composites, ceramics, polymers revision

Composites

• composites are made from two or more different types of materials.
• Materials for composites are chosen because they have different properties that combine to make more useful materials.

Composite material examples

• MDF- made from wood fibres and glue, fibreglass is made from mesh of fibre glass set intough polymer.
  
• Steel-reinforced concrete- made by pouring concrete around a mesh of steel cables, when set, material is: strong when streched (because of the steel) and squashed (because of the concrete). 
• Waterproof clothing made from nylon.

• Most polymers are held together with covaelant bonds.
• All atoms in a polymer are joined together by strong covaelant bonds.
• Intermolecular forces between polymer molecules are larger meaning more energy is neede to break them , so most polymers are solid at room tempertaure.
• The intermolecular forces are still weaker than ionic and covaelant bonds so thehy have lower boiling points than ionic or giant molecular forces.
• Polymers are made by chemical reactions that join lots of small molecules together to make long molecules.
• General properties of polymers: chemically unreactive, solids at room temperature, plastic (can be moulded into shape), electrical insulators, strong, hard-wearing.

For diagram visit: http://www.bbc.co.uk/education/guides/ztxnsbk/revision/2

Key info and ceramic materials

• They're non-metal solids with high temperatures and they're not carbon based
• some ceramics are made from clay.
• Solids made by baking a starting material in a very hot oven 
• Are hard and tough
• have very many different uses
• Ceramic materials are coated in a tough glaze in bathrooms. They are hard and tough, and waterproof.

Clay and glass

• clay is soft when dug out of ground can be moulded
• when fired at high temperature clay hardens to form a type of ceramic, clay
• glass is transparent moulded when hot but brittle when thin
• most galss- made of soda lime glass (heated mixture of limestone, sand + sodium carbonate)
• broscilater glass- higher melting point than soda lime glass, made in the same way but with and boron trioxide