1926263
Description
Flashcards by Hannah Munday, updated more than 1 year ago
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Created by Hannah Munday
about 9 years ago
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| Question | Answer |
| Atoms | Are around 10 to the power of -10 meters in size Contain a nucleus consisting of protons and neutrons and rings of electrons |
| Metals | Have low ionisation enthalpies Are held together by delocalised electrons and electrostatic attractive forces Bonds are equal in all directions Good conductors of heat and electricity Strong but malleable and ductile |
| Ceramics | Strong and brittle Have high melting and boiling points Usually ionic or covalently bonded Prone to crack propagation |
| Ionic Bonds | Electrons are transferred from one atom to another Strong electrostatic attractive forces Atoms cannot 'slip' past each other |
| Covalent Bonds | Electrons are shared between atoms Very strong bonds High melting and boiling points Not good conductors |
| Molecular Solids | Molecules held together by weak forces (dipoles) Low melting and boiling points Not good conductors - mostly polymers or organic materials |
| Polymers | Chains of monomers Covalent bonds Angled bonds to allow for rotation Quite strong and flexible Good insulators |
| Bending | When a material bends elastic / strain energy is stored and released as fracture energy when broken |
| Crack Propagation | Atomic bonds are broken one by one from a particular point |
| Pre-stressed Glass | Strain energy is stored in the glass so that it shatters into tiny pieces when broken to prevent damage by large shards of broken glass Mostly used in car windows |
| Dislocations | Impurity in metals in the form of a gap in the atomic structure which acts as a weakness |
| Alloys | Adds an impurity atom to 'pin' dislocations in place by forming bonds with the surrounding atoms This makes it stronger but more brittle |
| Toughness | Toughness = energy of fracture / cross-sectional area = J / m2 |
| Strength | Strength = breaking force / cross-sectional area = N / m2 |
| Composite materials | Composites combine the useful properties of more than one material |
| Elastomers | Highly elastic polymers which can be toughened by vulcanisation (cross-linking chains) |
| Thermoplastics | Polymers that are not cross-linked Can be recycled Weaker thank other polymers |
| Thermoset Plastics | Polymers that are cross-linked as the plastic sets When heated, the plastic undergoes decomposition Cannot be reformed or recycled (except as fillers) |
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