C15.04: Glass, ceramics, and composites

• Glass ceramics:

  Glass is transparent and hard but it is brittle. Most of the glass we use is soda-lime glass. This is made by melting a mixture of sand (silicon oxide), sodium carbonate and limestone, then allowing the molten liquid to cool and solidify
• Borosilicate glass is made by heating sand with boron trioxide
• Borosilicate glass has a much higher melting point than soda-lime glass
• Clay ceramics include brick, china and porcelain
• Clay ceramics are made by shaping wet clay and then heating it to a high temperature in a furnace, which causes crystals to form and join together
• Crystal: a solid containing particles (atoms, molecules or ions) joined together by a regular arrangement or repeating pattern
• Clay ceramics are often coated with a glaze, which hardens on heating to form a hard, smooth, opaque and water proof layer. This explains why they are often used for dinner plates and bowls.
• Composite materials: Materials made from two or more different materials with constructing properties. They are combined to produce a material with improved properties.
• Most composite materials have two components:

  • the reinforcement - fibres or other material that make up the bulk of a composite material
  • the matrix - substance which binds the reinforcement together
• Reinforced concrete:

  Reinforcement - steel

  Matrix - concrete
• Fibre glass:

  Reinforcement - glass fibres

  Matrix - polymer resin
• Carbon fibre reinforced polymer:

  Reinforcement - carbon fibres

  Matrix - polymer resin
• Chipboard:

  Reinforcement - wood chips

  Matrix - resin glue
• It is often possible to separate the reinforcement from the matrix by physical processes
• Reinforced concrete can be broken up using machinery. This is one stage in recycling components of reinforced concrete
• Fibre glass and carbon reinforced polymer (cFRP):

  The fibres in these composite materials have low density. They are strong in tension, so they are not easily stretched, but they are flexible. The polymer resin which binds the fibres together is not strong but it is stiff
• Resin: raw plastic, especially in semi-liquid form
• Tension: pulling force exerted by each end of an object such as a string or rope
• Fibre: long, thin strands
• Chipboard:

  Wood itself is a natural composite material. It consists of a reinforcement of cellulose fibres bonded together by a matrix of lignin. The fibres are aligned alongside each other, so wood is strong in one direction than it is in the other. Chipboard contains randomly arranged wood chips bonded together by a glue so it is strong in all directions.
• Reinforced concrete:

  The properties of concrete can be improved by reinforcing with steel rods or mesh.
• Compressive strength: a measure of how well a material resists being crushed when a force is applied
• Tensile strength: the tension a material can withstand without breaking
• The compressive strength of concrete is higher than its tensile strength but the tensile strength of steel is higher than its compressive strength.
• The combination of concrete and steels rods or mesh is strong in tension and in compression. This allows reinforced concrete to be strong and slightly flexible, which is important in constructing large buildings and structures.
• Lead is toxic