Lecture 4 Flashcards
What must the chemical potentials equal to be in equilibrium??
They must equal each other
For a system to be in two-phase equilibrium, what three conditions must be satisfied?
- Thermal equilibrium
- Mechanical equilibrium (pressure of both phases must be equal)
- Chemical equilibrium (chemical potentials of each component must be the same in both phases)
What are the solidus and liquidus lines?
Phase boundaries that mark the transition between different phases
What is a eutectic point in a non ideal solution?
The lowest melting temp where 3 phases coexist simultaneously
How do you determine phase composition?
- Found at the solvus boundaries
- Use lever rule
What does the lever rule determine?
The relative amounts of two phases when they coexist in equilibrium
In lever rule, what does the average composition depend on?
The position of P (point on a phase diagram that corresponds to the overall composition of a system)
How does a lamellar microstructure form?
If you cool the system slowly at the eutectic composition
What is a eutectic system?
liquid forms into two solid phases simultaneously at a specific temp
What is a peritectic system?
a liquid and one solid phase turn into a different solid phase at a specific temp
When does a peritectic system typically form?
When the melting temp of one pure component is much higher than the other
What is an intermediate phase?
- A crystal structure distinct from both pure components
- typically has a fixed stoichiometry (vertical line)
- typically very brittle
What are the Hume-Rothery rules for substitutional solid solutions?
- atomic size factor
- electrochemical effect
- relative valency effect (not a good rule because lots of exceptions)
What are some qualities of ternary phase diagrams (3 components)?
- At fixed T & P, f=0
- each corner represents a pure component
- each side represents a binary system and the component at the opposite corner is 0
