What kind of connection is ice

ice

The title of this article is ambiguous. Further meanings are listed under ice (disambiguation).
ice
Ice crystals under the microscope
chemical formula

H2O

Mineral grade Oxide - cation: anion (M: O) = 2: 1 (and 1.8: 1)
4.AA.05 (8th edition: IV / A.01) according to Strunz
04.01.02.01 to Dana
Crystal system hexagonal
Crystal class; Symbol after Hermann-Mauguin dihexagonal-dipyramidal 6 /m 2/m 2/m[1]
colour colorless, white, shimmering faintly blue-green in thick layers
Line color White
Mohs hardness 1,5
Density (g / cm3) 0,9167
shine Glass gloss
transparency transparent to opaque
fracture shell-like
Cleavage is missing
Habitus prismatic, dendritic, needle-like to fibrous crystals; granular to massive aggregates
Twinning {0001} and {0001}
Crystal optics
Refractive index α = 1.320; β = 1.330 [2]
Birefringence
(optical character)
δ = 0.01 [1] ; uniaxial (direction not defined)
Pleochroism unavailable
Other properties
Melting point 0 ° C

As ice is generally referred to as frozen water, which - in addition to liquid water and water vapor - represents its third possible physical state. It generally forms at zero degrees Celsius and, as a naturally occurring crystalline solid with a defined chemical composition, is a mineral. Due to its chemical structure, H2O belongs to the group of oxides.

Ice crystallizes in the hexagonal crystal system and occurs in nature in a wide variety of forms, from hailstones to ice cubes to glaciers. Its density of 0.9168 g / cm³ (at 0 ° C) is lower than that of water (1 g / cm³), which is why it floats on the surface of the water and there Ice sheets, Ice floes and icebergs forms. Around 90 percent by volume of the ice is under water (buoyancy force of the water against the weight of the ice) and only around 10 percent by volume above the water surface.

In its pure form, ice consists of colorless, transparent crystals. Blocks of ice however, they usually contain many fine air bubbles that form during the solidification of the Ice crystals are enclosed and therefore appear white due to multiple refraction. As a chemical substance, it is characterized by some special properties based on the anomalies of the water.

Ice plays an important role in numerous meteorological phenomena. The ice caps of the polar regions are of great importance for the global climate and especially for the global water cycle. Accordingly, it also has a decisive influence on our biosphere.

The science of the shapes, occurrences and properties of ice and snow is called glaciology.

Special properties

Drops of water solidified into ice

Solidification process

The melting or freezing point of ice is under normal conditions at zero degrees Celsius. Crystallization nuclei, i.e. impurities such as dust particles, etc., are, however, a condition for ice crystal formation, since the crystallizing water molecules have to attach to them. In so-called “supercooled water”, not frozen water below zero, the molecules have a short-range order that differs from the normal case, and icosahedral structures are formed. B. clean, supercooled mineral water spontaneously freezes on the gas pearls produced when the bottles are opened. Without an external trigger, water freezes at minus 48 degrees Celsius.[3] Very pure (distilled) water can be subcooled down to -70 ° C.[4]

The freezing point can be reduced by sprinkling with salt (road salt). This is a colligative property, the lowering of the freezing point depends only on the amount of dissolved particles, not on their type. The same effect can also be achieved with sugar.

In addition, the heat of solution in a substance can melt ice. It is crucial that the added substance is insoluble in the solid solvent. This effect is achieved by lowering the chemical potential of the liquid phase. At the same time, this effect increases the boiling point of the water.

bluish translucent ice cover of the Fryxellsee

colour

Ice changes its color with the air content and can therefore also be divided into different groups. Ice that contains a lot of air is white; ice that contains little air is transparent and blue or green. A special case of "colored" ice are so-called green icebergs, which are old overturned icebergs whose algae-covered underside is now visible.

Ice and snow reflect the sunlight. Ice particles cause columns of light in the earth's atmosphere. (The related halos, on the other hand, are created by the refraction of light in ice crystals.) Astronomically and geophysically, ice and snow are often the cause of high reflections from an object.

Sound propagation

The speed of sound in ice at maximum density is 3250 m / s. In contrast to most solids, the dispersion for sound propagation in ice is negative. This effect can be observed on frozen lakes. For example, if there is a crack in the ice surface at a sufficiently large distance from the observer (e.g. from sunlight), a whistling noise can be heard in which the pitch drops from very high frequencies to very low frequencies in a fraction of a second. The sound is similar to that of a projectile flying past, which creates a falling pitch due to the Doppler effect.

Load capacity

According to the Mohs hardness scale, ice only has a low hardness of 1.5 and can be scratched with a fingernail. Yet it is able to carry people and even heavy vehicles such as trucks. A prerequisite for this, however, is a certain minimum thickness of the ice cover, which must be adapted to the required load capacity and either based on empirical values ​​or can be calculated using various methods.

The following ice thicknesses are considered sufficient[5]:

  • Individuals: 5 cm
  • Groups of people: 8 cm
  • Sleigh vehicles: 12 cm
  • Cars, other vehicles: 18 cm

The load-bearing capacity of an ice sheet is based on the one hand on its buoyancy and on the other hand on the resulting hollow shape as a result of the deflection under concentrated load. In both cases, the thickness of the ice sheet is the decisive parameter for the load-bearing capacity. The load capacity due to the buoyancy depends linearly on the ice thickness, while the load capacity due to the deflection is proportional to the square of the ice thickness.

If the load is evenly distributed over large areas without deflection, the load-bearing capacity is limited by the raft-like buoyancy of the ice cover. Corresponding to the buoyancy of bubble-free ice with a density of 917 kg / m³, the maximum mass in relation to the area is $ q $ for large areas of thickness $ h $[6]:

$ q = h \ cdot 83 {\ rm \, \ frac {kg} {m ^ 3}} $

Due to the deflection generated by a load, limited partial areas of an ice sheet can be subjected to significantly higher loads. It must therefore always be ensured that the permissible load on partial areas does not exceed the maximum load on the entire ice cover.

The load-bearing capacity of an ice road can also be estimated using the so-called "gold formula" (named after Lorne W. Gold)[7]:

$ m = h ^ 2 \ cdot 7.03 {\ rm \, \ frac {kg} {cm ^ 2}} {\ rm \ quad {} or \ quad} m = (h + 0.5 \, w) ^ 2 \ cdot 7.03 {\ rm \, \ frac {kg} {cm ^ 2}} $

With

  • $ m $ = total mass of a single vehicle (as an indication of the loading capacity of the ice)
  • $ h $ = thickness of the blue ice
  • $ w $ = thickness of the white ice

The Canadian province of Manitoba uses these formulas to determine the carrying capacity of an ice sheet for use as a winter road. The formula is used as an aid to the decision. The decision as to which load the ice road is released for is always made by an ice road expert.

Entering ice surfaces is in principle dangerous and should be avoided in case of doubt. This is especially true because the thickness and texture of the ice often cannot be reliably determined. The ice screw is suitable for determining the thickness of the ice.

Anomalies

Water exhibits numerous anomalies: properties that deviate from the expected norm. The following anomalies are important for its solid state, as ice:

  • Ice is less dense, so it is lighter than water, so it floats on the water. This density anomaly occurs because the water molecules in the hexagonal lattice have a greater distance from one another than in the liquid, disordered state.
  • In the phase diagram, water has more solid modifications than any other substance: 16 crystalline, five amorphous as well as one liquid, one supercritical and one gaseous. The phase diagram contains eleven triple points - a further, undetectable triple point at 0 K can be assumed - and two critical points.
  • Water enables hypothermia to a greater extent than other substances: even under natural conditions it can remain liquid down to −23 ° C.
  • Water has a second critical point at −91 ° C.
  • Subcooled water has two phases (ES and CS). It is liquid under high pressure even at temperatures down to −149 ° C.
  • Amorphous ice is a state in which solid, glassy water appears like a liquid, but the molecules in it cannot move against each other. Physicists in Canada discovered this around 1985 when they pressed on a block of ice at minus 200 degrees. In the meantime, three types of glass water are known, two dense and one that has a lower density than liquid water.
  • Hot water sometimes freezes faster than cold water (Mpemba effect); the effect also occurs with other liquids, so it is not necessarily an anomaly of the water.
  • Increased pressure lowers the melting point of water instead of increasing it (see phase diagram). The melting point drops by around 0.0077 K for every bar of pressure increase. This is also known as pressure melting.
  • Magnetic fields can change the melting point slightly. It is believed that the magnetic field indirectly strengthens the hydrogen bonds of the water molecules. With a magnetic field of six Tesla, the melting point of normal water increases by 5.6 mK and that of heavy water by 21.8 mK.[8]

classification

According to the 8th and 9th edition of the Strunz system of minerals, because of its chemical composition, ice belongs to the mineral class of oxides with a molar ratio of 2: 1 and 1: 1.

The 9th edition of the mineral classification according to Strunz, however, subdivides the oxides further, so that ice belongs to the group with an unspecified ion size and a cation-to-anion ratio of 2: 1 and 1.8: 1.

Dana’s mineral system classifies the minerals according to their crystal structure. Here, ice belongs to the division of simple oxides with a cation charge of +1 and, due to its special crystal structure, forms its own group.[9]

Education and Locations

Ice in dendritic form on a snowflake
needle-shaped hoar frost on a tree branch

On earth

Ice forms around the world where the humidity is high enough and the temperature has dropped to and below freezing point.

Free ice crystals arise in the form of frost and hoar frost through resublimation (direct transition from the gaseous to the crystalline state) of the atmospheric water vapor. Sleet and hail consist of roundish grains of ice. They form in thunderclouds from water droplets, which condense in deep cloud layers and are then transported by updrafts to higher and colder air layers, where they then freeze. Larger hailstones are often agglomerations of smaller ice particles and go through the process of rising through winds and sinking through their weight several times in the history of their formation. Snow consists of more or less filigree ramified ice crystals. Snowflakes are formed by the slow accumulation and freezing of the finest water droplets on a crystallization nucleus (e.g. dust particles).

Ice surfaces that are permanently connected to the mainland are called ice shelves. The ice shelves are mostly fed by flowing glaciers. Icebergs are masses of ice broken off (calved) by glaciers.

So-called sea ice is formed during the crystallization of sea water; the salt is released into the sea or collects in brine (salt) inclusions (ice itself is always solid fresh water). Depending on the size and agglomeration of the ice, a distinction is made between needle ice, semolina ice, pancake ice cream, ice floes and pack ice. A natural ice-free area that is completely surrounded by pack ice is called polynya. Artificial gullies and holes made in the ice are called Wuhnen.

Ice, which is exceptionally located at the bottom of a body of water because of its history of formation, is called ground ice. The formation of new ice on the sea is known as the Nilas.

The ice conditions in marine areas are marked with an international Ice Code designated:

0:No ice; no ice, ice-free
1:Slush or young ice; Mud or new ice (young ice)
2:Fast ice; Fast ice
3:Drift ice; Drift ice, ice rush
4:Packed slush or strips of hummocked ice; packed muddy ice or hump ice strips (ice hump strips)
5:Open lead near shore; open ice channel (continuous shipping channel in the ice) near the coast
6:Heavy fast ice; strong fast ice
7:Heavy drift ice; strong drift ice
8:Hummocked ice; Ice cusps, ice cusps (ice pyramids rising above the smooth ice), pressed ice
9:Ice jamming; Ice blocking

In the solar system

Ice deposits have been detected in our solar system in comets and asteroids [10] on Mars and on some of the moons of the outer planets.

Numerous comets are known to consist largely of water ice, which is why they are sometimes referred to as "dirty snowballs". It is speculated that a large part of the earth's water resources can be traced back to a long-lasting bombardment of the still young earth by comets. Most of the water in the universe is in the form of ice.

Apart from Earth, Mars is the only planet on which ice has been proven. In addition to the polar ice caps, which undoubtedly consist partly of frozen water, there may also be ice deposits in other regions, namely as permafrost in deeper soil layers.[11][12]

In 1975, the Mariner 10 space probe provided evidence of the presence of ice in meteorite craters near the poles near Mercury, the planet closest to the sun. More detailed investigations with the aid of the MESSENGER mission planned for 2009 should confirm or refute this.

Some moons of the outer planets are known or suspected to be covered by an ice crust. Examples are the Jupiter moons Europa, Ganymede and Callisto, the Saturn moons Enceladus and Titan, the Neptune moon Triton and the Pluto moon Charon. Also, some of these moons are said to have layers of ice modifications under their surface, which only occur at high pressure[13]

Early radar images of the lunar south pole from the 1990s with many, small, strikingly bright spots gave rise to the hope of numerous researchers that the moon has large water reserves, which, among other things, may have survived as relics of comet impacts at the bottom of deep craters . Such deposits would be important sources of water and oxygen for future lunar bases. Investigations in 2006 with radio telescopes were negative.[14] In 2009 the LCROSS mission was able to detect water ice.[15][16][17]

Structure and modifications

Crystal structure of ice. The dashed bonds mark the hydrogen bonds

In the solid state of the water, a high long-range order is usually achieved as ice through the formation of a crystal lattice in the course of crystallization. In the liquid state there is a mixture of order and chaos, with the molecules filling a larger volume due to their higher speed.

Natural ice crystallizes in the hexagonal crystal system in the space groupP63/mmc with the grid parametersa = 6.27 Å and c = 5.79 Å and four formula units per unit cell. [1][18]

Six water molecules combine to form a ring via hydrogen bonds, with each molecule also being part of two neighboring rings. The hexagonal symmetry of the crystal structure is reflected in the macroscopic shape of the ice crystals. In this structure, each oxygen atom is tetrahedrally surrounded by four other O atoms.[19]

Hexagonal ice comes with Ice cream I.H designated. Its density is around 0.92 g / cm3 (0 ° C), which - in contrast to most other substances - is lighter than in the liquid state.

Below −22 ° C and above 207.5 MPa, however, other, for example cubic, ice shapes form, such as the metastable, cubic one Ice cream I.cin which the oxygen atoms have a diamond structure.[19] So far, 16 crystalline and 5 amorphous modifications are known (as of January 2010). The latter are forms without a crystal structure.

The 16 crystalline forms are called Ice cream I.H, Ice cream I.c, as Ice II to Ice XV designated.[20]

Ice clouds in interstellar space have a temperature of approx. -260 ° C and are amorphous in structure ("flow").[21][22]

Use and disability

Ice for cooling freshly caught fish
Burst beer bottle due to the expansion of the liquid when it freezes

Even the Romans used expensive imported glacier ice to cool food and to make soft drinks.

In the 19th century, winter ice began to be used commercially in North America, initially as a luxury item for people in tropical countries, and later as a bulk item for household use. The Ice cream man brought ice blocks, by means of which perishable food, typically in one Icebox, could be kept fresh longer. With the electrification and introduction of the refrigerator, this trade came to an end. Today almost all ice cream used by humans for food purposes is made by chillers or in refrigerators.

Ice formation on the window of an airplane, formed by the low outside temperatures

Ice cream, on the other hand, is a mass of snow or ice sludge made from fruit juices or mixed milk beverages.

The resulting frictional heat from runners on firm ice creates a layer of water a few µm thick under an ice skate, on which the rear part of the runners then glides relatively smoothly. Ice skating, but also skiing, sledding or sledging as a means of transport are therefore possible. The pressure under the narrow runners only lowers the freezing point of the water by a few tenths of a degree. [23]

Frozen bodies of water can, on the one hand, hinder shipping, but on the other hand, they can also shorten transport routes, as land transports can be carried out directly over the water, for example on Lake Baikal.

In the past, Inuit ice was also used to build igloos.

Ice sculptures are made from blocks of ice. Ice houses are also possible.

Ice deposits have a hindering effect especially on traffic in the form of pack ice for shipping (see also icebreaker), as a smooth ice film on roads (see also snow chains), footpaths or on airplanes, as well as snow drifts on all land modes of transport. To reduce the risk of slipping, ice surfaces are blunted with sand or thawed away with salt.

Ice flowers on window panes obstruct the view, but are often artistically very attractive.

Construction projects can also be hampered by the solidification of the ground by ice. On the other hand, the consolidation of the soil can be intentional and, for example, make tunneling work in loose soil possible in the first place. The icing is usually created artificially with large cooling units. In permafrost areas, the softening of the soil due to the lack of frost poses a threat to structures. For this purpose, parts of the Lhasa railway are cooled with large heat pipes.

Water pipes burst when they freeze. For protection, such pipes are laid in the ground below the frost line or a minimum flow is ensured or emptied in good time.

See also

  • Ice age
  • Synthetic ice, blue ice field
  • Ice hotel, ice climbing, ice sculpture

literature

  • Astrid Döppenschmidt: The ice surface - investigations with the atomic force microscope. GCA-Verl., Herdecke 2000, ISBN 3-934389-71-6
  • Werner F. Kuhs: Physics and chemistry of ice. RSC Publ., London 2007, ISBN 978-0-85404-350-7
  • Victor F. Petrenko, Robert W. Whitworth: Physics of ice. Oxford Univ. Press, Oxford 2006, ISBN 0-19-851894-3
  • Miles McPhee: Air-ice-ocean interaction - turbulent ocean boundary layer exchange processes. Springer, New York 2008, ISBN 978-0-387-78334-5
  • John D.Castello: Life in ancient ice. Princeton Univ. Press, Princeton 2005, ISBN 0-691-07475-5
  • Pat Dasch: Icy worlds of the solar system. Cambridge Univ. Press, Cambridge 2004, ISBN 0-521-64048-2
  • Gurij N. Jakovlev: Studies in ice physics and ice engineering. Israel Program for Scientific Translation Jerusalem 1973, ISBN 0-7065-1275-8

Web links

 Commons: ice cream - Collection of pictures, videos and audio files
Template: Commonscat / WikiData / Difference
 Wiktionary: ice cream - Explanations of meanings, word origins, synonyms, translations
  • Mineral Atlas: Ice (Wiki)
  • Detailed information
  • Ice Testing Information. Formulas for calculating the load-bearing capacity of an ice surface, (English, PDF)
  • Hayley, Proskin: Managing the safety of ice covers used for transportation in an environment of climate warming, 4th Canadian Conference on Geohazards, Université Laval, Québec, Qc, Canada - An article about the carrying capacity of ice roads
  • Assessment of the load-bearing capacity of ice sheets - BLfW leaflet
  • Christine Reinke-Kunze: (Almost) everything about ice and snow. In: NZZ Folio. 7/97.
  • Ice Crystals Growth (Time Lapse Video)
  • Planet Earth. Ice Worlds. (OT: Ice Worlds), Documentary, Great Britain, 2006, 43 min., A film by Alastair Fothergill, production: BBC, synopsis at Arte

items

  • "Nassforschers Träume", Die Zeit, November 27, 2003, No. 49, p. 38, "Square snowflakes, ice at 500 degrees, watery glass - science is always amazed at H2O"
  • Researchers freeze water at room temperature, Wissenschaft.de, August 19, 2005
  • Kay D. Bidle, (et al.) Fossil genes and microbes in the oldest ice on Earth. PNAS August 2007, Vol. 104, no.33, 13455-13460
  • L.W. Gold, Use of ice covers for transportation. Canadian Geotechnical Journal, 1971, Vol. 8, pp. 170-181. doi: 10.1139 / t71-018

Individual evidence

  1. 1,01,11,2Webmineral - Ice
  2. ↑ MinDat - Ice
  3. ↑ jom: Just ask !: The core of the ice. In: badische-zeitung.de, opinion, just ask !, February 18, 2012 (February 19, 2012)
  4. ^ Service centers in the rural area of ​​Rhineland-Palatinate - undercooled water.
  5. ↑ Water rescue service of the DRK: Behavior in and on wintry waters. pdf, 760 KB
  6. Assessment of the bearing capacity of ice sheets - Leaflet of the Bavarian State Office for the Environment. Bavarian State Office for the Environment. Retrieved February 12, 2012.
  7. ↑ L. W. Gold: Use of Ice Covers for Transportation. In: Canadian Geotechnical Journal. 8, No. 2, 1971, pp. 170-181, doi: 10.1139 / t71-018.
  8. ↑ Dörte Saße: "Magnetic fields change the melting point of water." In: Die Welt, January 8, 2005.
  9. ^ Webmineral - New Dana Classification of Oxide Minerals.
  10. ^ Confirming Water Ice on the Surface of Asteroid 24 Themis 2009: American Astronomical Society
  11. ↑ scinexx - the knowledge magazine: "Phoenix finds first Mars ice cream".
  12. ↑ Water Ice in a Martian Crater - Astronomy Picture of the Day, July 20, 2005 (English).
  13. ↑ Tilmann Althaus: Planet moon, Titan - a world with character, in ASTROnews, Date: February 24, 2012, Accessed: February 27, 2012
  14. ↑ raumfahrer.net - But no ice on the moon.
  15. ^ Probe impact NASA finds water on the moon mirror online, November 13, 2009
  16. ↑ Lunar Impactor Finds Clear Evidence of Water Ice on Moon Wired Science, November 13, 2009
  17. ↑ LCROSS Impact Data Indicates Water on Moon nasa, 11.13.09
  18. ↑ American Mineralogist Crystal Structure Database - Ice
  19. 19,019,1R. Steudel, Y. Drozdova: Chemistry of the non-metals: With atomic structure, molecular geometry and bond theory. 2nd edition, pp. 206-208, de Gruyter, 1998, ISBN 978-3-11-012322-7
  20. ↑ H2O - the nerd welt.de, June 27, 2010; A very special snowball sciencenews.org, October 10, 2009; Ice XV: A New Thermodynamically Stable Phase of Ice, ucl.ac.uk, September 22, 2009; Retrieved July 20, 2010
  21. ↑ alpha-Centauri: How is ice formed in the cosmos?
  22. ↑ David F. Blake, et al .: Ice cream - cradle of life? P.22 - 27 in: Life in space. Spectrum of Science Dossier 2002/3, Spektrum-d.-Wiss.-Verl., Heidelberg 2002, ISBN 3-936278-14-8, An amorphous journey P.25
  23. ↑ Skating: Why is ice slippery ?, publication of the German Physical Society