Childrens Illustrated Encyclopedia

342

Aluminum

The most common

metal in Earth’s

crust is aluminum.

The metal comes

from an ore called

bauxite, which

contains alumina,

a compound of

aluminum and

oxygen. Aluminum is light, conducts

electricity and heat, and resists corrosion.

These qualities mean that the metal and

its alloys can be used in many things,

including aircraft and bicycles, window

frames, paints, cookware, and electricity

supply cables.

Find out more

Bronze age

Iron age

Iron and steel

Rocks and minerals

Science

WEldIng

Metal parts can be joined by

welding. Welders apply heat

from a gas flame or an electric

spark to the edges of two pieces

of metal. The heat causes the

edges to melt so that they can

be joined together.

AlloyS

Most metal objects are

made of steel or other

alloys. This is because alloys

are often stronger or easier

to process than pure metals.

Copper and tin are weak

and pliable, but when

mixed together they make

a strong alloy called bronze.

Brass is a tough alloy of

copper and zinc that resists

corrosion. Alloys of

aluminum are light and

strong and are used

to make aircraft.

ElECTRolySIS

Passing an electric

current through

alumina separates

it into aluminum

and oxygen. This

process is called

electrolysis.

Molten

aluminum

Carbon

electrode

IMAgInE A WoRld WIThouT METAlS. There would be no cars or airplanes,

and skyscrapers would fall down without the metal frames that support them.

Metals have countless uses because they possess a unique combination

of qualities. They are very strong and easy to shape, so they can be used to

make all kinds of objects—from ships to bottle tops. Almost all metals conduct

electricity. Some are ideal for wires and electrical equipment. Metals also

carry heat, so they make good cooking pots. These qualities can be

improved by mixing two or more metals to make alloys. Most metallic

objects are made of alloys rather than pure metals. There are more

than 80 kinds of pure metals, though some are very rare. Aluminum

and iron are the most common metals. A few metals, such as gold,

occur in the ground as pure metals; the rest are found as ores in

rock. Metals can also be obtained by recycling old cars and cans.

This reduces waste and costs less than processing metal ores.

Gold

watch

Alumina

poured

in here

Metals

Silver-

plated

frame

Airplane fuselage made

of aluminum alloys

Thin, flexible aluminum foil is

useful for cooking and storing

food because it is nonreactive

and can stand high temperatures.

A lump of

bauxite

Mercury thermometer

METAlWoRkIng

There are many ways of

shaping metal. Casting

is one method of

making objects such as

metal statues. hot,

molten metal is

poured into a mold

where it sets and

hardens into the

required shape. Metal

can also be pressed,

hammered, or cut

into shape.

METAl fATIguE

Metals sometimes fail even

though they may be very

tough and strong. Corrosion

weakens some metals, as in

the case of rusty steel.

Repeated bending can cause

metal parts to break—an

effect called metal fatigue.

Keys may break after

considerable use.

PuRE METAlS

The rarity and luster

of gold and silver have been prized

for centuries. other pure metals

have special uses. Electrical wires are

made of copper, which conducts

electricity well. Mercury, a liquid

metal, is used in thermometers.

Copper

wire

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