Ceramics, polymers and composites — AQA GCSE Chemistry
Verified courseTeaching note checked against the official specification.
Ceramics, polymers and composites explained
Ceramics, polymers and composites covers 11 specification points, including Most of the glass we use is soda-lime glass,… and Borosilicate glass, made from sand and boron….
Read the full explanation
Open a point below for its explanation and revision guidance.
Most of the glass we use is soda-lime glass, made by heating a mixture of sand, sodium carbonate and limestone.
Soda-lime glass is the common glass used for windows, bottles and drinking glasses. It is made by heating a mixture of sand, sodium carbonate and limestone to a high temperature. Sand supplies silicon dioxide, the main network former; sodium carbonate lowers the melting point so the mixture fuses more easily; limestone, mainly calcium carbonate, stabilises the glass and helps it resist water. The molten mixture is then cooled quickly so it solidifies without forming an ordered crystal lattice, giving a rigid, transparent, non-crystalline solid. In an exam, name all three starting materials and state that they are heated together, then cooled.
Borosilicate glass, made from sand and boron trioxide, melts at higher temperatures than soda-lime glass.
Glass is a ceramic material made mainly from sand, which is silicon dioxide. Soda-lime glass is produced by heating sand with sodium carbonate and calcium carbonate; it softens at a relatively low temperature, so it is easy to shape into bottles and windows. Borosilicate glass is made by heating sand with boron trioxide instead. The boron trioxide alters the structure of the silicon dioxide network, raising the melting point, so borosilicate glass softens only at much higher temperatures. This makes it suitable for laboratory glassware, ovenware and other items that must withstand heating without deforming. When comparing the two glasses, state both the raw materials and the property difference: borosilicate contains boron trioxide and melts at a higher temperature than soda-lime glass.
Clay ceramics, including pottery and bricks, are made by shaping wet clay and then heating in a furnace.
Clay is a naturally occurring material made of tiny mineral particles. When mixed with water it becomes soft and mouldable, so it can be shaped by hand, pressed into a mould or extruded. The shaped object is then heated in a furnace or kiln to a high temperature. Heating drives off water and causes the particles to fuse together, producing a hard, strong, brittle ceramic that keeps its shape. Pottery and bricks are common examples. The key sequence is: mix clay with water, shape the wet clay, then heat it in a furnace. The heating stage is essential because unheated clay would soften again if it got wet, whereas the fired ceramic is durable and water-resistant.
The properties of polymers depend on what monomers they are made from and the conditions under which they are made.
Polymers are large molecules built from many small monomer molecules joined together. The identity of the monomer controls the chemical composition of the polymer chain, so different monomers give polymers with different properties. The conditions used during polymerisation, such as temperature, pressure and the presence of a catalyst, also affect how the chains form and pack together. Chains that are long, straight and closely packed give a denser, stronger, more rigid polymer with a higher softening temperature. Chains that are shorter or more branched pack less closely, giving a less dense, more flexible polymer with a lower softening temperature. Both factors therefore matter: what the monomer is and how the polymer is made.
For example, low density (LD) and high density (HD) poly(ethene) are produced from ethene.
Ethene is the monomer used to make poly(ethene). The same monomer can produce two different polymers depending on the conditions used. Low density poly(ethene), or LD poly(ethene), is made using very high pressure and a trace of oxygen as an initiator. This encourages branching. The branched chains cannot pack closely together, so the polymer is less dense, more flexible and has a lower softening temperature; it is used for bags and film. High density poly(ethene), or HD poly(ethene), is made using a catalyst, lower pressure and a slightly elevated temperature. This produces straighter chains. These straight chains pack closely, so the polymer is denser, stronger and more rigid; it is used for bottles and pipes. This shows that conditions control polymer properties.
Thermosoftening polymers melt when they are heated.
Thermosoftening polymers consist of long, flexible carbon-based chains held together only by weak intermolecular forces. When heated, the thermal energy supplied makes the chains vibrate more strongly until these weak forces between chains are overcome, so the chains slide over one another and the solid softens and eventually flows as a liquid. Because no covalent bonds between chains are broken, the change is physical and reversible: on cooling, the chains settle back into a rigid arrangement and the polymer hardens again. This is why thermosoftening polymers such as poly(ethene) can be repeatedly melted and remoulded, making them suitable for plastic bottles, bags and food containers.
Thermosetting polymers do not melt when they are heated.
Thermosetting polymers have polymer chains that are joined to one another by strong covalent cross-links, forming a rigid three-dimensional network. When the material is heated, the chains cannot slide past each other because the cross-links hold them firmly in place. The thermal energy makes the atoms vibrate more, but the covalent bonds in the network are far too strong to be overcome by the temperatures normally used, so the polymer does not soften or flow. Instead it may char or decompose at very high temperatures. This rigid, infusible behaviour makes thermosetting polymers such as those used in electrical plugs, pan handles and some adhesives suitable where heat resistance and strength are needed.
Students should be able to: explain how low density and high density poly(ethene) are both produced from ethene explain the difference between thermosoftening and thermosetting polymers in terms of their structures.
Ethene molecules can be joined by addition polymerisation to form poly(ethene), but the conditions used change the polymer's structure and properties. Low density poly(ethene), LDPE, is made at high pressure with a catalyst that produces branched chains, so the chains pack loosely and the polymer is flexible and less dense. High density poly(ethene), HDPE, is made at lower pressure with a different catalyst that produces straighter, less branched chains, so the chains pack closely, giving a denser, stronger, more rigid polymer. The same structural idea explains the difference between thermosoftening and thermosetting polymers: thermosoftening polymers have separate chains held by weak intermolecular forces and can slide when heated, whereas thermosetting polymers have covalent cross-links forming a rigid network that cannot slide, so they do not melt.
Most composites are made of two materials, a matrix or binder surrounding and binding together fibres or fragments of the other material, which is called the reinforcement.
A composite combines two or more materials so that the product has properties better than either material alone. In most composites, one material forms a matrix or binder that surrounds and holds together the other material, called the reinforcement, which may be fibres or fragments. The matrix keeps the reinforcement in position and transfers stress between the parts, while the reinforcement provides strength and stiffness. For example, in fibreglass, a polymer resin matrix binds together glass fibres; the resin alone is flexible and the glass fibres alone are brittle, but together they form a strong, lightweight material used for boat hulls and sports equipment. Reinforced concrete, with steel bars in a concrete matrix, is another common example.
Students should be able to recall some examples of composites.
A composite combines two or more materials so that the useful properties of each are retained in the finished article. One material, often called the reinforcement, provides strength or stiffness; the other, the matrix, holds the reinforcement in place and spreads any load. Fibreglass is glass fibres set in a polymer resin: the fibres give tensile strength while the resin binds them and resists impact. Carbon fibre composites use carbon fibres in a resin matrix and are valued where low mass and high strength matter, such as bicycle frames and aircraft parts. Reinforced concrete embeds steel rods in concrete, combining concrete's compressive strength with steel's tensile strength. Wood and bone are natural composites. To recall examples, link each named composite to its two components and one use.
Students should be able to, given appropriate information: compare quantitatively the physical properties of glass and clay ceramics, polymers, composites and metals explain how the properties of materials are related to their uses and select appropriate materials.
Given data such as density, melting point, tensile strength or electrical conductivity, compare materials numerically rather than by impression. Read the table, identify the property being compared, and state which material has the higher or lower value, quoting the figures. Then link that property to a use: low density and high strength suit aircraft panels, high melting point suits furnace linings, electrical insulation suits cable sheathing, and malleability suits shaped metal components. Selecting a material means matching the demands of the job to the data, not choosing the cheapest or most familiar option. For example, if a table shows a polymer with low density and a metal with high density, the polymer is preferable where mass must be kept low, provided its strength and melting point are adequate.
Your focus
- Name the three raw materials used to make soda-lime glass.
- Describe the process of heating the mixture and cooling it to form glass.
- State a common use of soda-lime glass and link it to a property.
Show all 33 objectives
- State the raw materials used to make soda-lime glass and borosilicate glass.
- Describe the difference in melting point between soda-lime glass and borosilicate glass.
- Relate the higher melting point of borosilicate glass to a suitable use such as laboratory glassware.
- Describe how wet clay is shaped into a required form.
- Explain why the shaped clay is heated in a furnace.
- Identify pottery and bricks as examples of clay ceramics.
- State that polymers are formed from monomers.
- Describe how the monomer and the polymerisation conditions affect polymer properties.
- Link chain length or branching to a property such as density or flexibility.
- Identify ethene as the monomer for both LD and HD poly(ethene).
- Describe the difference in chain structure between LD and HD poly(ethene).
- Relate the chain structure of each polymer to its density, flexibility and typical use.
- Describe the arrangement of polymer chains in a thermosoftening polymer.
- Explain, in terms of intermolecular forces, why a thermosoftening polymer softens and flows when heated.
- Relate the reversible melting of thermosoftening polymers to their everyday uses such as plastic bottles.
- Describe the cross-linked network structure of a thermosetting polymer.
- Explain why strong covalent cross-links prevent a thermosetting polymer from melting when heated.
- Compare thermosoftening and thermosetting polymers in terms of structure and behaviour on heating.
- Explain how the conditions and catalysts used in addition polymerisation produce low density and high density poly(ethene) with different chain structures.
- Relate chain branching and packing in poly(ethene) to density, strength and flexibility.
- Explain the difference between thermosoftening and thermosetting polymers in terms of intermolecular forces and covalent cross-links.
- Describe the roles of the matrix and the reinforcement in a composite material.
- Explain how combining a matrix with a reinforcement produces useful properties such as strength with low density.
- Identify examples of composites, including fibreglass and reinforced concrete, and state the materials involved.
- Name at least two examples of composites.
- Describe the two components of a named composite and the role of each.
- Relate a named composite to a use that depends on its combined properties.
- Compare physical properties of materials quantitatively using supplied data.
- Explain how a named property makes a material suitable for a stated use.
- Select an appropriate material for a given purpose and justify the choice with data.
Ceramics, polymers and composites exam tips
Marking Points
- Soda-lime glass is made from sand, sodium carbonate and limestone.
- The three materials are heated together to a high temperature and then cooled.
- Sand provides silicon dioxide, the main component of the glass.
- Sodium carbonate lowers the melting point of the mixture, and limestone helps stabilise the glass.
- Soda-lime glass is used for windows, bottles and drinking glasses because it is transparent, rigid and relatively cheap.
- Both glasses are ceramics based on sand, which is mainly silicon dioxide.
- Soda-lime glass is made from sand with sodium carbonate and calcium carbonate.
- Borosilicate glass is made from sand with boron trioxide.
- Borosilicate glass has a higher melting point than soda-lime glass.
- The higher melting point makes borosilicate glass suitable for laboratory glassware and heat-resistant ovenware.
- A comparison must mention both types of glass and the direction of the difference in melting point.
- Clay is mixed with water to make it soft and mouldable.
- The wet clay is shaped, for example by hand, in a mould or by extrusion.
- The shaped clay is heated in a furnace or kiln.
- Heating causes the clay particles to fuse, producing a hard, brittle ceramic.
- Pottery and bricks are named examples of clay ceramics.
- The order of the process must be shaping first and heating second.
- Polymers are made from small monomer molecules that join together.
- The type of monomer determines the chemical composition of the polymer.
- The conditions of polymerisation include temperature, pressure and the use of a catalyst.
- Different conditions can produce polymers with different chain lengths, branching or packing.
- Chain length and packing affect properties such as density, strength, flexibility and softening temperature.
- A full answer refers to both the monomer used and the manufacturing conditions.
- Ethene is the monomer used to produce both LD and HD poly(ethene).
- LD poly(ethene) is made under high pressure with a trace of oxygen, resulting in branched chains.
- HD poly(ethene) is made using a catalyst at lower pressure, resulting in straighter chains.
- Branched chains pack less closely, so LD poly(ethene) is less dense and more flexible.
- Straight chains pack closely, so HD poly(ethene) is denser, stronger and more rigid.
- The two forms have different uses, such as bags and film for LD poly(ethene) and bottles and pipes for HD poly(ethene).
- Thermosoftening polymers are made of long polymer chains that are not joined to each other by covalent bonds.
- The forces between separate chains are weak intermolecular forces, not covalent bonds.
- Heating transfers energy that makes the chains vibrate; when the vibrations are strong enough the weak forces between chains are overcome.
- Once the intermolecular forces are overcome, the chains can slide over one another, so the material softens and can flow.
- The process is physical and reversible: cooling allows the weak forces to re-form and the polymer hardens again.
- This behaviour explains why thermosoftening polymers can be remelted and reshaped, for example poly(ethene) bottles.
- Thermosetting polymers contain polymer chains joined together by strong covalent cross-links.
- The cross-links produce a rigid three-dimensional network rather than separate, free-moving chains.
- Heating makes the atoms vibrate more, but the strong covalent bonds of the network are not overcome at normal temperatures.
- Because the chains cannot slide over one another, the polymer does not soften or flow when heated.
- At very high temperatures the material may char or decompose rather than melt.
- This heat-resistant, rigid behaviour suits uses such as electrical plugs, pan handles and adhesives.
- Ethene undergoes addition polymerisation, in which many ethene molecules join to form a long poly(ethene) chain.
- Low density poly(ethene) is produced using high pressure and a catalyst that gives branched polymer chains.
- The branching in low density poly(ethene) prevents close packing, so the chains are held by weaker forces overall and the polymer is flexible and less dense.
- High density poly(ethene) is produced using lower pressure and a different catalyst that gives straighter, less branched chains.
- Straighter chains pack closely together in high density poly(ethene), giving stronger intermolecular forces, a denser and more rigid polymer.
- Thermosoftening polymers consist of separate chains with weak intermolecular forces, so the chains can slide when heated and the polymer softens.
- Thermosetting polymers have covalent cross-links between chains forming a rigid three-dimensional network, so the chains cannot slide and the polymer does not melt.
- A composite is made from two or more materials combined so that the product has improved properties compared with the separate materials.
- The matrix, also called the binder, surrounds and binds together the other material.
- The reinforcement is the material being bound, and it may be in the form of fibres or fragments.
- The matrix holds the reinforcement in place and helps transfer forces through the composite.
- The reinforcement usually provides strength and stiffness to the composite.
- Examples include fibreglass, where a polymer resin matrix binds glass fibres, and reinforced concrete, where a concrete matrix binds steel bars.
- Names at least two composites, such as fibreglass, carbon fibre composite or reinforced concrete.
- Identifies the two components of a named composite, for example glass fibres and a polymer resin in fibreglass.
- States that the reinforcement provides strength or stiffness while the matrix binds the materials together.
- Links a named composite to a use that depends on its combined properties, such as reinforced concrete in building foundations.
- Recognises that a composite is not a simple mixture or alloy but a material whose components keep distinct roles.
- Reads values from supplied data and quotes them when comparing two materials.
- Uses comparative language such as higher, lower, greater or smaller, supported by the figures.
- Compares materials across more than one property, for example density and melting point, rather than a single value.
- Explains a use by referring to a specific property, such as using a ceramic with a high melting point for a furnace lining.
- Selects a material for a stated purpose and justifies the choice using the data provided.
- Recognises that a material may be suitable for one use but not another because different uses demand different properties.
Examiner Tips
- 💡Learn the three raw materials as a set: sand, sodium carbonate and limestone.
- 💡State that the materials are heated together, not simply mixed.
- 💡Link the properties of soda-lime glass to a common use such as windows or bottles.
- 💡Write the comparison as a full sentence that names both glasses and states which one has the higher melting point.
- 💡Link the higher melting point to a named use, such as laboratory glassware, to show understanding rather than recall alone.
- 💡Check that chemical names are spelled correctly, especially boron trioxide and silicon dioxide.
- 💡Use the words shape and furnace or kiln to make the two main stages clear.
- 💡Give a named example such as a brick or a plant pot to anchor the general description.
- 💡If asked to sequence the process, write the stages in order rather than as a list of separate facts.
- 💡Use the phrase depends on both to signal that two factors are involved.
- 💡Give a specific condition such as temperature, pressure or a catalyst rather than writing conditions in general terms.
- 💡Link a structural feature such as chain length or branching to a named property such as density or flexibility.
- 💡Name ethene as the shared monomer before comparing the two products.
- 💡Use the words branched and straight when comparing the chain structures.
- 💡Link each form to a use, such as film for LD poly(ethene) and bottles for HD poly(ethene), to demonstrate understanding.
- 💡Link the melting behaviour directly to structure: weak forces between chains are overcome, not the strong covalent bonds along each chain.
- 💡Use the word 'intermolecular' when describing the forces between polymer chains to show precise understanding.
- 💡Give a named example such as poly(ethene) and state that it can be remelted and remoulded, which is why it is used for bottles and bags.
- 💡Contrast the two polymer types directly: thermosoftening has weak forces between separate chains, whereas thermosetting has strong covalent cross-links between chains.
- 💡Use the phrase 'three-dimensional network' to describe the cross-linked structure of a thermosetting polymer.
- 💡Explain the consequence, not just the structure: because chains cannot slide, the polymer does not melt, which makes it useful for heat-resistant items.
- 💡For each polymer, link production conditions to chain structure and then to a property, for example high pressure gives branched chains, which pack loosely and make LDPE flexible.
- 💡When comparing thermosoftening and thermosetting polymers, always refer to the forces or bonds between chains, not within them.
- 💡Use clear comparative language such as 'branched versus straighter chains' and 'weak intermolecular forces versus covalent cross-links' to structure your answer.
- 💡Name the two roles clearly in every answer: matrix or binder surrounds and binds, reinforcement is the fibres or fragments being bound.
- 💡Support your explanation with a named example such as fibreglass or reinforced concrete and state the benefit of combining the materials.
- 💡Use the phrase 'properties of the composite are better than those of the separate materials' to show why composites are useful.
- 💡Learn two composites in detail, naming both components and one use for each, so a recall question can be answered quickly.
- 💡When asked for examples, give the composite name rather than only its components, for example reinforced concrete rather than steel and concrete.
- 💡Use the words reinforcement and matrix to show understanding of why the components are combined.
- 💡Underline the property named in the question before reading the table, so you compare the right column.
- 💡Quote at least one figure for each material you compare, then state the consequence for the use.
- 💡If asked to select a material, name it and give a property-based reason, not a personal preference.
Common Mistakes
- Naming only sand as the raw material; correct this by listing sand, sodium carbonate and limestone.
- Saying the mixture is melted and left to form crystals; correct this by stating it is cooled quickly to form a non-crystalline solid.
- Confusing limestone with limewater; correct this by naming limestone as calcium carbonate used in the mixture.
- Saying borosilicate glass melts at a lower temperature than soda-lime glass; the correct comparison is that borosilicate melts at a higher temperature.
- Naming boron trioxide as the only raw material for borosilicate glass and omitting sand; the correct composition includes sand and boron trioxide.
- Confusing the additives used in the two glasses, for example stating that soda-lime glass contains boron trioxide; the correct additive for soda-lime glass is a mixture of sodium carbonate and calcium carbonate.
- Stating that clay is heated before it is shaped; the correct order is to shape the wet clay first and then heat it.
- Describing clay ceramics as flexible or elastic after firing; the correct description is hard and brittle.
- Omitting water from the process; the correct method mixes clay with water so that it can be shaped.
- Claiming that only the monomer determines the properties; the correct explanation also includes the conditions used during polymerisation.
- Claiming that only the conditions determine the properties; the correct explanation also includes the identity of the monomer.
- Confusing monomers with polymers by saying that monomers are large molecules; the correct description is that monomers are small molecules that join to form a large polymer.
- Stating that LD and HD poly(ethene) are made from different monomers; the correct statement is that both are made from ethene.
- Saying that HD poly(ethene) is made under higher pressure than LD poly(ethene); the correct comparison is that LD poly(ethene) uses the higher pressure.
- Reversing the chain structures by saying LD poly(ethene) has straight chains; the correct description is that LD poly(ethene) has branched chains.
- Thinking that heating breaks covalent bonds within the polymer chains; in fact only the weak intermolecular forces between chains are overcome, so the chains themselves stay intact.
- Describing the change as a chemical reaction; it is a physical change because the polymer can reharden on cooling and be remelted.
- Saying the polymer 'dissolves' when heated; it softens and flows because chains slide past each other, not because a solvent is present.
- Saying thermosetting polymers have no intermolecular forces; they do, but the covalent cross-links between chains dominate the behaviour.
- Claiming the cross-links break on heating so the polymer melts; the covalent bonds are too strong to be overcome at normal temperatures.
- Confusing the two polymer types and stating that thermosetting polymers can be remelted and reshaped; they cannot, because of their cross-linked network.
- Thinking that low density and high density poly(ethene) are made from different monomers; both are made from ethene, and only the polymerisation conditions and chain branching differ.
- Stating that high density poly(ethene) has stronger covalent bonds between its chains; the difference lies in how closely the chains pack and the resulting intermolecular forces.
- Describing thermosetting polymers as having no forces between chains; they have covalent cross-links that hold the network rigid.
- Confusing the matrix with the reinforcement; the matrix surrounds and binds, while the reinforcement is the fibres or fragments being held.
- Thinking a composite is simply a mixture with no bonding; the matrix binds the reinforcement together into a single material.
- Assuming a composite must be stronger than both starting materials in every way; it combines useful properties, such as strength with low density, rather than being superior in all respects.
- Treating any mixture as a composite; the correction is that a composite has a reinforcement held in a matrix with a structural purpose.
- Naming only one component, such as saying fibreglass is glass; the correction is to name both the glass fibres and the polymer resin.
- Confusing composites with alloys; the correction is that alloys are mixtures of metals, whereas composites combine materials such as fibres and resins.
- Comparing materials without quoting any figures; the correction is to cite the relevant values from the table.
- Choosing a material because it is strong while ignoring another critical property such as melting point; the correction is to check all stated requirements.
- Writing that a material is better without saying better for what; the correction is to name the property and the use it suits.