Solidification and Nucleation Quiz

What is the first step of solidification?

• Melting

• Nucleation

• Evaporation

• Condensation

During nucleation, what happens to the free energy of the system when a new surface is formed?

• It decreases

• It remains constant

• It increases

• It becomes zero

What is the relationship between the radius of a particle and the volume during nucleation?

• Volume is proportional to r

• Volume is proportional to r^2

• Volume is proportional to r^3

• Volume is proportional to r^4

What is the effect of a higher degree of undercooling on the likelihood of developing stable nuclei?

• It decreases the likelihood

• It has no effect

• It increases the likelihood

• It makes the process impossible

What is homogeneous nucleation?

• Nucleation that occurs when nuclei form around impurities

• Nucleation that occurs when the degree of undercooling is large enough to form a stable nucleus

• Nucleation that occurs at high temperatures

• Nucleation that occurs without any undercooling

What is a characteristic of heterogeneous nucleation?

• It requires extreme degrees of undercooling

• It occurs exclusively in laboratory settings

• It reduces the surface energy of the solid-liquid interface

• It only occurs at temperatures above 0°C

How does temperature affect the rate of nucleation?

• Higher temperatures always increase nucleation rate

• Lower temperatures always increase nucleation rate

• Undercooling speeds up nucleation, but lower temperatures slow diffusion

• Temperature has no effect on nucleation rate

What is grain refinement?

• A process to increase grain size by adding heat

• A process to create artificial nucleation sites for smaller grain size

• A method to remove impurities from the melt

• A technique to solidify grains at higher temperatures

What is precipitation hardening also known as?

• Grain refinement

• Age hardening

• Glass-ceramics

• Homogeneous nucleation

What is a characteristic of glass-ceramics?

• They are formed by rapid cooling

• They are shaped in a crystalline state before heat treatment

• They are processed in a glassy state before forming crystalline ceramics

• They do not require nucleating agents