2.25C-2.27C - Uses of metals and alloys
Metals are chosen for jobs because of their properties: how strong, light, conductive, malleable or corrosion-resistant they are. In this lesson, the important exam skill is not just naming a use, but linking that use to the property that makes the material suitable. You will also see why changing a pure metal into an alloy can make it much harder.
Linking properties to uses
A property is a feature of a material. A use is a job the material is chosen for. In this topic, an answer only becomes a Chemistry answer when it links the two.
For example, "aluminium is used for aircraft" is a named use, but it does not explain anything. "Aluminium is used for aircraft bodies because it has a low density, so the aircraft has less mass" links the use to a relevant property.
Common properties in this lesson are:
| Property | Meaning in this topic | Why it can matter |
|---|---|---|
| Low density | Low mass for a given volume | Useful when a material must be light |
| Malleable | Can be hammered, rolled or pressed into shape | Useful for sheets, cans, foil and shaped parts |
| Ductile | Can be drawn into wires | Useful for electrical wiring |
| Good conductor of electricity | Allows charge to flow easily | Useful for wires, cables and electrical equipment |
| Good conductor of heat | Transfers thermal energy quickly | Useful for pans and heat exchangers |
| Strong or hard | Resists breaking, bending, scratching or wearing away | Useful for structures and tools |
| Corrosion-resistant | Does not react away quickly in air or water | Useful outdoors, in kitchens and in chemical equipment |
For a use question, write a use and the property that makes that use suitable.
The next example shows why a vague reason is not enough for full credit.
Aluminium and copper
Aluminium is useful when a metal needs to be light, shaped easily and resist corrosion. It has a low density compared with many other metals, so aluminium parts can have a lower mass. It is malleable, so it can be made into foil, cans and shaped panels. It also forms a thin oxide layer on its surface, which helps protect it from further corrosion.
Aluminium is also a good conductor of heat and electricity. This explains uses such as cooking pans and overhead power cables. In overhead cables, low density matters as well as conductivity because the cable must be supported over long distances.
Copper is especially useful for electrical equipment because it is an excellent conductor of electricity and is ductile. It can be drawn into wires without breaking, so it is used in wiring, motors and other electrical components. Copper is also a good conductor of heat, which explains uses such as heat exchangers, and it resists corrosion well enough for plumbing and roofing.
Use this pattern when you answer property-use questions:
| Metal | Suitable uses | Properties that explain the uses |
|---|---|---|
| Aluminium | Aircraft parts, transport bodies, drinks cans, foil, window frames, overhead cables | Low density; malleable; corrosion-resistant; good thermal and electrical conductor |
| Copper | Electrical wiring, motors, plumbing, roofing, heat exchangers | Excellent electrical and thermal conductor; ductile; malleable; corrosion-resistant |
Iron and steels
Iron is strong, cheap compared with many other metals, and magnetic, but it rusts in damp air and pure iron is not hard enough for many demanding uses. A lot of iron is therefore converted into steel, where small amounts of carbon or other elements change the properties.
Steel is based on iron. The specification only expects these three types of steel: low-carbon (mild) steel, high-carbon steel and stainless steel.
Low-carbon steel, also called mild steel, contains a small amount of carbon. It is tough, relatively malleable and easier to shape and weld than high-carbon steel. It is used for car bodies, nails, girders, sheet metal and general construction where the material must be strong but still shapeable. It can rust, so it may need painting, coating or another protective finish.
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