Tin pest, 4.24

Zinn-ozydverbia uig, /. stannic compound, tin(IV) compound, -pest, /. tin plague, tin pest, -pfanne,/. (Tinning) tin pot. -platte, /. tin plate, sheet of tin (plate). 

Another element that exhibits allotropy because of variations in the crystal structure is tin. The common allotrope is tin metal, also known as a alpha) tin, which is stable at ambient temperatures. The other allotrope, which generally occurs as a gray powder and is known as p beta) tin, but also as tin pest, is formed only at very low temperatures when tin cools down to temperatures below -18°C, the ordinary allotrope, a tin, is converted to p tin, and the transformation is irreversible under ordinary temperatures. Tin objects exposed to temperatures below -18°C in very cold regions of the world, for example, are generally severely damaged when part of the tin converts to tin pest. In extreme cases, when exposure to low temperatures extends for long periods of time, the allotropic conversion may result in the transformation of tin objects into heaps of gray p-tin powder. 

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... 

Figure 5.3 shows the phase diagram of tin, and clearly shows the transition from tin(white) to tin(grey). Unfortunately, the tin allotropes have very different densities p, so p(tm, grey) = 5.8 gem-3 but p(tm, white) = 7.3 g cm-3. The difference in p during the transition from white to grey tin causes such an unbearable mechanical stress that the metal often cracks and turns to dust - a phenomenon sometimes called tin disease or tin pest . 

Tin is a soft, silvery metal with a slight bluish color. Metallic tin has three forms that exist at different temperatures. At temperatures above 13.2 °C, the stable form has metallic properties, and it is known as white tin. When tin is heated above 161 °C, the white form is converted to a form known as brittle tin. This form does not behave as a metal, and it fractures when struck with a hammer. The form of tin that is stable below 13.2 °C is known as gray tin because it is easily crumbled to yield a gray powder. Even at temperatures below 13.2 °C, this transformation from the white form to the gray form is very slow unless the temperature is approximately -50 °C. The crumbling of gray tin (the low temperature form) is known historically as tin disease or tin pest. ... 

Tin has two allotropes the stable modification above 13.2°C is white, tetragonal, jS-Sn. Below 13.2 °C, the thermodynamically stable form is gray a-Sn, which has a cubic diamond structure however, the transformation is very slow and requires long exposure much below this temperature for extensive transformation. The transformation of /3-Sn to Qf-Sn is also termed tin pest or tin disease and involves a stmctural distortion along the c-axis, with a density increase of 26%, i.e. the high temperature form is the more dense form. 

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 ... 

Metallic tin exists in two allotropes. White tin, or (3-tin, is a silvery-white, electrically conducting, metal, with a distorted cubic structure. Below about 10 °C, it slowly coverts into grey tin, or a-tin, with a 26% increase in volume, which creates excrescences on the surface, called tin pest or plague. a-Tin is a semiconductor with a diamond structure, with A//f = 2.51 kJ moP compared with metalhc tin. ... 

Note Tin will undergo a phase transformation, becoming a powdery form (called Tin Pest) if Tin plated parts are stored for more than 1 week at temperatures below 13°C). 

Tin is a silvery white metal, with great malleability, permitting it to be hammered into thin sheets, called tin foil. Ordinary white tin, which has metallic properties, slowly changes at temperatures below 18 C to a non-metallic allotropic modification, gray tin, which has the diamond structure. (The physical properties given in Table 18-3 pertain to white tin.) At very low temperatures, around —40°C, the speed of this conversion is sufficiently great that metallic tin objects sometimes fall into a powder of gray tin. This phenomenon has been called the tin pest. ... 

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