Nucleation

Examples of nucleation

• Pure water ice nucleus.
• Presence of cloud condensation nuclei is important in meteorology because they are often in short supply in the upper atmosphere (see cloud seeding).
• All natural and artificial crystals from a homogeneous solution) starts with a nucleation event.
• Bubbles of Diet Coke and Mentos eruptions are a dramatic example.
• Nucleation in wetting properties. Substantial superheating of a liquid can be achieved after the liquid is de-gassed and if the heating surfaces are clean, smooth and made of materials well wetted by the liquid.
• Nucleation is a key concept in ceramic systems.
• In amyloidogenesis.
• In molecular biology, nucleation is used to term the critical stage in the assembly of a molecules bind weakly, but addition of a third stabilizes the complex. This trimer then adds additional molecules and forms a nucleation site. The nucleation site serves the slow, or lag phase of the polymerization process.

Mechanics of nucleation

Homogeneous nucleation

Nucleation generally occurs with much more difficulty in the interior of a uniform substance, by a process called homogeneous nucleation. Liquids cooled below the maximum heterogeneous nucleation temperature (casting.

The creation of a nucleus implies the formation of an interface at the boundaries of the new phase. Some energy is consumed to form this interface, based on the thermodynamic equilibrium is restored.

The spontaneous nucleation rate in, say, water changes very rapidly with temperature, so the spontaneous nucleation temperature can be quite well defined. 'Film boiling' on very hot surfaces and the Leidenfrost effect are both believed to be stabilized by spontaneous nucleation phenomena.

Heterogeneous nucleation

In the case of heterogeneous nucleation, some energy is released by the partial destruction of the previous interface. For example, if a carbon dioxide bubble forms between water and the inside surface of a bottle, the energy inherent in the water-bottle interface is released wherever a layer of gas intervenes, and this energy goes toward the formation of bubble-water and bubble-bottle interfaces. The same effect can cause precipitation strengthening, which relies on homogeneous nucleation to produce a uniform distribution of precipitate particles.

Theory of the spinodal region nucleation

Nucleation processes can also be explained in terms of Cahn-Hilliard Equation.

See also

• Cloud condensation nuclei, the basis for the development of a cloud droplet
• Critical radius
• Seed crystal
• Freezing
• Ice nucleus, the center of an ice crystal
• Manganese nodule
• Supercooling
• Diet Coke and Mentos eruption

References