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4 - Nucleation

from Part I - Basic thermodynamics and kinetics of phase transformations

Published online by Cambridge University Press:  05 September 2014

Brent Fultz
Affiliation:
California Institute of Technology
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Summary

As discussed in Sect. 1.5.2, phase transformations can occur continuously or discontinuously. The discontinuous case begins with the appearance of a small but distinct volume of material having a structure and composition that differ from those of the parent phase. A discontinuous transition can be forced by symmetry, as formalized for some cases in Sect. 14.4. There is no continuous way to rearrange the atoms of a liquid into a crystal, for example. The new crystal must appear in miniature in the liquid, a process called “nucleation.” If the nucleation event is successful, this crystal will grow. The process of nucleation is an early step for most phase transformations in materials. It has many variations, but two key concepts can be appreciated immediately.

  • Because the new phase and the parent phase have different structures, there must be an interface between them. The atom bonding across this interface is not optimal, so the interfacial energy must be positive. This surface energy is most significant when the new phase is small, because a larger fraction of its atoms are at the interface. Surface energy plays a key role in nucleation.

  • For nucleation of a new phase within a solid, a second issue arises when the new phase differs in shape or specific volume from the parent phase. The mismatch creates an elastic field that costs energy. This is not a concern for nucleation in a liquid or gas, since the surrounding atoms can flow out of the way.

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Publisher: Cambridge University Press
Print publication year: 2014

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  • Nucleation
  • Brent Fultz, California Institute of Technology
  • Book: Phase Transitions in Materials
  • Online publication: 05 September 2014
  • Chapter DOI: https://doi.org/10.1017/CBO9781107589865.006
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  • Nucleation
  • Brent Fultz, California Institute of Technology
  • Book: Phase Transitions in Materials
  • Online publication: 05 September 2014
  • Chapter DOI: https://doi.org/10.1017/CBO9781107589865.006
Available formats
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To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.

  • Nucleation
  • Brent Fultz, California Institute of Technology
  • Book: Phase Transitions in Materials
  • Online publication: 05 September 2014
  • Chapter DOI: https://doi.org/10.1017/CBO9781107589865.006
Available formats
×