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An alloy is a mixture of a metal with at least one other element.

The final alloy may have very different properties to the original metal.

By changing the amount of each element in an alloy, material scientists can custom-make alloys to fit a given job.

What is an alloy?

Steel is a common example of an alloy. It contains iron mixed with carbon and other elements. Adding other elements to a metal changes its structure and so changes its properties.

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What types of alloys are there?

Alloys have been used for thousands of years. Bronze, an alloy of copper and tin, was commonly used by civilizations before iron extraction methods were developed.

brass: an alloy of copper and zinc. It does not tarnish and is used for door knobs, buttons and musical instruments.

solder: an alloy of zinc and lead. It is used in electronics to attach components to circuit boards.

amalgam: an alloy of mercury and silver or tin. It is used for dental fillings because it can be shaped when warmand resists corrosion.

Other well-known alloys include:

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Although pure gold is sometimes used in electronics, gold jewellery is always a mixture of gold and other metals.

Pure gold is actually quite soft. Adding small amounts of other metals makes the gold hard enough to use in jewellery.Alloying gold with different metals also affects its colour.

The familiar yellow gold is an alloy of gold with copper and silver. Adding more copper than silver gives redder shades.

White gold is an alloy of gold with nickel, platinum or palladium. Around 12% of people may be allergic to the nickel in white gold.

Is gold an alloy?

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When is a copper coin not a copper coin?

When it is a copper-coated alloy!

Since 1992, UK copper coins have been made from copper-plated steel and are magnetic. A magnet can be used to separate copper coins by age.

Copper coins used to be made from pure copper but most ‘copper’ coins used around the world are now made from copper alloys.

Previously, as the value of copper increased, the metal used to make the coin became worth more than the actual coins. A melted-down, pure copper coin could have been sold for more than the face value of the coin!

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Steel is an alloy of iron and other elements, including carbon, nickel and chromium.

Steel is stronger than pure iron and can be used for everything from sauce pans… …to suspension bridges!

What is steel?

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The atoms of other elements are different sizes. When other elements are added to iron, their atoms distort the regular structure of the iron atoms.

The atoms in pure iron are arranged in densely-packed layers. These layers can slide over each other. This makes pure iron a very soft material.

Why is steel stronger than iron?

It is more difficult for the layers of iron atoms in steel to slide over each other and so this alloy is stronger than pure iron.

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Steel can contain up to 2% carbon.

low carbon steel contains less than 0.25% carbon high carbon steel contains more than 0.5% carbon.

Two other important types of steel are:

What types of steel are there?

stainless steel – an alloy of iron that contains at least 11% chromium and smaller amounts of nickel and carbon titanium steel – an alloy of iron and titanium.

Varying the amount of carbon gives steel different properties. For example, a higher carbon content makes a hard steel.

Different types of steel are classified by how much carbon they contain.

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Using different types of steel

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Using different types of steel

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What’s so clever about smart alloys?

Shape memory alloy is a type of smart material made from metals that returns to its original shape after being deformed.

A smart material can change one or more of its physical characteristics under the influence of an external stimulus.

Nitinol is a type of shape memory alloy made from nickel and titanium.

Nitinol has also been used to hold badly broken bonesin place while they heal.

This material can be used to make a pair of glasses that ‘remembers’ its shape and does not break when crushed.