Chemistry

7.9 - Uses of Metals & Polymers

3 min

note 1 of 2

Why a metal suits its job

A metal is picked for a job because of its properties.
While all metals conduct heat and electricity and have relatively high strength, they differ in density, conductivity, hardness, and reactivity.
Melting points: iron 1,538 °C, titanium 1,668 °C, copper 1,085 °C, aluminium 660 °C.

Aluminium - Low density

Aluminium has a low density (light for its size):

Aircraft and bicycle frames - Low density keeps the mass down.
Overhead electrical cables - Low density combined with good electrical conductivity allows cables to hang between pylons without breaking under their own weight.
Food containers and window frames - Resists corrosion from food and weather.

Aluminium bars on blue scales labelled low density, a machine drawing a bar into wire on a spool, aluminium cables lighting a bulb labelled good conductor, and crossed-out corroded bars labelled resists corrosion.

Copper - Conductor and ductile

Copper is a very good conductor of heat and electricity, and it's ductile (can be drawn into a wire without snapping):

Electrical wiring - Good conductivity carries the current efficiently, and ductility allows it to be drawn into thin wires.
Water pipes and tanks - Malleable enough to bend, hard enough to hold its shape, unreactive with water, and has high thermal conductivity.
Decorative work - Chosen for its distinctive colour and lustre.

A copper bar is drawn through a machine into copper wire wound on a spool labelled ductile, and the wire lights a bulb labelled good conductor.

Iron and steel - Cheap and strong

Chosen where high strength is needed and weight isn't a problem:

Wrought iron is almost pure iron. It's malleable, making it easy to shape for gates and railings.
Steel is harder and stronger than iron, used for bridges, girders, engine parts, machinery, tools, and car bodies.
Drawback: iron rusts in damp air.

A hammer bends a grey bar labelled wrought iron and malleable, a hammer strikes a stack of bars labelled steel and stronger, and iron bars with a price tag carry brown patches labelled rust.

Titanium - Light, hard and corrosion resistant

Titanium has a low density, is very hard and strong, and resists corrosion:

Aircraft parts and bicycle frames - low density like aluminium, but harder and more resistant to wear.

Titanium bars on blue scales labelled low density, a hammer striking bars labelled hard & strong, and rust-patched bars crossed out by a no symbol labelled corrosion resistant.

note 2 of 2

Why a polymer suits its job

Plastics are materials made up of polymer molecules, with shared properties that make them widely useful.

Properties polymers share

Usually cheaper than metals and ceramics.
Generally strong.
Low density compared to most metals and ceramics.
Many are flexible and almost all can be moulded into shape.
Thermal and electrical insulators.
Resist corrosion and don't rot.

Individual polymers and their uses

Poly(ethene) (polythene) - low density, flexible, easy to mould, unreactive, waterproof, and an electrical insulator. Used for carrier bags, bottles, and electrical wire insulation.
Poly(propene) - Low density, rigid, tough, and easy to mould. Used for packing crates, moulded furniture, and ropes.
Poly(chloroethene) (PVC) - rigid, hard, strong, unreactive, and fire resistant. Used for drainpipes, water pipes, and window frames.
Poly(tetrafluoroethene) (PTFE) - tough, strong, high melting point for a polymer, unreactive, and extremely non-stick. Used for non-stick pan coatings, and for waterproof and stain-resistant clothing because water and stains do not stick to it.

key terms

TermDefinition

DuctileAble to be drawn into wires.

end of notes

Key points to remember

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7.10 - Transition MetalsNext up

Why a metal suits its job

A metal is picked for a job because of its properties.

While all metals conduct heat and electricity and have relatively high strength, they differ in density, conductivity, hardness, and reactivity.

Melting points: iron 1,538 °C, titanium 1,668 °C, copper 1,085 °C, aluminium 660 °C.

Aluminium - Low density

Aluminium has a low density (light for its size):

Aircraft and bicycle frames - Low density keeps the mass down.

Overhead electrical cables - Low density combined with good electrical conductivity allows cables to hang between pylons without breaking under their own weight.

Food containers and window frames - Resists corrosion from food and weather.

Why a polymer suits its job

Plastics are materials made up of polymer molecules, with shared properties that make them widely useful.

Properties polymers share

Usually cheaper than metals and ceramics.

Generally strong.

Low density compared to most metals and ceramics.

Many are flexible and almost all can be moulded into shape.

Thermal and electrical insulators.

Resist corrosion and don't rot.

Individual polymers and their uses

Poly(ethene) (polythene) - low density, flexible, easy to mould, unreactive, waterproof, and an electrical insulator. Used for carrier bags, bottles, and electrical wire insulation.

Poly(propene) - Low density, rigid, tough, and easy to mould. Used for packing crates, moulded furniture, and ropes.

Poly(chloroethene) (PVC) - rigid, hard, strong, unreactive, and fire resistant. Used for drainpipes, water pipes, and window frames.

Poly(tetrafluoroethene) (PTFE) - tough, strong, high melting point for a polymer, unreactive, and extremely non-stick. Used for non-stick pan coatings, and for waterproof and stain-resistant clothing because water and stains do not stick to it.