Dry ice

Dry ice, also known as ‚Cardice’ or ‚Card ice’(in British English), is the solid form of carbon dioxide. It’s mainely used as a cooling agent and it has a couple of advantages such as lower temperature than that of water ice and not leaving any residue. If wondering what is it useful for, you have to know that in case of mechanical cooling being unavailable, you can preserv frozen foods, ice cream and so on by using dry ice.

It sublimates at -78.5°C (−109.3 °F) at atmospheric pressure. Using solid at this low temperature without good protection may be very dangerous due to the burns caused by freezing (frostbite). Although not very toxic, the outgassing from it can cause hypercapnia due to buildup in confined locations.

Properties

Dry ice is the solid form of carbon dioxide (having the chemical formula CO2), containing two oxygen atoms bonded to a single carbon atom. It is colorless, having a sour zesty odor, non-flammable, and slightly acidic.

When they reach temperatures below −56.4 °C (−69.5 °F) and pressures below 5.13 atm (the triple point), CO2 changes from a solid to a gas with no intervening liquid form, through a process called sublimation. The opposite process is called deposition, where CO2 changes from the gas to solid phase (dry ice). At atmospheric pressure, sublimation/deposition occurs at −78.5 °C (−109.3 °F).

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 ice and leaves no residue as it changes state. Its enthalpy of sublimation is 571 kJ/kg (25.2 kJ/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 conductivity.

History

Dry ice was first discovered in 1834 by French chemist Charles Thilorier, who published the first account of the substance. During his several experiments, he noticed 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, saw in dry ice a good opportunity to earn money, so he applied for a US patent to sell it commercially. Later after that, he became the first to make dry ice successful 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”. (in British English)

Manufacture

It takes no complicated process for dry ice to be manufactured.Gases with a high concentration of carbon dioxide are produced first. These gases can be a byproduct of another process, such as producing ammonia from nitrogen and natural gas, or large-scale fermentation. After producing those gases, the carbon dioxide-rich gas is pressurized and refrigerated until it liquifies. After that, the pressure is reduced. When these are  having contact, some of the liquid carbon dioxide vaporizes causing that way a fast  process of lowering of the temperature of the remaining liquid. This way, the extreme cold causes the liquid to solidify into a snow-like consistency. In the end, these snow-like solid carbon dioxide are being condensate into either granules or larger blocks of dry ice.

Dry ice is usually found in two forms, as mentioned before: blocks and cylindrical granulas. The first ones (blocks) are most common and they reach about 30kg. They are mainely used  in shipping, since they are able to sublimate relative slowly due to a low ratio of surface area to volume. The others (granulas) are around 1cm (0.4in) in diameter and they get the advantage of being easily bagged. Granulas are properly for small scale use, such as a grocery store or a laboratory.

Applications

Commercial

The main use of dry ice (aka ‘Cardice’), it’s to preserve food, by not using cyclic refrigeration.

Storing different items such as food, ice-cream, carbonate beverages or biological samples to keep them cold or even flash frozen without using other forms of freezing such as mechanical cooling, it’s its principal quality. Adding other qualities of it, we can mention  the arrest and prevention of the insects activity in closed containers of grains or any other grain products, displacing the oxygen, but not altering the taste or the quality of such foods. Exact for the same reason, it can also prevent or retard food oils and fats from becoming rancid.

Immediately after dry ice is placed into the water, the sublimation proccess is being accelerated and low-sinking and dense clouds of smoke-like fog are created. You’ll discover such things in places like theaters, discothèques, haunted house attractions, and nightclubs, places where fog machines are used for creating dramatic effects.

Another surprising thing dry ice can do (a medical thing this time), is freezing and removing warts. In this situation, given the low temperature, the liquid nitrogen performs better in this role, requiring less time to act and less pressue. However, regarding storage, there’s a huge plus for dry ice, since it can be generated  from compressed carbon dioxide gas as needed.

Plumbers usually use a special type of equipment that forces pressurised liquid CO2 into a jacket around a pipe; when fry ice forms, this causes the water to freeze, forming an ice-plug, offering them the possibility to repair things without turning off the water mains. This is a tehnique that can be also used on pipes up to 4 inches (100mm) in diameter.

Being attracted to the carbon dioxide, mosquitoes, bedbugs, and other insects, can be trapped when using dry ice.

Industrial

 Dry ice can be used for loosening asphalt floor tiles or car sound deadening making it easy to pry off,  as well as freezing water in valveless pipes to enable repair.

Blast cleaning has successfully became one of the largest mechanical uses of dry ice. A nozzle with compressed air shouts out the dry ice granulas, combining the power of the speed of the pellets with the action of the sublimation. This is how residues like glue, oil, ink, mold or rubber are removed from the industrial equipment. 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. With blast cleaning becoming successful, specialists have decided to introduce it into the industry of removing smoke damage from structures after fires.

Another use of dry ice may be the de-gassing of flammable vaporous 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.

Once the cylinder liners of the large marine engines are being removed and fitted, the use of dry ice is being required for chilling and thus shrink the liner so that it freely slides within the block. When warmed in place the resulting interference fit prevents motion. Same or similar procedures may be used in fabricating mechanical assemblies with a high resultant strength.

It is also useful as a cutting fluid.

Scientific

A very useful freezing mixture for cold chemical reactions and for condensating solvents in rotary evaporators is a slurry made of dry ice in an organic solvent. The process of altering cloud precipitation can be done with the use of dry ice. Before being replaced by silver iodide, dry ice was widely used in experiments in the US in the 1950s and early 60s. The fact that dry ice is not expensive and it’s completely non-toxic, it’s a huge advantage of it. If needed a disadvantage of it, it would probably be that it needs to be delivered directly into the supercooled region of clouds being seeded.

Dry ice bombs

The main ingredient of dry ice bombs is obviously dry ice. A dry ice bomb is a bomb-like device using dry ice and water-filled container, such as a plastic bottle. As the dry ice sublimates, pressure increases, usually causing the bottle to explode.

California law defines “destructive device” as a type of weapon, including “any sealed device containing dry ice (-CO2) or other chemically-reactive substances assembled for the purpose of causing an explosion by a chemical reaction.” However, dry ice bombs operate not via chemical reaction but via a phase change. The approximate volume of carbon dioxide gas produced by sublimating 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. It was also featured in an episode of Time Warp.

Safety

Regarding the safety , it is good to know that long time exposure to dry ice can cause severe skin damage through frostbites. It is recommended dry ice should only be exposed to open air in a well-ventilated environment, since it could pose a danger of hypercapnia when it sublimates into large quantities of carbon dioxide gas. 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 direct contact with foodstuffs.

Although not considered a toxic substance by the European Union, 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 labeled specially, including a diamond-shaped black-and white label. The Federal Aviation Administration in the US 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.

Occurrence on Mars

Following the Mars flyby of the Mariner 4 spacecraft in 1966, scientists concluded that Mars’ polar caps consist entirely of dry ice. After a much bigger interest shown by the researchers at the California Institute of Technology, findings made in 2003 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. 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.

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