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Dry ice is the genericized trademark for solid carbon dioxide. It is commonly used as a versatile cooling agent. Dry ice sublimes, changing directly to a gas at atmospheric pressure. Its sublimation and deposition point is -78.5 °C (-109.3 °F). Its enthalpy of sublimation (ΔHsub) @ -78.5 °C (-109.3 °F) is 199.0 kJ/kg (245.5 BTU/lb). The low temperature and direct sublimation to a gas makes dry ice a very effective coolant, since it is colder than ice and leaves no moisture as it changes state.
Additional recommended knowledge
In 1835 the French chemist Charles Thilorier published the first account of dry ice. Upon opening the lid of a large cylinder containing liquid carbon dioxide he noted much of the carbon dioxide rapidly evaporated leaving solid dry ice in the container. Throughout the next 60 years, dry ice was observed and tested by scientists.
Dry ice is readily manufactured: 
Dry ice is typically produced in two standard forms, blocks and cylindrical pellets. A standard block is most common and is approximately 30 kg. These are commonly used in shipping, because they sublime slowly due to a relatively small surface area. Pellets are around 1 cm in diameter and can be bagged easily. This form is suited to small scale use, for example at grocery stores and laboratories. Dry ice is also inexpensive; it costs about US$2 per kilogram.
Dry ice is commonly used to package items that need to remain cold or frozen, such as ice cream, without the use of mechanical cooling. In medicine it is used to freeze warts to make removal easier. In the construction industry it is used to loosen floor tiles by shrinking and cracking them, as well as to freeze water in valveless pipes to allow repair. In laboratories, a slurry of dry ice in an organic solvent is a useful freezing mixture for cold chemical reactions.
Dry ice can also be used for making ice cream.
Dry ice is also used as a source of carbon dioxide. It can be used to carbonate water and other liquids such as beer. It can be used as bait to trap mosquitoes and other insects
When dry ice is placed in water sublimation is accelerated, and low-sinking dense clouds of fog are created. This is used in fog machines at theaters and nightclubs for dramatic effects.
Use in blast cleaning
One of the largest alternative uses of dry ice is blast cleaning. Dry ice pellets are shot out of a nozzle with compressed air. This can remove residues from industrial equipment. Examples of materials being removed include ink, glue, oil, paint, mold and rubber. Dry ice blasting can replace sandblasting, steam blasting, water blasting or solvent blasting. The primary environmental effect of dry ice blasting is the sublimed CO2. As the source of dry ice is typically pre-existing CO2, the net CO2 release derives only from the energy expended to compress the gas to liquid.
Dry ice blasting involves three factors:
The kinetic energy of the dry ice pellets is transferred when it hits the surface, directly dislodging residues as in other blasting methods. The thermal shock effect occurs when the cold dry ice hits a much warmer surface and rapid sublimation occurs. The thermal kinetic effect is the result of the rapid sublimation of the dry ice hitting the surface. These factors combined cause small "micro-explosions" of gaseous carbon dioxide where each pellet impacts, dislodging the residue.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Dry_ice". A list of authors is available in Wikipedia.|