Tins

Tin is a chemical element in the periodic table that has the symbol Sn (Latin: stannum) and atomic number 50. more...

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This silvery, malleable poor metal that is not easily oxidized in air and resists corrosion is found in many alloys and is used to coat other metals to prevent corrosion. Tin is obtained chiefly from the mineral cassiterite, where it occurs as an oxide. It can be alloyed with copper to make bronze.

Notable characteristics

Tin is a malleable, ductile, highly crystalline, silvery-white metal; when a bar of tin is bent, a strange crackling sound known as the "tin cry" can be heard due to the breaking of the crystals. This metal resists corrosion from distilled, sea and soft tap water, but can be attacked by strong acids, alkalis, and by acid salts. Tin acts as a catalyst when oxygen is in solution and helps accelerate chemical attack. Tin forms the dioxide SnO₂ when it is heated in the presence of air. SnO₂, in turn, is feebly acidic and forms stannate (SnO₃^-2) salts with basic oxides. Tin can be highly polished and is used as a protective coat for other metals in order to prevent corrosion or other chemical action. This metal combines directly with chlorine and oxygen and displaces hydrogen from dilute acids. Tin is malleable at ordinary temperatures but is brittle when it is heated.

Allotropes

Tin's chemical properties fall between those of metals and non-metals, just as the semiconductors silicon and germanium do. Tin has two allotropes at normal pressure and temperature: gray tin and white tin.

Below 13.2 °C, it exists as gray or alpha tin, which has a cubic crystal structure similar to silicon and germanium. Gray tin has no metallic properties at all, is a dull-gray powdery material, and has few uses, other than a few specialized semiconductor applications.

When warmed above 13.2 °C tin changes into white or beta tin, which is metallic and has a tetragonal structure. Converting gray tin powder into white tin produces white tin powder. To convert powdery gray tin into solid white tin the temperature must be raised above the melting point of tin.

Gray tin can cause undesirable effects in applications where the metallic properties of tin are important, since metallic white tin will slowly convert to gray tin if it is held for a long time below 13.2 °Celsius. The metallic surface of white tin becomes covered with a gray powder which is easily rubbed off. The gray patches slowly expand until all of the tin in the object is converted from the metal to the powder, at which point it loses its structural integrity and may fall to pieces. This process is known as tin disease or tin pest. Tin pest was a particular problem in northern Europe in the 18th century as organ pipes made of tin would sometimes completely disintegrate during long cold winters. Some sources also say that during Napoleon's Russian campaign of 1812, the temperatures became so cold that the tin buttons on the soldiers' uniforms disintegrated, contributing to the defeat of the Grande Armée. However, the veracity of this story is debatable, because Napoleon would likely have foreseen this problem, and the transformation to gray tin often takes a reasonably long time. This transformation, however, may be prevented by the addition of antimony or bismuth.

Read more at Wikipedia.org