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

Phase Equilibrium Flashcards

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
Q

(T/F) P has an effect in a solid state system

A

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
Q

What is the gibs phase rule

A

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
Q

In the gibs phase rule, what does the 2 represent

A

That temperature and pressure can change

28
Q

In the gibs phase rule, what does C represent

A

The number of chemical independent components

29
Q

In gibs phase rule what does P represent

A

The number of phases present

30
Q

In gibs phase rule, what does F represent

A

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
Q

What is the solubility limit

A

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
Q

Why can the lowest energy be multiple phases

A

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
Q

What is the solvus line

A

Describes the solubility limit and changes with temoretures - the line of solubility limits across tempreture

34
Q

What does isomorphous mean

A

Having then same crystal structure or complete solid solubility for all compositions

35
Q

What is complete solid solubility

A

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
Q

How can the composition of a POI on a phase diagram be broken down

A

1) phases present and their recpective weights (Phase composition)
2) elements present in each phase and their respective compositions (elemental composition)

37
Q

Do we care about the phase composition of L

A

No, we don’t care if its one phase or multiple

38
Q

Why is there a region of transition in the Center of phase diagrams

A

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
Q

What is the liquidous line

A

The minimum temperature at which the entire system is liquid

40
Q

What is the solidous line

A

The maximum temperature at which the entire system is solid

41
Q

How do we determine the elemental composition of the phases at certain point

A

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
Q

How to find the phase composition of a point

A

Identify phases present
Use lever rule

43
Q

What is the lever rule

A

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
Q

What unit does the lever rule give

A

Whatever unit the bottom scale is in

45
Q

What marks a 0 width phase feild

A

A rotated label

46
Q

What are invariant points

A

Points where the degree of freedom is zero

47
Q

What is a triple point

A

A point on a phase diagram where three phases may exist simultaneously in equillibrium

48
Q

What are the four types of invariant points

A

Eutectic
Eutectoid
Peritectic
Peritectoid

49
Q

What is a eutectic reaction

A

An invariant reaction in which a liquid become two solids
L <-> a(s) + B (s)

50
Q

How are invariant reactions listed

A

Higher temperature to low temp
L <-> a(s) + b(s) means that as temperature decreases, L goes to a and B

51
Q

What is a peritectic reaction

A

An invariant reaction where solid + L goes to solid
Y(s) + L <-> S(s)

52
Q

What is a eutectoid point

A

An invariant point where solid goes to two solids
S(s) <-> Y(s) + E(s)

53
Q

What is a peritectoid reaction

A

A invariant reaction where two solids go to one solid
Y(s) + E(s) <-> S(s)

54
Q

What does the “ Eutect” mean in terms of invariant points/reactions

A

One thing going to two things with decreasing tempreture

55
Q

What does the “Peritect” mean in terms of invariant points/reactions

A

Two things going to one thing with decreasing tempreture

56
Q

What does “ic” mean in terms of invariant points/reactions

A

Liquid is involved as one of the phases

57
Q

What does “oid” mean in terms of invarent points/reactions

A

No liquid phase is present

58
Q

What is a congruent transformation

A

A transformation that does not involve composition change
Represented by a vertical line on a phase diagram
Often involves inter metallics

59
Q

What are intermetalics

A

Compounds formed with 2 (or more) metallic atoms with specified stoicheometry

60
Q

What governs the rate of transformation/diffusion

A

The distribution of element and rate of exchange of atoms between phases

61
Q

What happens in equilibrium solidification

A

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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