Seed crystal

Seed crystals are small crystals, they are used as the starting crystal for the growth of larger crystals.

Production

Seed crystals are produced under laboratory conditions, with the same crystal orientation (for example ) that should also have the finish grown crystal.

Example

Consider, for example, the following reaction equation:

The rate constant for the forward reaction is a function of temperature according to Arrhenius:

Wherein A is a material-specific constant, is the molar energy of activation, the universal gas constant and temperature.

With the given constant it can be seen that at high temperatures, the rate constant increases. So the forward reaction has become faster, it will go more ions in solution, but it still remains a solid back. This is then filtered off, and obtained as a filtrate the saturated solution. Upon cooling the rate constant decreases again, the forward reaction is no longer enhanced and the reverse reaction occurs: there is alum as a solid. That this adsorbed on the seed crystal and the crystal growth begins, both a so-called cooperative effect as a result of the reduction of the surface energy at the Impfkristalloberfläche caused by decreased Galvani potential.

Use

With the aid of seed crystals can bring supersaturated solutions or melts to crystallize. The seed crystals serve as nuclei to which substance separates from solution or melt. This process is called seeding (English seeding ). In the crystallization of proteins, a distinction depending on the size of the seed crystals between Micro and Macro seeding seeding. The practical procedure will be described in the Czochralski method.

For the growth of single crystals, it is necessary that the seed crystal is chemically identical to the pure substance to be recovered. In inoculants however, it is sufficient if chemically closely related crystals are used for seeding. On basis of the crystal structure of the crystal orientation of the shape and orientation of the seed crystals is crucial for the appearance of the grown larger crystals.

Most of the seed crystals are used in the semiconductor industry, to grow the single crystal wafer, which are used for example as a carrier for photovoltaic products, integrated circuits or transistors.

• Solid State Chemistry