Phase Equilibrium Flashcards
What does studying thermodynamics allow us to do
Predict the natural tendencies of mateirals
1st law of thermodynamics
Energy can not be created or destroyed
Law of conservation of energy
1st law of thermodynamics
Energy can not be created or destroyed
Law of conservation of energy
2nd law of thermodynamics
Entropy must remain constant or increase in the universe/isolated system
What are a systems natural tendency
All systems tend towards lowest energy to achieve a more stable configuration
We tend from high potential energy to low potential energy (exothermic)
What is activation energy
Energy Barrier
Energy that needs to be added to a reaction in order to start it from the initial configuration
What is the second natural tendency of a system
All systems disorder themselves
The second law of thermodynamics
Systems tend towards chaos in that the choices for a given option increase (entropy)
What is entropy
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
What is a macrostate compared to a micro state
A macrostate is a end result
A macrostate is a path to get to an end result
What is Gibb’s free energy
Available energy in a system
It assumes constant temperature and pressure
A combinations of the enthalpy and entropy
What is entropy majorly effected by
Tempreture
What is enthalpy
The internal energies in a structure
Relates to the first law of thermodynamics
When is free energy the most stable
When it is closest to negative infinity
Interpret delta Gibbs free energy
< 0 - spontaneous formed, exothermic
> 0 - spontaneous going backwards, endothermic
= 0 - equilibrium, nothing happens
What is a exothermic reaction
Releases energy into environment
Final form has less energy then starting form
What is an endothermic reaction
Absorbs energy from environment
Final form has more energy then initial form
What is the transition tempreture
The temperature where the state of a substance changes
What determines which state a substance will take at a given tempreture
Which ever state has lower energy
What is the system
1) The body under considerations
2) A series of possible alloys of the same components but with regard to alloy composition
What is a phase
A homogenous portion of a system
There is uniform chemical and physical characteristics
Homogenous on the atomic/microstructure level
What is a component
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
What is equilibrium
When characteristics of a system persist indefinitely as long as it remains at the same:
Temperature
Pressure
Composition
What is a phase boundary
A part of a phase diagram
Divides the phase fields and describes transition conditions from one state to another (Tm, Tv, Ts)
What is a phase feild
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)
(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
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
In the gibs phase rule, what does the 2 represent
That temperature and pressure can change
In the gibs phase rule, what does C represent
The number of chemical independent components
In gibs phase rule what does P represent
The number of phases present
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
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
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
What is the solvus line
Describes the solubility limit and changes with temoretures - the line of solubility limits across tempreture
What does isomorphous mean
Having then same crystal structure or complete solid solubility for all compositions
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
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)
Do we care about the phase composition of L
No, we don’t care if its one phase or multiple
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
What is the liquidous line
The minimum temperature at which the entire system is liquid
What is the solidous line
The maximum temperature at which the entire system is solid
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
How to find the phase composition of a point
Identify phases present
Use lever rule
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
What unit does the lever rule give
Whatever unit the bottom scale is in
What marks a 0 width phase feild
A rotated label
What are invariant points
Points where the degree of freedom is zero
What is a triple point
A point on a phase diagram where three phases may exist simultaneously in equillibrium
What are the four types of invariant points
Eutectic
Eutectoid
Peritectic
Peritectoid
What is a eutectic reaction
An invariant reaction in which a liquid become two solids
L <-> a(s) + B (s)
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
What is a peritectic reaction
An invariant reaction where solid + L goes to solid
Y(s) + L <-> S(s)
What is a eutectoid point
An invariant point where solid goes to two solids
S(s) <-> Y(s) + E(s)
What is a peritectoid reaction
A invariant reaction where two solids go to one solid
Y(s) + E(s) <-> S(s)
What does the “ Eutect” mean in terms of invariant points/reactions
One thing going to two things with decreasing tempreture
What does the “Peritect” mean in terms of invariant points/reactions
Two things going to one thing with decreasing tempreture
What does “ic” mean in terms of invariant points/reactions
Liquid is involved as one of the phases
What does “oid” mean in terms of invarent points/reactions
No liquid phase is present
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
What are intermetalics
Compounds formed with 2 (or more) metallic atoms with specified stoicheometry
What governs the rate of transformation/diffusion
The distribution of element and rate of exchange of atoms between phases
What happens in equilibrium solidification
The weight fraction of solid/liquid changes and the elemental composition of each phase changes
