Encyclopedia of Global Resources part 22 potx

The most widely produced cement is portland cement used in con-crete, which is generally made from limestone and silica- and alumina-bearing material such as clay or shale.. Magnesite is

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CNa2CO3C2H2O), hydromagnesite (Mg5(CO3)4(OH)2

C4H2O), and artinite (Mg2(CO3)(OH)2C3H2O)

The most abundant carbonate mineral is calcite

(CaCO3), which comprises limestone, chalk,

traver-tine, tufa (sedimentary rocks), and marble

(meta-morphic rock) Most limestone forms in warm,

shal-low seas, far from sources of land-derived sediment

Chalk is made of the shells of microscopic floating

or-ganisms which once lived in the sea Spring deposits

are travertine or tufa, and cave deposits (stalactites

and stalagmites) are travertine These deposits form

from the evaporation of groundwater carrying

dis-solved calcium carbonate Marble is limestone which

has been changed by heat and pressure Malachite

and azurite are associated with the oxidized portions

of copper deposits and with copper veins through

limestone deposits

Sodium carbonate minerals are present in

associa-tion with dry salt lake deposits in some parts of the

world These include trona, natron (Na2CO3C10H2O),

thermonatrite (NaCO3CH2O), nahcolite (NaHCO3),

gaylussite (CaCO3CNa2CO3C5H2O), pirssonite (CaCO3

CNa2CO3C2H2O), and shortite (2CaCO3CNa2CO3)

History

Calcite, because of its abundance, has a rich history

Because calcite can preserve fossil records, its

pres-ence helps date cultural artifacts Chalk has been used

for writing for thousands of years

Obtaining Carbonate Minerals

The most important use of calcite is in the production

of cements and lime When limestone is heated to

about 900° Celsius, it loses CO2and is converted to

quicklime or lime (CaO) Mixed with sand, quicklime

forms mortar When mixed with water, it hardens

or “sets,” swelling and releasing heat The most widely

produced cement is portland cement (used in

con-crete), which is generally made from limestone and

silica- and alumina-bearing material such as clay or

shale The raw materials are ground together, and

the mixture is heated in a kiln until it fuses into a

“clinker,” which is then crushed to a powder

Uses of Carbonate Minerals

Lime (CaO) is also used in agriculture to neutralize

acid in soils, in the manufacture of paper, glass, and

whitewash, and in tanning leather It is used in

refin-ing sugar, as a water softener, and as a flux for smeltrefin-ing

various types of ores Fine-grained limestone has been

used in lithography (printing) Blocks of cut lime-stone and marble are used as building lime-stone and orna-mental stone and may be polished Crushed lime-stone is used as aggregate in concrete and as road metal Dolomite has uses similar to those of calcite Several carbonates are metal ores: dolomite and magnesite (ores of magnesium), rhodochrosite (man-ganese), siderite (iron), smithsonite (zinc), strontian-ite (strontium), witherstrontian-ite (barium), cerrusstrontian-ite (lead), malachite and azurite (copper), and trona (sodium) Magnesite is used in the manufacture of refractory materials capable of withstanding high temperatures, for special types of cements, and in the paper, rubber, and pharmaceutical industries Strontianite is also used in the manufacture of fireworks, producing a purplish-red flame Malachite (green) and azurite (blue) are used as pigments Sodium carbonate and sodium bicarbonate are important in the manufac-ture of washing soda (or sal soda) and are used as cleaning agents and water softeners They are used in the manufacture of glass, ceramics, paper, soap, and sodium-containing compounds (such as sodium hy-droxide) as well as in petroleum refining Sodium bi-carbonate, also known as baking soda, is an important part of baking powder, is a source of carbon dioxide in fire extinguishers and is used medicinally to neutral-ize excess stomach acid Several carbonates are used

as ornamental stone and in jewelry, including mala-chite, azurite, aragonite (alabaster), rhodochrosite, and smithsonite

Pamela J W Gore

Further Reading

Klein, Cornelis, and Barbara Dutrow The Twenty-third Edition of the Manual of Mineral Science 23d ed.

Hoboken, N.J.: J Wiley, 2008

Pellant, Chris Rocks and Minerals 2d American ed.

New York: Dorling Kindersley, 2002

Pough, Frederick H A Field Guide to Rocks and Min-erals Photographs by Jeffrey Scovil 5th ed Boston:

Houghton Mifflin, 1996

Tegethoff, F Wolfgang, Johannes Rohleder, and

Evelyn Kroker, eds Calcium Carbonate: From the Cre-taceous Period into the Twenty-first Century Boston:

Birkhäuser Verlag, 2001

Tucker, Maurice E., and V Paul Wright Carbonate Sedimentology Boston: Blackwell Scientific, 1990 Warren, John K Evaporite Sedimentology: Importance in Hydrocarbon Accumulation Englewood Cliffs, N.J.:

Prentice Hall, 1989

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Web Site

Carbonate-hydroxylapatite Mineral Data

http://webmineral.com/data/Carbonate-hydroxylapatite.shtml

See also: Carbon cycle; Crystals; Evaporites; Lime;

Limestone; Minerals, structure and physical

proper-ties of; Sedimentary processes, rocks, and mineral

de-posits

Carnegie, Andrew

Category: People

Born: November 25, 1835; Dunfermline, Scotland

Died: August 11, 1919; Lenox, Massachusetts

Carnegie established the Carnegie Steel Company,

which he eventually sold for $250 million The

explo-sive growth of the steel industry that Carnegie’s success

exemplified initiated the final phase of the Industrial

Revolution; it ultimately led, for example, to the mass

production of automobiles and the exploitation of a

va-riety of resources worldwide.

Biographical Background

In 1848, Andrew Carnegie moved from Scotland to

the United States He began working in an Allegheny,

Pennsylvania, cotton mill for $1.20 per week Later, he

moved to Pittsburgh, becoming involved in the

rap-idly growing railroad business Carnegie soon became

the superintendent of the Pittsburgh division of the

Pennsylvania Railroad By investing wisely in what

be-came the Pullman Company and in oil lands,

Carne-gie established the foundation for his fortune

Impact on Resource Use

Following service in the War Department during the

Civil War, Carnegie left the Pennsylvania Railroad and

formed a company to build iron railroad bridges This

led to the next step: the production of steel He

founded a steel mill and began using the new

Besse-mer process of making steel The extensive use of steel

that resulted from Carnegie’s work led to a greater

ex-ploitation of iron ore deposits in the United States

and abroad The need for oil and rubber, which grew

alongside the booming steel industry, also

acceler-ated resource exploitation and had profound effects

on succeeding generations

By 1899, the Carnegie Steel Company controlled

25 percent of steel production in the United States Two years later, Carnegie sold the company to J P Morgan, who organized it into the U.S Steel Corpora-tion, the first billion-dollar corporation in the United States

When Carnegie was thirty-three years old, with an annual income of fifty thousand dollars, he declared that a person should never seek to build a fortune un-less intending to give the surplus for benevolent pur-poses Although he did not always follow his own ad-vice, he did eventually give more than $350 million to philanthropic projects, including the endowment of seventeen hundred libraries, the Tuskegee Institute, and the Peace Palace at The Hague in the Nether-lands

Glenn L Swygart

See also: Bessemer process; Capitalism and resource exploitation; Iron; Steel; Steel industry

Andrew Carnegie was the leading figure in the steel industry at the end of the nineteenth century (Library of Congress)

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Carson, Rachel

Category: People

Born: May 27, 1907; Springdale, Pennsylvania

Died: April 14, 1964; Silver Spring, Maryland

Carson made a major contribution to the

environmen-tal movement in the United States by educating the

public about the natural geological evolution of the

Earth and the dangers associated with the widespread

use of chemicals Her book Silent Spring was

pub-lished in 1962.

Biographical Background

Rachel Carson was educated at the Pennsylvania

Col-lege for Women in Pittsburgh and Johns Hopkins

University in Baltimore, Maryland She did research

at the Woods Hole Marine Biological Laboratory and

subsequently worked for the U.S Fish and Wildlife

Service in Washington, D.C

Carson published Under the Sea-Wind (1941); The Sea Around Us (1951), which received the National Book Award for nonfiction; The Edge of the Sea (1955); and her most famous work, Silent Spring (1962) Her

writ-ings took a naturalist’s approach to explaining the ocean environment and the origin of the Earth, and they were praised for their clear explanations in lay

terms The Edge of the Sea revealed Carson’s growing

in-terests in the interrelationships of Earth’s systems and

a holistic approach to human interaction with nature

In Silent Spring Carson warned of the environmental

contamination that results from widespread use of pes-ticides, particularly dichloro-diphenyl-trichloroethane (DDT) She described how the ecology of the soil had been largely ignored in the rush to apply chemicals, drew attention to the effects on wildlife where chemi-cal mixing in runoff channels turned streams into le-thal cauldrons of chemical soup, and accused the chemical companies of aggressive marketing policies that ignored the impact on the environment The first Earth Day (April 22, 1970) and the creation of the En-vironmental Protection Agency in 1970 can both be attributed in part to Carson’s role in changing the way Americans thought about their surroundings

Pat Dasch

See also: Environmental movement; Food chain; Pesticides and pest control

Carter, Jimmy

Category: People Born: October 1, 1924; Plains, Georgia

As the thirty-ninth president of the United States, James Earl “Jimmy” Carter deregulated domestic crude oil prices and established the Department of Energy.

Biographical Background Jimmy Carter graduated from the United States Naval Academy and served in the Navy until his father’s death Assuming his father’s business responsibilities, Carter expanded the family business and ran for politi-cal offices He was elected governor of Georgia in 1970

At the end of his term as governor, Carter began a cam-paign for the presidency He ran against incumbent Gerald Ford in 1976 and won by a narrow margin

Rachel Carson’s seminal text Silent Spring helped spearhead the

modern environmental movement (Library of Congress)

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The years before and during President Carter’s term

were times of instability in the world economy World

petroleum demand was increasing, and Congress had

capped domestic crude oil prices, discouraging

do-mestic petroleum exploration In 1979, the

Organiza-tion of Petroleum Exporting Countries (OPEC) raised

crude oil prices by 50 percent Because most goods

were moved to market by gasoline- or diesel-powered

transport, the increase in world petroleum prices

con-tributed significantly to inflation, which reached an

annual rate of 12 percent Interest rates tracked

infla-tion and rose 20 percent, a level unprecedented in the

twentieth century

In response to these problems, President Carter

proposed an energy program that included creation

of a Department of Energy, deregulation of domestic

crude oil prices, and promotion of conservation and

alternative energy sources An advocate of

environ-mentalism, President Carter was also successful in

obtaining congressional action that preserved vast wilderness areas in Alaska

Robert E Carver

See also: Department of Energy, U.S.; Energy eco-nomics; Oil embargo and energy crises of 1973 and 1979; Synthetic Fuels Corporation

Carver, George Washington

Category: People Born: July 12, 1861?; near Diamond Grove (now Diamond), Missouri

Died: January 5, 1943; Tuskegee, Alabama

A pioneering African American agricultural scientist, Carver is best known for popularizing and promoting the economic potential of peanuts and sweet potatoes as alternative crops for southern farmers.

Biographical Background George Washington Carver was born into slavery near the end of the Civil War near Diamond Grove (now Diamond), Missouri His early education was spo-radic, though he did attend high school in Minneapo-lis, Kansas He was briefly a homesteader in Ness County, Kansas, before he returned to school, first at Simpson College in Indianola, Iowa, where he studied fine arts, then at Iowa State University in Ames, Iowa, where he studied agriculture After Carver completed his bachelor of agriculture degree in 1894, he was ap-pointed to the faculty at Iowa State and received a master of agriculture degree in 1896

Impact on Resource Use Carver immediately began working as director of agri-culture and director of the agricultural experiment station at Tuskegee University in Alabama Carver won international acclaim for the educational efforts

he began in the early 1900’s to promote sound conser-vation practices and sustainable agricultural activity

in the rural South, which had previously been depen-dent on cotton production He is best known, how-ever, for popularizing and promoting the economic potential of peanuts and sweet potatoes as alternative crops for southern farmers He was instrumental in persuading Congress to protect the peanut industry from foreign competition shortly after World War I

Jimmy Carter, the thirty-ninth president of the United States, was an

early advocate of alternative energy use (Library of Congress)

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In the later stages of his career, he investigated the

po-tential uses of peanuts and sweet potatoes, which

in-cluded uses in dyes, milk substitutes, and cosmetics

Mark S Coyne

See also: Agricultural products; Agriculture

indus-try; Agronomy

Cement and concrete

Category: Products from resources

Cement and concrete have played crucial roles in

shap-ing humankind’s physical environment Of all

manu-factured construction materials worldwide, concrete is

the most widely used.

Background

Cement is an important construction material

be-cause of the ready availability of its raw materials, its

capacity to be shaped prior to setting, and its durabil-ity after hardening When combined with an aggre-gate (such as sand, gravel, or crushed rock), cement becomes concrete—a durable, load-bearing construc-tion material

Cements with the ability to set and harden under-water are called hydraulic cements The most mon of these is portland cement, consisting of com-pounds of lime mixed with silica, alumina, and iron oxide Gypsum is also added to retard the setting time When water is added, these ingredients react to form hydrated calcium silicates that will set into a hardened product

History Cement has been used for construction purposes for the past six thousand years The Egyptians are known

to have used a simple cement, and the Greeks and Ro-mans advanced the technology by creating hydraulic cements from various volcanic materials and lime Many examples of their concrete structures remain today—some underwater, where they were used in harbors

The quality of cementing materials declined greatly during the Middle Ages but began to improve again in the late eighteenth century In 1756, the famed Brit-ish engineer John Smeaton was commissioned to re-build the Eddystone Lighthouse near Cornwall, En-gland He undertook a search for lime mortars that would resist the action of the water and discovered that the best limestone contains a high proportion of clayey material For his project he used lime mixed with pozzolana from Italy (the same volcanic material the Romans had used) Smeaton was followed by a number of researchers, including Joseph Aspdin, a Leeds builder, who patented “portland” cement, named for the high-quality building stone quarried at Portland, England

Manufacturing Cement Cement is a manufactured product, made from raw materials that are found relatively easily in nature Ce-ment manufacturers have a number of sources for lime, but the most common are limestone and chalk Coral and marine shell deposits are also used as sources of lime, when available Silica, alumina, and iron oxide are found in clays, shales, slates, and cer-tain muds Some raw materials concer-tain almost all the ingredients of cement, especially marl (a compact clay), cement rock, and blast-furnace slag Industrial

Scientist George Washington Carver is best known for his work with

agricultural crops such as peanuts (National Archives)

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Global Resources Cement and concrete • 185

Data from the U.S Geological Survey, U.S Government Printing Office, 2009.

40,000,000 37,000,000 36,000,000 35,000,000 35,000,000 33,000,000 30,000,000 30,000,000 22,000,000

Metric Tons

1,500,000,000 1,250,000,000

1,000,000,000 750,000,000

500,000,000 250,000,000

Saudi Arabia

Thailand

Iran

Indonesia

Vietnam

Mexico

Germany

Pakistan

France

Egypt

Italy

Turkey

Brazil

Spain

South Korea

Russia

Japan

United States

India

China

40,000,000 47,000,000 48,000,000 48,000,000 55,000,000 56,000,000 61,000,000 67,000,000 89,100,000 175,000,000

1,450,000,000

Cement: Top Producers, 2008

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wastes such as fly ash and calcium carbonate are also

used as raw materials for cement, but not on a large

scale

Raw materials in the form of hard rock—such as

limestone, slate, and some shales—are usually

quar-ried, but they may also be mined If the limestone is of

low quality, it may need to go through a concentrating

process Softer materials such as chalk, clay, and mud

can be dug by various types of machinery, depending

on the physical setting and type of material Once

ex-tracted, the raw materials are transported to the

ce-ment manufacturing plant by truck, rail, conveyor

belt, or pipeline (when in a slurry)

At the plant, the raw materials are ground into a

fine powder and then mixed in predetermined ratios

The mixing can be done wet, semidry, or dry In the

wet process the materials are ground wet and mixed

into a slurry In the semidry process they are ground

dry, then moistened for adhesion; and in the dry

pro-cess the raw materials remain dry throughout

After mixing, the raw materials are burned in a large

rotating kiln Kilns are usually from four to eight

me-ters in diameter and from 90 to 200 meme-ters long, and

they consist of a steel cylindrical shell inclined slightly

from the horizontal The mixture is introduced at the

upper end of the kiln, and as it flows

down the incline (with the help of

gravity and the kiln’s steady rotation),

it reaches a maximum temperature

between 1,300° Celsius and 1,500°

Celsius, at which point the raw

mate-rials interact to form calcium

sili-cates The heated material exits the

kiln in the form of rough lumps or

pellets—called clinker—no larger

than 5 centimeters in diameter After

the clinker cools, the manufacturer

adds gypsum and grinds the mixture

into the fine powder known as

port-land cement

Uses of Concrete

Concrete is generally used in four

common forms: ready-mixed,

pre-cast, reinforced, and prestressed

Ready-mixed concrete is transported

to a construction site as a cement

paste and is then poured into forms

to make roadways, foundations,

driveways, floor slabs, and much

more Precast concrete—cast at a plant and then transported to the site—is used for everything from lawn ornaments to major structural elements Rein-forced concrete is created by adding steel mesh, rein-forcing bars, or any other stiffening member to the concrete before it sets Prestressed concrete, the most recently developed form, increases the strength of a beam by using reinforcing steel to keep the entire beam under compression Concrete is much stronger under compression (pushed in on itself) than under tension (pulled apart)

Brian J Nichelson

Further Reading

Gani, M S J Cement and Concrete New York: Chapman

& Hall, 1997

Lea, F M Lea’s Chemistry of Cement and Concrete 4th ed.

Edited by Peter C Hewlett New York: J Wiley, 1998

Mehta, P K., and Paulo J M Monteiro Concrete: Microstructure, Properties, and Materials 3d ed New

York: McGraw-Hill, 2005

Mindess, Sidney, J Francis Young, and David Darwin

Concrete 2d ed Upper Saddle River, N.J.: Prentice

Hall, 2003

2009

Data from the U.S Geological Survey, U.S Government Printing Office, 2009.

Ready-mix concrete 75%

Concrete products 13%

Contractors (road paving) 6%

U.S End Uses of Cement

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Neville, A M Properties of Concrete 4th ed Harlow,

Essex, England: Longman Group, 1995

Web Sites

Natural Resources Canada

Canadian Minerals Yearbook, Mineral and Metal

Commodity Reviews

http://www.nrcan-rncan.gc.ca/mms-smm/busi-indu/cmy-amc/com-eng.htm

Portland Cement Association

Cement and Concrete Basics

http://www.cement.org/basics

U.S Geological Survey

Cement: Statistics and Information

http://minerals.usgs.gov/minerals/pubs/

commodity/cement/index.html#mcs

See also: Clays; Gypsum; Lime; Limestone; Sand and

gravel; Shale; Silicates; Slate

Central Arizona Project

Category: Organizations, agencies, and programs

Date: Established September 30, 1968; substantially

completed 1993

The Central Arizona Project (CAP), a series of

pump-ing plants, dams, aqueducts, and pipelines stretchpump-ing

more than 540 kilometers, is the largest water transfer

project in the United States Drawing water from Lake

Havasu has supported agriculture in southwest

Ari-zona and made possible the growth of major cities,

while harming several species of fish and animals

downstream.

Background

As the area that makes up the southwestern United

States was settled and populated by Europeans in the

nineteenth century, the need for more water became

apparent In the early 1900’s, the Southwest looked to

the Colorado River basin as a source of water, and a

se-ries of laws and court decisions called the “Law of the

River” were established to ensure that each state was

treated equitably Decades of court cases attempted to

determine the amount of the water to which Arizona

was entitled Through the 1950’s Arizona lobbied for

authorization of a Central Arizona Project, and the

U.S secretary of the interior called for a comprehen-sive Colorado River plan to address the future water needs of seventeen Western states Passed on

Septem-ber 30, 1968, Public Law 90-537, 82 Stat 885 created

the Colorado River Basin Project and the Lower Colo-rado River Basin Development Fund, which autho-rized in turn the development of the Dixie Project in Utah and the Central Arizona Project in Arizona and New Mexico

Provisions The Central Arizona Project was designed to move 4,000 square kilometers of water from Lake Havasu, fed by the Colorado River, to agricultural lands in Maricopa, Pima, and Pinel Counties in Arizona, and

to Catron, Grant, and Hidalgo Counties in New Mex-ico Because of high costs and lower-than-expected demand, however, the New Mexico portion of the project was never built During the years of construc-tion, the economy of Arizona began to shift from agri-culture to industry, and the metropolitan areas of Phoenix, Scottsdale, and Tucson experienced rapid growth As a result, CAP waters were reallocated, so that over time more water would be designated for municipal and industrial use, and less for agriculture

Impact on Resource Use The purpose of CAP, as it was conceived in the late 1940’s, was to keep agriculture thriving without de-pleting groundwater supplies By most accounts, this goal was not realized In addition, the diversion of water from its natural course has created environmen-tal problems downstream from Lake Havasu, includ-ing the extinction of fish and wildlife, in spite of sev-eral successful conservation efforts along the project itself Dams along the project provide hydroelectric power, reducing the region’s dependence on other forms of power generation

Cynthia A Bily

Web Sites Central Arizona Project http://www.cap-az.com/

U.S Department of the Interior Bureau of Reclamation

Colorado River Basin Project: Central Arizona Project

http://www.usbr.gov/dataweb/html/crbpcap.html

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See also: Hydroenergy; Los Angeles Aqueduct; Three

Gorges Dam

Ceramics

Category: Products from resources

Ceramics are inorganic, nonmetallic materials—such

as naturally occurring silicates, oxides, nitrates,

car-bonates, chlorides, and sulfates—that are subjected to

high temperatures during their manufacture and

pro-cessing Ceramic materials are high strength but

brit-tle As a result of modern research and development,

they have multiple and varied uses.

Background

Paradoxically, ceramic science is one of the oldest yet

one of the newest technologies Much of what is

known of prehistoric humans and of the earliest

civili-zations has been learned from the pottery that was left

behind This longevity illustrates one of the greatest

assets of ceramic materials, their durability The fact

that most of the surviving pieces are fragments gives

evidence of the greatest weakness, their brittleness

The term “ceramics” is derived from the Greek

term keramos, which means “potter’s clay.” Ceramics is

defined in some dictionaries as “the art of making

things from baked clay.” “Clay” is used in describing

ceramics because it was an essential material in

tradi-tional ceramic compositions The term “baked” is

im-portant, since high temperatures are used in most

processing of ceramics Although simple, this

descrip-tion of ceramics was an accurate one until the time of

World War II In the early 1940’s, the field of materials

science, of which ceramics is a part, experienced a

push to develop new materials and processing

meth-ods Today, a more accurate present-day description

of ceramics might be “the art and science of making

and using implements and other articles that are

es-sentially composed of inorganic and nonmetallic

compounds.”

Traditional Ceramics

The ceramic industries may be grouped into several

divisions according to the products produced

Tradi-tional divisions include whitewares, refractories,

abra-sives, structural clay products, glass, cement, and

por-celain enamels Developments in the second half of

the twentieth century in the fields of nuclear physics and electronics resulted in many new ceramic prod-ucts, collectively known as technical ceramics Whitewares are materials such as clay, feldspar, whiting, and potter’s flint that fire to a white color The mineral mixtures are shaped and then partially melted at high temperatures to produce a dense hard material The term whiteware is misleading, since products in this class are produced in a wide variety of colors, depending on the amounts of impurities in the raw materials Common whitewares include earth-enware, porcelain or other tableware products as well

as casseroles and bowls, floor and wall tile, and decora-tive products such as vases and lamp bases Important commercial whitewares include laboratory ware such

as porcelain crucibles, combustion tubes, and grind-ing balls for the chemist as well as electrical porcelains such as spark plugs and insulators

A worker carries ceramic cylinders in Jungdezhen City, China, home

to what is believed to be the oldest egg-shaped ceramics kiln in the world (Zhang Wu/Xinhua/Landov)

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Refractories are structural materials manufactured

for the purpose of withstanding corrosive

high-tem-perature conditions in furnaces and process vessels

Refractories have high melting temperatures, good

hot strength, and resistance to chemical attack and

abrasion They are made from the refractory clays,

ka-olin, magnesite, chrome ore, olivine, and bauxite For

more special services, refractory products are made

from synthetic compositions such as carbides and

bor-ides Among the most important users of refractories

are the metallurgical industries, including the steel

industry

Glasses are ceramics that do not return to

crystal-line form after being melted and cooled These

noncrystalline ceramics behave as high viscosity

liq-uids They are essentially rigid at room temperature

but gradually soften and flow as the temperature is

in-creased This viscosity allows glasses to be formed by

processes that will not work for other ceramic

materi-als Glasses can be pressed into shallow shapes, drawn

or rolled into tubes and sheets, blown into hollow

shapes, or spun into fibers

Most glasses are naturally transparent to visible

light and are commonly used as windows, bottles,

lightbulbs, lenses, and optical fibers The basic

ingre-dient in most glasses is silica sand, but a wide range of

other materials can be added to produce glasses

pos-sessing a wide variety of tailored properties

Borosili-cate glasses are resistant to both chemicals and heat,

properties that make them useful both in the home

and in the laboratory Oxides of the transition metals

may be added to produce glass of almost any desired

color

The porcelain enamels are glassy coatings fused

onto metals to provide decoration and protection

from corrosion They are hard, rigid ceramics that

are electrical and thermal insulators as well as

wear-resistant and chemically inert Available in all colors,

they are found on household appliances, on

struc-tures used for food storage, in medical and hospital

equipment, and in vessels used in the production of

food and chemicals

Technical Ceramics

Research after World War II made possible a wide

vari-ety of nontraditional ceramic products based on

high-purity synthetic materials processed by special

tech-niques A few items will illustrate the scope of this

relatively new field

Ceramics have played an essential role in the

devel-opment of the computer industry The ceramic pro-cess is used in the fabrication of the complex inte-grated circuits that perform the basic operations of a computer on silicon semiconductor wafers These in-tegrated circuits are packaged on ceramic substrate materials

Oxides and carbides of uranium, plutonium, and thorium are ceramic materials that are used in the production of fuels for nuclear fission reactors High-strength concrete, often containing lead, is used in shielding structures around nuclear reactors “Hot cell” windows, made of leaded glass, maintain optical transparency when exposed to radiation Ceramic materials are also used in virtually all segments of the aerospace industry Refractory materials are used in building launching pads, rocket nozzles, and heat shields

Lasers, which came into prominence in the 1960’s, utilize the various quantum transitions that atoms and molecules undergo to produce intense beams of in-frared, visible, or ultraviolet light The original ruby laser used as its light-emitting medium a crystalline aluminum oxide ceramic that contained a small amount of chromium Another important ceramic la-ser is the yttrium aluminum garnet doped with neo-dymium to emit light in the infrared region of the spectrum As the need for more specialized materials grows, the field of ceramic science will continue to produce more and more exotic materials

Grace A Banks

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