Lecture 6 Flashcards
Where does heterogeneous nucleation occur?
At specific locations
Which is more likely to occur and easier: Homo or heterogeneous nucleation?
Heterogeneous
when does nucleation form mould walls or impurities?
Solidification process of heterogeneous nucleation
What does the addition of S(θ) for energy change account for?
Effect of a substrate on nucleation
Where can heterogeneous nucleation happen?
At smaller undercooling
How does wetting relate to nucleation in heterogeneous nucleation?
Makes it easier
For homogenous nucleation of a solid in liquid, what can the liquid do?
move freely without any strain
For a homogenous solid nucleation in a solid matrix…?
- the surrounding matrix is rigid
- cannot accommodate the solid nucleus easily if there is a lattice mismatch
- induce addition strain energy
What increases due to strain energy in homogenous nucleation in solids?
critical nucleus size and barrier
What is a coherent interface?
When lattice constants are close
What is a semi coherent interface?
When lattice mismatch is large (form misfit dislocations)
What is heterogeneous nucleation of solid in solid?
Nucleation of B solid phase at a grain boundary in the alpha phase
What are you assuming about alpha and beta for heterogeneous nucleation of solid in solid?
that alpha and beta have the same lattice constants so there is no strain energy
When does YGB = 0 for heterogenous nucleation of solid in solid?
- no grain boundary in the system
- nucleation occurs in the bulk region
- recovers the homogenous nucleation
Why does heterogenous nucleation of solid in solid prefer to occur at the grain boundary?
the critical nucleus size is reduced to half
