Tin pest

Tin pest is an allotropic transformation of tin, destroyed the objects of tin.

It is to be distinguished from Zinnfraß or from lead corrosion, an aggressive substances produced by inclusions in the surface chemical corrosion process. Tin pest is also not related to the zinc pest, a corrosion process of zinc.

White silver, metallic tin ( β - tin), the 16 ° C to 181 ° C is stable, changing less than 13.2 ° C in the gray-black α -tin has to offer. α - tin and β -tin have different crystal structures and densities ( see properties of the tin ).

This transformation starts from individual centers and spreads slowly. It manifests itself in pewter by large and small spots, followed by wart-like bubbles to the surface, which fall apart when touched lightly. Since α -tin occupies a larger volume than β - tin, the material loses its integrity: the grain structure dissolves and there is tin powder.

The tendency for the conversion increases with decreasing temperature, the reaction rate becomes lower. The ideal transformation temperature is about -48 ° C. The conversion may be accelerated by alloying with other metals (e.g., zinc, aluminum) or prevent (e.g., antimony, bismuth ). The contact with an alcoholic solution of Pink Salt ( Ammoniumhexachlorostannat, (NH4 ) 2 [ SnCl6 ] ) accelerates the conversion also.

Examples

• Many organ pipes in the field of view (brochure ) are made of optical reasons of pure tin and particularly susceptible to tin pest. This process can also be observed in organ pipes of a tin -lead alloy.
• In the Russian campaign in 1812 by Napoleon supposedly disintegrated tin buttons of the uniforms of his soldiers because of the cold.
• Also tin figures are - depending on their quality - threatened the inexorable decay within a few months following infection by the tin pest.