbon refining Common salt will adsorb up to 10% of itsweight of sodium in a thin film on its surface, and this sodium is100% available for chemical reaction It is used in reducing titanium

tetrachloride to titanium metal Sodium vapor is used in electric

lamps When the vapor is used with a fused alumina tube, it gives agolden-white color A 400-W lamp produces 42,000 lm and retains85% of its efficiency after 6,000 h

Sodium compounds are widely used in industry, particularly

sodium chloride, sodium hydroxide, and soda ash Sodium

bichro-mate, Na2Cr2O7 2H2O, a red, crystalline powder, is used in leathertanning, textile dyeing, wood preservation, and pigments Whenheated, it changes to the anhydrous form which melts at 673°F(356°C) and decomposes at about 752°F (400°C) In a hot water solu-tion with sulfuric acid, sodium bichromate gives a golden-brown,brasslike finish to zinc parts The sodium bichromate liquor fromalkali production is used for making pigments When combined withlead compounds, the bichromate precipitate is yellow The addition of

iron blue, or ferric cyanide, develops greens Sodium date, NaVO3, is used as a corrosion inhibitor to protect some chemi-cal-processing piping It dissolves in hot water, and a small amount inthe water forms a tough, impervious coating of magnetic iron oxide on

metavan-the walls of metavan-the pipe Sodium iodide crystals are used as

scintilla-tion probes for the detecscintilla-tion and analysis of nuclear energies

Sodium oxalate is used as an antienzyme to retard tooth decay In

the drug industry, sodium is used to compound with pharmaceuticals

to make them water-soluble salts Gas-generating pellets or wafers of

sodium azide are used as a propellant in auto airbag inflators Upon

ignition, the gas burns and liberates large amounts of nitrogen gas,inflating the bag Sodium is a plentiful element, easily available, and

is one of the most widely used

SODIUM CYANIDE. A salt of hydrocyanic acid of composition NaCN,used for carbonizing steel for case hardening, for heat-treatingbaths, for electroplating, and for the extraction of gold and silver

from their ores For carburizing steel it is preferred to potassiumcyanide because of its lower cost and its higher content of availablecarbon It contains 53% CN, as compared with 40% in potassiumcyanide The nitrogen also aids in forming the hard case on thesteel The 30% grade of sodium cyanide, melting at 1156°F (679°C),

is used for heat-treating baths instead of lead, but it forms a slightcase on the steel Sodium cyanide is very unstable, and on exposure

to moist air it liberates the highly poisonous hydrocyanic acid

gas, HCN For gold and silver extraction it easily combines with themetals, forming soluble double salts, NaAu(CN)2 Sodium cyanide ismade by passing a stream of nitrogen gas over a hot mixture ofsodium carbonate and carbon in the presence of a catalyst It is a

white, crystalline powder, soluble in water The white copper

cyanide used in electroplating has composition Cu2(CN)2, ing 70% copper It melts at 887°F (475°C) and is insoluble in water,

contain-but is soluble in sodium cyanide solution Sodium ferrocyanide,

or yellow prussiate of soda, is a lemon-yellow, crystalline solid of

composition Na4Fe(CN)6 10H2O, used for carbonizing steel for casehardening It is also employed in paints, in printing inks, and forthe purification of organic acids; in minute quantities, it is used in

salt to make it free-flowing It is soluble in water Calcium

cyanide in powder or granulated forms is used as an insecticide It

liberates 25% of hydrocyanic acid gas Cyanogas, of American

Cyanamid Co., is gaseous HCN from calcium cyanide

SODIUM HYDROXIDE Known commonly as caustic soda, and also as

sodium hydrate Lye is an old name used in some industries and in

household uses It is a white, massive, crystalline solid of compositionNaOH used for scouring and cleaning baths, for etching aluminum, inquenching baths for heat-treating steel, in cutting and soluble oils, inmaking soaps, and in a wide variety of other applications It is usu-ally a by-product in the production of chlorine from salt The specificgravity is 2.13 and melting point 604°F (318°C) It is soluble in water,alcohol, and glycerin Sodium hydroxide is sold in liquid and in solid

or powder forms on the basis of its Na2O content A high-grade mercial caustic soda contains 98% minimum NaOH equivalent to 76minimum Na2O The liquid contains 50% minimum NaOH Pels, of

com-PPG Industries, is a caustic soda in bead form It is less irritating to

the skin when used in detergents Phosflake, of PPG Industries,

used in washing machines, is a mixture of caustic soda and trisodium

phosphate Caustic potash is potassium hydroxide, KOH, which

has the same uses but is more expensive Caustic potash is a white,lumpy solid It is soluble in water and makes a powerful cleansingbath for scouring metals It is marketed as solid, flake, granular, or

broken, and also is 40 to 50% liquid solutions It is used in soaps andfor bleaching textiles When used in steel-quenching baths, it gives ahigher quenching rate than water alone and does not corrode thesteel as a salt solution does.

SODIUM NITRATE Also called soda niter and Chile saltpeter.

A mineral found in large quantities in the arid regions of Chile,Argentina, and Bolivia, where the crude nitrate with iodine and other

impurities is called caliche It is used for making nitric and sulfuric

acids, for explosives, as a flux in welding, and as a fertilizer The position is NaNO3 It is usually of massive, granular, crystallinestructure with a Mohs hardness of 1.5 to 2 and specific gravity of2.29 It is colorless to white, but sometimes colored by impurities It isreadily soluble in water In other parts of the world it occurs in bedswith common salt, borax, and gypsum Sodium nitrate is also made

com-by nitrogen fixation and is marketed granulated, in crystals, or insticks It is colorless and odorless, and it has a specific gravity of2.267 and a melting point of 601°F (316°C) It has a bitter, saline

taste Sodan, used for spraying on soils, is a clear liquid solution of

sodium nitrate and ammonium nitrate containing 20% nitrogen

Norway saltpeter, used in fertilizers and explosives, is calcium nitrate, Ca(NO3)2, in colorless crystals soluble in water Calciumnitrate of fine crystal size is used as a coagulant for rubber latex

SODIUM SILICATE A water-soluble salt commonly known as water

glass or soluble glass Chemically, it is sodium metasilicate of

composition Na2SiO3or NaSiO3 9H2O Two other forms of the silicate

are also available, sodium sequisilicate, 3Na2O 2SiO2, and sodium

orthosilicate, 2Na2O SiO2 All of these are noted for their powerfuldetergent and emulsifying properties and for their suspending power.The material has good adhesion, and large quantities are used inwater solutions for industrial adhesives It is also used to inhibit cor-rosion in potable- and industrial-water systems, forming an oxidation-resistant film on pipe walls If corrosion has begun, pH-neutral reconditioning solutions can remove the rust or scale with-out pH adjustment of flush water When solid, sodium silicate is glassy

in appearance and dissolves in hot water It melts at 1864°F(1018°C)

It is obtained by melting sodium carbonate with silica, or by meltingsand, charcoal, and soda The fused product is ground and dissolved in

water by long boiling Potassium silicate is made in the same way, or

a complex soluble glass is made by using both sodium and potassiumcarbonates Potassium silicate is more soluble than sodium silicate

Kasil, of Philadelphia Quartz Co., is a potassium silicate in fine

pow-der containing 71% SiO2 and 28.4 K2O It is used in ceramic coatings

and refractory cements Corlok is potassium silicate free of fluorides

and sodium compounds It is resistant to strong oxidizing acids, hasgood bond strength, and is used as a cement for acid tanks

Ammonium silicate has an ammonium group instead of the sodium Quram 220, of Philadelphia Quartz Co., is this material in the form

of white powder or in opalescent solution The intermediate silicagrades act like sodium silicates and are used as binders for refractoryceramics

Sodium silicate is marketed as a viscous liquid or in powder form

It is used as a detergent, as a protection for wood and porous stone, as

a fixing agent for pigments, for cementing stoneware, for lute cementsfor such uses as sealing lightbulbs, for waterproofing walls, forgreaseproofing paper containers, for coating welding rods, as a fillerfor soaps, and as a catalyst for high-octane gasoline It increases thecleansing power of soaps but irritates the skin However, it is used in

cleansing compounds because it is a powerful detergent Brite Sil is

a spray-dried sodium silicate powder which dissolves more easily andmore uniformly

Sodium silicate is also used for insulating electric wire It is applied

in solution, and the coated wire is then heated, leaving a flexible ing Mixed with whiting, it is used as a strong cement for grindingwheels Sodium metasilicate marketed by Philadelphia Quartz Co as

coat-a clecoat-aner of metcoat-als is coat-a crystcoat-alline powder Hot solutions of this scoat-alt

in water are caustic and will clean grease readily from metals

Drymet is the anhydrous sodium metasilicate It is a fine, white

pow-der with total alkalinity of 51% Na2O It is easily soluble in water and

is used as a detergent in soap powders to give free-flowing, noncakingproperties The anhydrous material for a given detergent strengthweighs little more than half the weight of the hydrous powder

Dryorth is the anhydrous material of 60% alkalinity It is a powerful

detergent and grease remover Crystamet is the material with 42% water of crystallization It is a free-flowing white powder Penchlor

is an acidproof cement made by mixing cement powder with a

sodium silicate solution It is used for lining chemical tanks and

drains Aquagel, of Silica Products Co., is a hydrous silicate of

alu-mina, used in the same manner for waterproofing concrete

SOLDER. An alloy of two or more metals used for joining other als together by surface adhesion without melting the base metals as

met-in weldmet-ing and without requirmet-ing as high a temperature as met-in

braz-ing However, there is often no definite temperature line between

sol-dering alloys and brazing alloys A requirement for a true solder is

that it have a lower melting point than the metals being joined and

an affinity for, or be capable of uniting with, the metals to be joined

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), and the electrical conductivity is 11% that of

copper SAE solder No 1 has 49.5 to 50.0% tin, 50 lead, 0.12

maxi-mum antimony, and 0.08 maximaxi-mum copper It melts at 359°F (181°C).Much commercial half-and-half, however, usually contains larger pro-portions of lead and some antimony, with less tin These mixtureshave higher melting points, and solders with less than 50% tin have awide melting range and do not solidify quickly Sometimes a wide

melting range is desired, in which case a wiping solder with 38 to

45% tin is used A narrow-melting-range solder, melting at 362 to365°F (183 to 185°C), contains 60% tin and 40 lead A 42% tin and 58lead solder has a melting range of 362 to 448°F (183 to 231°C)

Slicker 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 have at least 40%tin, as the electrical conductivity of lead is only about half that oftin, but conductivity is frequently sacrificed for better wiping ability,and the wiping solders are usually employed for electrical work

Soft solders should not contain zinc because of poor adhesion from

the formation of oxides Various melting points to suit the work areobtained with solders by varying the proportions of the metals The

low-melting solders are those that melt at 446°F (230°C) or lower,

and the high-melting solders melt at higher temperatures The

flow point, at which the solder is entirely liquid, is often ably above the melting point Tin added to lead lowers the meltingpoint of the lead until, at 356°F (180°C), at 68% tin, the meltingpoint rises as the tin content increases until the melting point ofpure tin is reached A standard solder with 48% tin and 52 leadmelts at 360°F (182°C) A 45–55 solder melts at 440°F (227°C) Cheap

consider-solders may contain much less tin, but they have less adhesion SAE

solder No 4 contains 22.5 to 23.5% tin, 75 lead, and 2 maximum

antimony It melts at 370°F (188°C)

A tin-silver-copper alloy, developed at the University of Iowa (Ames),

is lead-free and intended to replace tin-lead solders Made by blending

spherical powder particles with a fluxing agent, the lead-free solder

melts at 421°F (216°C) and wets similarly to tin-lead solders The ver and copper form hard, intermetallic phases, reinforcing the tin andstrengthening the solder The toxicity of lead has been the impetus in

the quest for its elimination in solder, especially for printed circuits inthe electronics industry where the 63tin-37lead eutectic alloy hasdominated for many years Five promising tin-based, lead-free alloysand their eutectic or melting temperatures are: tin-3.5silver (430°F,221°C), tin-3silver-2bismuth (428°F, 220°C), tin-2.6silver-0.8 copper-0.5antimony (412°F, 211°C), tin-3.4silver-4.8bismuth (410°F,210°C) and tin-3.5silver-0.5copper-1zinc (430°F, 221°C) With an ulti-mate tensile strength of about 8,000 lb/in (55 MPa) and a shearstrength of about 4,600 lb/in2 (32 MPa), the tin-3.5 silver alloy isstronger than the tin-37lead alloy; it is also more creep resistant.

Solders with low melting points are obtained from mixtures of lead,

tin, cadmium, and bismuth Bismuth solder is also more fluid, as

bismuth lowers surface tension Bismuth, however, hardens the alloy,although to a lesser extent than antimony A bismuth solder contain-ing equal parts of lead, tin, and bismuth melts at 284°F (140°C)

Cerrolow alloys, of Cerro Metal Products Co., are bismuth solders

containing sufficient indium to be designated as indium solders.

Cerrolow 147, which melts at 142°F (61°C), contains 48% bismuth,

25.6 lead, 12.8 tin, 9.6 cadmium, and 4 indium Cerrolow 105,

melt-ing at 100°F (38°C), contains 42.9% bismuth, 21.7 lead, 8 tin, 5 mium, 18.3 indium, and 4 mercury Cadmium solders have lowmelting points, are hard, and are usually cheaper than tin solders;but they have the disadvantage of blackening and corroding, and the

cad-fumes are toxic Cadmium-zinc solders were used in wartime

because of the scarcity of tin A solder containing 80% lead, 10 tin,and 10 cadmium has about the same strength as a 50–50 tin-lead sol-

der and has greater ductility, but is darker in color Cadmium-tin

solder, with high cadmium, is used to solder magnesium alloys Soft

solders for soldering brass and copper, especially for electric

connec-tions, may be of tin hardened with antimony Solder wire for this

purpose contains 95% tin and 5 antimony Thallium may be used inhigh-lead solders to increase strength and adhesion

Hard solder may be any solder with a melting point above that of

the tin-lead solders; more specifically, hard solders are the brazing

solders, silver solders, or aluminum solders Aluminum solders may

contain up to 15% aluminum A solder prepared by the NationalBureau of Standards contains 87% tin, 8 zinc, and 5 aluminum It has

good strength and ductility Alcoa solder 805, for joining aluminum

to steel or other metals, has 95% zinc and 5 aluminum The meltingrange is 715 to 725°F (379 to 385°C) For soldering aluminum to alu-minum, an alloy of 91% tin and 9 zinc is used

The solder known as Richard’s solder is a yellow brass with 3%

aluminum and 3 phosphor tin Solders containing nickel are used forsoldering nickel silver, and silver and gold solders are used for jewelry