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ME 230: Control Of Properties Of Materials > Phase Equilibrium > Flashcards

Phase Equilibrium Flashcards

(61 cards)

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1
Q

What does studying thermodynamics allow us to do

A

Predict the natural tendencies of mateirals

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2
Q

1st law of thermodynamics

A

Energy can not be created or destroyed
Law of conservation of energy

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3
Q

1st law of thermodynamics

A

Energy can not be created or destroyed
Law of conservation of energy

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4
Q

2nd law of thermodynamics

A

Entropy must remain constant or increase in the universe/isolated system

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5
Q

What are a systems natural tendency

A

All systems tend towards lowest energy to achieve a more stable configuration
We tend from high potential energy to low potential energy (exothermic)

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6
Q

What is activation energy

A

Energy Barrier
Energy that needs to be added to a reaction in order to start it from the initial configuration

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7
Q

What is the second natural tendency of a system

A

All systems disorder themselves
The second law of thermodynamics
Systems tend towards chaos in that the choices for a given option increase (entropy)

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8
Q

What is entropy

A

The number of micro states that can represent a given macrostructure
Having the option to choose
There are many ways (micro states) to achieve a given energy state (macro state)
Having a permutation of possibilities is better

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9
Q

What is a macrostate compared to a micro state

A

A macrostate is a end result
A macrostate is a path to get to an end result

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10
Q

What is Gibb’s free energy

A

Available energy in a system
It assumes constant temperature and pressure
A combinations of the enthalpy and entropy

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11
Q

What is entropy majorly effected by

A

Tempreture

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12
Q

What is enthalpy

A

The internal energies in a structure
Relates to the first law of thermodynamics

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13
Q

When is free energy the most stable

A

When it is closest to negative infinity

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14
Q

Interpret delta Gibbs free energy

A

< 0 - spontaneous formed, exothermic
> 0 - spontaneous going backwards, endothermic
= 0 - equilibrium, nothing happens

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15
Q

What is a exothermic reaction

A

Releases energy into environment
Final form has less energy then starting form

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16
Q

What is an endothermic reaction

A

Absorbs energy from environment
Final form has more energy then initial form

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17
Q

What is the transition tempreture

A

The temperature where the state of a substance changes

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18
Q

What determines which state a substance will take at a given tempreture

A

Which ever state has lower energy

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19
Q

What is the system

A

1) The body under considerations
2) A series of possible alloys of the same components but with regard to alloy composition

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20
Q

What is a phase

A

A homogenous portion of a system
There is uniform chemical and physical characteristics
Homogenous on the atomic/microstructure level

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21
Q

What is a component

A

1) The base unit of the system
2) The pure metals and or other complement which an alloy is composed of

Phases may contain multiple components

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22
Q

What is equilibrium

A

When characteristics of a system persist indefinitely as long as it remains at the same:
Temperature
Pressure
Composition

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23
Q

What is a phase boundary

A

A part of a phase diagram
Divides the phase fields and describes transition conditions from one state to another (Tm, Tv, Ts)

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24
Q

What is a phase feild

A

A part of a phase diagram
A region of stability for the labelled phase- system is most stable in that range of given pressure and temperature at that microstructure configuration (phase)

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25
(T/F) P has an effect in a solid state system
F In most solid state systems, P has a negligible effect on phase state except in the extreme > GPa state We only care about T vs composition % in this state
26
What is the gibs phase rule
Describe how many phases will likley exist in given conditions In a solid, the 2 becomes a 1 since only the temp can vary, not preassure
27
In the gibs phase rule, what does the 2 represent
That temperature and pressure can change
28
In the gibs phase rule, what does C represent
The number of chemical independent components
29
In gibs phase rule what does P represent
The number of phases present
30
In gibs phase rule, what does F represent
The degrees of freedom These are the number of independent variables we can change without changing the phase state of the system Ex Temp, pressure, composition
31
What is the solubility limit
Solubility limit of A in B is the most amount of A that can be added to B before the substance goes from one phase to 2 phases
32
Why can the lowest energy be multiple phases
So there can be multiple phases on a graph that have the lowest energy as the lowest energy can be a certain percentage in one phase + a certain percentage in another phase
33
What is the solvus line
Describes the solubility limit and changes with temoretures - the line of solubility limits across tempreture
34
What does isomorphous mean
Having then same crystal structure or complete solid solubility for all compositions
35
What is complete solid solubility
When a secondary substance is being added to a composition but it never splits into multiple phases as a result of reaching the solubility limit
36
How can the composition of a POI on a phase diagram be broken down
1) phases present and their recpective weights (Phase composition) 2) elements present in each phase and their respective compositions (elemental composition)
37
Do we care about the phase composition of L
No, we don’t care if its one phase or multiple
38
Why is there a region of transition in the Center of phase diagrams
Represents the transition temps, since it hard to define exactly as there are various phases, the entire region represents transition with the liquidous line being the upper limit and the solidous line being the lower limit So different phases exist within the substance, some phases may already be liquid at the soldious line, as we increase tempreture more and more of these phases become liquid and transition. Depending on the composition of solid and the type of solids in the phases, the temperature it become liquid varies
39
What is the liquidous line
The minimum temperature at which the entire system is liquid
40
What is the solidous line
The maximum temperature at which the entire system is solid
41
How do we determine the elemental composition of the phases at certain point
1) Determine what phases are in the transition region by drawing a line to either end, the phase on the other side of the line is a phase present, only left and right 2) find where the line drawn in intersects the phase and find the weight percentage from there by the scale on the bottom and the other by subtracting 100
42
How to find the phase composition of a point
Identify phases present Use lever rule
43
What is the lever rule
Used to find the phases present in a phase diagram 1) locate POI 2) Draw a horizontal line from POI in each direction until a phase boundary 3) The x value of each end of the line gives each phases’s elemental composition 4) Use lever rule to find phase composition
44
What unit does the lever rule give
Whatever unit the bottom scale is in
45
What marks a 0 width phase feild
A rotated label
46
What are invariant points
Points where the degree of freedom is zero
47
What is a triple point
A point on a phase diagram where three phases may exist simultaneously in equillibrium
48
What are the four types of invariant points
Eutectic Eutectoid Peritectic Peritectoid
49
What is a eutectic reaction
An invariant reaction in which a liquid become two solids L <-> a(s) + B (s)
50
How are invariant reactions listed
Higher temperature to low temp L <-> a(s) + b(s) means that as temperature decreases, L goes to a and B
51
What is a peritectic reaction
An invariant reaction where solid + L goes to solid Y(s) + L <-> S(s)
52
What is a eutectoid point
An invariant point where solid goes to two solids S(s) <-> Y(s) + E(s)
53
What is a peritectoid reaction
A invariant reaction where two solids go to one solid Y(s) + E(s) <-> S(s)
54
What does the “ Eutect” mean in terms of invariant points/reactions
One thing going to two things with decreasing tempreture
55
What does the “Peritect” mean in terms of invariant points/reactions
Two things going to one thing with decreasing tempreture
56
What does “ic” mean in terms of invariant points/reactions
Liquid is involved as one of the phases
57
What does “oid” mean in terms of invarent points/reactions
No liquid phase is present
58
What is a congruent transformation
A transformation that does not involve composition change Represented by a vertical line on a phase diagram Often involves inter metallics
59
What are intermetalics
Compounds formed with 2 (or more) metallic atoms with specified stoicheometry
60
What governs the rate of transformation/diffusion
The distribution of element and rate of exchange of atoms between phases
61
What happens in equilibrium solidification
The weight fraction of solid/liquid changes and the elemental composition of each phase changes

ME 230: Control Of Properties Of Materials (7 decks)

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