Ceramics, polymers and composites (HT)
Modern materials science gives chemists a vast palette beyond pure metals. Three major classes are ceramics, polymers and composites.
Ceramics
Hard, brittle, heat-resistant materials made from inorganic, non-metallic compounds.
Examples
- Clay ceramics (pottery, bricks): made by shaping wet clay then heating in a kiln. The water evaporates and the silicate structure fuses.
- Glass:
- Soda-lime glass: most common — sand + sodium carbonate + limestone, heated and cooled. Melts at lower temperature.
- Borosilicate glass (Pyrex): heat-resistant — sand + boron trioxide, withstands rapid temperature change.
Properties
- Hard.
- Brittle (snaps under impact).
- Excellent electrical and thermal insulator.
- Resistant to chemical attack.
Polymers
Long-chain molecules of repeating monomer units (see C7.7).
Two structural types
- Thermosoftening (e.g. polyethene, polypropene): chains held by weak intermolecular forces. Melts when heated → can be reshaped/recycled.
- Thermosetting (e.g. melamine, Bakelite, polyurethane foams, epoxy resins): chains held by strong covalent crosslinks. Doesn't melt → rigid, heat-resistant, cannot be recycled by melting.
Effect of polymer conditions
The same monomer can give different polymers depending on conditions:
- High pressure / radical initiator: low-density polyethene (LDPE) — branched chains, soft, flexible. Used for plastic bags.
- Low pressure / Ziegler-Natta catalyst: high-density polyethene (HDPE) — straight chains, harder, more rigid. Used for milk bottles.
Composites
A composite is two or more materials combined; the resulting properties differ from those of the individual components.
Structure
- Matrix: surrounds and binds.
- Reinforcement: fibres or particles that take the load.
Examples
- Concrete: cement matrix + sand/gravel reinforcement. Strong in compression.
- Reinforced concrete: concrete + steel rods. Strong in tension AND compression.
- Fibreglass: polymer resin matrix + glass fibres. Strong, lightweight — boat hulls, car bodies.
- Carbon fibre: polymer matrix + carbon fibres. Light, very strong — aircraft, racing bikes.
- Wood: natural composite — cellulose fibres in lignin matrix.
⚠Common mistakes
- Saying glass is a metal — it's a ceramic.
- Confusing thermosoftening and thermosetting — first melts, second doesn't.
- Treating composite as a single material — it's a combination.
- Saying composites are always synthetic — wood is natural.
Links
Builds on C7.7 (polymers), C2.3 (giant covalent — silica). Connects to C10.6 (recycling).
AI-generated · claude-opus-4-7 · v3-deep-chemistry