Materials Handbook 15th ed - G. Brady_ H. Clauser_ J. Vaccari (McGraw-Hill_ 2002) Episode 11 pps

Caroba wood is chocolate-colored and is used for fine furni- ture and knife handles.. Normally, when gum rosin is heated, the natural pimaric acid isomerizes to form abietic acid; but in

molybdenite, which contains 0.0001 to 0.05% of the metal But the

usual source is from the flue dusts and from the sublimed rhenium

oxide, Re2O7, of stack gases in the smelting of copper and other ores

It is precipitated from the flue dust of molybdenum-bearing copper

ores in the form of potassium perrhenate, KReO4, or of

ammo-nium perrhenate, NH4ReO4 The Russians also obtain some

rhe-nium from the Ural platinum ores The stable rhenia, used in alloying, is rhenium trioxide, ReO3, which comes as a red powder.The metal is obtained as a dense, silvery powder which can be com-pacted, sintered, and cold-rolled with frequent annealing It is mar-keted in the form of rod, strip, foil, and wire

At the Technical University of Munich in Germany, pure, cally conductive ReO3 ceramic films have been made by heating the

electri-polymer methyl-trioxorhenium Ch3ReO3, above 460°F (240°C),causing it to lose its methyl groups and water

Rhenium has a higher electrical resistivity than tungsten, has higharc resistance, and does not become brittle after prolonged heating, astungsten does Rhenium is used as an undercoat for tungsten coat-ings on graphite nozzles to prevent the formation of tungsten carbideand thus give the full heat resistance of the tungsten Rhenium andrhenium-tungsten alloys used for electric contacts give very long ser-vice life Rhenium-tungsten versus tungsten thermocouples are goodfor service to 5072°F (2800°C) Substantial amounts of rhenium areused in select tungsten- and molybdenum-base alloys

RHODIUM. A rare metal, symbol Rh, found in platinum ores such as

the nickel-copper ores of Canada and pyroxenite of South Africa It is

very hard and is one of the most infusible of the metals The meltingpoint is 3565°F (1963°C) It is insoluble in most acids, including aquaregia, but is attacked by chlorine at elevated temperatures and by hotfuming sulfuric acid Liquid rhodium dissolves oxygen, and ingots aremade by argon-arc melting At temperatures above 2192°F (1200°C),

rhodium reacts with oxygen to form rhodium oxide, Rh2O3 The cific gravity is 12.44 Rhodium is used to make the nibs of writingpens, to make resistance windings in high-temperature furnaces, forhigh-temperature thermocouples, as a catalyst, and for laboratorydishes As a catalyst, it is used with platinum and palladium in autocatalytic converters to convert nitrogen oxide emission to nitrogen gas

spe-It is the hardest of the platinum-group metals, the annealed metalhaving a Brinell hardness of 135 Rhodium also has considerablestrength and rigidity, ultimate tensile strengths ranging from 138,000

to 300,000 lb/in2 (952 to 2,068 MPa), and tensile modulus from 42 

106 to 55  106lb/in2 (290,000 to 379,000 MPa), depending on tion or hardness Rhodium is also valued for electroplating jewelry,

electric contacts, hospital and surgical instruments, and especially

reflectors For electrodepositing rhodium, an electrolyte of rhodium

sulfate, Rh2(SO4)3, is used The coatings are wear-resistant and tarnish-resistant The plated metal has a pinkish-white luster of highcorrosion resistance and a light reflectivity of 80% Decorative fin-ishes are seldom more than 0.0002 in (0.0005 cm) thick, but plates for

electric contacts may be up to 0.005 in (0.013 cm) Rhodium

car-bonyl has the general formula Rh(CO), but with several variations in

the number of CO groups They are used for depositing rhodium

coatings.

The most important alloys of rhodium are rhodium-platinum.

They form solid solutions in any proportion, but alloys of more than40% rhodium are rare Rhodium is not a potent hardener of platinumbut increases its high-temperature strength It is easily workable anddoes not tarnish or oxidize at high temperatures These alloys are

used for thermocouples and in the glass industry A rhodium-iron

alloy with equiatomic proportions of the metal has an ordered crystalstructure and changes from antiferromagnetic to ferromagnetic in anelectric field Rhodium is sold by the troy ounce (31 g), 1 in3 (16 cm3)weighing 6.56 troy oz (204 g)

RICE. The white seed of the large annual grass Oryza sativa,

grow-ing to a height of 2 to 4 ft (0.6 to 1.2 m) It is a tropical plant native toAsia, but grows in hot, moist regions well into the temperate zonesand is cultivated in many parts of the world Rice fields are floodedafter planting to control weeds The rice seed grows in an inflores-cence composed of a number of fine branches, each terminating in asingle grain enclosed in a brown husk Rice forms the staple food of

more than half the populations of the world Wild rice was used by

the Indians of North America before the first Asiatic rice was brought

to South Carolina in 1694 Rice is high in starch and low in proteins

It is used as a direct food, also as flour, as cereal, in puddings, and for

the manufacture of starch and for alcoholic beverages Rice hulls are used as stock feed, and rice straw is used for packing, hats, and other articles Maxflo and Profix, of EnviroGuard, Inc., are filtration aids made from rice hull ash, a by-product of rice milling The tex-

tured surface of the ash speeds solids separation from wastestreams

A low-ash version has some caloric value so that it can be used to sop

up waste oils during filtering and produce a recyclable waste fuel.Rice in the husk before hulling is known by the Hindu name of

paddy Brown rice is rice that has been cleaned but not polished.

Broken grains are sold in the India trade as coodie or khood, and about 20% of the rice produced from paddy is broken Patna rice

does not refer to the Patna district of India, but to a variety of rice

with bold and hard grains especially suited for soups, as it holds its

shape in boiling Malekized rice, developed by General American

Transportation Co., is produced by steaming unpolished rice to forcethe soluble part of the bran and the vitamins into the core of thegrain, and then sealing the rice kernal by gelatinization, after which

it is polished The treated rice holds its shape and does not becomegummy when cooked, and the nutritional value is improved The bev-

erage known in Japan as saké is rice wine containing 14% alcohol, made by fermenting rice with the mold tané koji Rice bran oil,

used as a salad and cooking oil and in lubricants, is produced fromrice bran By wet-milling whole rice in a rice oil solutions, a higheryield of oil and wax is obtained together with a yield of proteins It isclear, odorless, and neutral, with a pleasant flavor, and is resistant to

oxidation and rancidity Rice wax is produced from rice bran by hot

hexane extraction after cold extraction of the oil It is a hard, brown,lustrous wax with a melting point of 174°F (79°C) used in polishes

Synthetic rice, used in Japan as a rice extender, is made from wheat

flour, potato starch, and powdered rice

ROSEWOOD. The wood of several species of Dalbergia of northern

South America, but chiefly from the jacaranda tree, D nigra It is

used for fine cabinetwork, pianos, novelties, and expensive furniture

It should not be confused with the wood of the tree Physocalymma

floridum, which also comes from Brazil and is there called pao rosa

or rosewood The color of rosewood is dark brown to purple, and ittakes a beautiful polish It has a characteristic fragrance Very hardwith a coarse, even grain, it has a density of 54 lb/ft3(865 kg/m3) The

tree grows to a height of 125 ft (38 m) Brazilian rosewood is the

preferred wood for guitar bodies, but its use was banned in 1969 bythe Convention on International Trade in Endangered Species

Another Brazilian wood, caroba, from the large tree Jacaranda

copaia, is also called jacaranda and is sometimes confused with

rose-wood The tree has purple flowers while the true rosewood has whiteflowers Caroba wood is chocolate-colored and is used for fine furni-

ture and knife handles Indian rosewood is from the tree D sissoo

of India It is also called sissoo and is a beautiful, brown hardwood

employed for carvings In Europe it is used for parquet floors

Borneo rosewood, also known as ringas, is the wood of several

species of trees of genus Melanorrhoea of Borneo The wood has a

deep-red color with light and dark streaks It has a close texture

suit-able for carving Satinee is a type of rosewood from the tree Ferolia

guianensis of the order Rosaceae, native to tropical America,

particu-larly the Guianas The wood is reddish brown, has a density of 54lb/ft3(865 kg/m3), is fairly hard, has a fine grain, and takes a lustrous

polish It is used for cabinetwork Bois de rose oil, or rosewood oil,

is not from rosewood, but is extracted from the heartwood of the tree

Aniba panurensis of Brazil and the Guianas, though the wood of this

tree is also used as a cabinet wood The oil is also called Cayenne

linaloe, or Cayenne oil It has a delicate rose odor with a suggestion

of orange and mignonette valued in perfumes It contains a high

per-centage of linalol, a colorless alcohol with a soft, sweet odor, also

found in the rose, lilac, lily, lavender, petitgrain, and other plants It

also contains geraniol Linaloe oil, or Mexican linaloe, is distilled

from the heartwood of the trees Bursera delpechianum and B.

aloeoxylon It contains less linalol and also terpineol and geraniol.

Linalol is closely related to geraniol and nerol Bois de rose is also

made synthetically from geraniol Oriental linaloe is distilled from

selected, highly perfumed parts of the wood of the large tree

Aquilaria agollocha of eastern India, Burma, and Java The odor of

the oil is like rose, ambergris, and sandalwood Like the linaloes ofthe American continent, the oil is a pathological product and comes

only from old trees It is also called aloe wood oil and agar attar,

and is a very ancient perfume The beautifully figured and fragrant,

reddish wood of this tree, called aloes wood, eagle wood, and

par-adise wood, is used for ornamental articles True original rosewood

oil known as rhodium oil was distilled from the wood of the plant

Convolvulus scoparius of the Canary Islands.

ROSIN. The common resin of several varieties of pine tree, foundwidely distributed in North America and Europe It is obtained bycutting a longitudinal slice in the tree and allowing the exudation todrip into containers The liquid resin is then distilled to remove the

turpentine, and the residue forms what is known as gum rosin, or

pine gum Wood rosin is obtained by distillation of old pine stumps.

It is darker than gum rosin and is inferior for general use

Rosin contains seven acids with very similar characteristics, but

consists chiefly of abietic acid, C19H29COOH Normally, when gum

rosin is heated, the natural pimaric acid isomerizes to form abietic

acid; but in the production of turpentine and rosin from pine sap, theturpentine is removed by steam distillation, and various acids arethen extracted Pimaric acid is closely related to abietic acid It reacts

with maleic and anhydride, and maleopimaric acid is used in

print-ing inks and coatprint-ings Rosin has a specific gravity of about 1.08 and amelting point of about 180°F (82°C), and it is soluble in alcohol, tur-pentine, and alkalis It is used in varnishes, paint driers, soluble oils,paper sizing, and belt dressings; for compounding with rubber andother resins; and for producing many chemicals

Rosin is generally graded commercially by letters according tocolor The darkest grade is B, and the lightest is W Extra grades are

A, nearly black, and WW, water-white Thirteen color grades are

designated under the Naval Stores Act The dark grades of woodrosin are considered inferior They have a high melting point andlow acid number and are used for making rosin oil; for battery wax,thermoplastics, and dark varnish; and for linoleum manufacture.The ruby-red wood rosin, obtained by extraction from fat pine wood,has high acid number, 155, and low melting point, 175°F (79°C) It

is used for printing inks, paper size, and adhesives Rosin is usually

marketed in barrels of 280 lb (127 kg) Naval stores is an old name for rosin and turpentine Pexite and Pamite are rosin grades from

Hercules Inc that cover the various color standards set by the U.S

Department of Agriculture Pelletized rosin consists of

free-flow-ing, dustless pellets produced by coating droplets of molten rosin

with inert powder Colophony is an old pharmacy name for rosin

before distillation of rosin oil Rosin was referred to by early writers

as Greek pitch, but the ancient incendiary known as Greek fire

was tow or pine sawdust impregnated with rosin, pitch, and sulfur

Burgundy pitch was originally the resin of the Norway spruce,

Picea abies, used in medicine, but the name was later applied to a

rosin, rubber, and mineral oil compound used for friction tape

Hardened rosin is a weak resinate made by adding 6 to 8%

high-calcium lime to melted rosin It is used in some varnishes

Fosfo rosin, of Newport Industries, Inc., is a lime-hardened rosin.

It is an FF rosin treated with 4.75% calcium hydrate, which raisesthe melting point, decreases the free rosin acids, and decreases thetendency to crystallize It is used in paints, varnishes, and molded

products Soda-treated rosins, with about 1% Na2O, but no free

alkali, are used for soap, paper size, and disinfectants Rosin size is

alkali-treated rosin in dry powder or emulsion form for sizing paper

Dresinite is such a sodium or potassium salt of rosin Cyfor, of

American Cyanamid Co., is a rosin size fortified with a synthetic

resin to give increased water and acid resistance to paper Rosin

ester, or ester gum, is prepared by heating rosin with glycerin It is

lighter in color than rosin, has a higher softening point, and has amuch lower acid number, usually 7 to 9 It is used with tung oil in

enamels and varnishes and in adhesives Resin V is a rosin glycerin

ester gum Rosin esterified with glycerin has lower molecular weightand is not as stable as rosin esterified with pentaerythritol or othertetrahydric alcohol; but modified rosin ester gums develop hardnessquickly in nitrocellulose and are used for such purposes as furniture

lacquers Cellolyn 102, of Hercules Inc., is a modified ester gum of this type, and Lewisol 28 is a maleic alkyd modified rosin ester used for hard, glossy furniture lacquers Hydroabietyl alcohol, used as

a plasticizer and tackifier for rubber and for sizing textiles, is a less, tacky liquid made by reduction of rosin The 85% alcohol has a

specific gravity of 1.008 and a flash point of 369°F (187°C) It is also

used for making rosin esters Abitol, of Hercules, is this material.

Abalyn is a methyl ester of abietic acid, methyl abietate, made by

treating rosin with methyl alcohol It is a liquid rosin used as a ticizer

plas-Hydrogenated rosin has greater resistance to oxidation than

common rosin, has less odor and taste, and has a pale color that ismore stable to light It is used in protective coatings, in paper size, inadhesives, in soaps, and as a tackifier and plasticizer in rubber.Because of its saturated nature, it cannot be used for rosin-modifiedplastics The average acid number is 162, saponification value 167,

and softening point 157°F (69°C) Staybelite resin, of Hercules, may

be glycerol ester or ethylene glycol ester of hydrogenated rosin

Another modified rosin, a perhydrogenated variety, is Foral Ax And

a disproportionated rosin from the same company is Rosin 731.

Vinsol resin is a hard, high-melting-point, dark resin produced from

the distillation of wood, or is the black residue left after rosin isextracted with petroleum solvents It is soluble in alcohols, has amelting point of 239°F (115°C), and is used for insulating varnisheswhere light color is not essential, and for compounding in thermoplas-

tics Hercolyn is Abalyn hydrogenated to saturate the double bonds with hydrogen Flexalyn, of the same company, is a pale-colored,

very tacky, semisolid resin produced by the esterification of rosinacids with diethylene glycol, and it has a complex chemical structure

It is used in adhesives to give added tack and strength Althoughrosin should be considered a natural resin, it is used primarily incoatings as a synthetic ester The principal materials are the glycerol

ester of rosin, or ester gum, and the pentaerythritol ester, or PE

ester gum The Pentalyn resins of Hercules are pentaerythritol

esters Pentalyn M is a phenol-formaldehyde-modified

pentaerythri-tol ester; it has a melting point of 329°F (165°C), and when used inlinseed oil varnishes, it gives a tough coating Maleic modified estergums have higher melting points and show better color retention in

varnishes than simple rosin esters Ester gum varnishes are used

primarily in low-cost, interior finishes that are not exposed to theweather

Rosin is hardened by polymerization to form a dipolymer of abieticacid The product is then pale in color, and has a lower acid number

and a higher melting point than rosin Poly-pale resin, of Hercules,

is a polymerized rosin with melting point of 208 to 217°F (98 to103°C), acid number 152 to 156, and saponification value 157 to 160

It can be substituted for natural copals in paints, and in gloss oil itgives water resistance and high viscosity In the making of metallicresinates, it gives higher melting points, higher viscosity, and better

solubility than natural rosin Another modified rosin of this company

is Dymerex resin It consists chiefly of dimeric rosin acids, is highly

soluble, is resistant to oxidation, and has a high softening point at282°F (139°C) It is used in synthetic resins and protective coatings

Rosin amine D, of the same company, is a primary amine made from

rosin It is a yellow, viscous liquid that wets glass and siliceous rials It is soluble in most organic solvents and emulsifies in water It

mate-is used in cutback asphalts, in road asphalts, in asphalt cements, inceramic inks, in foundry core binders, and in paper pulp to improve

adhesion of resins Nuroz is a polymerized rosin with a melting point

of 169°F (76°C) and acid value 161 It has high resistance to oxidationand is used in varnishes and soaps

Rosin oil is an oil produced by the dry distillation of rosin at a

tem-perature of 392 to 680°F (200 to 360°C) There are two qualities of the

oil: a light spirit, pinolin, which forms from 1 to 5% of the rosin, and a

bluish, heavy oil, which forms 80 to 84% It contains abietic acid andhas an acid value of about 28 The commercial oil has a specific gravity

of 1.020 with a flash point of 320 to 338°F (160 to 170°C) The refinedoil is a yellow liquid with a pleasant odor and is used for blending withturpentine It is also employed as a plasticizer in rubber, as a tack pro-ducer in rubber cements, and in synthetic molding resins Whentreated with lime, it may be used to mix with lubricating oils The

light distillate is used sometimes in pharmacy under the name of oil

of amber Blended rosin oil is a mixture with mineral oils.

ROUGE. A hydrated iron oxide used for polishing metals and inbreak-in lubricants for aluminum bronze bearings It has a Mohshardness of 5.5 to 6.5 and is made by calcining ferrous sulfate anddriving off the sulfur The color is varying shades of red; the darkerthe color, the harder the rouge The grains are rounded, unlike thegrains of crocus The pale-red rouge is used for finishing operations;the other grades are used for various polishing of metal surfaces

Stick rouge is made of finely crushed powder Although the word

rouge means red, materials of other colors are used for buffing and

are called rouge Black rouge, also called Glassite, is magnetic iron

oxide made by precipitating ferrous sulfate with caustic soda It is

used for buffing but is not popular because it stains the skin Green

chrome rouge is chromium oxide, CrO, made by the strong

heat-ing of chromic hydroxide It is used for buffheat-ing stainless steels When

used as a paint pigment, it is called Guignet’s green Satin rouge

is a name applied to lampblack when used as a polishing medium in

the form of brick for polishing silverware Crocus is a name applied

to mineral powders of a deep-yellow, brown, or red color made into

cakes with grease for polishing Polishing crocus is usually red

ric oxide used for a buffing glass and jewelry Crocus cloth is a fabric

coated with red iron oxide, marketed in sheets and used for polishingmetals

RUBBER. A gum resin exudation of a wide variety of trees and

plants, but especially of the tree Hevea brasiliensis and several other species of Hevea growing in all tropical countries and cultivated on

plantations in southern Asia, Indonesia, Sri Lanka, Zaire, and

Liberia, from which natural rubber elastomers are made.

The gum resin was formerly referred to as India rubber, and the name given it by Charles Goodyear was gum elastic The first highly

compounded rubber for insulation, developed in 1867, was called

Kerite Brazilian rubber is sometimes called Pará rubber Caoutchouc was an early name for the crude rubber then cured over

a fire into a dark, solid mass for shipment Castilla rubber, or

castilloa, is from the large tree Castilla elastica, and was the

origi-nal rubber of the Carib and Mayan Indians, but was cultivated only

in Mexico and in Panama where it was called Panama rubber The latex and rubber are identical with heavea rubber after purifica-

tion Euphorbia rubber is from vines of the genus Euphorbia, of

which there are 120 species in tropical Africa Much mangabeira

rubber was formerly produced in the Amazon Valley It is the latex of

the mangabeira tree which comprises various species of the genus

Hancoria and yields the edible fruit mangaba The latex is

coagu-lated with alum or sodium chloride, but the native Indians coagucoagu-lated

it with the latex of the caxiguba tree, Ficus anthelmintica, giving a

better rubber The rubber is softer than hevea rubber, but ages better

The low-grade Assam rubber is from a species of ficus tree, F

elas-tica, of India and Malaya Ceara rubber comes from the small,

rapid-growing tree, Manihot glaziovii, native to the semidesert

regions of Brazil but now grown in India and Sri Lanka The rubber

is of good grade

Rubber latex is a colloidal emulsion of the gathered sap,

contain-ing about 35% of rubber solids, blended from various sources to giveaverage uniformity The latex is coagulated with acid and milled into

ribbed sheets called crepe rubber, or into sheets exposed to wood smoke to kill bacteria and called smoked sheet rubber These sheets constitute the commercial crude rubber, although much rub-

ber latex is used directly, especially for dipped goods such as gloves,toys, and balloons; for coatings; and for making foam rubber Rubberhas the property of being vulcanized with sulfur and heat, removingthe tackiness and making it harder and more elastic in the low-sulfurcompounds All natural rubber except adhesive rubbers is thus vul-

canized rubber Ordinary soft rubber contains only 3 to 6% sulfur,

but usually also contains softeners, fillers, antioxidants, or other pounding agents, giving varying degrees of elasticity, strength, andother qualities When as much as 30% sulfur is added, the product is

com-called hard rubber Vapor-cured rubber is rubber vulcanized by

sulfur chloride fumes and neutralized with magnesium carbonate It

is used for thin goods only Acid-cured rubber is rubber cured in a

bath of sulfur chloride in a solvent

The tensile strength of rubber of low vulcanization is 800 to 1,200lb/in2(6 to 8 MPa) of the original cross section A good soft rubber can

be stretched as much as 1,000% without rupture and will return toclose to the original length with little permanent set The specificgravity is about 1.05, but with fillers may be as high as 1.30 When the

term vulcanized rubber is now used, it generally refers to hard

rubber vulcanized to a rigid but resilient solid, used for electrical

parts and tool handles Ace hard rubber has a specific gravity of

1.27, a tensile strength of 8,700 lb/in2(60 MPa), dielectric strength of

485 V/mil (19  106V/m), heat distortion temperature of 172°F (78°C),

and water absorption 0.04% Vulcanite and Ebonite are old names for hard rubber Reclaimed rubber is produced largely from old tires

and factory scrap It is usually lower in cost than new rubber, but it iseasier to process and is employed in large quantities even when theprice is higher It is sold in sheets, slabs, pellets, and powder, but

much of the rubber powder, or granulated rubber, used for

adhe-sives and molding is not reclaimed rubber but is made by spray-dryinglatex In a reclamation system developed by American ResourceRecovery Corp., waste tires depolymerized in a high-temperature vac-uum chamber are converted into oil, carbon black, steel, and ash

Several types of modified natural rubber are used in the production

of coatings, protective films, and adhesives These types are

chlori-nated rubber, rubber hydrochloride, and cyclized rubber or isomerized rubber Chlorinated rubber, for example, modified with

any one of a number of plastic resins, provides maximum protectionagainst a wide range of chemicals, and the coatings are widely used

in chemical plants, in gas works, and as tank-car linings

Red rubber is now simply rubber colored red, but was originally

rubber vulcanized with antimony pentasulfide which broke downwith the heat of vulcanization, yielding sulfur to the rubber and color-ing it red with the residual antimony trisulfide Many trade-nameaccelerators, fillers, and stiffeners are marketed for rubber com-

pounding Crumb rubber is any rubber in the form of porous

parti-cles that can be dissolved easily without milling, cutting, or

pelletizing It is used in adhesives and plastics Magnetic rubbers,

produced in sheets and strips of various magnetic strengths, aremade of synthetic rubbers compounded with magnetic metal powders

RUBIDIUM. A rare metallic element, symbol Rb, atomic weight 85.45,belonging to the group of alkali metals The chief occurrence of rubid-ium is in the mineral lepidolite There is no real rubidium ore, but theelement is widely disseminated over the earth in tiny quantities It is

a necessary element in plant and animal life and is found in tea, fee, tobacco, and other plants It is a silvery-white metal, with a spe-cific gravity of 1.53, melting point, of 102°F (39°C), and boiling at1270°F (688°C) It takes fire easily in air and decomposes water Ofall the alkali metals it is next to cesium in highest chemical activity

cof-It can be obtained by electrolysis, but has few industrial applicationsowing to its rarity Its chief use is in electronics For photoelectriccells it is preferred to cesium, and a very thin film is effective Likepotassium, it has a weak radioactivity by the emission of beta parti-cles, the beta emission being only about one-thousandth that of anequal weight of uranium

Rubidium titanyl arsenate (RTA), a derivative of potassium

titanyl phosphate (KTP), is a nonlinear optical crystal material forimproved optical parametric oscillators (OPOs), modulators, and Q-switches OPOs are used to tune laser frequency; Q-switches areused to control release of laser energy Because RTA crystals retainclarity with increasing laser power, they can extend a laser’s operat-ing transmission range 15% into the infrared Developed at WrightLaboratory’s Materials Directorate and Crystal Associates Inc., RTAwill increase the tunable range of solid-state lasers in industrial,medical, and military applications

RUBY A red variety of the mineral corundum which ranks with the

best grades of precious stones as a gemstone, while the off-colorstones are used for watch and instrument bearings Most of the bestrubies come from upper Burma, Thailand, and Cambodia, but thecenter of natural-ruby cutting is near Bombay Some deep-red rubiesare found in east Africa, and they also occur in western NorthCarolina The carmine-red, or pigeon’s-blood, stones are the mosthighly prized Before the advent of the synthetic ruby, the largerstones were more valuable than diamond The pink to deep-red colors

of the ruby are due to varying percentages of chromic oxide Star

rubies contain also a small amount of titania which precipitates

along crystallographic planes of the hexagonal crystal and shows as amovable six-ray star when the gem is cut with the axis normal to the

base of the stone Spinel ruby is not corundum but magnesium

alu-minate and is a spinel, often occurring in the same deposits

Synthetic rubies are equal in all technical qualities to the natural,and synthetic star rubies surpass the natural stones in perfection andquality Most of the ruby used for instrument bearings is synthetic

corundum colored with chromic oxide, since the instrument makers

prefer the red color, but the name ruby is often applied regardless of

color The U.S practice in bearing manufacture is to start with acylindrical rod of the diameter of the desired bearing and to slice tothe required thickness The single-crystal rods are flame-polished

For industrial uses the name ruby is often applied to the synthetic

material even when it is not red Synthetic rubies with 0.05%

chromium are also used for lasers, or light amplifiers, to produce

high-intensity light pulses in a narrow beam for communications.Lasers have a wide range of uses, and various other materials are

used for specific purposes Crystals of potassium dihydrogen

phos-phate are used to control the direction of narrow beams of light The

crystal is mounted on the face of the cathode-ray tube Platelets ofzinc oxide with a phosphor, when activated at 15,000 to 20,000 V by apulsated electron stream, give a beam of pure ultraviolet light at14,764 nin (375 nm) for use in chemical synthesis

Rubies are also used in masers to detect radio signals for space

rockets at great distances The word maser means microwave cation by stimulated emission of radiation Ruby has the same physical

amplifi-and chemical properties as the sapphire amplifi-and corundum But the color

inclusions do affect the electronic properties The ruby-sapphire

crystals produced by Linde for optical masers are grown with a core

of ruby and an overlay sheath of sapphire The ruby core containing0.05% chromic oxide emits a beam of extremely high frequency, 4.2 1014cycles, for sending messages The sapphire has a high refrac-tive index, 1.76, and when the sheath is surrounded by a helical xenonarc, the light from the arc excites the chromium atoms in the ruby toemit a concentrated beam of parallel rays from one end

The cutting of rubies, sapphires, and other hard crystals into tinyshaped bearings was formerly a specialized hand industry, and largestocks of cut stones were kept in the National Stockpile for wartimeemergencies But the slicing and shaping of hard crystals are nowwidely dispersed on a production basis to meet the needs of the elec-tronic industries, and the equipment is regularly manufactured For

example, the Accu-Cut wheels of Aremco Products, for slicing and

notching crystals and hard electronic ceramics, are metal disks0.010 to 0.030 in (0.025 to 0.076 cm) thick and 1 to 4 in (2.54 to 10.2cm) in diameter, with diamond grit metallurgically bonded to theperiphery

RUTHENIUM. A hard, silvery-white metal, symbol Ru, having a cific gravity of 12.4, a melting point of about 4190°F (2310°C), and aBrinell hardness of 220 in the annealed state The metal is obtained

spe-from the residue of platinum ores by heat reduction of ruthenium

oxide, RuO2, in hydrogen Ruthenium is the most chemically tant of the platinum metals and is not dissolved by aqua regia It is

resis-used as a catalyst to combine nitrogen in chemicals As ruthenium

tetroxide, RuO4, it is a powerful catalyst for organic synthesis, dizing alcohols to acids, ethers to esters, and amides to imides.Ruthenium has a close-packed hexagonal crystal structure It has ahardening effect on platinum, 50% addition of ruthenium raisingBrinell hardness from 30 to 130 and the electrical resistivity to dou-

oxi-ble that of pure platinum Ruthenium-platinum alloys are used for

electric contacts, electronic wires, chemical equipment, and jewelry.The alloy with 5% ruthenium has a tensile strength, annealed, of60,000 lb/in2(414 MPa) with elongation of 34% and Brinell hardness

of 130 The hard metal has a Brinell hardness of 210 The alloy with10% ruthenium as a tensile strength of 85,000 lb/in2(586 MPa), and aBrinell hardness of 190 in the soft condition and 280 when hard-drawn

Several ruthenium intermetallic compounds hold promise forpotential high-temperature, aircraft-turbine parts because of theirhigh melting temperature and evidence of room-temperature duc-tility Identified at General Electric’s Research & Development

Center are aluminum ruthenium with a specific gravity of 7.95 and a melting temperature of 4100°F (2060°C); ruthenium scan-

dium, 7.40, 3992°F (2200°C); and ruthenium tantalum, 14.83,

3776°F (2080°C) AlRu and RuSc are the most promising because

of their light weight and better ductility Al47Ru53 is the most oxidation-resistant, and Al48RuY could be used at temperatures up

to 2280°F (1250°C)

RYE. The seed of the plant Secale cereale used as a food grain, but in

the United States and Great Britain it is valued chiefly for the duction of whiskey and alcohol and for feeding animals Only 4% ofthe world production is in the United States The grain looks likewheat, and the stalks of the plant are slender and tough, growing to aheight of up to 6 ft (1.8 m) But flour made from the grain producesbread that is dark in color, bitter, and soggy When used for flour inthe United States, it is mixed with wheat and other flours The planthas the advantage that it will grow on poor soil, in arid regions, athigh altitudes, and in regions of severe winter It is thus a grain of

pro-poor agricultural countries, and it has been called the grain of

poverty Rye straw is the dried and sun-bleached stalks of the

plant It is very tough and resilient and is the most valued of all the

commercial straw derived from grains It is used for packing,

bed-ding, and the manufacture of strawboard

SAGO FLOUR. A starch extracted from the pith of the sago palm,

Metroxylon sagu, of Indonesia and Malaya, and from the aren palm.

Sago is valued industrially for sizing and filling textiles because, liketapioca, it holds mineral fillers better than other starches It gives atougher and more flexible feel than tapioca, but its tan color limits itsuse From 600 to 800 lb (272 to 363 kg) of crude sago is obtained from

a tree, which is destroyed in the process Pearl sago, used for food, is

the same material made into dough and forced through a sieve

Bullet sago, a lower grade, is used for sizing The aren palm, or sugar palm, is the species which yields arenga fiber It contains only

20% as much sago as the sago palm, but a juice called taewak is duced from the cut flower stems and is used to make palm wine, or

pro-arak The juice is also boiled down to produce a brown palm sugar

used for sweetening

SALMON OIL. A pale-yellow oil obtained as a by-product in thesalmon canning industry and employed as a drying oil for finishesand in soaps There are different classes of the oil, depending upon

the type of salmon The oil contains an average of 23.5%

arachi-donic acid, C19H31COOH; 16.2 clupanodonic; 11.5 linoleic; 17.1 oleic;

15 palmitic; 10.6 palmitoleic acid, C15H29COOH; 4 myristic; and 2stearic acids The specific gravity is 0.926 It has a high iodine num-ber, up to 160, but does not form an elastic skin on drying and is not agood varnish oil untreated It is, however, a valuable source of fattyacids for paint-oil blends and for plastics The salmon is a valuablefood fish and is extensively canned There are five commercial species

of North Pacific salmon of the genus Oncorhynchus; the steelhead

trout, or salmon trout, Salmo gairdneri, is of the Atlantic The Atlantic salmon, caught off Newfoundland, is S salar The red salmon, or sockeye salmon, is O nerka; the pink salmon is O gor- buscha; and the Chinook, or king salmon, is O tschawytscha The

catch is in the rivers on both sides of the Alaskan peninsula and inthe Columbia River where the fish enter the rivers to spawn

Australian salmon, which is the chief fish canned in Australia, is of

a different genus, Arripis trutta.

SALT The common name for sodium chloride, known in mineralogy

as halite but chemically a salt; it is any compound derived from an

acid by replacing hydrogen atoms of the acid with the atoms of a

metal Common salt, or sodium chloride, is widely used as a

preserv-ative, for flavoring food, in freezing mixtures, for salt-brine quenchingbaths, and for the manufacture of soda ash and many chemicals.Common salt has such a variety of uses that its curve of consumptionpractically parallels the curve of industrial expansion It is a stable

compound of composition NaCl, containing theoretically 60.6% rine, but it usually contains impurities such as calcium sulfate andcalcium and magnesium chlorides The hardness of salt is 2.5, specificgravity 2.1 to 2.6, and melting point 1472°F (800°C) It is colorless towhite, but when impure, it may have shades of yellow, red, or blue Itoccurs in crystalline, granular masses with cubical cleavage, known as

chlo-rock salt, or mineral salt Vast deposits of salt are found

under-ground in Louisiana, and a large area of Kansas is underlain with asalt deposit reaching 800 ft (244 m) in thickness The rock salt occur-ring in immense quantities on the island of Hormuz in the PersianGulf contains 97.4% NaCl, 1.83 CaCO3, and only very small amounts

of magnesium chloride, iron oxide, and silica Bay salt is an old name for salt extracted from seawater, now known as solar salt Seawater

also contains more than 20% of magnesium chloride and magnesium,calcium, and potassium sulfates, which are extracted to give a purity

of at least 99% sodium chloride A short ton (907 kg) of seawater tains about 55 lb (25 kg) of common salt But some sea salt containing all the original elements is marketed for corrosion tests Sea-Rite salt

con-of Lake Products Co is a synthetic sea salt containing all the elements

of natural sea salt except those of less than 0.0004% From the saltwells of Michigan, magnesium, bromine, and other elements areextracted, and the salt brine is an important source of these elements.Commercial salt is marketed in many grades, depending chiefly on

the size of the grain The term industrial salt refers rather to the method of packing and shipping than to a grade distinct from domes-

tic salt, but most of the industrial salt is rock salt; the bulk of the

domestic salt is evaporated salt Producers of salt for the food ing industries usually guarantee a quality 99.95% pure since smallamounts of calcium, magnesium, copper, and iron in the salt may give

process-a bitter tprocess-aste, discolor some foods, or cprocess-ause oxidprocess-ation rprocess-ancidity in foods

containing fats Crystal Flake salt, of Diamond Salt, is 99.5% pure with less than 1.5 parts per million of copper or iron Micronized salt, tradenamed MicroSized salt, of the same company, is 99.9% pure

with thin flake particles of super fineness which have a solubility 5

times greater than that of granulated salt Improved Fine Flake salt

has a precisely sized grain for better flow properties as a builder, rier, and diluent in dishwashing detergents, dry bleaches, floor care

car-products, and cosmetics The CMF salt is purified to have less than 20

parts per million of calcium and magnesium, to increase the sudsingproperties of bar soaps, shampoos, and conditioners in personal-care

products Flour salt and coarse-grain salt grades are used as sives Dendritic salt, of Morton Salt, is highly purified salt evaporated

abra-by a process that produces tiny dendritic crystals instead of the regularcubic from It has a faster dissolving rate This company produces

Calacid salt, a formulated salt in tablet form for regulating acidity in

canned foods It contains 60.9% sodium chloride with citric acid,

cal-cium sulfate dihydrate, and sodium carbonate for effervescence See

100, of Diamond Salt, is a noncaking, free-flowing salt for use in

auto-matic food processing equipment It contains 5 ppm of prussiate ofsoda, which blocks the interchemical action of the salt crystals withoutdecreasing solubility, and 0.04% glycerin to increase the free-flowingproperties

Domestic consumption of salt for direct human consumption islarge in all countries It is required in the bloodstream up to about

3.5% and is rapidly exhausted in hot weather Salt tablets, used in

hot weather or by workers in steel mills, are made with about 70%salt and 30 dextrose To make domestic salt free-flowing in humidweather, 2% of calcium sulfate may be added Salt obtained by simpleevaporation of seawater contains salt-resistant bacteria which arecapable of developing in salted hides or fish and injuring the mate-rial Mineral salt is thus preferred for these purposes The glasslike

salt crystals, called struvite, that form in canned fish and some other

products in storage are not common salt, but are crystals of sium ammonium phosphite hexahydrate, Mg(NH4)PO4 6H2O Theyare harmless, but objectionable in appearance, and common salt is

magne-added to inhibit their growth In making salt brines for steel

treat-ing and other industrial purposes, 100 parts of water at ordinary perature will dissolve 36 parts of common salt, but no more than 15%

tem-is ordinarily used because of the corrosive effect

Sodium hypochlorite, or sodium oxychlorite, NaOCl, is a

sta-ble, noncorrosive salt used in tanneries Merclor D is a trade name

of Monsanto Co for this material in water solution Javel water is a

name given in the laundry industry to a water solution of NaOCl used

as a bleach Household bleach contains 5% NaOCl When used as a bleach in the textile industry, it is called chemic In lower chlorine

concentrations it is also used to disinfect potable water in

municipali-ties Chloramone, named after its manufacturer, is such a product.

Sodium chlorite, NaClO2, is a white to yellow, crystalline, uble powder used as a bleaching agent for textiles and paper pulp It

water-sol-is stable up to 302°F (150°C) It yields ClO2 in solution, is an ing agent, and attacks the coloring matter without injuring the fibers

oxidiz-It is also used for waterworks purification Textone is a trade name for sodium chlorite as a bleach for textiles Sodium chlorate,

NaClO3, is used in large quantities as a weed killer and for cottondefoliation and is also used for paper pulp and textile bleaching Itcomes in water-soluble, colorless crystals melting at 482°F (250°C) It

is used as the electrolyte in the chemical machining of metals

SAND. An accumulation of grains of mineral matter derived from thedisintegration of rocks It is distinguished from gravel only by the size

of the grains or particles, but is distinct from clays which containorganic materials Sands that have been sorted out and separatedfrom the organic material by the action of currents of water or bywinds across arid lands are generally quite uniform in size of grains.Usually commercial sand is obtained from river beds or from sanddunes originally formed by the action of winds Much of the earth’ssurface is sandy, and these sands are usually quartz and other

siliceous materials The most useful commercially are silica sands,

often above 98% pure Silica sands for making glass must be free from

iron The sand mined near Hot Springs, Arkansas, called amosil, is

99.5% pure silica and comes in transparent, rounded grains of 118-
in (3-
m) average size Beach sands usually have smooth,spherical to ovaloid particles from the abrasive action of waves andtides and are free of organic matter The white beach sands arelargely silica but may also be of zircon, monazite, garnet, and other

minerals, and are used for extracting various elements Monazite

sand is the chief source of thorium The black sands of Oregon

con-tain chromate, and those of Japan concon-tain magnetite Kyanite isfound in the Florida sands

Sand is used for making mortar and concrete and for polishing andsandblasting Sands containing a little clay are used for makingmolds in foundries Clear sands are employed for filtering water.Sand is sold by the cubic yard (0.76 m3) or ton (0.91 metric ton) but isalways shipped by weight The weight varies from 2,600 to 3,100lb/yd3 (1,538 to 1,842 kg/m3), depending on the composition and size

of grain Construction sand is not shipped great distances, and thequality of sands used for this purpose varies according to local supply

Standard sand is a silica sand used in making concrete and cement

tests The grains are free of organic matter and pass through a

20-mesh sieve, but are retained on a 30-mesh Engine sand, or

trac-tion sand, is a high-silica sand of 20 to 80 mesh washed free of soft

bond and fine particles, used to prevent the driving wheels of tives or cars from slipping on wet rails

locomo-Molding sand, or foundry sand, is any sand employed for

mak-ing molds for castmak-ing metals, but especially refers to sands that arerefractory and also have binding qualities Pure silica is ideal for heatresistance, but must contain enough alumina to make it bindtogether Molding sands may contain from 80 to 92% silica, up toabout 15 alumina, about 2 iron oxide, and not more than a trace oflime Some molding sand contains enough clay or loam to bond it

when it is tamped into place The amount of bond in Grant sand and

in Tuscarawa sand is 17 to 18% About 33% of these natural sands

pass through a No 100 screen, and 20 through a No 150 screen Thefiner the grain, the smoother the casting, but fine-grained sand is notsuitable for heavy work because of its impermeability to gases Sandswithout natural bond are more refractory and are used for steel mold-ing Sands for steel casting must be silica sands containing 90% silica,

or preferably 98, and are mixed with 2 to 10 fireclay For precisioncasting, finely ground aluminum silicate is used in the silica sand

mixes, and it requires less of a bonding agent Calamo, of

Harbison-Walker Refractories Co., is aluminum silicate for this purpose

Zircon sand has high heat resistance and is used for alloy steel

casting Zircon flour is finely milled zirconite sand used as a mold wash Zirconite sand for molding is 100 to 200 mesh in its natural

state It is 70% heavier than silica sand and has a higher heat ductivity that gives more rapid chilling of castings The zirconitesands have melting points from 3650 to 3850°F (2010 to 2121°C).Common molding sands may contain from 5 to 18% of clay materialsand may be mixtures of sand, silt, and clay, but they must have thequalities of refractoriness, cohesiveness, fineness of grain, and perme-ability To have refractory quality, they must be free of calcium car-

con-bonate, iron oxide, and hydrocarbons Core sands also have these

qualities, but they are of coarser grain and always require a bondthat will bake solidly but will break down easily at the temperature ofpouring About 25% of a medium molding sand will be retained on a150-mesh sieve, and about 10% on a 200-mesh sieve Sand withrounded grains is preferred, and the grains must be very uniform insize to prevent filling When a molding sand is burned out, it is madesuitable for reuse by adding bond; but when fireclay is used as abond, it adheres to the sand grains and that makes it unsuitable for

reuse Parting sand is a round-grained sand without bond used on the joints of molds Foundry parting is usually tripoli or bentonite Cores are made with sand mixed with core oils Greensand cores

are unbaked cores made with molding sand

Sandblast sand is sand employed in a blast of air for cleaning

castings, removing paint, cleaning metal articles, giving a dull, roughfinish to glass or metal goods, or renovating the walls of stone or brickbuildings Sandblast sand is not closely graded, and the grades varywith different producers The U.S Bureau of Mines gives the follow-ing usual range: No 1 sand should pass through a 20-mesh and beretained on a 48-mesh screen; No 2 should pass through a 10-meshand be retained on a 28-mesh screen; No 3 through a 6-mesh and beretained on a 14-mesh screen; No 4 should pass through a 4-meshand be retained on an 8-mesh screen Number 1 sand is used for lightwork where a smooth finish is desired; No 4 sand is employed forrough cast-iron and cast-steel work Sharp grains cut faster, but

rounded grains produce smoother surfaces The sand is usuallyemployed over and over, screening out the dust The dust and fine

used sand may be blasted wet This is known as mud blasting and

produces a dull finish

SANDALWOOD. The heartwood of the evergreen tree Santalum

album and other species of southern Asia The heartwood is usually

equivalent to about one-third of the log It is sweet-scented and isused for chests, boxes, and small carved work The chips and sawdust

are used for incense and for oil production Sandalwood oil is a

yel-lowish essential oil of specific gravity 0.953 to 0.985, distilled fromthe wood, which yields 5 to 7% of the oil It is used in medicine, per-

fumery, and soaps West Indian sandalwood oil is called anyris oil.

Australian sandalwood oil is from the tree S spicatum It has a

very strong and lasting sandalwood odor Sandela, of Givaudan

Corp., is a synthetic sandalwood oil It is a polycyclic alcohol productwith the odor and properties of the natural oil

SANDARAC Known also as white gum, or Australian pine gum A

white, brittle resin obtained as an exudation from various species of

the coniferous tree Callitris, known as Cyprus pine The north

African sandarac is from the tree C quadrivalis of the Atlas Mountains, and it resembles the resin from the Australian tree C.

arenosa The trees in Morocco are tapped from May to June, and two

months later the small tears of gum are gathered Sandarac is used invarnishes and is soluble in turpentine and alcohol It melts at 275 to284°F (135 to 140°C) It gives a hard, white spirit varnish used forcoating labels and for paper and leather finishes The product isavailable from O.G Innes Corp Ground sandarac, under the name of

pounce, was formerly used as a pouncing powder and for smoothing

parchment and tracing cloth, but is now replaced by pumice

SANDPAPER. Originally a heavy paper coated with sand grains onone side, used as an abrasive, especially for finishing wood Sharpgrains obtained by crushing quartz later replaced sand, and the prod-

uct was called flint paper But most abrasive papers are now made with aluminum oxide or silicon carbide, although the term sandpa-

pering is still employed in wood polishing Quartz grains, however,

are still much used on papers for the wood industries For this pose the quartz grains are in grades from 20 mesh, known as No 3.5through No 3, 2.5, 2, 1.5, 0, 00, and 000 All the No 000 grains passthrough a 150-mesh sieve, with 25% retained on a 200-mesh sieve

pur-and 80% on a 325-mesh sieve Good spur-andpaper quartz will contain

at least 98.9% silica The paper used is heavy, tough, and flexible,

usually 70- or 80-lb (32- or 36-kg) paper, and the grains are bondedwith a strong glue A process is also employed to deposit the grains onend by electrostatic attraction so that the sharp edges of the grainsare presented to the work.

SANDSTONE. A consolidated sand rock, consisting of sand grainsunited with a natural cementing material The size of the particlesand the strength of the cement vary greatly in different natural sand-stones The most common sand in sandstone is quartz, with consider-able feldspar, lime, mica, and clayey matter The cementing material

is often fine chalcedony Silica sandstones are hard and durable but difficult to work Calcareous sandstone, in which the grains are cemented by calcium carbonate, is called freestone and is easily

worked, but it disintegrates by weathering Freestone is homogeneous

and splits almost equally well in both directions Chert, formerly

used as an abrasive and, when employed in building and paving,

known under local names as hearthstone, firestone, and

malm-stone, is a siliceous stone of sedimentary origin It has a radiating

structure and splintery fracture and is closely allied to flint In color

it is light gray to black or banded The colors of sandstones are due toimpurities, pure siliceous and calcareous stones being white or cream-colored The yellow to red colors usually come from iron oxides, black

from manganese dioxide, and green from glauconite Crab Orchard

stone of Tennessee is high in silica with practically no CaO and is

often beautifully variegated with red and brown streaks It splits inuniform slabs and is used for facing The compressive strength ishigh, up to 24,000 lb/in2 (165 MPa), and the density is 165 lb/ft3(2,643 kg/m3) The water absorption is less than 2%

About half of the commercial sandstone block in the United Statescomes from Ohio It has a density of 140 lb/ft3 (2,243 kg/m3) and acompressive strength of 10,000 lb/in2 (69 MPa), but the average ofmuch other sandstone is 135 lb/ft3 (2,163 kg/m3) with a compressivestrength of 12,000 lb/in2 (83 MPa) Sandstones for building purposesare produced under innumerable names, usually referring to the

locality The bluestone of New York State is noted for its even grain

and high crushing strength, up to 19,000 lb/in2(131 MPa) It contains

about 70% silica sand with clay as the binder Amherst sandstone

from Ohio contains up to 95% silica with 4 aluminum oxide and is

col-ored gray and buff with iron oxides Flexible sandstone, which can

be bent, comes from North Carolina It is itacolumite and has

sym-metrically arranged quartz grains which interlock and rotate againstone another in a binder of mica and talc

Holystone is a block of close-grained sandstone, formerly used for

rubbing down the decks of ships and still used for rubbing down

niture and concrete work Briar Hill stone and Macstone are trade

names for building blocks consisting of lightweight concrete faced

with a slab of sandstone Kemrock is a sandstone impregnated with

a black furfural resin and baked to a hard finish It is used for tops and chemical equipment to resist acids and alkalies The term

table-reservoir rock refers to friable, porous sandstone that contains oil

or gas deposits The porosity of such sandstone or compacted sand ofPennsylvania is from 15 to 20%, while that of California and the GulfCoast is 25 to 40% A sandstone of 20% porosity may contain as much

as 75,000 bbl of oil per acre-foot (1,234 m3)

SANDWICH MATERIALS A type of laminar composite composed of a

relatively thick, low-density core between faces of comparatively

higher density Structural sandwiches can be compared to I

beams The facings correspond to the flanges, the object being toplace a high-density, high-strength material as far from the neutralaxis as possible, thus increasing the section modulus The bulk of asandwich is the core Therefore, it is usually lightweight for highstrength-to-weight and stiffness-to-weight ratios However, it mustalso be strong enough to withstand normal shear and compressiveloadings, and it must be rigid enough to resist bending or flexure.Core materials can be divided into three broad groups: cellular,solid, and foam Paper, reinforced plastics, impregnated cotton fab-rics, and metals are used in cellular form Balsa wood, plywood, fiber-board, gypsum, cement-asbestos board, and calcium silicate are used

as solid cores Plastic foam cores—especially polystyrene, urethane,

cellulose acetate, phenolic, epoxy, and silicone—are used for thermal

insulating and architectural applications Foamed inorganics such

as glass, ceramics, and concrete also find some use Foam cores are

particularly useful where the special properties of foams are desired,such as in insulation And the ability to foam in place is an addedadvantage in some applications, particularly in hard-to-get-at areas

Of all the core types, however, the best for structural applications

are the rigid, cellular cores The primary advantages of the cellular

core are that (1) it provides the highest possible strength-to-weightratio and (2) nearly any material can be used, thereby satisfying vir-tually any service condition

There are, essentially, three types of cellular cores: honeycomb, rugated, and waffle Other variations include small tubes or conesand mushroom shapes All these configurations have certain advan-

cor-tages and limitations Honeycomb sandwich materials, for

exam-ple, can be isotropic, and they have a high strength-to-weight ratio,good thermal and acoustical properties, and excellent fatigue resis-

tance Corrugated-core sandwich is anisotropic and does not have

as wide a range of application as honeycomb, but it is often morepractical than honeycomb for high production and fabrication intopanels.

Theoretically, any metal that can be made into a foil and thenwelded, brazed, or adhesive-bonded can be made into a cellular core

A number of materials are used, including aluminum,

glass-rein-forced plastics, and paper Tubulam VF is a propylene copolymer

honeycomb from the Swiss firm Alusuisse The cells are 0.33-in (8.5-mm) -diameter extruded tubes, both sides of which are coveredwith a polypropylene film and a nonwoven polyester veil for good sur-face bonding with sandwich skin materials In addition, stainlesssteel, titanium, ceramic, and some superalloy cores have been devel-oped for special environments

One of the advantages of sandwich construction is the wide choice

of facings, as well as the opportunity to use thin sheet materials Thefacings carry the major applied loads and therefore determine thestiffness, stability, and, to a large extent, strength of the sandwich.Theoretically, any thin, bondable material with a high tensile- or compressive-strength–weight ratio is a potential facing material Thematerials most commonly used are aluminum, stainless steel, glass-reinforced plastics, wood, paper, and vinyl and acrylic plastics,although magnesium, titanium, beryllium, molybdenum, and ceram-ics have also been used

SAPELE. The figured woods of various species of trees of tropicalAfrica which are mixed with khaya and exported from west Africa as

African mahogany Sapele woods are harder and heavier than red

khaya, but shrink and swell more than khaya with changes in

mois-ture They are also darker with a purplish tinge Sapele mahogany, also called scented mahogany and West African cedar, is from the

Entandrophragma cylindricum, a very large tree growing on the

Ivory Coast and in Ghana and Nigeria On the Ivory Coast it is called

aboundikro Another species, E angolense, is called Tiama

mahogany on the Ivory Coast and in Nigeria is known as brown

mahogany and gedunohor A less heavy wood, from the tree E utile, is known on the Ivory Coast as Sipo mahogany and in the

Cameroons as Assie mahogany It is one of the chief woods exported

as mahogany from the Cameroons The wood known on the Ivory

Coast as heavy mahogany and omu in Nigeria is from the tree E.

candollei, and it is much heavier than other sapeles Nigerian wood, from species of Guarea, notably G cedrata and G thompsonii,

pear-is also exported as African mahogany The woods are more properly

called guarea The color is pale pink to reddish The weight is about

the same as for sapele The wood is of a finer texture than khaya, but

is not figured like sapele of khaya Another wood marketed as African

mahogany is lingue, from the tree Afzelia africana of the west coast

of Africa from Senegal to Nigeria The wood is light brown, turningdark when seasoned, and is beautifully figured

SAPONIN. Glycosides of the empirical formula C32H54O18which havethe property of frothing with water They are found in soap bark, soapnut, licorice, and other plants; when separated out, saponin is awhite, amorphous powder of a disagreeable odor Before the advent ofthe synthetic detergents saponin was important for replacing soaps inwashing compounds where high sudsing was undesirable, and it wasused in industrial scouring compounds, soapless shampoos, and toothpowders It is still used in some detergents, in fire extinguishers, as

an emulsifying agent, and for synthesizing other complex chemicals

It is found to some extent in sweets, such as Turkish halva Saponin

is not a single compound, but is a great group of alicyclic

com-pounds, or five-member or more highly complex ring compounds

having aliphatic, or fatty acid, properties The saponins occur directly

in plants where they have a triterpene structure and may be eitherconverted to or derived from a great variety of acids, vitamins, andother products by photosynthesis or catalyzation They are closelyrelated to the styrols of animal life, and in both plant and animal lifeslight catalytic rearrangements with nitrogen produce the natural

venoms and poisonous compounds The saponins thus form one of

the most useful of the basic chemical groups for biological and

phar-maceutical work Chemically, they are called polymethylene

com-pounds and can be synthesized from petroleum In the drug industry

they are called sapogenines Diosgenin and its derivative,

heco-genin, are saponic compounds that are important raw materials formaking steroids

The saponins can be obtained from many plants Soap nut is the

fruit of the trees Sapidus mukorossi and S laurifolia of northern

India known locally as ritha The soap nut has been used as a

deter-gent in washing fabrics since ancient times The ground nut is prized

as an herbal shampoo, generically known as Shikakai The nut has

56% of pericarp and 44 of seed, and saponin is found in the pericarp

It is extracted with solvents from the dried, powdered fruit Saponin

is soluble in water but insoluble in petroleum spirits Soapbark, also

called morillo bark, is the dried, inner bark of the tree Quillaja

saponaria of the west coast of South America It was used by the

Incas, and the botanical name comes from the Inca word quillean,

meaning to wash The bark produces suds in water, but the powderedbark is highly sternutatory owing to fine crystals of calcium oxalate

It is marketed in brownish-white pieces and is used as a source of

saponin It has been used in beverages to produce froth, but is highlytoxic, affecting the heart and respiration In medicine it is called

quillaja and is used as an irritant and expectorant Soapwort

con-sists of the leaves of the plant Saponaria officinalis, growing in North

America The leaves contain saponin which dissolves out in water to

produce a lather useful for cleaning silk and fine woolens Soapberry

is the fruit of the tropical tree Sapindus saponaria, used in hair and

toilet preparations The soapberry of the American southwest consists

of the fleshy berries of the small tree S drummondii Soaproot is

the bulb root of the plant Chlorogalum pomeridianum of California.

Mexican soaproot is the thick rootstock of Yucca baccata and of the wild date, Y glauca, growing in the dry regions of Mexico and the

southwestern United States Both plants are called yucca, and in Mexico they are called amole The Indians used the roots, which were called vegetable soap by the settlers, for washing In the pro-

cessing of yucca leaves to obtain fiber, about 20% of a powder is

obtained which contains 3% saponin Yucca powder is used in

scour-ing compounds or for the extraction of saponin The long, stout stems

of the soap plant, Chenopodium californicum, also yield saponin.

SAPPHIRE. A transparent variety of the mineral corundum When ithas the beautiful blue hue for which it is noted, it ranks with dia-mond, ruby, and emerald among precious gemstones The off-colorstones are cut for pointers and wearing points of instruments Thespecific gravity of sapphire is 3.98, and the Mohs hardness is 9 Theblue color is from iron and titanium oxides and is rarely uniformthroughout the stone in the natural material The green is producedwith cobalt, and the yellow comes from nickel and magnesium The

pink sapphire contains a tiny proportion of chromic oxide, and

larger amounts produce the dark-red ruby The best gem sapphires

come from India A valuable black sapphire comes from Thailand.

Industrial stones are found in Montana Most natural sapphires are

small, but a large one known as the Star of Artaban weighs 300

carats

Synthetic sapphire is produced by flame-fusing a pure alumina

powder made from calcined ammonium aluminum sulfate The fusedmaterial forms a boule as a single crystal The average boule is 200carats, but sometimes they are as large as 400 carats, or about 0.75 in(1.9 cm) in diameter and 2 in (5.1 cm) long The rods are single crys-tals up to 0.23 in (0.58 cm) in diameter and 18 in (45.7 cm) long

Sapphire balls, for bearings and valves, are produced by Linde to

great accuracy in diameters from 0.0625 to 0.625 in (0.16 to 1.59 cm).The balls are single crystals with a Knoop hardness from 1,525 to2,000, a coefficient of friction of 0.140, and a compressive strength of

300,000 lb/in2(2,069 MPa) The material has a melting point of 3686°F(2030°C) and is resistant to acids and alkalies It also has a very lowcoefficient of expansion and is used for ring and plug gages, and forsuch wear parts as the thread guides on textile machines Stones freefrom strains, and as large as 0.75 in (1.9 cm) square, for use as lenses,prisms, and optical windows, are made by Bell Laboratories by recrys-tallization at high temperature and pressure They transmit light bet-ter than quartz into the infrared and ultraviolet areas, and sapphire is

used as an infrared detector in antiaircraft missiles The dielectric

constant of sapphire is also high, about 10.6

Sapphire whiskers are alumina fibers 39
in (1
m) in ter and 0.125 in (0.3 cm) long They may be matted without bond into

diame-ceramic papers for electrical insulation and filters As a

reinforce-ment for light metals, sapphire fibers increase tensile and fatigue strengths Whiskerloy AA20 is an aluminum alloy with 20% sap-

phire fiber It has a tensile strength of 48,000 lb/in2 (331 MPa) and amodulus of 18  106lb/in2(124,110 MPa)

SCHEELITE. An ore of the metal tungsten, occurring usually withquartz in crystalline rocks associated with wolframite, fluorite, cassi-terite, and some other minerals It is found in various parts of the

United States, Brazil, Asia, and Europe Scheelite is calcium

tungstate, CaWO4, containing theoretically 80.6% tungsten trioxide

and 19.4 lime It is called powellite when it contains some

molybde-num to replace a part of the tungsten It occurs massive granular or

in crystals The color is white, yellow, brown, or green, with a vitreousluster Chinese scheelite from Kiangsi averages 65% WO3 and can be

used directly for adding tungsten to steel Tungstic acid is a yellow

powder of composition H2WO4 made from the ore by treating withhydrochloric acid It is not soluble in water, but is soluble in alkaliesand in hydrofluoric acid, and it is used as a mordant in dyeing, inplastics, and for making tungsten wire by reducing Tungstic acid isalso obtained as a by-product in the manufacture of alkalies from thebrine of Owens Lake and is a source of tungsten, 1,000 lb (454 kg) of

acid yielding about 800 lb (363 kg) of metallic tungsten

Phospho-tungstic acid, H3[P(W3O10)4] 5H2O, called heavy acid, is used as a

catalyst in difficult synthesis operations on complex ring-compoundchemicals The molecular weight is 2,879, of which three-fourths istungsten The three hydrogens produce the strong acid activity Theacid is soluble in water and in organic solvents

Pure crystals of scheelite suitable for scintillation-counter phosphorsfor gamma-ray detection are found, but the natural crystal is rare.Calcium tungstate is grown synthetically as a clear, water-white crys-tal of tetragonal structure in rods and boules with the axis oriented

perpendicular to the growth axis of the rod It has a specific gravity of6.12, a Mohs hardness of 4.5 to 5, a melting point of 2795°F (1535°C),and a refractive index of 1.9368 It has a blue luminescence underultraviolet light The crystals can be made in shiny, crystalline scales,

and the material is also used in fluorescent pigments Cadmium

tungstate, CdWO4, is similarly grown in clear, yellowish-green, clinic crystals with a refractive index of 2.25, and it is superior to cal-cium tungstate for scintillation counters The crystals can also begrown with a cleavage much like mica, and it is used in fluorescentpigments

mono-SCOURING ABRASIVE. Natural sand grains or pulverized quartzemployed in scouring compounds and soaps, buffing compounds, andmetal polishes Federal specifications require that the abrasive grainsused in grit cake soap and scouring compounds all pass a No 100screen; the grains for scouring compounds for marble floors must allpass a No 100, and 95% pass a No 200 screen For ceramic floors90% must pass a No 80, and 95% must pass a No 60 screen Veryfine air-floated quartz is employed in metal polishes, and all grainspass a 325-mesh screen, but the extremely fine powders of metal

oxides for polishes and fine finishes are generally called soft abrasives

and are not classified as scouring materials

SCREW STOCK. A common term for steels and nonferrous metals,notably brass, having superior machinability and used to makescrews and small turned parts on automatic screw machines Insteels, free-cutting, or free-machining, quality is imparted by theaddition of small amounts of alloying elements, such as sulfur, phos-phorus, lead, tellurium, bismuth, calcium, or selenium, sometimes invarious combinations In brass, lead is the usual free-machiningadditive

SEAL OIL. An oil resembling sperm oil obtained from the blubber of

the oil seal, Phoca vitulina, a sea mammal native to the Atlantic

Ocean The oil has a saponification value as high as 195 and aniodine value up to 150, and it was once valued for lubricating andcutting oils but is now scarce In the nineteenth century, as many as

400 ships at a time operated from Newfoundland in seal catching, butthe unrestricted catch resulted in the destruction of the herds, andNorth Atlantic sealing was reduced to three ships by the middle ofthe twentieth century The industry now centers on South Georgia inthe south Atlantic as an adjunct to the whale industry, but consider-

able oil and seal meal come as by-products of the Alaskan fur seal

industry

Some seal oil is obtained from Steller’s sea lion, a large-eared sealfound from southern California to the Bering Sea The adult maleweighs up to 2,200 lb (998 kg) The blubber is about 75% oil, with aniodine value of 143 and saponification value of 190 From 40 to 50% ofthe carcass is a dense, dark-red, edible meat, but in the United States

seal meat is used only in animal foods Seal leather, from the skin,

is used for fancy specialty articles, but it has too many defects for

general use The product known as sealskin is a valuable fur skin

from the fur seal, about 80% of which are caught off the PribilofIslands where they return in June to breed No killing is now permit-ted at sea Each bull seal has as many as 50 females, and the killing

is usually restricted to the surplus males About 30% of the skins are

black fur which brings the highest price Next in value is the Matara

fur, or dark-brown, which is 60% of the catch The Safari fur is light

brown

SEAWEED. A plant growing in the sea, belonging to the extensive

plant division known as algae About 17,000 varieties of seaweed are

listed, but only a few are exploited commercially Algae are bearing plants containing photosynthetic pigments They have novascular or food-conveying system and must remain submerged in themedium from which they acquire their food They occur in both freshand salt waters

non-seed-The brown seaweeds, which are the true kelps, grow in ate and polar waters They produce algin, fucoidin, and laminarin The red seaweeds are the carrageens, which produce carrageenin, and the agarophytes, which yield agar and agaroid They grow in

temper-warm waters But color is an indefinite classification; the chlorophyll

in the green Irish moss is often so masked by other pigments that theweed may be purplish black All the seaweed colloids, or phycocol-loids, are polysaccharides, having galactose units linked in longchains of molecular weights from 100,000 to 500,000, varying in theirchemical structure They are anionic polyelectrolytes, with negative

radicals on each repeating polymer unit Irish moss, also called

chondrus (pronounced chone-droosh), pearl moss, and carrageen,

is a dwarf variety of brown seaweed, Chondrus crispus, and

Gigantina mamillosa, found off the west coast of Ireland and in New

England The weed used mostly for alginic acid is the brown kelp

Laminaria saccharium, L ditata, and other species, found off the

Hebrides It is a cold-water plant

The seaweed G stellata, of the north Atlantic, is also used to

pro-duce agar and algin It is bleached and treated to propro-duce gelatin used

in foodstuffs, as a clarifying agent, and as a sizing for textiles It is abetter suspending and gelatinizing medium than agar for foodstuffs

and cosmetic emulsions At least 25 mineral salts are known to bepresent in seaweed as well as several vitamins In the utilization of

the seaweed as gelatin or alginate these are left in the kelp meal

which is marketed as poultry and stock feed In Asia the whole plant

is cooked and eaten Seaweed flour, made in Germany from Iceland

seaweed, Phaeophyceen, is the ground, dry seaweed containing all

the minerals and vitamins It is mixed with wheat and rye flours to

make algenbrot, a bread with higher food value and better keeping

qualities than ordinary wheat bread But more than 8% gives a

pecu-liar flavor to the bread The Irish name dulse is applied to the dried or cooked seaweed, Rhodymenia palmata, used in the Canadian

Maritime Provinces for food It is purple and rich in iodine and

min-eral salts Other species, known as laver and murlins, are also used

in Iceland, Ireland, and Scotland for food When used for producing

iodine in Scotland, the seaweed goes under the general name of

tan-gle Much of the 4,500 mi (7,607 km) of coastline of Scotland contains

brown kelp The kelp found along the Chilean and Peruvian coasts,when dried for making algin products, is called by the Quechua name

cochayuyo Kombu, used by the Japanese for food, is a brown

sea-weed from the coast of Hokkaido

Dry seaweed contains up to 30% alginic acid; the water-soluble

salts of this acid are called algin It belongs to the group of complex,

open-chain uronic acids which occur widely in plant and animal

tis-sues and are related to the proteins and pectins All the algins areedible, but they pass unchanged through the alimentary tract andadd no food value Carageenin is much used as a stabilizer for choco-

late in milk Laminarin is used as laminarin sulfate as a blood-clotting agent Sodium alginate is used as a stabilizer and

ice-crystal retarder in ice cream, as an emulsifier in medicines, and toreplace gum arabic It is a colorless, water-soluble gum made by dis-solving algin in sodium carbonate solution and neutralizing with

hydrochloric acid Protan jelly, used for coating fish for freezing, is

algin in a dilute edible acid When frozen, the jelly is impervious toair and prevents oxidation It can be washed off with water

Kelgin, of the Kelco Div of Merck & Co., Inc., is sodium alginate

used as a foodstuff stabilizer, and Keltrex is the material in granular form for textile coating Kelset, of the same company, is an algin used

as a suspending agent for foodstuffs It does not alter flavor or texture

and is stable up to 200°F (93°C) Dariloid is sodium alginate to replace gelatin in ice cream; Kelcosol is an alginate to replace starch

in foodstuffs One part of algin can replace six parts of starch, and it

does not smother flavor as starch does Protakyp K, of Croda, Inc.,

used as a thickener for textile printing inks, is an alginate compatible

with gums Viscobond is a modified sodium alginate for finishing

cellulosic textiles Kim-Ko gel is a light-buff, scaly powder easily

sol-uble in water, made from Irish moss, used as a collodial gelling agent

It has a pH of 6.4 to 7.2 Carrigar is a purified alginate for

pharma-ceuticals and foodstuffs It contains the natural mineral salts and hasfood value It has high capacity for water absorption, making rigid,

sugar-free jellies with less than 2% in solution Algaloid and Agagel

are algins of this type

Alginic fibers are silklike fibers made by forcing a sodium

algi-nate solution through spinnerets into a calcium chloride bath andinsolubilizing with beryllium acetate; but the fiber is soluble insodium soaps, and the fabrics must be dry-cleaned Soluble alginicyarns are used for making fancy fabrics where uneven spacing ofthreads is desired without change in the loom The alginate yarn iswashed out of the fabric after weaving, leaving the desired spacing

SELENIUM. An elementary metal, symbol Se, found native in cavities

in Vesuvian lavas and in some shales The volcanic tuff of Wyomingcontains 150 parts per million of selenium, and the black shale ofIdaho has up to 1 lb (0.45 kg) of selenium per ton (0.9 metric ton) It

also occurs in many minerals, chiefly in cucairite, (AgCu)2Se,

nau-mannite, Ag2Se, zorgite, (ZnCu)2Se, and in crooksite andclausthalite Production in the United States and Canada is largely

as a by-product of copper refining, the blister copper anodes ing 0.03 to 0.04%, and the refinery slimes having a content of 8 to 9%.The commercial recovery is 0.66 lb/ton (0.33 kg/metric ton) of copper

contain-In England it is recovered from the residues of roasting iron sulfideores in sulfuric acid production

Like sulfur, selenium exists in various forms Six allotropic formsare recognized, but four well-defined forms are usually listed

Amorphous selenium, produced by reducing selenous acid, is a

finely divided, brick-red powder with a specific gravity of 4.26 It

yields the vitreous form on heating Vitreous selenium is a

brownish-black, brittle, glassy mass with a specific gravity of 4.28 It

is a dielectric and is electrified by friction The monoclinic

crys-talline selenium is produced by crystallization from carbon

disul-fide, and it is a deep-red glass material with a specific gravity of 4.46and a melting point of 347°F (175°C) The hexagonal crystalline sele-nium is produced by heating the monoclinic It is a stable metal and

is a good conductor of electricity It has a specific gravity of 4.79 andmelts at 422°F (217°C) All of the forms become gaseous at 1270°F(688°C) Selenium is marketed as a blackish powder, the high gradebeing 99.99% pure and the commercial grade 99.5% pure

Selenium metal is odorless and tasteless, but the vapor has a putridodor The material is highly poisonous and is used in insecticides and

ship-hull paints Foods grown on soils containing selenium may havetoxic effects, and some weeds growing in the western states have highconcentrations of selenium and are poisonous to animals eating them.

Selenium burns in air with a bright flame to form selenium dioxide,

SeO2, which is in white, four-sided, crystalline needles The oxide

dis-solves in water to form selenous acid, H2SeO3, resembling sulfurous

acid but very weak Oxidation of this acid forms selenic acid,

H2SeO4, a strong acid resembling sulfuric acid By burning loco weedand converting to the acids, selenium has been extracted from theweeds

The photoelectric properties of selenium make it useful for measuring instruments and for electric eyes Amorphous or vitreousselenium is a poor conductor of electricity, but when heated, it takesthe crystalline form and its electrical resistance is reduced, and itchanges electrical resistance when exposed to light The change of elec-trical conductivity is instantaneous, even the light of small lamps hav-ing a marked effect since the resistance varies directly as the square ofthe illumination The pure amorphous powder is also used for coatingnickel-plated steel or aluminum plates in rectifiers for changing alter-nating current to pulsating direct current The coated plates are sub-jected to heat and pressure to change the selenium to the metallicform, and the selenium coating is covered with a layer of cadmium-bis-muth alloy Selenium rectifiers are smaller and more efficient thancopper oxide rectifiers, but they require more space than silicon recti-fiers and are limited to an ambient temperature of 185°F (85°C)

light-Selenium is also used in steels to make them free-machining, up to0.35% being used Up to 0.05% of selenium may also be used in forg-ing steels From 0.6 to 0.85 oz (0.017 to 0.024 kg) of selenium per ton(0.9 metric ton) of glass may be used in glass to neutralize the greentint of iron compounds Large amounts produce pink and ruby glass.Selenium gives the only pure-red color for signal lenses Pigment for

glass may be in the form of the black powder, barium selenite,

BaSeO3, or as sodium selenite, Na2SeO3, and may be used with mium sulfide Selenium is also used as an accelerator in rubber and

cad-to increase abrasion resistance Vandex, of R T Vanderbilt Co., is a selenium powder used as a rubber vulcanizer Novac, used for curing

synthetic rubbers, is selenium dibutyl dithiocarbonate in the form of

a liquid easily dispersed in the rubber Selsun, of Abbott Laboratories, is selenium sulfide suspended in a detergent, used to

control dandruff in hair In copper alloys, selenium improves

machin-ability without hot-shortness Selenium copper is a free-cutting

copper containing about 0.50% selenium It machines easily, and theelectrical conductivity is nearly equal that of pure copper The tensilestrength of annealed selenium copper is about 30,000 lb/in2 (207

MPa) Small amounts of selenium salts are added to lubricating oils

to prevent oxidation and gumming

SEMICONDUCTORS. Materials that are capable of being partly ductors of electricity and partly insulators and are used in rectifiersfor changing alternating current to pulsating direct current, and intransistors for amplifying currents They can also be used for the con-version of heat energy to electric energy, as in the solar battery In anelectric conductor, the outer rings of electrons of the atoms are free tomove and provide a means of conduction In a semiconductor the

con-outer electrons, or valence electrons, are normally stable, but when

a doping element that serves to raise or lower energy is

incorpo-rated, the application of a weak electric current will cause ment of valence electrons in the material Silicon and germanium,each with a single stable valence of four outer electrons, are the mostcommonly used semiconductors Elements such as boron, with a lowerenergy level but with electrons available for bonding and thus accept-

displace-ing electrons into the valence rdisplace-ing, are called hypoelectronic

ele-ments Elements such as arsenic, which have more valence

electrons than are needed for bonding and may give up an electron,

are called hyperelectronic elements Another class of elements, like cobalt, can either accept or donate an electron, and these are called buffer atoms All of these types of elements constitute the

doping elements for semiconductors

In a nonconducting material, used as an electrical insulator, the

energy required to break the valence bond is very high, but there isalways a limit at which an insulator will break the bond and become

a conductor with high current energy The resistivity of a conductorrises with increasing temperature, but in a semiconductor the resis-tivity decreases with temperature rise, and the semiconductor

becomes useless beyond its temperature limit Germanium can be used as a semiconductor to about 200°F (93°C), silicon can be used to about 400°F (204°C), and silicon carbide can be used to about 650°F (343°C) Silicon carbide–germanium alloys, developed by scien-

tists at the University of Delaware and U.S Army ResearchLaboratory, may portend high-performance semiconductors to controlhot, high-power and high-frequency microelectronic and small electro-mechanical machines better than silicon With 1 to 4% germanium,the alloys can conduct twice as much current as silicon carbide

Metals for use as semiconductors must be of great purity, sinceeven minute quantities of impurities would cause erratic action The

highly purified material is called an intrinsic metal, and the desired

electron movement must come only from the doping element, or

extrinsic conductor, that is introduced The semiconductors are

usually made in single crystals, and the positive and negative ments need be applied only to the surfaces of the crystal, but methodsare also used to incorporate the doping element uniformly throughoutthe crystal.

ele-The process of electron movement, although varying for differentuses and in different intrinsic materials, can be stated in generalterms In the silicon semiconductor, the atoms of silicon with fourouter valence electrons bind themselves together in pairs surrounded

by eight electrons When a doping element with three outer electrons,such as boron or indium, is added to the crystal, it tends to take anelectron from one of the pairs, leaving a hole and setting up an imbal-

ance This forms the p-type semiconductor When an element with

five outer electrons, such as antimony or bismuth, is added to the

crystal, it gives off electrons, setting up a conductive band, which is

the n-type semiconductor Fusing together the two types forms a

pn junction, and a negative voltage applied to the p side attracts the

electrons of the three valence atoms away from the junction so that

the crystal resists electronic flow If the voltage is applied to the n

side, it pushes electrons across the junction and the electrons flow

This is a diode, or rectifier, for rectifying alternating current into

pulsating direct current When the crystal wafers are assembled in

three layers, pnp or npn, a weak voltage applied to the middle wafer

increases the flow of electrons across the whole unit This is a

tran-sistor Germanium and silicon are bipolar, but silicon carbide is

unipolar and does not need a third voltage to accelerate the electrons.Semiconductors can be used for rectifying or amplifying, or they can

be used to modulate or limit the current By the application of heat toionize the atoms and cause movement they can also be used to gener-ate electric current; or in reverse, by the application of a current theycan be used to generate heat or remove heat for heating or coolingpurposes in air conditioning, heating, and refrigeration But for usesother than rectifying or altering electric current, the materials areusually designated by other names and are not called semiconductors

Varistors are materials, such as silicon carbide, whose resistance is a

function of the applied voltage They are used for such applications as

frequency multiplication and voltage stabilization Thermistors are

thermally sensitive materials Their resistance decreases as the perature increases, which can be measured as close as 0.002°F(0.001°C), and they are used for controlling temperature or to controlliquid level, flow, and other functions affected by rate of heat transfer.They are also used for the production or the removal of heat in air

tem-conditioning and may then be called thermoelectric metals.

Indium antimonide, InSb, has a cubic crystal structure, with

three valence electrons for each indium atom and five for each

mony atom Between each atom and its four nearest neighbors thereare four electron-pair bonds, and there are an average of four elec-

trons per atom in the compound It is used for infrared detectors and for amplifiers in galvanomagnetic devices Indium arsenide,

InAs, also has a very high electron mobility and is used in tors for heat-current conversion, since the number of electrons free toconstitute the electric current increases about 3% with each 1°F(0.56°C) rise in temperature It can be used to 1500°F (816°C) Somematerials can be used only for relatively low temperatures Copperoxide and pure selenium have been much used in current rectifiers,but they are useful only at moderate temperatures, and they have the

thermis-disadvantage of requiring much space Indium phosphide, InP, has

a mobility higher than that of germanium and can be used in

transis-tors above 600°F (316°C) Aluminum antimonide, AlSb, can be used

at temperatures to 1000°F (538°C) In lead selenide, PbSe, the

mobility of the charge-carrying electrons decreases with rise in perature, increasing resistivity It is used in thermistors

tem-The thermoelectric generation, set up when the junction of two similar thermoelectric metals is heated and which is used in ther-mostats for temperature measuring and control, is essentially the

dis-same as the energy conversion and heat pumping with p-type and

n-type materials The difference is in mechanical applications When

a semiconductor is operated thermoelectrically as a heat pump, theelectric charge passing through the heat-absorbing junction is carried

by electrons in the n-type material and holes in the p-type material,

and the charge carriers both move away from the junction and carryaway heat, thus reducing temperature at the junction By reversingthe current, heat is produced Each material has a definite tempera-ture difference, or gradient, and the efficiency is proportional to thetemperature difference across the material, while the power rating isproportional to the square of the temperature difference Thus, amaterial with low efficiency may have a high power rating if it can beoperated at a high enough temperature, but some materials do notmaintain chemical stability at high temperatures Also, for many uses

it is undesirable to operate at advanced temperatures

Bismuth telluride, Bi2Te3, maintains its operating propertiesbetween 50 and 400°F (46 and 204°C), which is the most useful

range for both heating and refrigeration When doped as a p-type

con-ductor, it has a temperature difference of 1115°F (601°C) and an

effi-ciency of 5.8% When doped as an n-type conductor, its temperature

difference is lower, 450°F (232°C), but the efficiency within this range

is more than doubled Lead telluride, PbTe, has a higher efficiency,

13.5%, and a temperature difference of 1080°F (582°C), but it is notusable below 350°F (177°C) and is employed for conversion of the

waste heat from atomic reactors at about 700°F (371°C) The

nanophase materials known as carbon nanotubes also can

behave as n-type and p-type materials.

Gallium arsenide has high electron mobility and can be used as a

semiconductor When polycrystalline semiconductors are used in thinfilms against a metal barrier, the minimum grain size of the depositedfilm must equal the thickness of the film so that the carrier is not inter-

cepted by a grain boundary Cadmium sulfide, CdS, is thus deposited

as a semiconductor film for photovoltaic cells, or solar batteries,

with film thickness of about 79
in (2
m) Thin-film cells of

copper-indium diselenide and gallium can convert 15.5% of sunlight

into electricity, and tandem cells of gallium-indium phosphide and

gallium arsenide can convert 29.5% When radioactive isotopes, instead

of solar rays, are added to provide the activating agent, the unit is

called an atomic battery, and the large area of transparent backing

for the semiconductor is not needed

Manganese telluride, MnTe, with a temperature difference of

1800°F (982°C), has also been used as a semiconductor Many othermaterials can be used, and semiconductors with temperature differ-ences at different gradients can be joined in series electrically toobtain a wider gradient, but the materials must have no diffusion atthe junction If intermetal compounds are of such a nature as to have

a pn balance, no doping is needed; but usually they are not in perfect

balance, causing scattering, and balancing is necessary Materials forthermoelectric use are usually doped higher than for semiconductors,but increased doping reduces resistivity, and for high emf and lowpower, only small amounts are used

Cesium sulfide, CeS, has good stability and thermoelectric

prop-erties at temperatures to 2000°F (1093°C) and has a high ture difference, 2030°F (1110°C) It can thus be used as a high-stageunit in conversion devices High conversion efficiency is necessary for

tempera-transducers, while a high dielectric constant is desirable for

capaci-tors Low thermal conductivity makes it easier to maintain the perature gradient, but for some uses high thermal conductivity is

tem-desirable Silver-antimony-telluride, AgSbTe2, has a high conversion efficiency for converting heat to electric current, and it has

energy-a very low thermenergy-al conductivity, energy-about 1% thenergy-at of germenergy-anium

Mechanical stress, as well as heat stress, produces an electric charge

in balanced semiconductors, and they can be used for controlling sure The semiconductor-type intermetals are also used in magneticdevices, since the ferroelectric phenomenon of heat conversion is the elec-

pres-trical analog of ferromagnetism Chromium-manganese-antimonide

is nonmagnetic below about 482°F (250°C) and magnetic above that perature Various compounds have different critical temperatures

Below the critical temperature, the distance between the atoms is lessthan that which determines the lineup of magnetic forces; but withincreased temperature the atomic distance becomes greater, and theforces swing into a magnetic pattern.

Organic semiconductors fall into two major classes: well-defined

substances, such as molecular crystals and crystalline complexes,isotatic and syndiotactic polymers; and disordered materials, such asatactic polymers and pyrolitic materials Few of these materials have

yet found commercial application Anthracene, an example of the

mol-ecular crystal type, has perhaps been given the most study Its transport

properties are not unlike those of silicon and germanium Amorphous

silicon containing hydrogen is promising for use in solar cells because

of its low cost and suitable electrical and optical properties

SENNA. The dried, small leaves and the pods of the bushy plant

Cassia acutifolia, the Alexandrian senna, and C angustifolia, the

Tinnevelly senna, of India, Arabia, and north Africa The plants are

cultivated in India, but the Sudan material comes mostly from wildplants The sun-dried leaves and pods are shipped in bales They areused directly as a laxative by steeping in water, or the extract is used

in pharmaceuticals It contains the yellowish, noncrystalline

cathar-tine, a powerful purgative Another species of the plant, C auricula,

yields avarem bark, which is an important tanning material in

India It is similar to algarobilla in action

SERPENTINE. A mineral of theoretical formula 3MgO 2SiO2 2H2O,containing 43% magnesium oxide It is used for building trim and formaking ornaments and novelties The chips are employed in terrazzoand for roofing granules Actually, the stone rarely approaches thetheoretical formula and usually contains 2 to 8% iron oxide withmuch silica and aluminum It has an asbestoslike structure Theattractively colored and veined serpentine of Vermont is marketed

under the name of verde antique marble The massive verde

antique of Pennsylvania is used with dolomite in refractories

Antigorite is a form of serpentine found in California which has a

platy rather than a fibrous structure The serpentine of ColumbusCounty, Georgia, contains 36 to 38% MgO and 2 to 5 chrome ore It isused as a source of magnesia

SESAME OIL. A pale-yellow, odorless, bland oil obtained from the

seeds of the tropical plant Sesamum orientale and other species, grown in India as S indicum, and in China, Africa, and Latin

America, and used for soaps, foodstuffs, and blending industrial oils

It is distinct from German sesame oil The seeds from different

species and localities vary greatly in size and color, from yellowish

white to reddish brown to black The oil from Nigeria is called benne

oil, and the seed benniseed In India it is known as til oil, and the

seed as til seed In Madras it is called gingelli In Mexico it is called

ajonjoli The seeds contain 50% of oil of a specific gravity of 0.920 to

0.925, with saponification value 188 to 193 Super Refined oil is a

high-purity, colorless, odorless oil for use as a pharmaceutical vehicle.Croda, Inc is the marketer of this variety

Sesame is one of the most ancient of food grains, but has been littlegrown in the United States because of the difficulty of harvesting and

collecting the seed Sesame seed is used as a flavor garnish for breads and bakery products Sesame protein, extracted from the

seed and marketed as a powder, contains the amino acids methionineand cystine which are low in other vegetable foods It is low in lycine

It is valued for blending in foodstuffs The oil contains the natural

antioxidants sesamol and sesamolin, making it very stable, and it is

also highly unsaturated These are present in concentrations of lessthan 1% The protein is marketed as a flour containing 60% proteinand less than 1 fat, and in granules containing 55 protein and up to

18 fat SesaLac 86 is a spray-dried blend of sesame protein and whey

for use in beverages, bakery products, and prepared foods, giving amore complete amino acid combination than milk powder

SHALE. A rock formed by deposition of colloidal particles of clay andmud, and consolidated by pressure It is fine-grained and has a lami-nated structure, usually containing much sand colored by metaloxides Unlike sandstones, shales are not usually porous, most shalesbeing hard, slatelike rocks Slate is a form of shale that has been sub-jected to intense pressure Some shales are calcareous or dolomiticand are used with limestone in making portland cement These are

called marlstone Oil shale is a hard shale with veins of greasy solid known as kerogen, which is oil mixed with organic matter Crude

shale oil is a black, viscous liquid containing up to 2% nitrogen and a

high sulfur content But when oil shale is heated above 750°F(399°C), the kerogen is cracked into gases condensable to oils, gases,and coke Some shales also yield resins and waxes, and the

Kvarmtorp shale of Sweden contains small amounts of uranium,

vanadium, and molybdenum The regular commercial by-products of

Swedish shale oil recovery are sulfur, fuel gas, ammonium sulfate,

tar, and lime Oil shales are widely distributed in many parts of theworld and are regularly distilled in most of the countries in Europe,the yield varying from 15 to 100 gal (57 to 379 L) per short ton (907kg) Scottish shales give an average yield of 24.5 gal (93 L) crude oiland 35.7 lb (16 kg) ammonium sulfate per short ton (907 kg) Shaleoccurs in strata and is mined as coal is The oil shales of Colorado

contain dawsonite, a hydrated carbonate of aluminum and sodium, and nacolite, a sodium bicarbonate mineral Alumina, soda ash, and other by-products can be produced from the shales Bituminous

shale was originally called boghead coal in England and torbane mineral in Scotland In the Green River Basin of northwestern

Colorado about 1,000 mi2(2,590 km2) is underlain by oil shale 500 ft(152 m) thick averaging 15 gal/ton (0.06 L/kg) The lower portion,about 100 ft (30 m) thick, averages 30 gal/ton (0.13 L/kg) Recovery in

a continuous retort extracts 94% of the oil, which is then cracked byheat and treated with hydrogen to remove impurities and improvethe quality before it is sent to the refinery It is estimated that theshale of the Mahogany Ledge in Colorado, extending into Utah andWyoming, has a content of 1.2 trillion bbl of extractable oil No oil isvisible in the shale, but it is present as the solid kerogen, which yieldsoil when heated Other deposits occur in Nevada, Tennessee, Indiana,

Ohio, and Kentucky Oil sands of Alberta, Canada, Utah, and

California are free-flowing sands impregnated with bituminous oil Adeposit on the Athabasca River covers 1,800 mi2(4,662 km2) and is 165

ft (50 m) thick Vast quantities of oil are available from these sands

SHARK LEATHER. A durable, nonscuffing leather used for ings, handbags, and fancy shoes, made from the skin of sharks Theshark is the largest of the true fishes, but has a skin unlike fishskin.When tanned, the surface is hard, the epidermis thicker than cowhide,and the long fibers lie in a crossweave The shark is split on the backinstead of the belly, as in cowhides, and the skins measure from 3 to 20

bookbind-ft2 (0.3 to 2 m2), averaging 10 ft2(1 m2) The hard denticle, called the

shagreen, is usually removed, after which the leather is pliable but

firm, the exposed grain not pulling out Shagreen leather is a hard,

strong leather with the grain side covered with globular granules made

to imitate the sharkskin Eastern shark leather has a deep grain withbeautiful markings The eastern shark includes about a dozen species

of shark caught off the Florida and Cuban coasts, except the nurse

shark and the sawfish which are graded separately The whale shark attains a length of 50 ft (15 m) and a weight of several tons It is

an offshore species, feeding on small organisms, and is harmless to

peo-ple The basking shark and the white shark grow to 40 ft (12 m) The nurse shark measures 6 to 10 ft (1.8 to 3 m) Olcotrop leather,

from a species of shark, has a smooth, fine grain with regular

mark-ings Galuchat leather, or pearl sharkskin, is from the Japanese ray It is used for trim on pocketbooks Boroso sharkskin, rousette

leather, or Morocco leather is from a small shark of the

Mediterranean, but the name is also applied to a vegetable-tannedSpanish goatskin on which a pebbly grain is worked up by hand board-ing It is now made from ordinary goatskin by embossing

Most of the sharkskin is now a by-product of the catch for oil, which

is used for medicinal purposes The shark liver is about one-fourth

the total weight of the animal, and shark-liver oil is 30 times higher

in vitamin A than cod-liver oil The oil is also used for soap, lubricant,and heat-treating oil, though normally it is too expensive for thesepurposes The Mexican shark-oil industry centers at Mazatlán, and

about 25 species are caught off the west coast Vitamin oil from

South Africa is from the liver of the stockfish, Merluccius capensis,

which is an important food fish The liver contains 30% oil

SHEEPSKIN. The skin of numerous varieties of sheep, employed forfine leather for many uses The best sheepskins come from the sheepyielding the poorest wool When the hair is short, coarse, and sparse,the nourishment goes into the skin The merino types having finewool have the poorest pelts Wild sheep and the low-wool crossbreeds

of India, Brazil, and South Africa have close-fibered, firm pelts parable in strength with some kidskin, and retain the softness ofsheepskin This type of sheepskin from the hair sheep is termed

com-cabretta and is used almost entirely for making gloves and for shoe

uppers None is produced in the United States The lambs grown inthe mountains of Wales, Scotland, and the western United States alsofurnish good skins The commercial difference between sheepskin and

lambskin is one of weight only Sheepskins usually run 3 to 3.5 lb

(1.4 to 1.6 kg) per skin without wool, and lambskins are those below 3

lb (1.4 kg) Sheepskins are tanned with alum, chrome, or sumac Thelarge, heavy skins from Argentina and Australia are often split, andthe grain side tanned in sumac for bookbinding and other goods; theflesh side is tanned in oil or formaldehyde and marketed as chamois.The fine-grained sheepskins from Egypt, when skived and specially

treated, are known as mocha leather Uda skins and white fulani

skins, from Nigerian sheep, are used for good-quality grain and

suede glove leather Sheepskin shearlings are skins taken from

heavy-wooled sheep a few weeks after shearing The wool is about 1

in (2.54 cm) in length They are tanned with the wool on, and theleather is used for aviation flying suits and for coats

SHEET MOLDING COMPOUND Typically SMC is an unsaturated,

ther-mosetting polyester reinforced with glass fibers for strength and ity and modified with additives to ease handling, improve surfacequality, control shrinkage, provide color and environmental resistance,and ease mold release It is used in the form of soft wads, typicallythickened with oxides to ease handling, and compression-molded inmetal dies at about 300°F (149°C) at pressures up to 1,000 lb/in2(6.9MPa) Depending on fiber content, tensile strength ranges from 5,000

rigid-to 30,000 lb/in2 (34 to 207 MPa), flexural strength from 10,000 to

50,000 lb/in2(69 to 345 MPa), and notched Izod impact strength from

7 to 25 ft lb/in (374 to 1,335 J/m) SMC is widely used for panels ofautos and truck cabs, underbody auto components, and many other

applications Hi-Flex SMC, of Budd Co., contains 20% glass fiber, a

thermoplastic-elastomer copolymer as a low-profile additive for rior surface quality, a polyurethane additive to enhance flexibility, and

supe-a csupe-alcium csupe-arbonsupe-ate filler The density is 0.054 lb/in3 (1,495 kg/m3),and the coefficient of thermal expansion is 5.6  106/°F (10.1 

106/K) Tensile and flexural strengths are 8,500 and 15,800 lb/in2 (59and 109 MPa), respectively, and the flexural modulus is 650,000 lb/in2(4,482 MPa) The impact strength is 21 ft lb/in (1,121 J/m)

The high pressure needed to mold traditional SMC is due to theoxide thickening additives used to ease room-temperature handling of

the soft mass Crystal Impreg, a crystalline unsaturated polyester

resin of Scott Bader of England, can be substituted for part of the ditional polyester to ease handling equally and reduce molding pres-sure to as low as 150 lb/in2 (1 MPa) This resin melts at 200°F (93°C),thus decreasing the viscosity of the compound at molding tempera-

tra-ture Such low-pressure sheet molding compounds also speed

molding Resulting properties are about the same as for traditionalSMC For example, with 27% glass fibers, density is 0.066 lb/in3(1,827kg/m3), tensile strength 11,900 lb/in2 (82 MPa), flexural strength24,500 lb/in2 (169 MPa), and impact strength 20 ft lb/in (1,084 J/m)

Aropreg 3230, of Ashland Chemical, is a low-pressure SMC.

Arotech 2000 compounds, of the same company, are vinyl ester SMCs The base resin is heat-resistant to 300°F (149°C), the 2001 is

a zero-shrink grade, and the 2002 provides good surface quality andshrink control Quantum Composites offers a urethane-toughened

vinyl ester SMC as well as a phenolic SMC, both with a high tent of glass fibers Cyglas 695, of Cytec Industries, is a reinforced

con-vinyl ester used for auto-engine valve covers

SHELLAC. A product of Tachardia lacca, an insect that lives on

vari-ous trees of southern Asia The larvae of the lac insect settle on thebranches, pierce the bark, and feed on the sap The lac secretion pro-duced by the insects forms a coating over their bodies and makes athick incrustation over the twig Eggs developed in the females aredeposited in a space formed in the cell, and the hatched larvaeemerge This swarming continues for 3 weeks and is repeated twice ayear The incrustation formed on the twigs is scraped off, dried in the

shade, and is the commercial stick lac It contains woody matter, lac resin, lac dye, and bodies of insects Seed lac is obtained by screen-

ing, grinding, and washing stick lac The washing removes the lac

dye Lac dye was once an important dyestuff, giving about the same

colors as cochineal but not as strong It gives a fast, bright-red tint to

silk and to wool, but is now replaced by synthetics Ari lac is stick lac

collected before the young insects have swarmed, and it contains

liv-ing insects Lac harvested after the swarmliv-ing is called phunki lac

and contains dead bodies of the insects Average yield of stick lac fromkusum trees is 12 lb (5.4 kg), from the ber tree 3 lb (1.4 kg), and fromthe palas tree 2 lb (0.9 kg) About 80% of lac production is in the state

of Bihar in India, but it is also obtained from Bengal, the CentralProvinces, and Assam The stick lac from Burma and Thailand isbrought to India for making shellac

Shellac is prepared from seed lac by melting or by extraction withsolvents The molten material is spread over a hot cylinder andstretched, and the cooled sheet is broken into flakes of shellac

Button lac is made by dropping molten lac on a flat surface which

spreads it into button-shaped cakes 3 to 4 in (7.6 to 10.2 cm) in

diam-eter Kiri is the refuse from the filtering bags It is marketed in

pressed cakes and contains 50 to 60% lac with resin and dirt Theyield of shellac from stick lac is about 57% When pure, shellac variesfrom pale orange to lemon yellow, but the color of commercial shellac

may be due to a high content of common resin White shellac is made by bleaching with alkalies Garnet lac is the material with lac dye left in Color may also be balanced with pigments Orange shel-

lac contains up to 1% powdered orpiment, and the yellow may have

smaller quantities Shellac is composed of polyhydric acids which dense with loss of water to form long-chain esters, thus giving poly-ester resins in the final coating It also contains resin and wax

con-Aleuritic acid, OH CH3(CH2)5(CH OH)2(CH2)7COOH, extractedfrom shellac, reacts with alcohols to produce odoriferous esters used

in perfumes It is a yellowish solid melting at 214°F (101°C) It can bemade synthetically and is also used in cellulose lacquers

Hard lac has the soft constituents removed by solvent extraction.

For electrical use the wax content should be below 3.5% By solventextraction of the seed lac, the wax may be reduced to 1% Shellac isgraded by color and by its freedom from dirt The first grade contains

no resin, but other grades may contain up to 12% Most Indianexports of seed lac to the United States are of the special grade which

has a high bleach index Cut shellac is shellac dissolved in alcohol,

but usually mixed with a high percentage of resin Shellac has goodadhesive properties and high dielectric strength, and is used in adhe-sives, varnishes, floor waxes, insulating compounds, and some mold-ing plastics Hard-face wax polishes contain a high percentage ofshellac, up to 80%, to conserve carnauba and other waxes

SILICA. A mineral of general composition SiO2, silicon dioxide,

which is the most common of all materials, and in the combined anduncombined states is estimated to form 60% of the earth’s crust

Many sands, clays, and rocks are largely composed of small silicacrystals When pure, silica is colorless to white The unit crystal, ormolecule, of ordinary silica has the formula SiO2, and the single-crys-tal grains are thus molecularly cryptocrystalline with no electronbonded lattice But the chemical formula of fused silica and quartz isgiven as Si2O7, which is the pattern of a continuous lattice in whicheach silicon atom is surrounded by two oxygen atoms and each oxy-gen atom is surrounded by four silicon atoms The varieties of natural

silica are crystalline silica, such as quartz and tridymite;

cryp-tocrystalline silica (minute crystals), such as flint, chert,

chal-cedony, and agate; and amorphous silica, such as opal Silica is

insoluble in water when anhydrous and is also insoluble in most acidsexcept hydrofluoric Crystallized silica in the form of quartz has a

Mohs hardness of 7 and a specific gravity of 2.65 Amorphous silica

glass has a specific gravity of 2.21 It is a transparent fused silica Vitreous silica is a silica glass of high transparency When impuri-

ties are no more than 1 ppm, it is the most transparent of the glassesand has high transmission of ultraviolet rays

Pure fused silica has a melting point of 3182°F (1750°C), but

soft-ens slightly at 2552°F (14000°C) In chemical and heat ware, it isused up to 2012°F (1100°C) The coefficient of expansion is very low, 3

 107/°F (5.4  107/K), and the dielectric strength is 500 V/mil (20

 106V/m) The infrared transmission of a 96% pure silica glassextends to 157
in (4
m) while retaining the lower reach of the band

to 15.7
in (0.4
m) Fused silica is used for chemical parts as it stands severe thermal shock and is resistant to acid except hydrofluo-

with-ric and hot phosphowith-ric Amersil, in the form of pipes and shapes,

withstands continuous temperatures of 2700°F (1482°C) Fused silicaparts may be made by pressing and sintering silica powder or by cast-ing Large cast parts for crucibles, molds, and furnace hearths aremade by remelting a powder produced by melting 99.9% pure silicasand and then crushing and grinding the glass Cast parts have a ten-sile strength of 1,500 lb/in2 (10 MPa) and compressive strength of20,000 lb/in2 (138 MPa) and withstand repeated heating and coolingfrom 2000°F (1093°C) The material is white

Fibrous silica, used for high-temperature insulation in jet

air-craft, is produced from silica minerals in the same manner as rock

wool and then extracting the nonsilica content of the fiber Refrasil,

of H I Thompson Co., is this material The fibers have a diameter of0.00023 in (0.00058 cm), fuse at 3100°F (1704°C), and withstand con-tinuous temperatures to 2000°F (1093°C) It is produced as fibers,

batts, cloth, and cordage Silica fiber in diameters as small as

0.00003 in (0.000076 cm) comes in random matted form or in rovings

Irish Refrasil is 98% silica and has a green color It is used for

abla-tive protecabla-tive coatings It resists temperatures to 2800°F (1588°C)