Title: Summary Part Nucleation and Growth

Choose the correct statement.

- Nucleation is the formation of a critical mass of a different phase that allows that new phase to be energetically stable.  It can be caused by random fluctations or aided by nucleation sites like surface defects or introduction of a seed crystal. (correct)
- Nucleation is the formation of a critical mass of a different phase that allows that new phase to be energetically stable.  It is always formed heterogeneously by defects in an exististing surface or interface.

- The critical mass of atoms required for nucleation is dependent on the balance between the increase in energy required to add a new surface and the decreas in energy associated with forming the new phase. (correct)
- The critical mass of atoms required for nucleation is dependent only on the total energy of the system and the energy required to form a new surface.

- After nucleation, growth of the phase is favored and will continue until it is thermodynaimcally in equilibrium with other phase(s) or kinetically trapped (not enough energy for the reaction to continue). (correct)
- After nucleation, growth of the phase is favored and will continue to grow until it is the only phase present as this is the only way to minimize the energy of the system.
- After nucleation, growth of the phase requires continual input of energy must to the system.
- After nucleation, growth of the phase is unfavored until the net energy of the system is below the initial energy before nucleation.

- During growth, atoms diffuse to the surface of the phase in order to increase the volume of the phase.  In solid-state diffusion, this typically is seen as movement of grain boundaries. (correct)
- During growth, atoms diffuse away from the new phase in order form the growth front of new material.
- During growth, atoms do not necessarily need to diffuse as long as the energy of the system is minimized.
- During growth, atoms can only diffuse along liquid solid interfaces to increase the volume of the newly formed phase.

- Some methods for controlling solid-state grain growth include: enhancing grain growth by increased temperature which allows for more diffusion; and, hindering grain growth through additives which pin the grain boundaries and reduce their mobility. (correct)
- Sintering, anneling, and quenching all increase grain growth as it brings a material to high temperatures.  Slowing grain growth can only be done through control of temperatures
- Grains will always become smaller at higher temperatures as more grain boundaries will form do to increased nucleation events.

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