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Dry ice is thesolid form ofcarbon dioxide. It is commonly used for temporary refrigeration as CO2 does not have aliquid state at normal atmospheric pressure andsublimes directly from the solid state to thegas state. It is used primarily as acooling agent, but is also used infog machines at theatres for dramatic effects. Its advantages include lower temperature than that ofwater ice and not leaving any residue (other than incidental frost from moisture in the atmosphere). It is useful for preservingfrozen foods (such as ice cream) wheremechanical cooling is unavailable.
Dry ice sublimes at 194.7 K (−78.5 °C; −109.2 °F) at Earthatmospheric pressure. This extreme cold makes the solid dangerous to handle without protection fromfrostbite injury. While generally not very toxic, theoutgassing from it can causehypercapnia (abnormally elevated carbon dioxide levels in the blood) due to a buildup in confined locations.
Dry ice is the solid form ofcarbon dioxide (CO2), a molecule consisting of a singlecarbon atombonded to twooxygenatoms. Dry ice is colorless, odorless, and non-flammable, and can lower thepH of a solution when dissolved inwater, formingcarbonic acid (H2CO3).[1]
At pressures below 5.13atm and temperatures below −56.4 °C (216.8 K; −69.5 °F) (thetriple point), CO2 changes from a solid to a gas with no intervening liquid form, through a process calledsublimation.[a] The opposite process is calleddeposition, where CO2 changes from thegas tosolid phase (dry ice). At atmospheric pressure, sublimation/deposition occurs at 194.7 K (−78.5 °C; −109.2 °F).[2]
Thedensity of dry ice increases with decreasing temperature and ranges between about 1.55 and 1.7 g/cm3 (97 and 106 lb/cu ft) below 195 K (−78 °C; −109 °F).[3] The low temperature and direct sublimation to a gas makes dry ice an effectivecoolant, since it is colder thanwater ice and leaves no residue as it changes state.[4] Itsenthalpy of sublimation is 571 kJ/kg (25.2 kJ/mol, 136.5 calorie/g).
Dry ice isnon-polar, with adipole moment of zero, so attractiveintermolecularvan der Waals forces operate.[5] The composition results in lowthermal andelectrical conductivity.[6]
It is generally accepted that dry ice was first observed in 1835 by French inventorAdrien-Jean-Pierre Thilorier (1790–1844), who published the first account of the substance.[7][8] In his experiments, he noted that when opening the lid of a large cylinder containingliquid carbon dioxide, most of the liquid carbon dioxide quickly evaporated. This left only solid dry ice in the container. In 1924, Thomas B. Slate applied for a USpatent to sell dry ice commercially. Subsequently, he became the first to make dry ice successful as anindustry.[9] In 1925, this solid form of CO2 was trademarked by the DryIce Corporation of America as "Dry ice", leading to its common name.[10] That same year the DryIce Co. sold the substance commercially for the first time, marketing it for refrigeration purposes.[9]
Dry ice is easily manufactured.[11][12] The most common industrial method of manufacturing dry ice starts with a gas having a high concentration of carbon dioxide. Such gases can be abyproduct of another process, such as producingammonia fromnitrogen andnatural gas, oil refinery activities or large-scalefermentation.[12] Second, the carbon dioxide-rich gas is pressurized and refrigerated until it liquefies. Next, the pressure is reduced. When this occurs some liquid carbon dioxide vaporizes, causing a rapid lowering of temperature of the remaining liquid. 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 small pellets or larger blocks of dry ice.[13][14]
Dry ice is typically produced in three standard forms: large blocks, small (1⁄2 or5⁄8 in [13 or 16 mm] diameter) cylindrical pellets and tiny (1⁄8 inch [3.2 mm] diameter) cylindrical, high surface to volume pellets that float on oil or water and do not stick to skin because of their high radii of curvature. Tiny dry ice pellets are used primarily fordry ice blasting, quick freezing, fire fighting, oil solidifying and have been found to be safe for experimentation by middle school students wearing appropriatepersonal protective equipment such as gloves and safety glasses. A standard block weighing approximately 30 kg (66 lb)[15] covered in a taped paper wrapping is most common. These are commonly used in shipping, because they sublime relatively slowly due to a low ratio of surface area to volume. 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 atgrocery stores andlaboratories where it is stored in a thickly insulated chest.[16] Density of pellets is 60–70% of the density of blocks.[17]
Dry ice is also produced as a byproduct of cryogenicair separation, an industry primarily concerned with manufacturing extremely cold liquids such asliquid nitrogen andliquid oxygen. In this process, carbon dioxide liquefies or freezes at a far higher temperature compared to that needed to liquefynitrogen andoxygen. The carbon dioxide must be removed during the process to prevent dry ice from fouling the equipment, and once separated can be processed into commercial dry ice in a manner similar to that described above.
The most common use of dry ice is to preserve food,[1] usingnon-cyclic refrigeration.
It is frequently used to package items that must remain cold or frozen, such as ice cream or biological samples, in the absence of availability or practicality ofmechanical cooling.
Dry ice is critical in the deployment of some vaccines, which require storage at ultra-cold temperatures along their supply line.[18]
Dry ice can be used toflash-freeze food[19] or laboratory biological samples,[20]carbonate beverages,[19] makeice cream,[21] solidifyoil spills[22] and stopice sculptures and ice walls from melting.
Dry ice can be used to arrest and prevent insect activity in closed containers of grains and grain products, as it displaces oxygen, but does not alter the taste or quality of foods. For the same reason, it can prevent or retard food oils and fats from becomingrancid.
When dry ice is placed in water,sublimation is accelerated, and low-sinking, dense clouds of smoke-like fog are created. This is used infog machines, attheatres,haunted house attractions, andnightclubs for dramatic effects. Unlike most artificialfog machines, in which fog rises like smoke, fog from dry ice hovers near the ground.[14] Dry ice is useful in theatre productions that require dense fog effects.[23] The fog originates from the bulk water into which the dry ice is placed, and not from atmospheric water vapor (as is commonly assumed).[24]
It is occasionally used to freeze and removewarts.[25] However,liquid nitrogen performs better in this role, as it is colder, thereby requiring less time to act, and needs less pressure to store.[26] Dry ice has fewer problems with storage, since it can be generated from compressed carbon dioxide gas as needed.[26]
Inplumbing, dry ice is used to cut off water flow to pipes to allow repairs to be made without shutting off water mains. Pressurised liquid CO2 is forced into a jacket wrapped around a pipe, which in turn causes the water inside to freeze and block the pipe. When the repairs are done, the jacket is removed and the ice plug melts, allowing the flow to resume. This technique can be used on pipes up to 4 inches or 100 mm in diameter.[27]
Dry ice can be used asbait to trapmosquitoes,bedbugs, and other insects, due to their attraction to carbon dioxide.[28]
It can be used to exterminate rodents. This is done by dropping pellets into rodent tunnels in the ground and then sealing off the entrance, thus suffocating the animals as the dry ice sublimates.[29]
Tiny dry ice pellets can be used to fight fire by both cooling fuel and suffocating the fire by excluding oxygen.[30]
The extreme temperature of dry ice can causeviscoelastic materials to change toglass phase. Thus, it is useful for removing many types ofpressure sensitive adhesives.
Dry ice can be used for loosening asphalt floor tiles or car sound deadening material, making them easy to prise off,[31] as well as freezing water in valveless pipes to enable repair.[32]
One of the largest mechanical uses of dry ice isblast cleaning. Dry ice pellets are shot from a nozzle withcompressed air, combining the power of the speed of the pellets with the action of the sublimation. This can remove residues from industrial equipment. Examples of materials 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.[33] Recently, blast cleaning has been introduced as a method of removing smoke damage from structures after fires.
Dry ice is also useful for the de-gassing of flammable vapours from storage tanks –the sublimation of dry ice pellets inside an emptied and vented tank causes an outrush of CO2 that carries with it the flammable vapours.[34]
The removal and fitting ofcylinder liners in large engines requires the use of dry ice to chill and thus shrink the liner so that it freely slides into the engine block. When the liner then warms up, it expands, and the resultinginterference fit holds it tightly in place. Similar procedures may be used in fabricating mechanical assemblies with a high resultant strength, replacing the need for pins, keys or welds.[35]
Dry ice has found its application in construction forfreezing soil, serving as an effective alternative toliquid nitrogen.[36] This method reduces the soil temperature to approximately -70 to -74 °C, rapidly freezing the groundwater. As a result, the soil's strength and impermeability significantly increase,[37] which is essential for the safe execution of underground construction projects.[38]
It is also useful as acutting fluid.
Inlaboratories, a slurry of dry ice in anorganic solvent is a usefulfreezing mixture for coldchemical reactions and for condensing solvents inrotary evaporators.[39] Dry ice andacetone forms a cold bath of −78 °C (−108 °F; 195 K), which can be used for instance to preventthermal runaway in aSwern oxidation.
The process ofaltering cloud precipitation can be done with the use of dry ice.[40] It was widely used in experiments in the US in the 1950s and early 1960s before it was replaced bysilver iodide.[40] Dry ice has the advantage of being relatively cheap and completely non-toxic.[40] Its main drawback is the need to be delivered directly into thesupercooled region of clouds being seeded.[40]
A "dry ice bomb" is a balloon-like device using dry ice in a sealed container such as aplastic bottle. Water is usually added to accelerate the sublimation of the dry ice. As the dry icesublimes, pressure increases, causing the bottle to burst with a loud noise. The screw cap can be replaced with a rubber stopper to make awater rocket.
The dry ice bomb device was featured onMythBusters, episode 57Mentos and Soda, which first aired on August 9, 2006.[41] It was also featured in an episode ofTime Warp, as well as in an episode ofArcher.
Following the Mars flyby of theMariner 4 spacecraft in 1966, scientists concluded thatMars' polar caps consist entirely of dry ice.[42] However, findings made in 2003 by researchers at theCalifornia Institute of Technology have shown that Mars' polar caps are almost completely made of water ice, and that dry ice only forms a thin surface layer that thickens and thins seasonally.[42][43] A phenomenon named dry ice storms was proposed to occur over the polar regions of Mars. They are comparable to Earth's thunderstorms, with crystalline CO2 taking the place of water in the clouds.[44] Dry ice is also proposed as a mechanism for thegeysers on Mars.[45]
In 2012, theEuropean Space Agency'sVenus Express probe detected a cold layer in the atmosphere ofVenus where temperatures are close to the triple point of carbon dioxide –hence it is possible that flakes of dry ice precipitate.[46]
Observations from theUranus flyby byVoyager 2 indicates that dry ice is present on the surface of its large moonsAriel,[47]Umbriel[47] andTitania.[47] Scientists speculate that the magnetic field of Uranus contributes to the generation of CO2 ice on the surfaces of its moons.[48]Voyager 2 observations of Neptune's moonTriton suggested the presence of dry ice on the surface, though followup observations indicate that the carbon ices on the surface are carbon monoxide but that the moon's crust is composed of a significant quantity of dry ice.[49]
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Prolonged exposure to dry ice can cause severe skin damage throughfrostbite, and thefog produced may also hinder attempts to withdraw from contact in a safe manner. Because it sublimes into large quantities of carbon dioxide gas, which could pose a danger ofhypercapnia, dry ice should only be exposed to open air in a well-ventilated environment.[31] For this reason, in the context of laboratory safety dry ice is assigned label precautionP403: "Store in a well-ventilated place." Industrial dry ice may contain contaminants that make it unsafe for direct contact with food.[51][failed verification] Tiny dry ice pellets used in dry ice blast cleaning do not contain oily residues.
Dry ice is assigned aUN number, a code for hazardous substances:UN 1845.[52] Dry ice is not classified as a dangerous substance by theEuropean Union, or as a hazardous material by theUnited States Department of Transportation for ground transportation.[53][52] However, in the US, it is regulated as a dangerous good when shipped by air or water.International Air Transport Association (IATA) regulations require specific diamond-shaped black-and white labelling to be placed on the package. The package must have adequate ventilation so that it will not rupture from pressure in the event that the Dry Ice begins to sublime in the packaging.[52] TheFederal Aviation Administration in the US allows airline passengers to carry up to 2.5 kg (5.5 lb) per person either aschecked baggage or carry-on baggage, when used to refrigerate perishables.[54]
At least one person has been killed by carbon dioxide gas subliming off dry ice in coolers placed in a car.[55] In 2020, three people were killed at a party in Moscow after 25 kg of dry ice was dumped in a pool; carbon dioxide is heavier than air, and so can linger near the ground, just above water level.[56]
Dry ice is sometimes used to give a fog effect tococktails. One bar patron who accidentally ingested pellets from a drink suffered severe burns to hisesophagus,stomach, andduodenum, causing permanent problems with eating.[57][58] Rapid sublimation could cause gas buildup that ruptures digestive organs or suffocation. Products that contain dry ice and prevent it from being accidentally ingested eliminate these risks while producing the desired fog effect.[59]
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Media related toDry ice at Wikimedia Commons
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