Dendrite (crystal)

As Dendrites (from Greek déndron " tree") is known in the metallo- and crystallography tree or bush-like crystal structures.

In geology, it is they, for example, as a crystallisation of iron and manganese oxides on rock surfaces; these are often confused with fossils of plant remains (pseudo fossils).

Formation of dendrites

Dendrites formed during the crystallization of a supersaturated gas phase or melt when the crystal structure has preferred growth directions.

An example is the snowflake (see left picture). After a crystallization nucleus has formed, growing structures along the six directions of the hexagonal lattice structure of ice, ie, along the basal planes at an angle of 60 ° to each other. The growth rate along the direction perpendicular to the basal planes is low. Would they compare in size, one would observe no flat snowflakes, but snow elongated needles.

Small snowflakes are symmetrical structure, unlike, for example, the ice structures on a window pane, see right picture. Because the crystallization environment is almost identical for all the pages of a small crystallization seed in the air. The growth of six appendages is almost identical. Disorders of the macro-environment, for example, change of supersaturation affect all processes from alike. Differences in the micro-environment on a scale of a few millimeters cause of the subtle differences between the 6 dendritic trees. The environment varies from seed to seed, so no snowflake like any other.

In solidifying molten metal dendrites arise at relatively small number of bacteria and a high crystallization rate coupled with a strong Kristallwachstumsanisotropie as they are for example found in shed, solidifying steel. Starting from internal or external germs grow single crystal needles in preferred directions, corresponding to the heat transfer in the melt. After short growth times more columnar crystals occur at right angles to the existing Transkristalliten in all directions. This leads to a fir -like crystallites, which represents the dendrites in the micrograph.

Dendritic growth in electrochemical elements

Electrochemical processes can grow on the electrodes of batteries dendrites. If they penetrate the separator between the electrodes, this leads to a short circuit in the cell. This has a complete failure or weaker in severe cases, an accelerated self-discharge of the cell. This process has nothing to do with the memory effect.

Metal Trees

Not only for electrolysis may occur dendrite metallic tree structures can also grow as the metal is deposited by a reducing agent, such as a less noble metal. This can result in the dendritic trees metal, for example silver tree made ​​of silver salt solutions.