Ice is made bywaterCrystallization formed by orderly arrangement of molecules. Water molecules are connected together by hydrogen bonds to form very "open" (low-density)Rigid structure。Water crystallization can directly form cubic ice[5]。
The distance between O-O nuclei of the nearest water molecule is 0.276 nm, and O-O-OBond angleAbout 109 °, very close to idealtetrahedronThe bond angle of is 109 ° 28 ′.But only adjacent and notDirect combinationThe O-O spacing of water molecules is much larger, and the farthest one is 0.347 nm.Each water molecule can combine with the other four water molecules to form a tetrahedral structure, so thecoordination numberIs 4.[1]
Ice is a colorless and transparent solid. It is a product formed by solidification of liquid and condensed in a freezing environment. It will liquefy and dissolve under high temperature. It is normalnatural phenomena, which can be formed naturally or manufactured artificially.
Molecules mainly rely on hydrogen bonding, but there are alsoVan der Waals，Lattice structureIt is generally hexagonal, and its density is smaller than that of water.However, there can be other lattice structures under different pressures.
physical property
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density
In aStandard atmospheric pressureThe freezing temperature of pure water is 0 ° C, and the density of water is 999.87kg/mthree(The maximum density of pure water is 1000 kg/m at 4 ° Cthree）, the density of ice is 917kg/mthree。[4]
melting point
Under normal pressure, the melting point of ice is 0 ℃.When 0 ℃ water freezes into ice, the volume will increase by about 1/11 (the minimum water volume is 4 ℃).
There is a relationship between the melting point of ice and the pressure：At 2200pressureBelow, the melting point of ice decreases with the increase of pressure, but it is not very obvious, about 1 ° C decreases for every 130 atmospheric pressure increases;When the pressure exceeds 2200 atmosphere, the melting point of ice increases with the increase of pressure, but the relationship is nonlinear.[4]The melting point of ice is - 17 ℃ at 3530 atmospheric pressure, 0 ℃ at 6380 atmospheric pressure, 60 ℃ at 16500 atmospheric pressure, and it only melts at 76 ℃ at 20670 atmospheric pressure, which is truly called "hot ice".The density of ice at 0 ℃ is 0.92g/cmthreeWhile the density of water is normally 1.00 g/cmthreeSo ice can float on water.Except water (HtwoO) In addition, diamond (C)silicon carbide（SiC）、silicon（Si）、gallium（Ga）、germanium（Ge）、silicon dioxide（SiOtwo, crystal)antimony（Sb）、bismuth(Bi) and other crystals that can form a tetrahedral structure also have solidsDensity ratioThe property of small liquid.
Other physical parameters
Various physical parameters of ice vary with pressure and temperature.Under a standard atmospheric pressure, the melting latent heat of pure ice at 0 ° C is equivalent to the freezing latent heat of water, about 333.5 kJ/kg (about 80 cal/g), and the sublimation latent heat is about 2837 kJ/kg (about 678 cal/g),Specific heat capacityIt is about 2.097 kJ/(kg · K), and the thermal conductivity is about 2.1 W/(m · K).As the temperature decreases, the specific heat capacity tends to decrease, whileThermal conductivityWill increase.[4]
melt
Ice is the solid form of water in nature. Under normal pressure, the temperature is higher than zerocentigradeThe ice will begin to melt and become liquid water.A Japanese research team found that when ice began to melt, it was an opportunity for a water molecule in the crystal to begin to break away from the crystal, and the relevant mechanism helped to clarify the water contentproteinThe mechanism of structural change.
If the strong light such as electric lamp is used to illuminate, the interior of ice will melt and emerge“Ice floe”Similar to the shape of snow crystals.From Japan Institute of Molecular Science andOkayama UniversityIn order to investigate the phenomenon of ice melting from the inside, the researchers ofIce blanketWhat will happen when heating.
The crystal of ice is a structure in which water molecules are regularly arranged in hexagonal shape.After heating, a water molecule first breaks away from the crystal and starts to move freely, but this water molecule will not return to its original position, which will lead to the distortion of the crystal.Once the crystal is distorted, it will gradually expand and eventually the whole crystal will decompose into liquid form.
Characteristics and efficacy
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characteristic
Water above 4 ℃ is qualifiedThermal expansion and cold contractionOf.When the temperature of water is lower than 4 ℃, it shrinks and expands with heat and cold, resulting in a decrease in density. When the temperature is higher than 4 ℃, it recovers the expansion with heat and contraction with cold.This is one of the most important and valuable characteristics of water.
This is an important point to ensure the existence of living things. WhenWater freezesAt that time, the density of ice is small, and it can float on the water surface, which can ensure the survival of underwater creatures.When the day is warm, the ice is on it, which is also the first to thaw.But if the density ratio of iceShuidaThe ice will continue to sink underwater and will not thaw when the weather is warm. The water above will continue to freeze next year until all the water becomes iceAquatic organismWill not exist.
[Usage and dosage] Internal use: containing.External use: poultice.
Relevant knowledge
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Special ice
Hot ice: In addition to the hot ice formed under high pressure mentioned above, heavy water (D ₂ O) freezes at 3.8 ℃, becoming another form of "hot ice".
Water has a property.It has the highest density at 4 ℃.The temperature is above 4 ℃,Liquid waterObserve generalThermal expansion and cold contractionlaw.Below 4 ℃, there is an ice like binding molecule with ice crystal structure in the condensed molecules with linear distribution in the original water, called "quasi ice"crystal". Because the density of ice is smaller than that of water, the existence of" quasi ice crystals "reduces the density of water, which is why the density of water is the largest at 4 ℃, and the density decreases again below 4 ℃.
Humans have been able to produce 19 kinds of ice crystals in the laboratory[2]。But onlyNatural iceCan benatural conditionThe others are high-pressure ice, which cannot exist stably in nature.
Natural iceThe combination of intermediate water molecules is based onHexagonal systemThey are arranged according to the rules.The simplest example of so-called crystal lattice is closely stacked bricks. If a hypothetical atom is substituted at the center of these bricks, a crystal lattice will be obtained.The ice lattice is a triangular prism with a top coneOxygen atomSix adjacentUnit cellAll in common.The oxygen atoms on the three edges are shared by three adjacent cells, the oxygen atoms on the two axis tops are shared by two cells, and only one oxygen atom in the center is unique to this cell.
"Medium density amorphous ice": a new form of ice, which helps to better understand the behavior of water at low temperatures.[6]
Ice and water
becausewaterThe tetrahedral structure determined by the structure of hydrogen bonding between molecules.According to modern timesX-rayIt is proved that ice has tetrahedralcrystal structure。This tetrahedron is formed by hydrogen bonding, which is an open open structure. Because five water molecules cannot occupy all the tetrahedrons, hydrogen bonding in ice connects these tetrahedrons into a whole.The directional and orderly arrangement formed by hydrogen bonding has a small space utilization rate, accounting for about 34%, so the density of ice is small, aboutCelsius92% of liquid water at 4 ℃.
When the ice melts, it breaks up a large number of hydrogen bonds, making it integrated into tetrahedral groups and sporadic smaller "water molecular groups" (i.e. some formed by hydrogen bond bondingAssociative molecule）Therefore, liquid water is not completely ordered like ice, but has a certain degree of disorder, that is, the distance between water molecules is not as fixed as in icetwoO molecule can enter another microcrystal from one tetrahedral microcrystal.In this way, the space between molecules decreases, and the relative density of ice increases.
When the temperature rises, the tetrahedron group of water molecules is constantly destroyed, and the disordered arrangement of molecules increases, which increases the density.But at the same time, intermolecularThermal movementIt also increases the distance between molecules and reduces the density.The two contradictory factors reach balance at 4 ℃, so the density of water is the largest at 4 ℃.After 4 ℃, the factor that the thermal movement of molecules increases the distance between molecules is dominant, and the density of water starts to decrease again.
River ice
freeze
Yellow River BasinyesChinese nationThe cradle of five thousand years of Chinese civilization.howeverYellow RiverNot all the benefits brought to the Chinese nation are benefits,Yellow River floodandIce damageThe property and lives of people on both sides of the Straits are often plundered.
As far back as 400 BCIce condition, which has been recorded in detail:“Meng DongIn the moon, water begins to ice and ground begins to freeze.MidwinterIn the moon, the ice becomes harder and the earth begins to collapse.In the month of winter, when the ice is strong and the water is hard, it is ordered to take ice.Meng ChunIn the month of January, the east wind thaws, the insects begin to shake, and the fish are frozen. "This is the world's earliest written record of ice conditions related to freezing, freezing and thawing.
Land ice
The total volume of ice on the global land surface is 26660000cubic kilometers , equivalent to 24000000 cubic kilometers of water.Most of the ice is concentrated inantarcticZone - 23820000 cubic kilometers.If the ice turns into water, it is equivalent to the 650 year flow of rivers all over the world, which is enough to raise the water level of the world's oceans by 66.3 meters.
Cubic ice
In 1943, German scientist K ö nig first reported the cubic ice structure through electron diffraction.Later, cubic ice was prepared by various methods in the laboratory, including freezing nano droplets, dissociating gas hydrates, and nano confined crystallization.Water crystallization can also directly form cubic ice, and the key factor affecting the formation of cubic ice may be the ubiquitous heterogeneous interface.[5]
