Small pellets of dry ice sublimating in air

Crystal structure of dry ice

Dry ice, sometimes referred to as "Cardice" or as "card ice" (chiefly British English), is the solid form of carbon dioxide. It is used primarily as a cooling agent. Its advantages include lower temperature than that of water ice and not leaving any residue (other than incidental frost from moisture in the atmosphere). It is useful for preserving frozen foods, ice cream, etc., where mechanical cooling is unavailable.

Dry ice sublimates at −78.5 °C (−109.3 °F) at atmospheric pressure. This extreme cold makes the solid dangerous to handle without protection due to burns caused by freezing (frostbite). While generally nontoxic, the outgassing from it can cause asphyxiation due to displacement of oxygen in confined locations.

Properties[link]

Dry ice is the solid form of carbon dioxide (chemical formula CO₂), comprising two oxygen atoms bonded to a single carbon atom. It is colorless, odorless, non-flammable, and slightly acidic.^[1]

Phase diagram of carbon dioxide

At 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).^[2] 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.^[3] 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.^[4] The composition results in low thermal and electrical conductivity.^[5]

History[link]

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.^[6][7] 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.^[6] In 1924, Thomas B. Slate applied for a US patent to sell dry ice commercially. Subsequently, he became the first to make dry ice successful as an industry.^[8] In 1925, this solid form of CO₂ was trademarked by the DryIce Corporation of America as "Dry ice", thus leading to its common name.^[9] That same year the DryIce Co. sold the substance commercially for the first time; marketing it for refrigerating purposes.^[8]

The alternative name "Cardice" is a registered trademark of Air Liquide UK Ltd.^[10] It is sometimes written as "card ice".^[11]

Manufacture[link]

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

Dry ice is easily manufactured.^[12][13] First, gases with a high concentration of carbon dioxide are produced. Such gases can be a byproduct of another process, such as producing ammonia from nitrogen and natural gas, or large-scale fermentation.^[13] Second, the carbon dioxide-rich gas is pressurized and refrigerated until it liquifies. 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 either small pellets or larger blocks of dry ice.^[14][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 relative 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 at grocery stores and laboratories.^{[citation needed]}

Applications[link]

Commercial[link]

An ice cream cart

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, without the use of mechanical cooling.

Dry ice can be used to flash freeze food,^[16] laboratory biological samples,^[17] carbonate beverages,^[16] and make ice cream.^[18]

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 such foods. For the same reason, it can prevent or retard food oils and fats from becoming rancid.

Sublimation

When dry ice is placed in water sublimation is accelerated, and low-sinking, dense clouds of smoke-like fog are created. This is used in fog machines, at theaters, discothèques, haunted house attractions, 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.^[19]

It is occasionally used to freeze and remove warts.^[20] However, liquid nitrogen performs better in this role, since it is colder so requires less time to act and less pressure.^[21] However, dry ice has the advantage of having fewer problems with storage, since it can be generated from compressed carbon dioxide gas as needed.^[21]

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 perform repairs without turning off the water mains. This technique can be used on pipes up to 4 inches (100 mm) in diameter.^[22]

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

Industrial[link]

Dry ice blasting used for cleaning a rubber mold

Dry ice can be used for loosening asphalt floor tiles or car sound deadening making it easy to pry off,^[24] as well as freezing water in valveless pipes to enable repair.^[25]

One of the largest mechanical uses of dry ice is blast cleaning. Dry ice pellets are shot out of a nozzle with compressed 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 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.^{[26][dead link]} Recently, blast cleaning has been introduced into the industry 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.^[27]

The removal and fitting of cylinder liners in large marine engines requires the use of dry ice to chill and thus shrink the liner so that it freely slides within the block. When warmed in place the resulting interference fit prevents motion. Similar procedures may be used in fabricating mechanical assemblies with a high resultant strength, replacing the need for pins, keys or welds.^[28]

It is also useful as a cutting fluid.

Scientific[link]

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.^[29]

The process of altering cloud precipitation can be done with the use of dry ice.^[30] It was widely used in experiments in the US in the 1950s and early 60s before being replaced by silver iodide.^[30] Dry ice has the advantage of being relatively cheap and completely non-toxic.^[30] Its main drawback is the need to be delivered directly into the supercooled region of clouds being seeded.^[30]

Dry ice bombs[link]

Dry ice bomb

Dry ice is an ingredient in dry ice bombs. 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."^[31] 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.^[32] It was also featured in an episode of Time Warp.

Safety[link]

Dry ice pellet sublimating in water

Prolonged exposure to dry ice can cause severe skin damage through frostbites, 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.^[24] 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.^[33]

Although dry ice is not classified as a dangerous substance by the European Union,^[34] 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 labeled 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.^[35] 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.^[36]

Occurrence on Mars[link]

Following the Mars flyby of the Mariner 4 spacecraft in 1966, scientists concluded that Mars' polar caps consist entirely of dry ice.^[37] However, findings made in 2003 by researchers at the California 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.^[37][38] 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.^[39]

References[link]

Bibliography[link]

• Yaws, Carl (2001). Matheson gas data book (7th ed.). McGraw-Hill Professional. p. 982. ISBN 978-0-07-135854-5. http://books.google.com/?id=Sfvbgvu9OQMC. Retrieved 2009-07-27. 
• Häring, Heinz-Wolfgang (2008). Industrial Gases Processing. Christine Ahner. Wiley-VCH. ISBN 978-3-527-31685-4. http://books.google.com/?id=93SPB4v1Lk8C. Retrieved 2009-07-31. 
• Treloar, Roy (2003). Plumbing Encyclopaedia (3rd ed.). Wiley-Blackwell. ISBN 978-1-4051-0613-9. http://books.google.com/?id=CEyW2EkaogEC&pg=PA175. Retrieved 2009-07-31. 
• Housecroft, Catherine; Sharpe, Alan G (2001). Inorganic Chemistry. Harlow: Prentice Hall. ISBN 0-582-31080-6. http://books.google.com/?id=3sy4ZAP4EGAC&pg=PA410. Retrieved 2009-07-31. 
• Mitra, Somenath (2003). Sample preparation techniques in analytical chemistry. Wiley-IEEE. ISBN 978-0-471-32845-2. http://books.google.com/?id=yk1RZ9HD6hcC. Retrieved 2009-07-31. 
• McCarthy, Robert E. (1992). Secrets of Hollywood special effects. Boston: Focal Press. ISBN 0-240-80108-3. http://books.google.com/?id=B4applRToVQC&printsec=frontcover&dq=isbn:0240801083#v=onepage&q&f=false. 
• 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. JSTOR 227174. 
• Khanna, S. K.; Kapila, Dr. B. (2008). Comprehensive Chemistry X. Laxmi Publications. ISBN 978-81-7008-596-6. http://books.google.com/?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 978-0-7817-7513-7. 
• Keyes, Conrad G (2006). Guidelines for cloud seeding to augment precipitation. American Society of Civil Engineers. ASCE Publications. ISBN 978-0-7844-0819-3. 

Wikimedia Commons has media related to: Dry ice

Look up dry in Wiktionary, the free dictionary.

Dry or dryness denotes a lack of water. It may also refer to

Common meanings[link]

• Prohibiting alcohol (see Dry county)
• Dryness (taste), the lack of sugar in a drink, especially an alcoholic one (not to be confused with the meaning listed above)
• Dryness (medical)
• Dryness (drought)
• "Dry", a style of writing
• Deadpan, dry humor

Places[link]

• Dry, Loiret, a commune of the Loiret département in France
• Dry River (disambiguation), various rivers and towns

Music[link]

• Dry (rapper), real name Landry Delica, rapper of Congolese origin
• Dry (album), an album by PJ Harvey
• "Dry", a song by Kutless from their self-titled album
• "Dry", a song by Welsh band Feeder, from the 1999 album Yesterday Went Too Soon
• audio unprocessed with reverb and delay

Other[link]

• Dry, a memoir by Augusten Burroughs
• Don't repeat yourself (DRY), a computer programming philosophy
• Wets & Dries, a faction in the British Conservative Party
• Dry cell, a type of battery

See also[link]

• All pages beginning with "Dry"

This disambiguation page lists articles associated with the same title. If an internal link led you here, you may wish to change the link to point directly to the intended article.

A natural block of (water) ice

Snowflakes (ice crystals) by Wilson Bentley, 1902

Ice is water frozen into the solid state. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions. The addition of other materials such as soil may further alter the appearance.

Ice appears in nature in forms of snowflakes, hail, icicles, glaciers, pack ice, and entire polar ice caps. It is an important component of the global climate, and plays an important role in the water cycle. Furthermore, ice has numerous cultural applications, from ice cooling of drinks to winter sports and the art of ice sculpting.

The molecules in solid ice may be arranged in different ways, called phases, depending on the temperature and pressure. Usually ice is the phase known as ice I_h, which is the most abundant of the varying solid phases on the Earth's surface. The most common phase transition to ice I_h occurs when liquid water is cooled below 0°C (273.15K, 32°F) at standard atmospheric pressure. It can also deposit from vapour with no intervening liquid phase, such as in the formation of frost.

The word is derived from Old English īs, which in turn stems from Proto-Germanic isaz.

Characteristics[link]

Crystal structure of hexagonal ice. Grey dashed lines indicate hydrogen bonds.

As a naturally occurring crystalline inorganic solid with an ordered structure, ice is considered a mineral.^[1] It possesses a regular crystalline structure based on the molecule of water, which consists of a single oxygen atom covalently bonded to two hydrogen atoms, or H-O-H. However, many of the physical properties of water and ice are controlled by the formation of hydrogen bonds between adjacent oxygen and hydrogen atoms. It is a weak bond, but is critical in controlling the structure of both water and ice.

An unusual property of ice frozen at atmospheric pressure is that the solid is approximately 8.3% less dense than liquid water. The density of ice is 0.9167 g/cm³ at 0 °C, whereas water has a density of 0.9998 g/cm³ at the same temperature. Liquid water is densest, essentially 1.00 g/cm³, at 4 °C and becomes less dense as the water molecules begin to form the hexagonal crystals^[2] of ice as the freezing point is reached. This is due to hydrogen bonding dominating the intermolecular forces, which results in a packing of molecules less compact in the solid. Density of ice increases slightly with decreasing temperature and has a value of 0.9340 g/cm³ at −180 °C (93 K).^[3]

The effect of expansion during freezing can be dramatic, and is a basic cause of freeze-thaw weathering of rock in nature. It is also a common cause of the flooding of houses when water pipes burst due to the pressure of expanding water when it freezes, then leak water after thawing.

The result of this process is that ice (in its most common form) floats on liquid water, which is an important feature in Earth's biosphere. It has been argued that without this property natural bodies of water would freeze, in some cases permanently, from the bottom up,^[4] resulting in a loss of bottom-dependent animal and plant life in fresh and sea water. Sufficiently thin ice sheets allow light to pass through while protecting the underside from short-term weather extremes such as wind chill. This creates a sheltered environment for bacterial and algal colonies. When sea water freezes, the ice is riddled with brine-filled channels which sustain sympagic organisms such as bacteria, algae, copepods and annelids, which in turn provide food for animals such as krill and specialised fish like the Bald notothen, fed upon in turn by larger animals such as Emperor penguins and Minke whales.^[5]

When ice melts, it absorbs as much energy as it would take to heat an equivalent mass of water by 80 °C. During the melting process, the temperature remains constant at 0 °C. While melting, any energy added breaks the hydrogen bonds between ice (water) molecules. Energy becomes available to increase the thermal energy (temperature) only after enough hydrogen bonds are broken that the ice can be considered liquid water. The amount of energy consumed in breaking hydrogen bonds in the transition from ice to water is known as the heat of fusion.

As with water, ice absorbs light at the red end of the spectrum preferentially as the result of an overtone of an oxygen-hydrogen (O-H) bond stretch. Compared with water, this absorption is shifted toward slightly lower energies. Thus, ice appears blue, with a slightly greener tint than for liquid water. Since absorption is cumulative, the color effect intensifies with increasing thickness or if internal reflections cause the light to take a longer path through the ice.^[6]

Other colors can appear in the presence of light absorbing impurities, where the impurity is dictating the color rather than the ice itself. For instance, icebergs containing impurities (e.g., sediments, algae, air bubbles) can appear brown, grey or green.^[6]

Slipperiness[link]

Frozen waterfall in southeast New York

It has long been believed that ice is slippery because the pressure of an object in contact with it causes a thin layer to melt. For example, the blade of an ice skate, exerting pressure on the ice, melts a thin layer, providing lubrication between the ice and the blade. This explanation, called "pressure melting", originated in 19th century. This however did not account for skating on ice temperatures lower than -3.5 °C, whereas skaters often skate on lower temperature ice. In 20th century an alternative explanation, called "friction heating" was proposed, whereby friction of the material was causing the ice layer melting. However, this theory also failed to explain skating at low temperature. In fact, neither explanation explained why ice is slippery when standing still even at below-zero temperatures.^[7]

This explanation has come into doubt with the proposal that ice molecules in contact with air cannot properly bond with the molecules of the mass of ice beneath (and thus are free to move like molecules of liquid water). These molecules remain in a semiliquid state, providing lubrication regardless of pressure against the ice exerted by any object.^[8]

Formation[link]

Feather ice on the plateau near Alta, Norway. The crystals form at temperatures below −30 °C (i.e. −22 °F).

Ice that is found at sea may be in the form of sea ice, pack ice, or icebergs. The term that collectively describes all of the parts of the Earth's surface where water is in frozen form is the cryosphere. Ice is an important component of the global climate, particularly in regard to the water cycle. Glaciers and snowpacks are an important storage mechanism for fresh water; over time, they may sublimate or melt. Snowmelt is often an important source of seasonal fresh water.

Rime is a type of ice formed on cold objects when drops of water crystallize on them. This can be observed in foggy weather, when the temperature drops during the night. Soft rime contains a high proportion of trapped air, making it appear white rather than transparent, and giving it a density about one quarter of that of pure ice. Hard rime is comparatively denser.

Aufeis is layered ice that forms in Arctic and subarctic stream valleys. Ice, frozen in the stream bed, blocks normal groundwater discharge, and causes the local water table to rise, resulting in water discharge on top of the frozen layer. This water then freezes, causing the water table to rise further and repeat the cycle. The result is a stratified ice deposit, often several meters thick.

Ice can also form icicles, similar to stalactites in appearance, or stalagmite-like forms as water drips and re-freezes.

Clathrate hydrates are forms of ice that contain gas molecules trapped within its crystal lattice.

Pancake ice is a formation of ice generally created in areas with less calm conditions.

Candle Ice is a form of Rotten Ice that develops in columns perpendicular to the surface of a lake.

Ice discs are circular formations of ice surrounded by water in a river.

The World Meteorological Organization defines several kinds of ice depending on origin, size, shape, influence and so on.^[9]

Ice pellets[link]

An accumulation of ice pellets

Ice pellets are a form of precipitation consisting of small, translucent balls of ice. This form of precipitation is also known as sleet.^[10] Ice pellets are usually (but not always) smaller than hailstones.^[11] They often bounce when they hit the ground, and generally do not freeze into a solid mass unless mixed with freezing rain. The METAR code for ice pellets is PL.^[12]

Ice pellets form when a layer of above-freezing air is located between 1,500 metres (4,900 ft) and 3,000 metres (9,800 ft) above the ground, with sub-freezing air both above and below it. This causes the partial or complete melting of any snowflakes falling through the warm layer. As they fall back into the sub-freezing layer closer to the surface, they re-freeze into ice pellets. However, if the sub-freezing layer beneath the warm layer is too small, the precipitation will not have time to re-freeze, and freezing rain will be the result at the surface. A temperature profile showing a warm layer above the ground is most likely to be found in advance of a warm front during the cold season,^[13] but can occasionally be found behind a passing cold front.

Hail[link]

A large hailstone, about 6 cm (2.36 in) in diameter

Like other precipitation, hail forms in storm clouds when supercooled water droplets freeze on contact with condensation nuclei, such as dust or dirt. The storm's updraft blows the hailstones to the upper part of the cloud. The updraft dissipates and the hailstones fall down, back into the updraft, and are lifted up again. Hail has a diameter of 5 millimetres (0.20 in) or more.^[14] Within METAR code, GR is used to indicate larger hail, of a diameter of at least 6.4 millimetres (0.25 in). GR is derived from the French word grêle. Smaller-sized hail, as well as snow pellets, use the coding of GS, which is short for the French word grésil.^[12] Stones just larger than golf ball-sized are one of the most frequently reported hail sizes.^[15] Hailstones can grow to 15 centimetres (6 in) and weigh more than .5 kilograms (1.1 lb).^[16] In large hailstones, latent heat released by further freezing may melt the outer shell of the hailstone. The hailstone then may undergo 'wet growth', where the liquid outer shell collects other smaller hailstones.^[17] The hailstone gains an ice layer and grows increasingly larger with each ascent. Once a hailstone becomes too heavy to be supported by the storm's updraft, it falls from the cloud.^[18]

Hail forms in strong thunderstorm clouds, particularly those with intense updrafts, high liquid water content, great vertical extent, large water droplets, and where a good portion of the cloud layer is below freezing 0 °C (32 °F).^[14] Hail-producing clouds are often identifiable by their green coloration.^[19][20] The growth rate is maximized at about −13 °C (9 °F), and becomes vanishingly small much below −30 °C (−22 °F) as supercooled water droplets become rare. For this reason, hail is most common within continental interiors of the mid-latitudes, as hail formation is considerably more likely when the freezing level is below the altitude of 11,000 feet (3,400 m).^[21] Entrainment of dry air into strong thunderstorms over continents can increase the frequency of hail by promoting evaporational cooling which lowers the freezing level of thunderstorm clouds giving hail a larger volume to grow in. Accordingly, hail is actually less common in the tropics despite a much higher frequency of thunderstorms than in the mid-latitudes because the atmosphere over the tropics tends to be warmer over a much greater depth. Hail in the tropics occurs mainly at higher elevations.^[22]

Snowflakes[link]

Snowflake viewed in an optical microscope

Snow crystals form when tiny supercooled cloud droplets (about 10 μm in diameter) freeze. These droplets are able to remain liquid at temperatures lower than −18 °C (255 K; −0 °F), because to freeze, a few molecules in the droplet need to get together by chance to form an arrangement similar to that in an ice lattice; then the droplet freezes around this "nucleus." Experiments show that this "homogeneous" nucleation of cloud droplets only occurs at temperatures lower than −35 °C (238 K; −31 °F).^[23] In warmer clouds an aerosol particle or "ice nucleus" must be present in (or in contact with) the droplet to act as a nucleus. Our understanding of what particles make efficient ice nuclei is poor — what we do know is they are very rare compared to that cloud condensation nuclei on which liquid droplets form. Clays, desert dust and biological particles may be effective,^[24] although to what extent is unclear. Artificial nuclei include particles of silver iodide and dry ice, and these are used to stimulate precipitation in cloud seeding.^[25]

Once a droplet has frozen, it grows in the water-supersaturated air, when the temperature remains below the freezing point. The droplet then grows by condensation of water vapor onto the ice surfaces. Air saturation with water is maintained by continuous simultaneous evaporation of water droplets. Thus ice crystals grow at the expense of water droplets in a process called the Wegner-Bergeron-Findeison process. These large crystals are an efficient source of precipitation, since they fall through the atmosphere due to their weight, and may collide and aggregate in clusters. These aggregates are snowflakes, and are usually the type of ice particle that falls to the ground.^[26] Guinness World Records list the world’s largest snowflakes as those of January 1887 at Fort Keogh, Montana; allegedly one measured 38 cm (15 inches) wide.^[27]

The exact details of the sticking mechanism remain controversial. Possibilities include mechanical interlocking, sintering, electrostatic attraction as well as the existence of a "sticky" liquid-like layer on the crystal surface. The individual ice crystals often have hexagonal symmetry. Although the ice is clear, scattering of light by the crystal facets and hollows/imperfections mean that the crystals often appear white in color due to diffuse reflection of the whole spectrum of light by the small ice particles.^[28] The shape of the snowflake is determined broadly by the temperature and humidity at which it is formed.^[26] Rarely, at a temperature of around −2 °C (28 °F), snowflakes can form in threefold symmetry — triangular snowflakes.^[29] The most common snow particles are visibly irregular, although near-perfect snowflakes may be more common in pictures because they are more visually appealing. It is unlikely that any two snowflakes are alike due to the estimated 10¹⁹ (10 quintillion) water molecules which make up a typical snowflake,^[30] which grow at different rates and in different patterns depending on the changing temperature and humidity within the atmosphere that the snowflake falls through on its way to the ground.^[31] The METAR code for snow is SN, while snow showers are coded SHSN.^[12]

Diamond dust[link]

Diamond dust, also known as ice needles or ice crystals, forms at temperatures approaching −40 °F (−40 °C) due to air with slightly higher moisture from aloft mixing with colder, surface based air.^[32] The METAR identifier for diamond dust within international hourly weather reports is IC.^[12]

Production[link]

Harvesting ice on Lake Saint Clair in Michigan, c. 1905

B&W film of 1919 ice harvest at Pocono Manor in the Poconos

An ice manufacturing plant in East Midnapore, India

Ice is now mechanically produced on a large scale, but before refrigeration was developed ice was harvested from natural sources for human use.

Ice harvesting[link]

Ice has long been valued as a means of cooling. In 400 BC Iran, Persian engineers had already mastered the technique of storing ice in the middle of summer in the desert. The ice was brought in during the winters from nearby mountains in bulk amounts, and stored in specially designed, naturally cooled refrigerators, called yakhchal (meaning ice storage). This was a large underground space (up to 5000 m³) that had thick walls (at least two meters at the base) made out of a special mortar called sārooj, composed of sand, clay, egg whites, lime, goat hair, and ash in specific proportions, and which was known to be resistant to heat transfer. This mixture was thought to be completely water impenetrable. The space often had access to a Qanat, and often contained a system of windcatchers which could easily bring temperatures inside the space down to frigid levels on summer days. The ice was used to chill treats for royalty.

There were thriving industries in the 16/17th century in UK whereby low lying areas along the River Thames estuary were flooded during the winter, and ice harvested in carts and stored inter-seasonally in insulated wooden houses as a provision to an icehouse often located in large country houses, and widely used to keep fish fresh when caught in distant waters. This was copied from the Chinese who had been doing it for thousands of years. This was reportedly copied by an Englishman who had seen the same activity in China.^[33] Ice was imported into England from Norway on a considerable scale as early as 1823.^[34]

In the United States, the first cargo of ice was sent from New York City to Charleston, South Carolina in 1799,^[34] and by the first half of the 19th century, ice harvesting had become big business. Frederic Tudor, who became known as the “Ice King,” worked on developing better insulation products for the long distance shipment of ice, especially to the tropics; this became known as the ice trade.

Triest sent ice to Egypt, Corfu, and Zante; Switzerland sent it to France; and Germany sometimes was supplied from Bavarian lakes.^[34]

Until recently,^[when?] the Hungarian Parliament building used ice harvested in the winter from Lake Balaton for air conditioning. Icehouses were used to store ice formed in the winter, to make ice available all year long, and early refrigerators were known as iceboxes, because they had a block of ice in them. In many cities, it was not unusual to have a regular ice delivery service during the summer. The advent of artificial refrigeration technology has since made delivery of ice obsolete.

Ice harvesting is still done for ice and snow sculpture events. A swing saw is used to get ice out of the river for the Harbin International Ice and Snow Sculpture Festival each year. A swing saws is used to cut ice out from the frozen surface of the Songhua River.^[35] Many ice sculptures are made from the ice.

Commercial production[link]

Ice is now produced on an industrial scale, for uses including food storage and processing, chemical manufacturing, concrete mixing and curing, and consumer or packaged ice.^[36] Most commercial ice makers produce three basic types of fragmentary ice: flake, tubular and plate, using a variety of techniques.^[36] Large batch ice makers can produce up to 75 tons of ice per day.^[37]

Ice production is a large business; in 2002, there were 426 commercial ice-making companies in the United States, with a combined value of shipments of $595,487,000.^[38]

For small-scale ice production, many modern home refrigerators can also make ice with a built in icemaker, which will typically make ice cubes or crushed ice. Stand-alone icemaker units that make ice cubes are often called ice machines.

Uses[link]

Sports[link]

Ice sailing on the Żnin Small Lake

Ice also plays a central role in winter recreation and in many sports such as ice skating, tour skating, ice hockey, ice fishing, ice climbing, curling, broomball and sled racing on bobsled, luge and skeleton. Many of the different sports played on ice get international attention every four years during the Winter Olympic Games.

A sort of sailboat on blades gives rise to ice yachting. The human quest for excitement has even led to ice racing, where drivers must speed on lake ice, while also controlling the skid of their vehicle (similar in some ways to dirt track racing). The sport has even been modified for ice rinks.

Other uses[link]

• Ice cubes or crushed ice can be used to cool drinks. As the ice melts, it absorbs heat and keeps the drink near 0 °C (32 °F).
• Ice can be used to reduce swelling (by decreasing blood flow) and pain by pressing it against an area of the body.^[39]

Ice pier during 1983 cargo operations. McMurdo Station, Antarctica

• Engineers used formidable strength of pack ice when they constructed Antarctica's first floating ice pier in 1973.^[40] Such ice piers are used during cargo operations to load and offload ships. Fleet operations personnel make the floating pier during the winter. They build upon naturally-occurring frozen seawater in McMurdo Sound until the dock reaches a depth of about 22 feet (6.7 m). Ice piers have a lifespan of three to five years.
• Structures and ice sculptures are built out of large chunks of ice. The structures are mostly ornamental (as in the case with ice castles), and not practical for long-term habitation. Ice hotels exist on a seasonal basis in a few cold areas. Igloos are another example of a temporary structure, made primarily from snow.
• During World War II, Project Habbakuk was a British programme which investigated the use of pykrete (wood fibers mixed with ice) as a possible material for warships, especially aircraft carriers, due to the ease with which a large deck could be constructed, but the idea was given up when there were not enough funds for construction of a prototype.
• Ice can be used to start a fire by carving it into a lens which will focus sunlight onto kindling. A fire will eventually start.^[41]
• Ice has even been used as the material for a variety of musical instruments, for example by percussionist Terje Isungset.^[42]
• Ice was once used to cool refrigerators in the 19th century, which is reflected in the name "iceboxes."
• Ice can be used to store cooling, which has the same effect as storing electricity Thermal energy storageAir conditioning

Ice and transportation[link]

U.S. Coast Guard icebreakers near McMurdo Station, February 2002

Ice can also be an obstacle; for harbors near the poles, being ice-free is an important advantage; ideally, all year long. Examples are Murmansk (Russia), Petsamo (Russia, formerly Finland) and Vardø (Norway). Harbors which are not ice-free are opened up using icebreakers.

Ice forming on roads is a dangerous winter hazard. Black ice is very difficult to see, because it lacks the expected frosty surface. Whenever there is freezing rain or snow which occurs at a temperature near the melting point, it is common for ice to build up on the windows of vehicles. Driving safely requires the removal of the ice build-up. Ice scrapers are tools designed to break the ice free and clear the windows, though removing the ice can be a long and laborious process.

Far enough below the freezing point, a thin layer of ice crystals can form on the inside surface of windows. This usually happens when a vehicle has been left alone after being driven for a while, but can happen while driving, if the outside temperature is low enough. Moisture from the driver's breath is the source of water for the crystals. It is troublesome to remove this form of ice, so people often open their windows slightly when the vehicle is parked in order to let the moisture dissipate, and it is now common for cars to have rear-window defrosters to solve the problem. A similar problem can happen in homes, which is one reason why many colder regions require double-pane windows for insulation.

When the outdoor temperature stays below freezing for extended periods, very thick layers of ice can form on lakes and other bodies of water, although places with flowing water require much colder temperatures. The ice can become thick enough to drive onto with automobiles and trucks. Doing this safely requires a thickness of at least 30 cm (one foot).

For ships, ice presents two distinct hazards. Spray and freezing rain can produce an ice build-up on the superstructure of a vessel sufficient to make it unstable, and to require it to be hacked off or melted with steam hoses. And icebergs — large masses of ice floating in water (typically created when glaciers reach the sea) — can be dangerous if struck by a ship when underway. Icebergs have been responsible for the sinking of many ships, the most famous probably being the Titanic.

Ice formation on window glass of high altitude flying airplane

For aircraft, ice can cause a number of dangers. As an aircraft climbs, it passes through air layers of different temperature and humidity, some of which may be conducive to ice formation. If ice forms on the wings or control surfaces, this may adversely affect the flying qualities of the aircraft. During the first non-stop flight of the Atlantic, the British aviators Captain John Alcock and Lieutenant Arthur Whitten Brown encountered such icing conditions – Brown left the cockpit and climbed onto the wing several times to remove ice which was covering the engine air intakes of the Vickers Vimy aircraft they were flying.

A particular icing vulnerability associated with reciprocating internal combustion engines is the carburetor. As air is sucked through the carburetor into the engine, the local air pressure is lowered, which causes adiabatic cooling. So, in humid near-freezing conditions, the carburetor will be colder, and tend to ice up. This will block the supply of air to the engine, and cause it to fail. For this reason, aircraft reciprocating engines with carburetors are provided with carburetor air intake heaters. The increasing use of fuel injection—which does not require carburetors—has made "carb icing" less of an issue for reciprocating engines.

Jet engines do not experience carb icing, but recent evidence indicates that they can be slowed, stopped, or damaged by internal icing in certain types of atmospheric conditions much more easily than previously believed. In most cases, the engines can be quickly restarted and flights are not endangered, but research continues to determine the exact conditions which produce this type of icing, and find the best methods to prevent, or reverse it, in flight.

Phases[link]

Ice may be any one of the 15 known solid phases of water.

Most liquids freeze at a higher temperature under pressure, because the pressure helps to hold the molecules together. However, the strong hydrogen bonds in water make it different: water freezes at a temperature below 0 °C under a pressure higher than 1 atm (0.10 MPa). Consequently, water also remains frozen at a temperature above 0 °C under a pressure lower than 1 atm. The melting of ice under high pressures is thought to contribute to the movement of glaciers.

Ice, water, and water vapour can coexist at the triple point, which is exactly 0.01 °C or 273.16 K (by definition) at a pressure of 611.73 Pa. Unlike most other solids, ice is difficult to superheat. In an experiment ice at −3 °C was superheated to about 17 °C for about 250 picoseconds.^[43]

Subjected to higher pressures and varying temperatures, ice can form in fifteen separate known phases. With care all these phases except ice X can be recovered at ambient pressure and low temperature. The types are differentiated by their crystalline structure, ordering and density. There are also two metastable phases of ice under pressure, both fully hydrogen-disordered; these are IV and XII. Ice XII was discovered in 1996. In 2006, XIII and XIV were discovered.^[44] Ices XI, XIII, and XIV are hydrogen-ordered forms of ices I_h, V, and XII respectively. In 2009, ice XV was found at extremely high pressures and −143 °C.^[45] At even higher pressures, ice is predicted to become a metal; this has been variously estimated to occur at 1.55 TPa^[46] or 5.62 TPa.^[47]

As well as crystalline forms, solid water can exist in amorphous states as amorphous solid water (ASW), low-density amorphous ice (LDA), high-density amorphous ice (HDA), very high-density amorphous ice (VHDA) and hyperquenched glassy water (HGW).

In outer space, hexagonal crystalline ice (the predominant form found on Earth) is extremely rare. Amorphous ice is more common; however, hexagonal crystalline ice can be formed via volcanic action.^[48]

Log-lin pressure-temperature phase diagram of water. The Roman numerals correspond to some ice phases listed below.

Other ices[link]

Detail of an ice cube

The solid phases of several other volatile substances are also referred to as ices; generally a volatile is classed as an ice if its melting point lies above ~100 K. The best known example is dry ice, the solid form of carbon dioxide.

A "magnetic analogue" of ice is also realized in some insulating magnetic materials in which the magnetic moments mimic the position of protons in water ice and obey energetic constraints similar to the Bernal-Fowler ice rules arising from the geometrical frustration of the proton configuration in water ice. These materials are called spin ice.

See also[link]

• Density of ice versus water
• Ice famine
• Pumpable ice technology

References[link]

External links[link]

Look up ice in Wiktionary, the free dictionary.

Wikimedia Commons has media related to: Ice

• The National Snow and Ice Data Center, based in the United States
• The phase diagram of water, including the ice variants
• Webmineral listing for Ice
• MinDat.org listing and location data for Ice
• The physics of ice
• The phase diagrams of water with some high pressure diagrams
• 'Unfreezable' water, 'bound water' and water of hydration
• Electromechanical properties of ice
• Estimating the maximum thickness of an ice layer
• Sandia's Z machine creates ice in nanoseconds
• Amazing ice at Lac Leman
• The Surprisingly Cool History of Ice