Looking Inside Materials

Hannah Munday
Flashcards by Hannah Munday, updated more than 1 year ago
Hannah Munday
Created by Hannah Munday over 5 years ago
5
1

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AS Level Physics (Chapter 5 - Looking Inside Materials) Flashcards on Looking Inside Materials, created by Hannah Munday on 01/28/2015.

Resource summary

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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