   #copyright

Ice

2007 Schools Wikipedia Selection. Related subjects: Chemical compounds;
General Physics

   Snowflakes by Wilson Bentley, 1902
   Enlarge
   Snowflakes by Wilson Bentley, 1902

   Ice is an Oxide class mineral that is referred to by any one of the 14
   known solid phases of water. However, in non-scientific contexts, it
   usually describes ice I[h], which is the most abundant of these phases
   in Earth's biosphere. This type of ice is a soft, delicate, crystalline
   solid, which can appear transparent or an opaque bluish-white colour
   depending on the presence of impurities such as air. The addition of
   other materials such as soil may further alter appearance. The most
   common phase transition to ice I[h] occurs when liquid water is cooled
   below 0  °C (273.15  K, 32  °F) at standard atmospheric pressure.
   However, it can also deposit from a vapor with no intervening liquid
   phase such as in the formation of frost. Ice appears in varied forms
   such as hail, ice cubes, and glaciers. It plays an important role with
   many meteorological phenomena. The ice caps of the polar regions are of
   significance for the global climate and particularly the water cycle.

Characteristics

   An unusual feature of ice frozen at a pressure of one atmosphere is
   that the solid is some 8% less dense than liquid water. Water is also
   one of the few substances to expand when it freezes. Ice has a density
   of 0.917 g/cm³ at 0 °C, whereas water has a density of 0.9998 g/cm³ at
   the same temperature. Liquid water is most dense, essentially 1.00
   g/cm³, at 4 °C and becomes less dense as the water molecules begin to
   form the hexagonal crystals of ice as the temperature drops to 0 °C.
   (In fact, the word "crystal" derives from Greek word for frost.) This
   is due to hydrogen bonds forming between the water molecules, which
   line up molecules less efficiently (in terms of volume) when water is
   frozen. The result of this is that ice floats on liquid water, an
   important factor in Earth's climate. Density of ice increases slightly
   with decreasing temperature (density of ice at −180 °C (93 K) is 0.9340
   g/cm³).

   When ice melts, it absorbs as much heat energy (the heat of fusion) as
   it would take to heat an equivalent mass of water by 80 °C, while its
   temperature remains a constant 0 °C.

   It is also theoretically possible to superheat ice beyond its
   equilibrium melting point. Simulations of ultrafast laser pulses acting
   on ice shows it can be heated up to room temperature for an extremely
   short period (250 ps) without melting it. It is possible that the
   interior of an ice crystal has a melting point above 0 °C and that the
   normal melting at 0 °C is just a surface effect.

   As a naturally occurring crystalline solid, ice is considered a
   mineral.

   The smallest ice was created by Roger Miller and Klaus Nauta in the
   University of North Carolina in 1999. It is 6 water molecules arranged
   in a hexagon, theoretically the smallest ice possible.

Types of ice

   Ice coating the branches of a tree.
   Enlarge
   Ice coating the branches of a tree.
   Half-melted glacier ice chunk.
   Enlarge
   Half-melted glacier ice chunk.

   Everyday ice and snow is hexagonal ice ( ice I[h]). Subjected to higher
   pressures and varying temperatures, ice can form in roughly a dozen
   different phases. Only a little less stable (metastable) than I[h] is
   cubic structure ice ( I[c]). Cooling I[h] causes a different
   arrangement to form in which the protons move, XI.

   With both cooling and pressure more types exist, each being created
   depending on the phase diagram of ice. These are II, III, V, VI, VII,
   VIII, IX, and X. With care all these types can be recovered at ambient
   pressure. 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. 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).

   Rime is a type of ice formed on cold objects when the humidity in the
   air crystalizes on them. This can be observed in foggy weather or when
   the temperature drops during night. It 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.

   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, 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.

   Some other substances (particularly solid forms of those usually found
   as fluids) are also called "ice": dry ice, for instance, is a popular
   term for solid carbon dioxide.

   In outer space hexagonal crystalline ice, the predominant form on
   Earth, is extremely rare. Amorphous ice is more common; however,
   hexagonal crystalline ice can be formed via volcanic action.

Uses of ice

Ice harvesting

   Harvesting ice on Lake Saint Clair in Michigan, circa 1905.
   Enlarge
   Harvesting ice on Lake Saint Clair in Michigan, circa 1905.

   Ice has long been valued as a means of cooling. Until recently, 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 year-round, 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. For the first half of the 19th century, ice
   harvesting had become big business in America. New Englander 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. The advent of artificial refrigeration technology has
   since made delivery of ice obsolete.

   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
   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 that could easily bring temperatures
   inside the space down to frigid levels in summer days. The ice was then
   used to chill treats for royalty during hot summer days.

Sports on ice

   Ice surfing on the Żnin Small Lake
   Enlarge
   Ice surfing on the Żnin Small Lake

   Ice also plays a role in winter recreation, in sports such as ice
   skating, tour skating, ice hockey, ice fishing, ice climbing, curling
   and sled racing on bobsled, luge and skeleton. A sort of sailboat on
   blades gives rise to iceboating.

   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.

Ice travel

   Coast Guard icebreakers near McMurdo Station, February 2002.
   Enlarge
   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 round. Examples are
   Murmansk (Russia), Petsamo (Russia, formerly Finland) and Vardø
   (Norway). Harbors that 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 glossy surface. Whenever
   there is freezing rain or snow that 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 labor-intensive.

   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 combat 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
   centimeters (one foot).

Other uses of ice

     * The manufacture and use of ice cubes or crushed ice is common for
       drinks.
     * Pagophagia, a type of pica eating disorder, is the compulsive
       consumption of ice.
     * 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.
     * It is possible to stab someone to death with an icicle. This can
       confound investigators, as once the icicle melts there will be no
       apparent murder weapon. A large lump of ice can be used to inflict
       blunt force trauma in a similar vein.

     * During World War II, Project Habbakuk was a British program which
       investiagted the use of pykrete (wood fibres 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 was not enough funds for construction of a
       prototype.

Ice at different pressures

   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. 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 why glaciers move. Ice formed at high pressure has a
   different crystal structure and density than ordinary ice. Ice, water,
   and water vapor can coexist at the triple point, which is 273.16 K at a
   pressure of 611.73  Pa.

Phases of ice

   Phase Characteristics
   Amorphous ice Amorphous ice is an ice lacking crystal structure.
   Amorphous ice exists in three forms: low-density (LDA) formed at
   atmospheric pressure, or below, high density (HDA) and very high
   density amorphous ice (VHDA), forming at higher pressures. LDA forms by
   extremely quick cooling of liquid water ("hyperquenched glassy water",
   HGW), by depositing water vapour on very cold substrates ("amorphous
   solid water", ASW) or by heating high density forms of ice at ambient
   pressure ("LDA").
   Ice Ih Normal hexagonal crystalline ice. Virtually all ice in the
   biosphere is ice I[h], with the exception only of a small amount of ice
   I[c].
   Ice Ic Metastable cubic crystalline variant of ice. The oxygen atoms
   are arranged in a diamond structure. It is produced at temperatures
   between 130-150 K, and is stable for up to 200 K, when it transforms
   into ice I[h]. It is occasionally present in the upper atmosphere.
   Ice II A rhombohedral crystalline form with highly ordered structure.
   Formed from ice I[h] by compressing it at temperature of 190-210 K.
   When heated it undergoes transformation to ice III.
   Ice III A tetragonal crystalline ice, formed by cooling water down to
   250 K at 300 MPa. Least dense of the high-pressure phases. Denser than
   water.
   Ice IV Metastable rhombohedral phase. Does not easily form without a
   nucleating agent.
   Ice V A monoclinic crystalline phase. Formed by cooling water to 253 K
   at 500 MPa. Most complicated structure of all the phases.
   Ice VI A tetragonal crystalline phase. Formed by cooling water to 270 K
   at 1.1 GPa. Exhibits Debye relaxation.
   Ice VII A cubic phase. The hydrogen atoms position is disordered, the
   material shows Debye relaxation. The hydrogen bonds form two
   interpenetrating lattices.
   Ice VIII A more ordered version of ice VII, where the hydrogen atoms
   assume fixed positions. Formed from ice VII by cooling it beyond 5 °C.
   Ice IX A tetragonal metastable phase. Formed gradually from ice III by
   cooling it from −65 to −108 °C, stable below 140 K and pressures
   between 200 and 400 MPa. It has density of 1.16 g/cm³, slightly higher
   than ordinary ice.
   Ice X Proton-ordered symmetric ice. Forms at about 40-45 GPa. A
   transformation of ice VII to ice X at 70 GPa is predicted.
   Ice XI An orthorhombic low-temperature equilibrium form of hexagonal
   ice. It is ferroelectric.
   Ice XII A tetragonal metastable dense crystalline phase. It is
   metastable in the phase space of ice V and ice VI. It can be prepared
   by heating high-density amorphous ice from 77 K to about 183 K at 810
   MPa.

Ice in fiction

   Kurt Vonnegut's novel Cat's Cradle features Ice IX as a central element
   of the plot, although real Ice IX does not have the properties of
   Vonnegut's fictional ice-nine (i.e. the ability to freeze all water on
   Earth with the introduction of one granule).

Related terms

     * A rusticle is a rust formation similar to an icicle.
     * Isaz is the Proto-Germanic rune for "ice".

Gallery

   Row of Icicles

   A natural, 4 tonne, block of ice on a beach in Iceland

   A glass of iced water.

   Ice on a fence, frozen during winter.

   Icicles forming on a cabin's roof at Dinner Plain Australia.

   Icicles at Big White Ski Resort, Canada.

   An ancient ice house ( yakhchal) in Kerman, Iran, built during the
   Middle Ages for storing harvested ice.

   Icicles formed at all angles by water splashes and wind-blown spray. A
   hillside, Harlech, Wales
   Retrieved from " http://en.wikipedia.org/wiki/Ice"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
