1Heat and handles
Metals are good thermal conductors, so pans are made of metal. Handles are made of polymers, which are thermal insulators.
conductorinsulator
Lesson 23.4 notes
Choosing materials
Matching properties to uses, alloys, and what happens to materials when we have finished with them.
2Why alloys are harder
In a pure metal, the layers of atoms slide over each other easily. In an alloy, atoms of a different size get in the way, so it is harder.
alloy
3Common alloys
Steel is iron with a little carbon. Brass is copper with zinc. Bronze is copper with tin. Stainless steel contains chromium and nickel, so it doesn't rust.
steelbrassbronze
4Gold for jewellery
Pure gold (24 carat) is soft. Mixing in copper or silver makes harder alloys, like 18 carat gold, that keep their shape.
carat
5Light and strong
Aluminium alloys are strong, resist corrosion and have a low density, so they are used for aircraft.
density
6Plastic waste
Most plastics are not biodegradable: microbes can't break them down, so plastic litter lasts for hundreds of years.
biodegradable
7Reduce, reuse, recycle
Using less and reusing things saves the most energy and raw materials. Recycling is next best; landfill is the worst.
reuserecycle
Explore: Alloy lab
Mix some atoms of another element into a pure metal and push it. See why alloys are harder than pure metals.
Common mistake: Strength is not the only property that matters
A material is chosen for the whole job: strength, weight, how it handles heat and electricity, cost, and how long it lasts. The strongest material is often the wrong choice.
Remember
- Choose a material by matching its properties to the job: strength, density, conductivity, melting point and cost.
- An alloy is a mixture of a metal with other elements. Alloys are harder because different-sized atoms make it harder for the layers to slide.
- Reduce and reuse first, then recycle. Most plastics are not biodegradable, so they last for hundreds of years as waste.
Going further at GCSE