9.1.3Metals
Alloys — Combined Science 0653 - Chemistry Revision Notes & Topical Questions
5 min read 6 parts Lesson 3 of 11 Unit quiz
Part 1 of 4What is an alloy?
Definition
- Definition An alloy is a mixture of a metal with one or more other elements, usually other metals but sometimes a non-metal such as carbon.
- Steel is iron with a small amount of carbon. Brass is about 70% copper and 30% zinc.
A mixture, not a compound
- A mixture, not a compound The elements in an alloy are not chemically bonded to each other.
- They are physically mixed, so an alloy is not a compound.
An example of a formulation
- An example of a formulation A formulation is a mixture designed as a useful product, made to an exact recipe with each component in a measured amount.
- Alloys, paints, medicines and foods are formulations.
Part 2 of 4Why pure metals are often unsuitable
1Regular layers
- Regular layers In a pure metal the atoms are all the same size and form neat layers.
2Layers slide
- Layers slide When a force is applied, the layers slide over each other easily, so pure metals are soft and malleable.
3Too soft
- Too soft Many pure metals, such as iron, copper and aluminium, are too soft for structures, tools or machines.
Part 3 of 4Why alloys are harder
1
Atoms of the added element are a different size from the atoms of the main metal.
2
These atoms distort the regular arrangement of the lattice.
3
The layers can no longer slide smoothly over each other.
4
A bigger force is needed to deform the material, so the alloy is harder and stronger, but less malleable than the pure metal.
Part 4 of 4Common alloys and uses
| Alloy | Made from | Properties and uses |
|---|---|---|
| Brass | Copper and zinc | Stronger than either metal; used in musical instruments, ornaments and door fittings. |
| Steel | Iron with a little carbon | Hard and strong; used in construction, vehicles and tools. More carbon makes it harder but more brittle. |
| Stainless steel | Iron with chromium, nickel and carbon | Resists corrosion; used in cutlery and kitchen equipment. |
| Aircraft aluminium alloy | Aluminium with copper, manganese and silicon | Strong yet with low density; used in aircraft bodies. |
Key terms
| Term | Meaning |
|---|---|
| Alloy | A mixture of a metal with at least one other element, designed to improve its properties. |
| Formulation | A mixture made to a set recipe so that it has useful properties. |
| Malleable | Able to be hammered or bent into shape without breaking. |
| Corrosion | The gradual destruction of a metal by reaction with substances in its surroundings. |
| Lattice | A regular arrangement of particles in a solid. |
Avoid these mistakes
1
Calling an alloy a compound — it is a mixture and its components keep their own properties.
2
Saying alloys are harder because of stronger bonds; it is the different atom sizes that stop the layers sliding.
3
Thinking that every alloy has all properties improved; many are stronger or more resistant but less malleable.
4
Forgetting that steel includes carbon, which is a non-metal.
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