1. Metals and alloys

2. What is an alloy?
An alloy is a mixture of a metal with at least one other element.
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.
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.

3. 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.
Other well-known alloys include:
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 warm and resists corrosion.

4. Is gold an alloy?
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.

5. When is a copper coin not a copper coin?
When it is a copper-coated alloy!
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!
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.

6. What is steel?
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!

7. Why is steel stronger than iron?
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.
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.
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.

8. What types of steel are there?
Steel can contain up to 2% carbon.
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.
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:
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.