Crystal Growth - Nucleation

Nucleation

Nucleation can be either homogeneous, without the influence of foreign particles, or heterogeneous, with the influence of foreign particles. Generally, heterogeneous nucleation takes place more quickly since the foreign particles act as a scaffold for the crystal to grow on, thus eliminating the necessity of creating a new surface and the incipient surface energy requirements.

Heterogeneous nucleation can take place by several methods. Some of the most typical are small inclusions, or cuts, in the container the crystal is being grown on. This includes scratches on the sides and bottom of glassware. A common practice in crystal growing is to add a foreign substance, such as a string or a rock, to the solution, thereby providing nucleation sites for facilitating crystal growth and reducing the time to fully crystallize.

The number of nucleating sites can also be controlled in this manner. If a brand-new piece of glassware or a plastic container is used, crystals may not form because the container surface is too smooth to allow heterogeneous nucleation. On the other hand, a badly scratched container will result in many lines of small crystals. To achieve a moderate number of medium sized crystals, a container which has a few scratches works best. Likewise, adding small previously made crystals, or seed crystals, to a crystal growing project will provide nucleating sites to the solution. The addition of only one seed crystal should result in a larger single crystal.

Some important features during growth are the arrangement, the origin of growth, the interface form (important for the driving force), and the final size. When origin of growth is only in one direction for all the crystals, it can result in the material becoming very anisotropic (different properties in different directions). The interface form determines the additional free energy for each volume of crystal growth.

Lattice arrangement in metals often takes the structure of body centered cubic, face centered cubic, or hexagonal close packed. The final size of the crystal is important for mechanical properties of materials. (For example, in metals it is widely acknowledged that large crystals can stretch further due to the longer deformation path and thus lower internal stresses.).

Read more about this topic:  Crystal Growth

Other articles related to "nucleation":

Champagne (wine) - Production - Bubbles
... These bubbles form on imperfections in the glass that facilitate nucleation or, to a lesser extent, on cellulose fibres left over from the wiping/drying process as shown with a ... are typically too small to consistently act as nucleation points as the surface tension of the liquid smoothes out these minute irregularities ... The nucleation sites that act as a source for the ongoing effervescence are not natural imperfections in the glass, but actually occur where the glass has been ...
Colloidal Crystal - Bulk Crystals - Kossel Lines
... crystal, the occurrence of Kossel lines in diffraction patterns were used to monitor the initial nucleation and subsequent motion caused distortion of the crystal ... produce a 'flowing crystal', where the nucleation site density increases significantly with increasing particle concentration ... be considered analogous to a homogeneous nucleation event—whereas the latter would clearly be considered a heterogeneous nucleation event, being catalyzed by the surface of the glass tube ...
Nucleation - Experimental
... It is sometimes difficult to experimentally measure nucleation rate ... For validity of this method, the nucleation rate, I, has to be greater at the nucleation temperature Tn than at the growth temperature Tg I(Tn)>> I(Tg), and the growth rate U must be greater ... Koster proposed a method for nucleation of metallic glasses ...
Crystaliser - Crystallization Dynamics - Nucleation - Secondary Nucleation
... Secondary nucleation is the formation of nuclei attributable to the influence of the existing microscopic crystals in the magma ... Fluid shear nucleation occurs when liquid travels across a Crystal at a high speed, sweeping away nuclei that would otherwise be incorporated into a Crystal, causing the swept-away nuclei to become new ... Contact nucleation has been found to be the most effective and common method for nucleation ...