Using resources: ceramics, composites and polymers as materials

What you'll learn

This topic covers three major classes of materials used in everyday life and industry: ceramics, polymers and composites. You'll understand how the structures of these materials relate to their properties, and why specific materials are chosen for particular applications. This knowledge is essential for answering questions about material selection and properties in your AQA GCSE Chemistry exam.

Key terms and definitions

Ceramics — non-metal solids with high melting points that are not made from carbon-based compounds, typically made by heating clay or other minerals to high temperatures

Polymers — very large molecules made up of many small repeating units (monomers) joined together by covalent bonds in long chains

Thermosoftening polymers — polymers with weak intermolecular forces between chains that soften when heated and can be remoulded repeatedly

Thermoset polymers — polymers with covalent cross-links between chains that do not soften when heated once formed

Composites — materials made from two or more different materials combined together to produce a material with improved properties

Glass — a ceramic made by heating sand (silicon dioxide) with sodium carbonate and limestone until molten, then cooling rapidly

Clay ceramics — materials made by shaping wet clay and then heating to high temperatures to harden it permanently

Soda-lime glass — the most common type of glass, made from sand, sodium carbonate and limestone, used for windows and bottles

Core concepts

Properties and structure of ceramics

Ceramics are ancient materials still widely used today. They include pottery, bricks, tiles and glass. All ceramics share certain structural features that give them characteristic properties.

Structure of ceramics:

Giant ionic or covalent structures
Strong bonds throughout the structure
Atoms arranged in rigid, fixed positions

Properties of ceramics:

Very high melting points (strong bonds require lots of energy to break)
Hard and strong in compression (rigid structure resists deformation)
Brittle (structure shatters rather than bends when stress is applied)
Poor conductors of electricity (no free electrons or ions to move)
Chemically unreactive in most conditions

Clay ceramics are made by:

Shaping wet clay (contains aluminium silicate minerals)
Heating to high temperatures (firing)
Chemical changes occur, forming new crystalline structures
Material hardens permanently and cannot be reshaped

Glass is technically a ceramic but has an amorphous (non-crystalline) structure:

Made by melting sand with sodium carbonate and limestone
Cooled quickly so atoms don't arrange into regular patterns
Transparent because amorphous structure allows light to pass through
Can be moulded when hot and viscous

Borosilicate glass is made by adding boron oxide to the glass mixture:

Higher melting point than soda-lime glass
Lower thermal expansion coefficient
Resistant to sudden temperature changes
Used for laboratory glassware and ovenware (Pyrex)

Structure and properties of polymers

Polymers are long-chain molecules formed when many small molecules (monomers) join together through polymerisation reactions. The properties of polymers depend on the monomers used and the conditions of polymerisation.

Thermosoftening polymers:

Consist of individual polymer chains
Weak intermolecular forces between chains (Van der Waals forces)
When heated, intermolecular forces break and chains can slide over each other
Material softens and can be remoulded
On cooling, intermolecular forces reform and material hardens again
Can be recycled by melting and reshaping
Examples: poly(ethene), polystyrene, PVC

Thermoset polymers:

Polymer chains connected by strong covalent bonds (cross-links)
Cross-links form during initial heating and setting
When heated again, cross-links do not break
Material does not soften
Cannot be remoulded or recycled by melting
Often decompose or burn rather than melt
Examples: epoxy resins, vulcanised rubber, melamine resins

The diagram below shows the structural difference:

Thermosoftening: Individual chains with weak forces between them Thermoset: Chains with covalent cross-links forming a rigid 3D network

Factors affecting polymer properties:

Chain length (longer chains = stronger polymer)
Cross-linking (increases strength and rigidity)
Crystallinity (regular arrangement = stronger, less flexible)
Side groups on the polymer chain
Temperature of formation

Composites and their applications

Composites combine two or more materials to produce a new material with enhanced properties. Typically, composites consist of a reinforcement material within a matrix (binder).

Structure of composites:

Reinforcement — provides strength (fibres, particles or fragments)
Matrix — surrounds and binds the reinforcement together
Properties depend on both components and their arrangement

Common composites:

Fibreglass (glass-reinforced plastic):

Reinforcement: glass fibres
Matrix: polymer resin
Properties: strong, lightweight, can be moulded
Applications: boat hulls, car body panels, surfboards

Carbon fibre composites:

Reinforcement: carbon fibres or carbon nanotubes
Matrix: polymer resin or epoxy
Properties: very strong, very lightweight, expensive
Applications: aircraft components, racing car bodies, sports equipment

Concrete:

Reinforcement: aggregate (sand and gravel)
Matrix: cement
Properties: strong in compression, cheap, durable
Applications: buildings, roads, bridges

Reinforced concrete:

Additional reinforcement: steel rods or mesh
Improves tensile strength (concrete alone is weak under tension)
Applications: high-rise buildings, bridges requiring both compressive and tensile strength

Wood:

Natural composite
Reinforcement: cellulose fibres
Matrix: lignin (natural polymer)
Properties: strong, lightweight, flexible

Why use composites?

Combine advantages of different materials
Overcome limitations of single materials
Tailor properties for specific applications
Often lighter than traditional materials with similar strength
Can be more cost-effective than pure materials

Selecting materials for specific uses

Material selection depends on matching properties to requirements. You must be able to justify choices based on properties.

Questions to consider:

What forces will act on the material? (compression, tension, impact)
What temperature range will it experience?
Does it need to conduct heat or electricity?
Does it need to be transparent?
What is the cost requirement?
Does it need to be lightweight?
Will it be exposed to chemicals or weather?
Does it need to be recycled?

Examples of material selection:

Saucepan handles:

Requirement: heat insulator, comfortable to hold
Material: thermosoftening polymer or wood
Reason: poor thermal conductor, can be moulded to ergonomic shape

Laboratory beakers:

Requirement: withstand heating, resist thermal shock, transparent
Material: borosilicate glass
Reason: high melting point, low thermal expansion, see contents

Aircraft components:

Requirement: very strong, lightweight, corrosion resistant
Material: carbon fibre composite or aluminium alloy
Reason: high strength-to-weight ratio essential for fuel efficiency

Roof tiles:

Requirement: waterproof, durable, withstand weathering
Material: clay ceramic
Reason: unreactive, hard, durable, cheap

Nanoparticles in materials

Nanoparticles (1-100 nanometres) can be incorporated into materials to modify properties.

Uses in materials:

Carbon nanotubes in composites (increase strength)
Nanoparticles in polymers (improve properties)
Silver nanoparticles (antibacterial properties in fabrics)
Titanium dioxide nanoparticles (sun creams, self-cleaning surfaces)

Advantages:

Very high surface area to volume ratio
Different properties from bulk materials
Small quantities can significantly improve material properties

Environmental considerations

Material choice must consider environmental impact:

Thermosoftening polymers:

Can be recycled by melting and remoulding
Reduces landfill waste
Requires less energy than producing new polymers from crude oil

Thermoset polymers:

Cannot be recycled by melting
Difficult to dispose of
May be ground up and used as filler material

Ceramics and glass:

Glass can be recycled indefinitely without loss of quality
Requires less energy than making new glass
Clay ceramics rarely recycled (expensive to process)

Composites:

Difficult to recycle (separation of components is challenging)
Research ongoing into recycling methods
Often end up in landfill

Worked examples

Example 1: Comparing polymer types

Question: A manufacturer needs to produce electrical plug casings. Explain whether a thermosoftening polymer or a thermoset polymer would be more suitable. [4 marks]

Answer: A thermoset polymer would be more suitable [1 mark].

Thermoset polymers have covalent cross-links between polymer chains [1 mark], which means they do not soften when heated [1 mark].

This is important for electrical plugs because they may become hot during use, and the casing must maintain its shape and not deform [1 mark].

(Note: A thermosoftening polymer would soften if the plug became hot, potentially creating a safety hazard.)

Example 2: Composite materials

Question: Concrete is a composite material. Describe the structure of concrete and explain why steel rods are often added to concrete in construction. [4 marks]

Answer: Concrete is made of aggregate (sand and gravel) as reinforcement [1 mark] within a cement matrix [1 mark].

Steel rods are added because concrete is strong in compression but weak in tension [1 mark].

The steel reinforcement provides tensile strength, allowing the concrete to withstand stretching and bending forces [1 mark].

Example 3: Glass types

Question: A student needs to choose between soda-lime glass and borosilicate glass for making a container to heat chemicals in a school laboratory.

Explain which type of glass would be more suitable and why. [3 marks]

Answer: Borosilicate glass would be more suitable [1 mark].

Borosilicate glass has a lower thermal expansion coefficient than soda-lime glass [1 mark], so it is less likely to crack when heated or cooled rapidly (resistant to thermal shock) [1 mark].

Common mistakes and how to avoid them

Confusing thermosoftening and thermoset polymers — Remember: thermosoftening polymers soften when heated; thermoset polymers have permanent set structure with cross-links
Stating ceramics are strong without qualification — Ceramics are strong in compression but brittle; they shatter under impact or tension rather than bending
Thinking all polymers are the same — Polymer properties vary enormously depending on monomers used, chain length, cross-linking and conditions of formation
Not explaining composite advantages — Always state which properties come from which component (reinforcement provides strength; matrix binds and transfers forces)
Forgetting to link structure to properties — Always explain why a material has certain properties by referring to its structure (types of bonds, arrangement of particles)
Confusing glass types — Soda-lime glass is common window/bottle glass; borosilicate glass contains boron oxide and resists thermal shock (used in labs)

Exam technique for "Using resources: ceramics, composites and polymers as materials"

"Explain" questions require structure AND properties — State the structural feature (e.g., "cross-links between chains") then link to property (e.g., "therefore cannot be remoulded when heated")
Material selection questions need justification — Don't just name a material; explain which specific property makes it suitable for the stated purpose
Compare questions need differences for both materials — If comparing thermosoftening and thermoset, describe the structure of both and explain how properties differ
Use precise terminology — "Intermolecular forces" not "bonds between molecules"; "covalent cross-links" not "strong connections"; "composite" not "mixture"

Quick revision summary

Ceramics have giant structures with strong bonds, making them hard, brittle and high-melting. Polymers are long-chain molecules; thermosoftening types have weak intermolecular forces and soften when heated, while thermoset types have covalent cross-links and don't soften. Composites combine reinforcement (provides strength) with a matrix (binds components), creating materials with enhanced properties. Material selection requires matching structural properties to application requirements. Understanding structure-property relationships is essential for explaining material behaviour and suitability.