CHAPTER 10

Question 1

What is the driving force for solidification?

Answer 1

Temperature

Question 2

What happens at minimum ΔG

Answer 2

Equilibrium

Question 3

What is homogeneous nucleation?

Answer 3

Nuclei form in the bulk of the liquid metal

Question 4

What is heterogeneous nucleation?

Answer 4

nucleating surface is already present…easier

Question 5

How does critical radius (r) and activation free energy (ΔG) change with temperature?

Answer 5

both decrease as T decrease or ΔT increases

Question 6

Are ΔHf and γ dependent on T?

Answer 6

Yes…weakly (can assume they aren’t as dependent)

Question 7

How are the number of stable nuclei related to temp?

Answer 7

As temp decreases (ΔT increases), n* increases

Question 8

How does short range diffusion change with temp?

Answer 8

As temp decreases (ΔT increases), vd decreases

Question 9

What happens at max rate in terms of ΔG* and Qd? What happens at the molecular level

Answer 9

ΔG* becomes smaller than Qd
low atomic mobility supresses the nucleation rate

Question 10

What is solidification?

Answer 10

Atomic arrangement changes from a random/short-range order to a crystal structure/long-range order

Question 11

Which is lower, r*, homo or hetero nucleation?

Answer 11

They’re the same

Question 12

Which is lower ΔG*, homo or hetero nucleation?

Answer 12

Hetero

Question 13

Which is lower ΔT, homo or hetero nucleation

Answer 13

Hetero

Question 14

How is the degree of transformation (y) measured?

Answer 14

-X-ray diffraction
-Electrical conductivity measurements
-Measure propagation of sound waves