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Types of phase transition

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The transitions between the solid, liquid, and gaseous phases of a single component, due to the effects of temperature and/or pressure:

A small piece of rapidly melting solid argon simultaneously shows the transitions from solid to liquid and liquid to gas.



Comparison of phase diagrams of carbon dioxide (red) and water (blue) explaining their different phase transitions at 1 atmosphere
A eutectic transformation, in which a two component single phase liquid is cooled and transforms into two solid phases. The same process, but beginning with a solid instead of a liquid is called a eutectoid transformation.

A peritectic transformation, in which a two component single phase solid is heated and transforms into a solid phase and a liquid phase.

A spinodal decomposition, in which a single phase is cooled and separates into two different compositions of that same phase.

Transition to a mesophase between solid and liquid, such as one of the "liquid crystal" phases.

The transition between the ferromagnetic and paramagnetic phases of magnetic materials at the Curie point.

The transition between differently ordered, commensurate or incommensurate, magnetic structures, such as in cerium antimonide.

The martensitic transformation which occurs as one of the many phase transformations in carbon steel and stands as a model for displacive phase transformations.

Changes in the crystallographic structure such as between ferrite and austenite of iron.

Order-disorder transitions such as in alpha-titanium aluminides.

The dependence of the adsorption geometry on coverage and temperature, such as for hydrogen on iron (110).

The emergence of superconductivity in certain metals and ceramics when cooled below a critical temperature.

The transition between different molecular structures (polymorphs, allotropes or polyamorphs), especially of solids, such as between an amorphous structure and a crystal structure, between two different crystal structures, or between two amorphous structures.

Quantum condensation of bosonic fluids (Bose–Einstein condensation). The superfluid transition in liquid helium is an example of this.

The breaking of symmetries in the laws of physics during the early history of the universe as its temperature cooled.
Isotope fractionation occurs during a phase transition, the ratio of light to heavy isotopes in the involved molecules changes. When water vapor condenses (an equilibrium fractionation), the heavier water isotopes (18O and 2H) become enriched in the liquid phase while the lighter isotopes (16O and 1H) tend toward the vapor phase.

Phase transitions occur when the thermodynamic free energy of a system is non-analytic for some choice of thermodynamic variables (cf. phases). This condition generally stems from the interactions of a large number of particles in a system, and does not appear in systems that are too small. It is important to note that phase transitions can occur and are defined for non-thermodynamic systems, where temperature is not a parameter. Examples include: quantum phase transitions, dynamic phase transitions, and topological (structural) phase transitions. In these types of systems other parameters take the place of temperature. For instance, connection probability replaces temperature for percolating networks.

At the phase transition point (for instance, boiling point) the two phases of a substance, liquid and vapor, have identical free energies and therefore are equally likely to exist.

Eutectic system. A phase diagram for a fictitious binary chemical mixture (with the two components denoted by A and B) used to depict the eutectic composition, temperature, and point.

Eutectic system

(L denotes the liquid state.) A eutectic system (US dict: yü-'tek-tik)[1] from the Greek "ευ" (eu = easy) and "Τήξις" (teksis = melting) describes a homogeneous solid mix of atomic and/or chemical species, to form a joint super-lattice, by striking a unique atomic percentage ratio between the components — as each pure component has its own distinct bulk lattice arrangement.

It is only in this atomic/molecular ratio that the eutectic system melts as a whole, at a specific temperature (the eutectic temperature) the super-lattice releasing at once all its components into a liquid mixture. Spinodal decomposition. Spinodal decomposition can be contrasted with nucleation and growth.

Spinodal decomposition

There the initial formation of the microscopic clusters involves a large free energy barrier, and so can be very slow, and may occur as little as once in the initial phase, not throughout the phase, as happens in spinodal decomposition. Spinodal decomposition is of interest for two primary reasons. Mesophase. Ferromagnetism. Not to be confused with Ferrimagnetism; for an overview see Magnetism.

Ferromagnetism

A magnet made of alnico, an iron alloy, with its keeper. Ferromagnetism is the theory which explains how materials become magnets. Ferromagnetism is the basic mechanism by which certain materials (such as iron) form permanent magnets, or are attracted to magnets. In physics, several different types of magnetism are distinguished. Ferromagnetism (including ferrimagnetism)[1] is the strongest type: it is the only one that typically creates forces strong enough to be felt, and is responsible for the common phenomena of magnetism in magnets encountered in everyday life.

Permanent magnets (materials that can be magnetized by an external magnetic field and remain magnetized after the external field is removed) are either ferromagnetic or ferrimagnetic, as are other materials that are noticeably attracted to them. History and distinction from ferrimagnetism[edit] Ferromagnetic materials[edit] Actinide ferromagnets[edit] Paramagnetism. Simple illustration of a paramagnetic probe made up from miniature magnets.

Paramagnetism

A trickle of liquid oxygen is deflected by a magnetic field, illustrating its paramagnetism. Paramagnetism is a form of magnetism whereby certain materials are attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, diamagnetic materials are repelled by magnetic fields and form induced magnetic fields in the direction opposite to that of the applied magnetic field.[1] Paramagnetic materials include most chemical elements and some compounds;[2] they have a relative magnetic permeability greater than or equal to 1 (i.e., a positive magnetic susceptibility) and hence are attracted to magnetic fields. The magnetic moment induced by the applied field is linear in the field strength and rather weak.

Diffusionless transformation. Diffusionless transformations classifications A diffusionless transformation is a phase change that occurs without the long-range diffusion of atoms but rather by some form of cooperative, homogeneous movement of many atoms that results in a change in crystal structure.

Diffusionless transformation

These movements are small, usually less than the interatomic distances, and the atoms maintain their relative relationships. The ordered movement of large numbers of atoms lead some to refer to these as military transformations in contrast to civilian diffusion-based phase changes.[1] The most commonly encountered transformation of this type is the martensitic transformation which, while being the most studied, is only one subset of non-diffusional transformations.

The martensitic transformation in steel represents the most economically significant example of this category of phase transformations but an increasing number of alternatives, such as shape memory alloys, are becoming more important as well. References[edit] Superfluidity. Superfluidity is a state of matter in which the matter behaves like a fluid with zero viscosity; where it appears to exhibit the ability to self-propel and travel in a way that defies the forces of gravity and surface tension.

Superfluidity

Superfluidity is found in astrophysics, high-energy physics, and theories of quantum gravity. The phenomenon is related to Bose–Einstein condensation, but neither is a specific type of the other: not all Bose-Einstein condensates can be regarded as superfluids, and not all superfluids are Bose–Einstein condensates. Fig. 1. Helium II will "creep" along surfaces in order to find its own level—after a short while, the levels in the two containers will equalize. Bose–Einstein condensate. Schematic Bose-Einstein Condensation versus temperature and the energy diagram A Bose–Einstein condensate (BEC) is a state of matter of a dilute gas of bosons cooled to temperatures very close to absolute zero (that is, very near 5000000000000000000♠0 K or 5000000000000000000♠−273.15 °C).

Bose–Einstein condensate

Under such conditions, a large fraction of bosons occupy the lowest quantum state, at which point macroscopic quantum phenomena become apparent. This state was first predicted, generally, in 1924–25 by Satyendra Nath Bose and Albert Einstein. Symmetry breaking. Symmetry breaking can be distinguished into two types, explicit symmetry breaking and spontaneous symmetry breaking, characterized by whether the equations of motion fail to be invariant or the ground state fails to be invariant.

Symmetry breaking

Explicit symmetry breaking[edit] In explicit symmetry breaking, the equations of motion describing a system are variant under the broken symmetry. Isotope fractionation. Magnetic sector mass spectrometer used in isotope ratio analysis, through thermal ionization.

Isotope fractionation

Isotope fractionation describes processes that affect the relative abundance of isotopes, often used in isotope geochemistry. Normally, the focus is on stable isotopes of the same element. Isotopic fractionation in the natural environment can be measured by isotope analysis, using isotope-ratio mass spectrometry, to separate different element isotopes on the basis of their mass-to-charge ratio, an important tool to understand natural systems. For example, in biochemistry processes cause a fluctuation in the amount of carbon isotope ratios incorporated into a biological being. Equilibrium fractionation. Definition[edit] Most equilibrium fractionations are thought to result from the reduction in vibrational energy (especially zero-point energy) when a more massive isotope is substituted for a less massive one.

Equilibrium fractionation

This leads to higher concentrations of the massive isotopes in substances where the vibrational energy is most sensitive to isotope substitution, i.e., those with the highest bond force constants.