Ceramics, Composites and Polymers

Ceramics, Composites and Polymers

1. Ceramics

   • Non-metal solids
   • High melting points
   • Are NOT made from carbon-based compounds
   • Some are made from clay
     • Clay is soft material when dug out of the ground
       • It can be moulded into different shapes
         • When fired at high temperatures, it hardens
           • This forms a clay ceramic
           • It's ideal for making pottery and bricks
   • Some ceramics are glass
     • Glass is generally transparent
       • Can be moulded when hot
         • Can be brittle when thin
     • Most glass made is soda-lime glass
       • It's made by heating a mixture of limestone, sand and sodium carbonate until it melts
         • When the mixture cools it comes out as glass
     • Borosilicate glass has a higher melting point than soda-lime glass
       • It's made the same way, using a mixture of sand and boron trioxide

2. Composites

   • They are made from one material embedded in another
     • Fibres or fragments of a material (known as reinforcements) are surrounded by a matrix acting as a binder
       • The properties of a composite depend on the properties of the materials it is made from
         • Fibreglass consists of fibres of glass embedded in a matrix made of polymer (plastic)
           • It has a low density (like plastic) but is very strong (like glass)
             • It's used for things like skis, boats and surfboards
         • Carbon fibre composites also have a polymer matrix
           • The reinforcement is either made from long chains of carbon atoms bonded together (carbon fibres) or from carbon nanotubes
             • They are very strong and light
               • Used in aerospace and sports car manufacturing
         • Concrete is made from aggregate (a mixture of sand and gravel) embedded in cement
           • Very strong
             • Ideal for use as building material e.g. skate parks
         • Wood is a natural composite of cellulose fibres held together by organic polymer matrix

3. Polymers

   • They can have very different properties
     • Influences for polymer properties are how they are made and what they are made from
       • The properties of poly(ethene) depend on the catalyst that was used and the reaction conditions (pressure and temperature)
         • Low density (LD) poly(ethene) is made from ethene at a moderate temperature under a high pressure and with a catalyst
           • It's flexible and is used for bags and bottles
         • High density (HD) polyethene is also made from ethene but at a lower temperate and pressure with a different catalyst
           • It's more rigid and is used for water tanks and drainpipes
   • The monomers that a polymer is made from determine the type of bonds that form between the polymer chains
     • These weak bonds between the different molecule chains can determine the properties of the polymer
       • Thermosoftening polymers contain individual polymer chains entwined together with weak forces between the chains. You can melt these plastics and mould them
       • Thermosetting polymers contain monomers that can form cross-links between the polymer chains, holding the chains together in a solid structure
         • Unlike thermosoftening polymers, these polymers don't soften when they're heated
           • They are strong, hard and rigid