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15.4 Glass, Ceramics and Composites

GCSE Chemistry · AQA · Chapter 15: Using Our Resources

A free GCSE Chemistry lesson for AQA (8462) from OBA School: how soda-lime and borosilicate glass and clay ceramics are made, what composites are, and how to compare materials using data. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

  • Describe how soda-lime glass and borosilicate glass are made and compare their properties
  • Describe how clay ceramics such as pottery and bricks are made, and explain their properties using their structure
  • Explain what a composite is, naming the matrix (binder) and the reinforcement
  • Compare the properties of glass, ceramics, polymers, composites and metals using data
  • Explain how the properties of a material make it suitable for a use

Key words

  • Soda-lime glass: The most common glass, made by heating sand, sodium carbonate and limestone.
  • Borosilicate glass: Glass made from sand and boron trioxide. It melts at a higher temperature and resists cracking when heated.
  • Clay ceramic: A hard material such as pottery or brick, made by shaping wet clay and heating it in a furnace.
  • Composite: A material made of two materials: a matrix (binder) that surrounds and binds together fibres or fragments of a reinforcement.
  • Matrix (binder): The material in a composite that holds the reinforcement together.
  • Reinforcement: The fibres or fragments in a composite that give it extra strength or stiffness.

Glass

Glass is made by melting raw materials together in a furnace at about 1500 °C, then cooling the liquid quickly so that it forms a transparent solid. Sand (silicon dioxide, SiO₂) is the main ingredient.

  • Raw materials; Soda-lime glass sand, sodium carbonate and limestone; Borosilicate glass sand and boron trioxide
  • Melting temperature; Soda-lime glass lower; Borosilicate glass higher
  • Heating; Soda-lime glass can crack if heated suddenly or unevenly; Borosilicate glass expands very little when heated, so resists cracking (thermal shock)
  • Uses; Soda-lime glass windows, bottles, jars, drinking glasses; Borosilicate glass laboratory glassware, ovenware, measuring jugs for hot liquids

As the molten glass cools, its particles do not have time to line up in a regular pattern. They are “frozen” in a random arrangement, which is why glass has no crystals. Broken glass (cullet) is also added to the furnace: it melts at a lower temperature than the raw materials, so recycling saves energy and raw materials.

Key fact: Glass is transparent, hard, brittle, resistant to most chemicals and an electrical insulator. It is easy to recycle by melting and remoulding.

Clay ceramics

Clay ceramics, including pottery, bricks, tiles and porcelain, are made by shaping wet clay and then heating it in a furnace (kiln), at around 1000 °C. Heating drives off the water and joins the clay particles together into a hard, rigid solid. Pottery is often glazed so that it is smooth and waterproof.

Clay is made of compounds of metals (such as aluminium and potassium) with silicon and oxygen. Its giant structure has ionic bonding and some covalent bonding, arranged in thin layers. In wet clay, water molecules get between the layers, so they slide and the clay is soft and slippery. Firing drives out the water and strong bonds form between the layers, so the ceramic becomes hard and rigid. The higher the firing temperature, the harder the ceramic.

  • Properties: hard, strong when squashed (in compression), brittle (shatter when hit), high melting points, poor conductors of heat and electricity, unreactive.
  • Uses that depend on these properties: bricks and roof tiles (strong in compression, do not rot or burn), plates and mugs (hard, easy to clean, do not react with food), insulators on electricity pylons, kiln and furnace linings.

Composites

A composite is made of two materials with different properties. One material, the matrix or binder, surrounds and binds together fibres or fragments of the other, the reinforcement. The composite combines the useful properties of both.

  • Glass fibre reinforced plastic (fibreglass); Matrix (binder) polymer resin; Reinforcement glass fibres; Properties and uses light, strong, can be moulded; boat hulls, canoes, helmets
  • Carbon fibre reinforced polymer (CFRP); Matrix (binder) polymer resin; Reinforcement carbon fibres; Properties and uses very strong and very light, but expensive; racing bikes, tennis rackets, aircraft parts
  • Concrete; Matrix (binder) cement; Reinforcement sand and gravel (aggregate); Properties and uses very strong in compression; buildings, roads
  • Reinforced concrete; Matrix (binder) concrete; Reinforcement steel rods or mesh; Properties and uses strong in compression and tension; bridges, beams, tall buildings
  • Wood (natural); Matrix (binder) lignin; Reinforcement cellulose fibres; Properties and uses strong along the grain; furniture, building
  • Plywood; Matrix (binder) glue (polymer resin); Reinforcement thin sheets of wood, grain of each layer at right angles to the next; Properties and uses does not split along the grain; shelves, flooring, boat decks
  • MDF (medium-density fibreboard); Matrix (binder) polymer resin; Reinforcement wood fibres, chips or sawdust pressed together; Properties and uses smooth, can be cut into detailed shapes without splintering; furniture
  • Glass-ceramic; Matrix (binder) glass; Reinforcement tiny ceramic crystals; Properties and uses hard and tough, not brittle, cracks cannot spread; cooker hob tops

Exam tip: Concrete is strong when squashed but cracks easily when stretched. Steel is strong when stretched. Reinforced concrete combines the two, so it can be used for beams that bend under a load.

Comparing materials with data

You need to compare materials using numbers. When an object must be strong and light, compare strength ÷ density: a bigger value means more strength for the same mass.

  • Low-carbon steel; Density (g/cm³) 7.9; Tensile strength (MPa) 400; Other properties cheap, easily shaped, rusts
  • Aluminium alloy; Density (g/cm³) 2.8; Tensile strength (MPa) 300; Other properties does not corrode, more expensive than steel
  • Carbon fibre composite (CFRP); Density (g/cm³) 1.6; Tensile strength (MPa) 600; Other properties very expensive, slow to make, hard to recycle
  • Glass fibre composite; Density (g/cm³) 1.9; Tensile strength (MPa) 250; Other properties cheaper than CFRP, can be moulded
  • Soda-lime glass; Density (g/cm³) 2.5; Tensile strength (MPa) 50; Other properties transparent, brittle
  • HDPE; Density (g/cm³) 0.95; Tensile strength (MPa) 30; Other properties flexible, low melting point

Worked example: strong but light

CFRP: 600 ÷ 1.6 = 375. Low-carbon steel: 400 ÷ 7.9 = 50.6
375 ÷ 50.6 = 7.4, so for the same mass CFRP is about 7 times as strong as steel.
A steel part with volume 500 cm³ has mass 500 × 7.9 = 3950 g; a CFRP part of the same volume has mass 500 × 1.6 = 800 g.

Answer: CFRP is about 7 times stronger for its mass; it saves 3150 g on this part

Common mistakes

  • Mixing up the raw materials: soda-lime glass uses sodium carbonate and limestone; borosilicate glass uses boron trioxide.
  • Saying a composite is a mixture of two materials “stirred together”. One material (matrix) surrounds and binds the other (reinforcement).
  • Getting matrix and reinforcement the wrong way round. The fibres or rods are the reinforcement.
  • Saying ceramics are strong without saying how. They are strong in compression but brittle.
  • Choosing a material from strength alone when the question says it must be light. Use strength ÷ density, and think about cost.

Revision questions

Try these, then check your answers below each one.

Question 1. Which raw materials are used to make borosilicate glass? (Choose from: Sand and boron trioxide, Sand, sodium carbonate and limestone, Clay and water, Limestone and boron trioxide.)

Answer: Sand and boron trioxide

Working: Borosilicate glass: sand + boron trioxide. Soda-lime glass: sand + sodium carbonate + limestone.

Question 2. True or false? In reinforced concrete, the steel rods are the reinforcement and the concrete is the matrix.

Answer: True

Working: True. Concrete surrounds and binds the steel rods, which add strength in tension.

Question 3. A clay plate shatters when it is dropped. Which explanation is correct? (Choose from: Layers of ions shift so that ions with the same charge are side by side and repel, The covalent bonds in the clay melt, Water between the layers makes them slide apart, The plate contains delocalised electrons.)

Answer: Layers of ions shift so that ions with the same charge are side by side and repel

Working: A sharp blow moves the layers, so like charges line up and repel; the ceramic cracks. This is why ceramics are brittle.

Related lessons

Continue in the full course

This lesson is section 15.4 (AGCCH1504) of our free GCSE Chemistry course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Chemistry course.

 

 

 

 

 

 

 

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