Materials lab: polymers, glass, ceramics and composites sim
Test eight real materials on one bench: melt or char them on a hot plate, float them in water–ethanol mixtures, stretch the two poly(ethene)s, put the glasses in a flame and bend bars until they break. Then look inside each one and choose the right material for a job.
Materials: thermosoftening and thermosetting polymers, LDPE and HDPE, soda-lime and borosilicate glass, clay ceramics, composites, and choosing a material for a job · covers the GCSE (chemistry only) topic
What the sim shows
Materials are chosen for a job by their properties. Thermosoftening polymers, such as low-density and high-density poly(ethene), are long chains held together only by weak intermolecular forces: heating overcomes these, the chains slide past each other, and they soften and melt and can be reshaped. Thermosetting polymers, such as melamine, have covalent cross-links between the chains, so they do not melt when heated; heated strongly, they char. Both poly(ethene)s are made from ethene: LDPE at very high pressure and about 200 °C, HDPE at low pressure with a catalyst. LDPE has branched chains that cannot pack closely, so it is less dense, softer and stretchier; HDPE has straight chains that pack closely. Soda-lime glass is made by heating sand, sodium carbonate and limestone; borosilicate glass is made from sand and boron trioxide, melts at a higher temperature and is much less likely to crack when heated suddenly (thermal shock goes beyond the AQA specification). Clay ceramics are made by shaping wet clay and heating it in a furnace: hard but brittle. A composite is made of two materials: fibres or rods (the reinforcement) held in a matrix, such as glass fibres in a resin (fibreglass) or steel rods in concrete. Each test uses a fresh piece, and every piece is the same size. The ethanol mixtures are made up by volume (a 50 % mix by mass would be less dense, and LDPE would sink in it too). Real plastics vary, so tap off any air bubbles before deciding; some LDPE is close to 0.93 g/cm³. Densities are rounded typical values. Model limits: the stretch and bend loads are illustrative, chosen to show what a school test shows; past its limit a real strip keeps creeping under the same load, but here each step is shown as a fixed jump.
- Eight samples: polymers, glasses, a ceramic, composites
- Hot plate, Bunsen, float beakers
- Stretch stand and bend rig: add load one step at a time
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