Phase Diagrams

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What do phase diagrams show?
They show the conditions at which thermodynamically distinct phases occur at equilibrium; It is used to predict phase transformations and the resulting micro-structure.
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Define the term 'solubility limit'
The maximum concentration for which only a solution is present. It is dependent on temperature and increases with it.
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What is a precipitate?
A phasethat forms when a maximum allowable amount of solute is reached. It can change mechanical properties.
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Define 'Allotrope'
Different structure but same composition
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Why is energy minimisation important?
All systems would like to adopt a state with the least free energy as that would be the most stable state
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What state are materials in at equilibrium?
They should be in their mst stable phases HOWEVER some materials do not have phase(s) that habe the lowest free energy so they adopt a meta-stable state/ dynamic state.
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What is a meta-stable state?
a long lived state that is not the 'ground' / minimum state that the system could be in.
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What is the driving force of solidification?
What is the driving force of solidification?
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Define under-cooling
The processof lowering the temp of a liquid below its freezing point without it becoming a solid
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Why is under-cooling important?
At the freezing point ,G_s =G_l
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How is the latent heat of solidification produced?
latent heat of solidification occurs as thermal energy is released due to transition from disordered liquid to ordered solid.
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Name differences between a 2-component and a 1-component (unary) cooling curve
The sample melts and freezes over a range pf temperatures
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Describe a single phase region
Thermodynamic stability region for a specific phase as a function of temperature, composition and pressure
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Describe a multiple phase region
Several phases are simultaneously in equilibrium with each other.
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Define 'liquidus' (Binary phase diagrams)
Specifies the temperature above which a material is completely liquid.
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Define 'solidus' (Binary phase diagrams)
Specifies the temperature below which a material is completely solid
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What is a binary isomorphous system?
When both components A and B dissolve in each other completely.
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Why are the two components completely soluble?
They have the same crystal structure, they have similar atomic radii and similar valences
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Name a consequence of isomorphous systems
Solid Solution strengthening
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What is Solid Solution Strengthening?
When larger atoms are added in local stress fields, which dislocations also have, are also added. The interaction between local stress field from the two local stress fields make it more difficult for the dislocations to move.
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Other cards in this set

Card 2

Front

Define the term 'solubility limit'

Back

The maximum concentration for which only a solution is present. It is dependent on temperature and increases with it.

Card 3

Front

What is a precipitate?

Back

Preview of the front of card 3

Card 4

Front

Define 'Allotrope'

Back

Preview of the front of card 4

Card 5

Front

Why is energy minimisation important?

Back

Preview of the front of card 5
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