Book contents
- Frontmatter
- Contents
- Preface
- 1 Energy in planetary processes and the First Law of Thermodynamics
- 2 Energy sources in planetary bodies
- 3 Energy transfer processes in planetary bodies
- 4 The Second Law of Thermodynamics and thermodynamic potentials
- 5 Chemical equilibrium. Using composition as a thermodynamic variable
- 6 Phase equilibrium and phase diagrams
- 7 Critical phase transitions
- 8 Equations of state for solids and the internal structure of terrestrial planets
- 9 Thermodynamics of planetary volatiles
- 10 Melting in planetary bodies
- 11 Dilute solutions
- 12 Non-equilibrium thermodynamics and rates of natural processes
- 13 Topics in atmospheric thermodynamics and radiative energy transfer
- 14 Thermodynamics of life
- Appendix 1 Physical constants and other useful numbers and conversion factors
- Appendix 2 Derivation of thermodynamic identities
- References
- Index
7 - Critical phase transitions
Published online by Cambridge University Press: 07 September 2011
- Frontmatter
- Contents
- Preface
- 1 Energy in planetary processes and the First Law of Thermodynamics
- 2 Energy sources in planetary bodies
- 3 Energy transfer processes in planetary bodies
- 4 The Second Law of Thermodynamics and thermodynamic potentials
- 5 Chemical equilibrium. Using composition as a thermodynamic variable
- 6 Phase equilibrium and phase diagrams
- 7 Critical phase transitions
- 8 Equations of state for solids and the internal structure of terrestrial planets
- 9 Thermodynamics of planetary volatiles
- 10 Melting in planetary bodies
- 11 Dilute solutions
- 12 Non-equilibrium thermodynamics and rates of natural processes
- 13 Topics in atmospheric thermodynamics and radiative energy transfer
- 14 Thermodynamics of life
- Appendix 1 Physical constants and other useful numbers and conversion factors
- Appendix 2 Derivation of thermodynamic identities
- References
- Index
Summary
The phase transitions that we discussed in Section 6.6 are all discontinuous phase transitions. They are step-wise changes in the structure of matter, for instance, the destruction of the crystalline structure during melting or sublimation, or the breakdown of molecular bonds in a liquid during boiling. These are microscopic changes that are accompanied by a macroscopic exchange of heat with the environment, what we call the enthalpy of transition (melting, vaporization, etc.), or also “latent heat”. There is another type of phase transition, which takes place without there being a discontinuity either in the microscopic structure of a substance or in its macroscopic properties, and during which there is no energy exchange with the environment. Such phase transitions are called continuous or critical phase transitions, and play important roles in many planetary processes. For example, they underlie exsolution phenomena such as are observed in feldspars, pyroxenes, oxides and meteoritic metal, hydrogen–helium unmixing in fluid planets and liquid immiscibility phenomena in magmatic systems. They also explain order–disorder transformations in crystalline substances. Critical phase transitions also play an important role in the study of fluids (Chapter 9).
An intuitive approach to critical phase transitions
Consider a binary solution between components A and B with unit site multiplicity.
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- Thermodynamics of the Earth and Planets , pp. 349 - 385Publisher: Cambridge University PressPrint publication year: 2011