Materials: metals, ceramics, polymers, composites

Predict, then check

Use your sort. Which clue actually separates these two?

Two bottles are almost the same size. One is a polymer (plastic), the other is a ceramic (glass). Which observation would tell you which is which?

From soft to hard: how ceramics are made

Follow both routes at once, clay to brick and sand to glass. Watch where the heat comes in.

1. 1Start softCeramics are made from soft substances. For bricks and pottery that's clay. For glass it's sand, which is silica.
2. 2Heat it — very hotThe clay is first moulded into shape, such as a brick, then heated to a very high temperature, for example in a kiln. The sand is heated to a very high temperature until it melts.+
3. 3Harden or solidifyThe heat helps the moulded clay to harden. The melted sand is left to cool, and it solidifies.
4. 4A hard ceramicThe brick comes out hard, brittle and opaque, so you can't see through it. The glass comes out transparent.+
5. 5Put it to workCeramics end up as pottery, glass, bricks, tableware such as cups, plates and mugs, electrical insulators, and art.

Chemistry · Materials

Alloy or composite?

Put each material in the right group. Ask: is this a mix of ELEMENTS (with a metal), or a mix of different TYPES of material?

8 of 8 still to sort.

When one material isn't good enough on its own, we combine it with something else. There are two very different ways to do it.

What you need to know

• Materials can be natural, like wood, or man-made, like plastic. Their physical properties decide what they are used for.
• Metals: good thermal and electrical conductors; strong, shiny, hard, malleable (hammered into shape) and ductile (stretched into wires).
• Ceramics: hard, brittle (likely to break or shatter if dropped), heavy, heat-resistant and chemically unreactive.
• Polymers: long chain molecules made of many smaller molecules called monomers. Most are lightweight, durable and flexible insulators, though some rigid plastics are brittle.
• An alloy is a mixture of two or more elements, at least one of them a metal. A composite combines two or more different types of material.

The big picture

Materials can be natural, like wood, or man-made, like plastic, and their properties decide what they're used for. Metals are good thermal and electrical conductors, and they're strong, shiny, hard, malleable and ductile. Ceramics are hard, brittle, heavy, heat-resistant and chemically unreactive. Polymers are long chain molecules. Most are lightweight, durable and flexible insulators. To tell materials apart, use a property only one of them has. When no single material is good enough, we make alloys (mixtures of elements with at least one metal) or composites (different types of material combined).

⚠ Watch out

Calling an alloy a compound. An alloy is a mixture: the elements are mixed, not chemically joined. And don't assume 'see-through means plastic'. Glass is a transparent ceramic.

Memory hook

Metals conduct, ceramics crack, polymers flex. And when one material isn't enough, team up: in reinforced concrete, steel takes the stretching and concrete takes the squashing.

Check yourself

Cover the page. What makes an alloy an alloy, and a composite a composite? Then explain why reinforced concrete is a composite even though it contains steel.