Dry ice

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Sublimation of dry ice when placed on the surface of water at room temperature

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.

Properties

Crystal structure of dry ice

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.^[1]

Carbon dioxide phase diagram

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).^[2] 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.^[3] Its enthalpy of sublimation (Δ _rH) is 393.5kJ/mol.^[4]

Dry ice is non-polar, with a dipole moment of zero, so attractive intermolecular van der Waals forces operate.^[5] The composition results in low thermal and electrical conductivity.^[6]

History

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.^[7][8] 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.^[7] 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.^[9] In 1925, this solid form of CO₂ was trademarked by the DryIce Corporation of America as "Dry ice", thus leading to its common name.^[10] That same year the DryIce Co. sold the substance commercially for the first time; marketing it for refrigerating purposes.^[9]

The alternative name "Cardice" is a registered trademark of Air Liquide UK Ltd.^[11] It is sometimes written as "card ice".^[12]

Manufacture

Small pellets of dry ice sublimating in air.

Dry ice is easily manufactured.^[13][14] 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.^[14] 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.^[15]

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 (0.4 in) in diameter and can be bagged easily. This form is suited to small scale use, for example at grocery stores and laboratories.^{[citation needed]}

Applications

Commercial

Sublimation

The most common use of dry ice is to preserve food,^[1] using non-cyclic refrigeration.

It is frequently used to package items that need to remain cold or frozen, such as ice cream or biological samples,^[16] without the use of mechanical cooling.^{[citation needed]}

Moreover, dry ice can be used to flash freeze food,^[17] laboratory biological samples,^[18] carbonate beverages,^[17] and make ice cream.^[19]

When dry ice is placed in water sublimation is accelerated, and low-sinking dense clouds of fog (smoke-like) are created. This is used in fog machines, at theaters, discothèques, haunted houses, and nightclubs for dramatic effects. Unlike most artificial fog machines, in which fog rises like smoke, fog from dry ice hovers above the ground.^[15] Dry ice is useful in theater productions that require dense fog effects.^[20]

It is occasionally used to freeze and remove warts.^[21] However, liquid nitrogen performs better in this role since it is colder so requires less time to act and less pressure.^[22] However, dry ice has the advantage of having fewer problems with storage since it can be generated from compressed carbon dioxide gas as needed.^[22]

Plumbers use equipment that forces pressurised liquid CO₂ into a jacket around a pipe; the dry ice formed causes the water to freeze, forming an ice plug, allowing them to do repairs without turning off the water mains. This technique can be used on pipes up to 100 millimetres (3.9 in) in diameter.^[12]

Dry ice can be used as bait to trap mosquitoes and other insects, due to their attraction to carbon dioxide.^[23]

An alternative method to cooling computer parts is with the use of dry ice. This purpose is overshadowed by more conventional ways with fans, heat transfer fluids, liquid nitrogen, or phase change cooling.^[24]

Industrial

Dry ice blasting used to clean a rubber mold

Dry ice can be used to loosen asphalt floor tiles making them easy to pry up.^[25] As well as freezing water in valveless pipes to enable repair.^[26]

One of the largest mechanical 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 residue of dry ice blasting is the sublimed CO₂, thus making it a useful technique where residues from other blasting techniques are undesirable.^{[27][dead link]}

Scientific

In laboratories, a slurry of dry ice in an organic solvent is a useful freezing mixture for cold chemical reactions and for condensing solvents in rotary evaporators.^[4]

The process of altering cloud precipitation can be done with the use of dry ice.^[28] It was widely used in experiments in the United States in the 1950s and early 60s before being replaced by silver iodide.^[28] Nevertheless, dry ice has the advantage of being relatively cheap and completely non-toxic.^[28] Yet its main drawback is that it has to be delivered directly into the supercooled region of any clouds being seeded.^[28]

Dry ice bombs

Dry ice bomb

Dry ice functions as an ingredient in dry ice bombs. A dry ice bomb is a bomb-like device constructed out of a dry ice and water-filled container, such as a plastic bottle. As the dry ice sublimates, pressure builds up, causing the bottle to explode.^{[citation needed]} Because of its simplicity, the dry ice bomb has become a popular recreational activity. However, like any explosive, it is unpredictable and dangerous. In California the relevant law defines a dry ice bomb as: "any sealed device containing dry ice (CO₂) or other chemically-reactive substances assembled for the purpose of causing an explosion by a chemical reaction."^[29] The approximate volume of carbon dioxide gas produced by melting a known mass of dry ice can be calculated using the Ideal gas law.

The bomb was featured on MythBusters - episode 57 Mentos and Soda, which first aired on August 9, 2006.^[30] It was also featured in an episode of Time Warp.^{[citation needed]}

Safety

Dry ice pellet sublimating in water

Prolonged exposure to dry ice can cause severe skin damage through cold burns, and the fog produced may also hinder attempts to withdraw from contact in a safe manner. Because it sublimates into large quantities of carbon dioxide gas, which could displace oxygen-containing air and pose a danger of asphyxiation, dry ice should only be exposed to open air in a well-ventilated environment.^[25] For this reason, dry ice is assigned the S-phrase S9 in the context of laboratory safety. Industrial dry ice may contain contaminants that make it unsafe for applications where it comes into direct contact with foodstuffs.^[31]

Although dry ice is not classified as a dangerous substance by the European Union,^[32] or as a hazardous material by the DOT for ground transportation, when shipped by air or water, it is regulated as a dangerous good and IATA packing instruction 904 (IATA PI 904) requires that it be labelled specially, including a diamond-shaped black-and white label, UN 1845. Also, arrangements must be in place to ensure adequate ventilation so that pressure build-up does not rupture the packaging.^[33] The Federal Aviation Administration in the United States allows airline passengers to carry up to 2 kg of dry ice in carry-on baggage and 2.3 kg in checked baggage, when used to refrigerate perishables.^[34]

Occurrence on Mars

Scientists following the Mariner 4 spacecraft in 1966 concluded that Mars' poles were made entirely of dry ice.^[35] However, findings made in 2003 by researchers at the California Institute of Technology have shown that the Mars' poles are almost completely made of water, and dry ice only covers the top layer of the poles.^[35][36] Scientists, such as Anthony Colaprete, have proposed the discovery of a phenomenon occurring on the polar regions of Mars known as dry ice storms. Colaprete compares Martian dry ice storms to Earth's thunderstorms, with crystalline CO₂ taking the place of water in the clouds.^[37]

References

Bibliography

• Yaws, Carl (2001), Matheson gas data book (7th ed.), McGraw-Hill Professional, pp. 982, http://books.google.co.uk/books?id=Sfvbgvu9OQMC, retrieved 2009-07-27 
• Häring, Heinz-Wolfgang (2008), Industrial Gases Processing, Wiley-VCH, ISBN 9783527316854, http://books.google.co.uk/books?id=93SPB4v1Lk8C, retrieved 2009-07-31 
• Treloar, Roy (2003), Plumbing Encyclopaedia (3rd ed.), Wiley-Blackwell, pp. 528, ISBN 9781405106139, http://books.google.co.uk/books?id=CEyW2EkaogEC&pg=PA175&lpg=PA175&dq=%5C%22card+ice%5C%22+%5C%22dry+ice", retrieved 2009-07-31 
• Housecroft, Catherine; Sharpe, Alan G (2001), Inorganic Chemistry, Harlow: Prentice Hall, ISBN 0582310806, http://books.google.co.uk/books?id=3sy4ZAP4EGAC&pg=PA410&dq=carbon+dioxide+intitle:chemistry&lr=&as_drrb_is=b&as_minm_is=0&as_miny_is=2000&as_maxm_is=0&as_maxy_is=&as_brr=3, retrieved 2009-07-31 
• Mitra, Somenath (2003), Sample preparation techniques in analytical chemistry, Wiley-IEEE, ISBN 9780471328452, http://books.google.co.uk/books?id=yk1RZ9HD6hcC, retrieved 2009-07-31 
• McCarthy, Robert E. (1992), Secrets of Hollywood special effects, Boston: Focal Press, ISBN 0-240-80108-3 
• Duane, H. D. Roller; Thilorier, M. (1952), "Thilyorier and the First Solidification of a "Permanent" Gas (1835)", Isis 43 (2): 109–113, doi:10.1086/349402, http://links.jstor.org/sici?sici=0021-1753%28195207%2943%3A2%3C109%3ATATFSO%3E2.0.CO%3B2-9 
• Khanna, S. K.; Kapila, Dr. B. (2008), Comprehensive Chemistry X, Laxmi Publications, ISBN 9788170085966, http://books.google.co.uk/books?id=qQQcOhxHdxoC&pg=PA161&dq=%22dry+ice%22+%22non-polar%22, retrieved 2009-07-31 
• Goroll, Allan H; Mulley, Albert G (2009), Primary Care Medicine: Office Evaluation and Management of the Adult Patient, Lippincott Williams & Wilkins, ISBN 9780781775137 
• Keyes, Conrad G (2006), Guidelines for cloud seeding to augment precipitation, American Society of Civil Engineers, ASCE Publications, ISBN 9780784408193 

External links

Wikimedia Commons has media related to: Dry ice

• CO₂ safety information on Inspectapedia
• How does dry ice work at HowStuffWorks
• Dry ice info
• Stirling Engine running on Dry Ice