Alloys
An An alloy is a mixture of two or more elements, at least one of which is a metal. is a Two or more substances that are not joined together. The substances can be elements, compounds, or both. of two or more A substance made of one type of atom only., where at least one element is a Shiny element that is a good conductor of electricity and heat, and which forms basic oxides.. 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. Alloy produced by mixing iron with one or more other metals. 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 structure of a metal. The metal atoms are arranged in a regular pattern of layers, with delocalised electrons able to move between them.. The atoms are arranged in layers. When a A push or a pull. The unit of force is the newton (N). 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.
Question
Explain why steel, which is an alloy of iron, is harder than pure iron.
Steel contains atoms of other elements as well as iron. These atoms have different sizes to iron atoms, so they distort the layers of atoms in the pure iron. This means that a greater force is required for the layers to slide over each other in steel, so steel is harder than pure iron.