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| [[Image:lighterstill.jpg]][[Image:Phase_change.jpg|right|frame]] | | [[Image:lighterstill.jpg]][[Image:Phase_change.jpg|right|frame]] |
− | Generally, phase is considered part or portion in recurring or serial activities or occurrences logically connected within a greater process, often resulting in an output or a change. | + | Generally, '''phase''' is considered part or portion in recurring or serial activities or occurrences [[logic]]ally connected within a greater [[process]], often resulting in an output or a change. |
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| In [[thermodynamics]], a '''phase transition''' is the transformation of a thermodynamic system from one [[phase]] to another. At phase-transition point, physical properties may undergo abrupt change- for instance, volume of the two phases may be vastly different. As an example imagine transition of liquid water into vapour at boiling point. | | In [[thermodynamics]], a '''phase transition''' is the transformation of a thermodynamic system from one [[phase]] to another. At phase-transition point, physical properties may undergo abrupt change- for instance, volume of the two phases may be vastly different. As an example imagine transition of liquid water into vapour at boiling point. |
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| In the [[English]] vernacular, the term is most commonly used to describe transitions between [[solid]], [[liquid]] and [[gas]]eous [[states of matter]], in rare cases including [[Plasma (physics)|plasma]]. Phase transitions happen when the [[Thermodynamic free energy|free energy]] of a system is [[analytic function|non-analytic]] for some choice of thermodynamic variables - see [[phases]]. This non-analyticity generally stems from the interactions of an extremely large number of particles in a system, and does not appear in systems that are too small. | | In the [[English]] vernacular, the term is most commonly used to describe transitions between [[solid]], [[liquid]] and [[gas]]eous [[states of matter]], in rare cases including [[Plasma (physics)|plasma]]. Phase transitions happen when the [[Thermodynamic free energy|free energy]] of a system is [[analytic function|non-analytic]] for some choice of thermodynamic variables - see [[phases]]. This non-analyticity generally stems from the interactions of an extremely large number of particles in a system, and does not appear in systems that are too small. |
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− | To put it simply, at phase-transition point (for instance, [[boiling point]] for water) the two phases of water - [[liquid]] and [[vapour]] have identical free energies and therefore are equally likely to exist. Below the boiling point, liquid-water is more stable state of the two. At [[boiling point]] [[liquid]] and [[vapour]] are equally stable and above boiling point [[vapour]] is more stable than liquid state of [[water]].
| + | At phase-transition point (for instance, [[boiling point]] for water) the two phases of water - [[liquid]] and [[vapour]] have identical free energies and therefore are equally likely to exist. Below the boiling point, liquid-water is more stable state of the two. At [[boiling point]] [[liquid]] and [[vapour]] are equally stable and above boiling point [[vapour]] is more stable than liquid state of [[water]]. |
| == Magnetic phases == | | == Magnetic phases == |
| Often also ''magnetic'' phases are used as the basis of a theory, and for introductory motivation. However, usually these are similar to the well-known liquid (ferromagnetic) or gaseous paramagnetic) phases, as can be seen by the two equivalent interpretations, the ''magnetic'' one ("up" or "down" spins) or the ''lattice-gas'' interpretation ("occupied" or "unoccupied" sites) of a prominent binary model, the [[Ising model]]. | | Often also ''magnetic'' phases are used as the basis of a theory, and for introductory motivation. However, usually these are similar to the well-known liquid (ferromagnetic) or gaseous paramagnetic) phases, as can be seen by the two equivalent interpretations, the ''magnetic'' one ("up" or "down" spins) or the ''lattice-gas'' interpretation ("occupied" or "unoccupied" sites) of a prominent binary model, the [[Ising model]]. |
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| == Properties of phase transitions == | | == Properties of phase transitions == |
| === Critical points === | | === Critical points === |
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| In any system containing liquid and gaseous phases, there exists a special combination of pressure and temperature, known as the [[critical point]], at which the transition between liquid and gas becomes a second-order transition. Near the critical point, the fluid is sufficiently hot and compressed that the distinction between the liquid and gaseous phases is almost non-existent. | | In any system containing liquid and gaseous phases, there exists a special combination of pressure and temperature, known as the [[critical point]], at which the transition between liquid and gas becomes a second-order transition. Near the critical point, the fluid is sufficiently hot and compressed that the distinction between the liquid and gaseous phases is almost non-existent. |
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| This is associated with the phenomenon of [[critical opalescence]], a milky appearance of the liquid, due to density fluctuations at all possible wavelengths (including those of visible light). | | This is associated with the phenomenon of [[critical opalescence]], a milky appearance of the liquid, due to density fluctuations at all possible wavelengths (including those of visible light). |
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| === Symmetry === | | === Symmetry === |
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| Phase transitions often (but not always) take place between phases with different [[symmetry]]. Consider, for example, the transition between a fluid (i.e. liquid or gas) and a [[crystal|crystalline solid]]. A fluid, which is composed of atoms arranged in a disordered but homogeneous manner, possesses continuous translational symmetry: each point inside the fluid has the same properties as any other point. A crystalline solid, on the other hand, is made up of atoms arranged in a regular [[crystal structure|lattice]]. Each point in the solid is ''not'' similar to other points, unless those points are displaced by an amount equal to some lattice spacing. | | Phase transitions often (but not always) take place between phases with different [[symmetry]]. Consider, for example, the transition between a fluid (i.e. liquid or gas) and a [[crystal|crystalline solid]]. A fluid, which is composed of atoms arranged in a disordered but homogeneous manner, possesses continuous translational symmetry: each point inside the fluid has the same properties as any other point. A crystalline solid, on the other hand, is made up of atoms arranged in a regular [[crystal structure|lattice]]. Each point in the solid is ''not'' similar to other points, unless those points are displaced by an amount equal to some lattice spacing. |
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| Symmetries which are only present at low temperatures are called [[accidental symmetry|accidental symmetries]]. For example, a symmetry which is broken by a process which requires a lot of energy, such as the creation of heavy [[virtual particles]], is an accidental symmetry at temperatures sufficiently low that this process is suppressed. | | Symmetries which are only present at low temperatures are called [[accidental symmetry|accidental symmetries]]. For example, a symmetry which is broken by a process which requires a lot of energy, such as the creation of heavy [[virtual particles]], is an accidental symmetry at temperatures sufficiently low that this process is suppressed. |
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| ==References== | | ==References== |
| #Chang, R., Chemistry, 7th Ed, McGraw-Hill (2002) | | #Chang, R., Chemistry, 7th Ed, McGraw-Hill (2002) |
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| #Chaisson, “Cosmic Evolution”, Harvard, 2001 | | #Chaisson, “Cosmic Evolution”, Harvard, 2001 |
| #David Layzer, Cosmogenesis, The Development of Order in the Universe", Oxford Univ. Press, 1991 | | #David Layzer, Cosmogenesis, The Development of Order in the Universe", Oxford Univ. Press, 1991 |
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| ===General references=== | | ===General references=== |
| *Philip Warren Anderson, ''Basic Notions of Condensed Matter Physics'', Perseus Publishing (1997). | | *Philip Warren Anderson, ''Basic Notions of Condensed Matter Physics'', Perseus Publishing (1997). |
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| *[[Hagen Kleinert and Verena Schulte-Frohlinde, ''Gauge Fields in Condensed Matter'', Vol. I, "[[SUPERFLOW]] AND [[VORTEX LINES]]; Disorder Fields, Phase Transitions,", pp. 1--742, [http://www.worldscibooks.com/physics/0356.htm World Scientific (Singapore, 1989)]; Paperback ISBN 9971-5-0210-0 '' (readable online [http://www.physik.fu-berlin.de/~kleinert/kleiner_reb1/contents1.html here]) | | *[[Hagen Kleinert and Verena Schulte-Frohlinde, ''Gauge Fields in Condensed Matter'', Vol. I, "[[SUPERFLOW]] AND [[VORTEX LINES]]; Disorder Fields, Phase Transitions,", pp. 1--742, [http://www.worldscibooks.com/physics/0356.htm World Scientific (Singapore, 1989)]; Paperback ISBN 9971-5-0210-0 '' (readable online [http://www.physik.fu-berlin.de/~kleinert/kleiner_reb1/contents1.html here]) |
| *Schroeder, Manfred R., ''Fractals, chaos, power laws : minutes from an infinite paradise'', New York: W.H. Freeman, 1991. Very well-written book in "semi-popular" style -- not a textbook -- aimed at an audience with some training in mathematics and the physical sciences. Explains what scaling in phase transitions is all about, among other things. | | *Schroeder, Manfred R., ''Fractals, chaos, power laws : minutes from an infinite paradise'', New York: W.H. Freeman, 1991. Very well-written book in "semi-popular" style -- not a textbook -- aimed at an audience with some training in mathematics and the physical sciences. Explains what scaling in phase transitions is all about, among other things. |
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| == External links == | | == External links == |
| * [http://www.ibiblio.org/e-notes/Perc/contents.htm Interactive Phase Transitions on lattices] with Java applets | | * [http://www.ibiblio.org/e-notes/Perc/contents.htm Interactive Phase Transitions on lattices] with Java applets |