Alloys

An is a of two or more , where at least one element is a . Many alloys are mixtures of two or more metals.

Comparing properties of alloys and pure metals

Many pure metals are too soft for many uses. They can be made harder by adding another element to the pure metal, so forming an alloy. This explains why an alloy often has more uses than the pure elements it is made from.

Pure iron, for example, is very soft. Adding a small amount of tungsten to iron makes tool steel, which is harder than pure iron. are examples of alloys. There are many types of steel.

Steel	Elements	Properties
Mild steel	Carbon and iron	Easy to bend and pull into wires
Tool steel	Tungsten and iron	Hard, can be heated to high temperatures
Stainless steel	Chromium and iron	Hard, does not rust easily

Steel	Mild steel
Elements	Carbon and iron
Properties	Easy to bend and pull into wires

Steel	Tool steel
Elements	Tungsten and iron
Properties	Hard, can be heated to high temperatures

Steel	Stainless steel
Elements	Chromium and iron
Properties	Hard, does not rust easily

Explaining alloy hardness

In the solid state, a pure metal has a . The atoms are arranged in layers. When a is applied, the layers may slide over each other. The greater the force needed, the harder and stronger the metal.

In a pure metal, the force needed to make the layers slide over each other is small. This explains why many pure metals are soft.

In an alloy, there are atoms of different sizes. The smaller or bigger atoms distort the layers of atoms in the pure metal. This means that a greater force is required for the layers to slide over each other. The alloy is harder and stronger than the pure metal.