Comparing classes of materials

Chemistry · Materials

Sort it twice: what is it, and where does it come from?

Sort every material by its class first. Then switch to 'By origin' and sort the same materials again.

Which class of material is it?

12 of 12 still to sort.

Pick a material, then pick where it goes. Then switch the rule and sort the same materials again.

Predict, then check

Glass has a higher tensile strength than clay ceramics. Think before you click.

Glass beats clay ceramics on tensile strength. So which of the two is the more brittle?

Composites: matrix and reinforcement

pick a composite, then click its parts

Concrete: a cement matrix with aggregate as the reinforcement.

Choose a view to switch composite. Click a part to read what it is. Peel a layer off to see what is underneath.

What you need to know

• A material is a physical substance that things can be made from. You can sort materials by class, and separately by origin.
• Natural materials need minimal processing. Synthetic materials are human-made, typically from petrochemicals or other chemical processes.
• Glass, ceramics, concrete and bricks are human-made from natural raw materials, using manufacturing processes or chemical reactions.
• Have a goMaya says: 'Brick is a natural material, it comes out of the ground.' Can you put her right in one sentence?

  Bricks are human-made from natural raw materials, which go through manufacturing processes.

  Natural materials need minimal processing, so material that is manufactured into its final form is human-made even when the raw materials are natural.

• Brittle means it can break easily under stress. A lower fracture toughness is how a material shows it is more brittle.
• Have a goMaterial X has a lower fracture toughness than material Y. Which one is more brittle?

  Material X.

  A lower fracture toughness is how a material shows it is more brittle, so the lower number is the one that breaks more easily.

• A polymer is a chain of monomers bonded together by polymerisation. Thermosoftening polymers melt when heated; thermosetting polymers, with cross-links, do not.
• Have a goA plug socket must not melt when the appliance gets hot. Thermosoftening or thermosetting?

  Thermosetting.

  Thermosetting polymers have cross-links between the chains and do not melt when heated, so they suit heat resistant jobs.

• A composite is a matrix that binds a reinforcement. It is engineered for enhanced properties, not a simple mixture.
• Carbon fibre is less dense than aluminium, with a higher tensile strength and higher corrosion resistance.
• Choose a material by comparing its properties with the job: performance, production processes, cost, sustainability and aesthetics.

The big picture

Materials can be sorted by class (ceramics, polymers, composites, metals, natural materials) and, separately, by origin (natural, synthetic, or human-made from natural materials). Each class has properties that follow from how it is made and built, and the best material for a job is found by comparing properties with the use. Strong, tough and metal are not interchangeable ideas.

⚠ Watch out

Treating class and origin as one question. Concrete is a composite (its class), but it is also human-made from natural materials (its origin). Ask 'what is it?' and 'where does it come from?' separately.

Memory hook

Matrix holds, reinforcement strengthens. Cross-links stop the melt. Strong is not tough.

Check yourself

Without scrolling up: in fibreglass, which part is the matrix and which is the reinforcement? Natural or synthetic? (Plastic matrix, glass fibre reinforcement, synthetic.)