Book contents
- Frontmatter
- Dedication
- Contents
- Preface
- Acknowledgments
- Notation
- Part I Basic thermodynamics and kinetics of phase transformations
- Part II The atomic origins of thermodynamics and kinetics
- Part III Types of phase transformations
- 10 Melting
- 11 Transformations involving precipitates and interfaces
- 12 Spinodal decomposition
- 13 Phase field theory
- 14 Method of concentration waves and chemical ordering
- 15 Diffusionless transformations
- 16 Thermodynamics of nanomaterials
- 17 Magnetic and electronic phase transitions
- 18 Phase transitions in quantum materials
- Part IV Advanced topics
- Further reading
- References
- Index
12 - Spinodal decomposition
from Part III - Types of phase transformations
Published online by Cambridge University Press: 05 September 2014
- Frontmatter
- Dedication
- Contents
- Preface
- Acknowledgments
- Notation
- Part I Basic thermodynamics and kinetics of phase transformations
- Part II The atomic origins of thermodynamics and kinetics
- Part III Types of phase transformations
- 10 Melting
- 11 Transformations involving precipitates and interfaces
- 12 Spinodal decomposition
- 13 Phase field theory
- 14 Method of concentration waves and chemical ordering
- 15 Diffusionless transformations
- 16 Thermodynamics of nanomaterials
- 17 Magnetic and electronic phase transitions
- 18 Phase transitions in quantum materials
- Part IV Advanced topics
- Further reading
- References
- Index
Summary
Figures 1.5c,d and 1.6a,b illustrate the difference between chemical unmixing that occurs by nucleation and growth (the topic of the previous Chapter 11) and spinodal decomposition (the topic of Chapter 12). Nucleation creates a distinct surface between the new phase and the parent phase, and the two phases differ significantly in their chemical composition or structure. In addition to the surface energy, an elastic energy is often important, too.
Spinodal decomposition does not involve a surface in the usual sense because it begins with infinitesimally small changes in composition. Nevertheless, there is an energy cost for gradients in composition, specifically the square of the gradient, since a region with a large composition gradient begins to look like an interface. The “square gradient energy” is an important new concept presented in this chapter, but it is also essential to phase field theory and to the Ginzburg–Landau theory of superconductivity.
At the end of Sect. 2.7 on unmixing phase diagrams, it was pointed out that there are conceptual problems with a free energy that is concave downwards because the alloy is unstable, but the free energy pertains to equilibrium states. An unstable free energy function may prove useful for short times, however. Taking a kinetic approach, we use the thermodynamic tendencies near equilibrium to obtain a chemical potential to drive a diffusion flux that causes unmixing.
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- Information
- Phase Transitions in Materials , pp. 298 - 314Publisher: Cambridge University PressPrint publication year: 2014