Section 1 of 4What Is an Alloy?
An alloy is designed to improve on the properties of a pure metal for a particular job.
Mixture
- An alloy is a mixture of two or more metals, or of a metal with a non-metal such as carbon.
Steel
- Steel is an alloy of iron and carbon, and its properties change with the amount of carbon present.
Brass
- Brass is an alloy of copper and zinc, and it is stronger than either pure metal.
Not a compound
- An alloy is not chemically combined, so its components are mixed rather than bonded in fixed ratios.
Section 2 of 4Why Alloys Are Harder
The explanation depends on the sizes of the atoms that make up the alloy.
1
Alloys contain atoms of different sizes, which distorts the regular arrangement of atoms found in the pure metal.
2
The distorted layers find it harder to slide over one another when a force is applied.
3
As a result, alloys are usually much harder and stronger than the pure metal they are based on.
4
Alloys can also be designed to resist corrosion or extreme temperatures, which makes them more useful than pure metals.
Section 3 of 4Examples and Uses
Examples and Uses
Stainless steel
- Iron mixed with chromium, nickel and carbon is used in cutlery because it resists corrosion.
Tungsten steel
- Iron alloyed with tungsten is extremely hard and resistant to high temperatures.
Aluminium alloy
- Aluminium mixed with copper, manganese and silicon is strong yet low in density, so it suits aircraft bodies.
Brass uses
- Brass is used in musical instruments, ornaments and doorknobs because it is strong and attractive.
| Alloy | Main components | Key property |
|---|---|---|
| Steel | Iron and carbon | Strong and hard |
| Brass | Copper and zinc | Stronger than either metal |
| Stainless steel | Iron, chromium, nickel and carbon | Resists corrosion |
Section 4 of 4Exam Checklist & Tips
3.1.2 – Key Points for the Exam
- Alloy A mixture of a metal with other metals or non-metals, with properties that differ from the pure metal.
- Corrosion Gradual destruction of a metal by chemical reaction with substances in its environment, such as oxygen and water.
- Brass An alloy of copper and zinc.
- Steel An alloy of iron containing carbon, often with other elements added.
Common Mistakes
- Calling an alloy a compound; its components are mixed, not chemically combined.
- Saying alloys are harder because they contain more electrons;
- the distorted layers of atoms are the key reason.
- Stating that steel is a pure element of iron.
- Forgetting that the atoms in an alloy have different sizes, which is the central point of the explanation.