Dry ice, sometimes referred to as "Cardice" or as "card ice" is the solid form of carbon dioxide. It is commonly used as a
versatile cooling agent.
Dry ice is the solid form of carbon dioxide (chemical formula: CO2), comprising two oxygen atoms bonded to a single
carbon atom. It is colourless, odourless, non-flammable, and slightly acidic.
CO2 changes from a solid to a gas at −78.5 °C (−109.3 °F) with no intervening liquid form, through a process called
sublimation. The opposite process is called deposition, where dry ice changes from the gas to solid phase.
The density of dry ice varies, but usually ranges between about 1.4 and 1.6 g/cm3 (87–100 lb/ft3). The low temperature
and direct sublimation to a gas makes dry ice an effective coolant, since it is colder than water or ice and leaves no
moisture as it changes state. Its enthalpy of sublimation (Δ rH) is 393.5kJ/mol.
Dry ice is non-polar, with a dipole moment of zero, so attractive intermolecular van der Waals forces operate. The
composition results in low thermal and electrical conduction.
It is generally accepted that dry ice was first observed in 1834 by French chemist Charles Thilorier, who published the
first account of the substance. In his experiments, he noted that when opening the lid of a large cylinder containing liquid
carbon dioxide, most of the liquid CO2 quickly evaporated. This left only solid dry ice in the container. In 1924, Thomas B.
Slate applied for a U.S. patent to sell dry ice commercially. Subsequently, he became the first to make dry ice
successfully as an industry. In 1925, this solid form of CO2 was trademarked by the DryIce Corporation of America as
"Dry ice", thus leading to its common name. That same year the DryIce Co. sold the substance commercially for the first
time; marketing it for refrigerating purposes.
The alternative name "Cardice" is a registered trademark of Air Liquide UK Ltd. It is sometimes written as "card ice".
Dry ice is easily manufactured. Generally there are common steps taken in producing dry ice. Firstly, gases containing a
high concentration of carbon dioxide are produced. Such gases can be a byproduct of some other process, such as
producing ammonia from nitrogen and natural gas, or large-scale fermentation. Secondly, carbon dioxide-rich gas is
pressurized and refrigerated until it changes into its liquid form. Furthermore, the pressure is reduced. When this occurs
some liquid carbon dioxide vaporizes, and this causes a rapid lowering of temperature of the remaining liquid carbon
dioxide. As a result the extreme cold causes the liquid to solidify into a snow-like consistency. Finally, the snow-like solid
carbon dioxide is compressed into either small pellets or larger blocks of dry ice.
Dry ice is typically produced in two standard forms: blocks and cylindrical pellets. A standard block weighing
approximately 30 kg is most common. These are commonly used in shipping, because they sublimate slowly due to a
relatively small surface area. Pellets are around 1 cm (0 in) in diameter and can be bagged easily. This form is suited to
small scale use, for example at grocery stores and laboratories
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