Powdery gray tin

Cu), solder (33% Sn and 67% Pb), and pewter (85% Sn, 7% Cu, 6% Bi, and 2% Sb). Tin exists as three allotropes white tin, stable at normal temperatures gray tin, stable at temperatures below 13.2°C and brittle tin, found at temperatures above 161°C. When tin is exposed to low temperatures, it gradually changes to powdery gray tin and crumbles away this is known as tin disease. 

It is also possible for a pure material to have several different solid phases. Hn, a material that was once used for organ pipes, can change from a uniformly solid white tin to a powdery gray tin at low temperatures. This phase transition has been termed tin disease, or tin pest Ice can solidify into several distinct forms, including ice IX. Reportedly, Kurt Vonnegut, a chemist by training, was unaware of the actual existence of ice IX when he used the name in the plot for his novel Cat s Cradle ... 

Arsenic, selenium, tin, antimony, and tellurium all exist in metallic and nonmetallic forms. For example, Sn occurs as white tin which has a metallic luster and is a good conductor of heat and electricity, and gray tin in which the atoms are covalently bonded in a diamond-type lattice. Below 18 C, the crystalline white tin slowly changes to the powdery gray tin. This transformation was first observed as blistery outbreaks (called tin pest ) on the surface of tin objects such as organ... 

FIGURE 7.14 Cray tin and white tin are two solid forms of tin. The denser white metallic form is the more stable phase above 13°C, and the powdery gray form is more stable below that temperature. 

The Aiiotropes of Tin Tin Pest. Metallic tin may occur in three allotropic forms (see Textbox 19) the common form of tin, also known as white tin or beta tin, is stable at ambient temperatures its stability extends between -18°C and 170°C below -18°C tin is converted to a gray powdery allotrope, known as alpha tin or tin pest. A third allotrope, known as rhombic tin, is the form of tin stable at temperatures above 170°C. If ordinary white tin remains for extended periods of time at temperatures below -18°C, therefore, it is slowly converted to the gray, brittle, and powdery allotrope tin pest the conversion is accelerated at still lower temperatures. Tin objects kept in regions of the world where extremely low temperatures (below -18°C) prevail, initially... 

Pure tin exhibits two common forms in the solid state — a gray tin and a white tin. At temperatures above 13°C or 55°F, the more stable form of tin is the denser white tin. At lower temperatures, the white tin is slowly converted to the gray form, a more powdery substance. Prolonged exposure to the cold winter temperatures of northern Europe contributed to the loss of integrity and disintegration of many cathedral organ pipes. As a consequence of the progressive nature of the structural transformation, as the white tin metallic surface becomes covered with... 

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