100 mmHg Art. at 54°C
Heavy water This term is usually used to refer to heavy hydrogen water, also known as deuterium oxide. Heavy hydrogen water has the same chemical formula as ordinary water, but instead of two atoms of the usual light isotope of hydrogen (protium), it contains two atoms of the heavy hydrogen isotope - deuterium, and its oxygen in isotopic composition corresponds to air oxygen. The formula of heavy hydrogen water is usually written as D 2 O or 2 H 2 O. Outwardly, heavy water looks like ordinary - a colorless liquid without taste or smell. She is not radioactive.
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Discovery history
Molecules of heavy hydrogen water were first discovered in natural water by Harold Urey in 1932, for which the scientist was awarded the Nobel Prize in Chemistry in 1934. And already in 1933, Gilbert Lewis isolated pure, heavy hydrogen water. During the electrolysis of ordinary water, which contains, along with ordinary water molecules, an insignificant amount of heavy (D 2 O) and semi-heavy (HOD) water molecules formed by the heavy isotope of hydrogen, the residue is gradually enriched with molecules of these compounds. From such a residue, after repeated electrolysis, Lewis in 1933 for the first time managed to isolate a small amount of water, consisting almost 100% of the molecules of the oxygen compound with deuterium and called heavy. This method of heavy water production remains the main one today, although it is used mainly at the final stage of enrichment from 5-10% to >99% (see below).
After the discovery of nuclear fission at the end of 1938 and the realization of the possibility of using chain nuclear fission reactions induced by neutrons, a need arose for a neutron moderator - a substance that can effectively slow down neutrons without losing them in capture reactions. Neutrons are most effectively moderated by light nuclei, and ordinary hydrogen (protium) nuclei should have been the most effective moderator, but they have a high neutron capture cross section. On the contrary, heavy hydrogen captures very few neutrons (the thermal neutron capture cross section for protium is more than 100 thousand times higher than for deuterium). Technically, the most convenient compound of deuterium is heavy water, and it can also serve as a coolant, removing the released heat from the area where the fission chain reaction occurs. From the earliest days of nuclear power, heavy water has been an important ingredient in some reactors, both power-generating and those designed to produce plutonium isotopes for nuclear weapons. These so-called heavy water reactors have the advantage of being able to operate on natural (unenriched) uranium without the use of graphite moderators, which during the decommissioning phase can present a dust explosion hazard and contain induced radioactivity (carbon-14 and a number of other radionuclides). However, most modern reactors use enriched uranium with normal "light water" as the moderator, despite the partial loss of moderated neutrons.
Production of heavy water in the USSR
Industrial production and use of heavy water began with the development of nuclear energy. In the USSR, during the organization of Laboratory No. 3 of the Academy of Sciences of the USSR (), the project manager A. I. Alikhanov was tasked with creating a heavy water reactor. This led to the need for heavy water, and the technical council of the Special Committee under the Council of People's Commissars of the USSR developed a draft Decree of the Council of People's Commissars of the USSR "On the construction of semi-industrial installations for the production of product 180", work on the creation of productive installations of heavy water in the shortest possible time was entrusted to the head of the nuclear project B. L Vannikov, People's Commissar of the chemical industry M. G. Pervukhin, State Planning Commission representative N. A. Borisov, People's Commissar for Construction of the USSR S. Z. Ginzburg, People's Commissar of Mechanical Engineering and Instrumentation of the USSR P. I. Parshin and People's Commissar of the Oil Industry of the USSR N. K. Baibakov. M. O. Kornfeld, Head of the Sector of the Laboratory No. 2 of the Academy of Sciences of the USSR, became the chief consultant in matters of heavy water.
Properties
Comparison of properties of ordinary and heavy water
| Parameter | D2O | HDO | H2O |
|---|---|---|---|
| Melting point (°C) | 3,82 | 0,00 | |
| Boiling point (°C) | 101,42 | 100,7 | 100,00 |
| Density (g/cm³, at 20 °C) | 1,1056 | 1,054 | 0,9982 |
| Maximum temperature density (°C) |
11,6 | 4,0 | |
| Viscosity (centipoise, at 20 °C) | 1,25 | 1,1248 | 1,005 |
| Surface Tension (dyne cm, at 25 °C) |
71,87 | 71,93 | 71,98 |
| Molar decrease in volume upon melting (cm³/mol) |
1,567 | 1,634 | |
| Molar heat of fusion (kcal/mol) | 1,515 | 1,436 | |
| Molar heat of vaporization (kcal/mol) | 10,864 | 10,757 | 10,515 |
| (at 25°C) | 7,41 | 7,266 | 7,00 |
Being in nature
In natural waters, one deuterium atom accounts for 6400 ... 7600 protium atoms. Almost all of it is in the composition of DHO molecules, one such molecule falls on 3200 ... 3800 molecules of light water. Only a very small part of deuterium atoms form heavy water molecules D 2 O, since the probability of two deuterium atoms to meet in one molecule in nature is small (about 0.5⋅10 −7). With an artificial increase in the concentration of deuterium in water, this probability increases.
Biological role and physiological impact
Heavy water is only slightly toxic, chemical reactions in its environment are somewhat slower compared to ordinary water, hydrogen bonds involving deuterium are somewhat stronger than usual. Experiments on mammals (mice, rats, dogs) showed that the replacement of 25% of hydrogen in tissues with deuterium leads to sterility, sometimes irreversible. Higher concentrations lead to rapid death of the animal; thus, mammals who drank heavy water for a week died when half the water in their body was deuterated; fish and invertebrates die only with 90% deuteration of water in the body. The simplest are able to adapt to a 70% solution of heavy water, and algae and bacteria are able to live even in pure heavy water. A person can drink several glasses of heavy water without visible harm to health, all deuterium will be removed from the body in a few days.
Thus, heavy water is much less toxic than, for example, table salt. Heavy water has been used to treat arterial hypertension in humans at daily doses ranging from 10 to 675 g D 2 O per day.
The human body contains as a natural impurity as much deuterium as 5 grams of heavy water; this deuterium is mainly included in the HDO semi-heavy water molecules, as well as in all other biological compounds that contain hydrogen.
Some information
Heavy water accumulates in the remainder of the electrolyte during repeated electrolysis of water. In the open air, heavy water quickly absorbs the vapors of ordinary water, so we can say that it is hygroscopic. The production of heavy water is very energy intensive, so its cost is quite high. In 1935, immediately after the discovery of heavy water, its price was approximately $19 per gram). Currently, heavy water with a deuterium content of 99 at.%, sold by chemical reagent suppliers, costs about 1 euro per gram for 1 kg, but this price refers to a product with a controlled and guaranteed quality of the chemical reagent; with lower quality requirements, the price can be an order of magnitude lower.
Application
The most important property of heavy hydrogen water is that it practically does not absorb neutrons, therefore it is used in nuclear reactors to moderate neutrons and as a coolant. It is also used as an isotope indicator in chemistry, biology and hydrology, physiology, agrochemistry, etc. (including experiments with living organisms and human diagnostic studies). In particle physics, heavy water is used to detect neutrinos; Thus, the largest solar neutrino detector SNO (Canada) contains 1000 tons of heavy water.
Deuterium is a nuclear fuel for the energy of the future, based on controlled thermonuclear fusion. In the first power reactors of this type, it is supposed to carry out the reaction D + T → 4 He + n + 17.6 MeV .
In some countries (for example, in Australia), the commercial circulation of heavy water is placed under state restrictions, which is associated with the theoretical possibility of using it to create "unauthorized" natural uranium reactors suitable for producing weapons-grade plutonium.
Other types of heavy water
semi-heavy water
There is also semi-heavy water (also known as deuterium water, monodeuterium water, deuterium hydroxide), in which only one hydrogen atom is replaced by deuterium. The formula for such water is written as follows: DHO or ²HHO. It should be noted that water having the formal composition DHO, due to isotopic exchange reactions, will actually consist of a mixture of DHO, D 2 O and H 2 O molecules (in a ratio of approximately 2:1:1). This remark is also true for THO and TDO.
Super heavy water
Superheavy water contains tritium, which has a half-life of over 12 years. According to its properties, superheavy water ( T2O) differs even more noticeably from the usual one: it boils at 104 °C, freezes at +9 °C and has a density of 1.21 g/cm³. All nine variants of superheavy water are known (that is, obtained in the form of more or less pure macroscopic samples): THO, TDO and T 2 O with each of the three stable oxygen isotopes (16 O, 17 O and 18 O). Sometimes superheavy water is simply referred to as heavy water, unless that can cause confusion. Superheavy water has a high radiotoxicity.
Heavy oxygen isotope modifications of water
Term heavy water are also used in relation to heavy oxygen water, in which the usual light oxygen 16 O is replaced by one of the heavy stable isotopes 17 O or 18 O. Heavy isotopes of oxygen exist in a natural mixture, therefore, in natural water there is always an admixture of both heavy oxygen modifications. Their physical properties also differ somewhat from those of ordinary water; so, the freezing point of 1 H 2 18 O is +0.28 ° C.
Heavy oxygen water, in particular, 1 H 2 18 O, is used in the diagnosis of oncological diseases (the fluorine-18 isotope is obtained from it at the cyclotron, which is used to synthesize drugs for the diagnosis of oncological diseases, in particular 18-fdg).
Total number of isotope modifications of water
If we count all possible non-radioactive compounds with the general formula H 2 O, then the total number of possible isotope modifications of water is only nine (since there are two stable isotopes of hydrogen and three of oxygen).
Many people wonder what exactly is lighter in the environment: water or ice? After all, ice is frozen water, and if you look from a different point of view, then liquid is melted masses of ice. Everything in our world can be turned upside down and presented in such a way that any process goes both ways. But, continuing the conversation about gravity and, consequently, density, it should be noted that in many respects it owes its small weight to ordinary air.
Ice Secrets
There is no need to guess: the reason lies in the small cavities that occur when water freezes. These cavities are filled with ordinary air and this gives the ice less weight. A very useful phenomenon, but not only for this reason, the ice layers are lighter. Not so long ago we talked about the fact that the highest density of water under normal conditions is achieved at a temperature of 4 degrees Celsius. This means that the zero temperature of the water gives a lower density, that is, a larger volume. It is for this reason (because ice cannot form at temperatures greater than 0) that pieces of ice float.
Everything interesting is simple
How can you tell more about this interesting phenomenon? So, imagine a process that takes place in water. This process is called convection: the exchange of energy through filaments. There are currents and trickles even in stagnant water, you can’t get away from them, and even modern scientists have not yet been able to figure out what exactly lies behind the nature of water movement. Therefore, the exchange of energies proceeds constantly. If there is an exchange of energy, then the temperature also changes. Adding to this the change in density, we get that the water, which has a higher density, sinks to the bottom. But she cannot freeze, because she is too warm for that.
Thus, a less dense one, that is, one that has already passed the point of +4 degrees and is approaching zero, moves forward to the vacant seat. This water has every chance to freeze. So, the main characteristics showing and proving that water is denser and heavier, and ice is lighter. First of all, this is the presence of air bubbles or some kind of gas (after all, both air and a single gas can freeze). Secondly, low density and, as a result, a larger volume. Together, this gives only a slightly lower density.
And if masses of ice are lighter than the same volume of water, then not by much. Imagine a difference of only ten percent. A piece of ice can have a huge number of cavities, but their total volume will be very small. One can imagine that if an iceberg floats on water, then 90% of the total mass of the iceberg is hidden under the water's edge. Incredible volumes and weights, which sometimes seem simply fantastic. And yet these objects float.
When there is salt in the water
All this applies to fresh water. What to say about salty? She is . Usually indicate something from -3.2 to -3.5 degrees. It turns out that in this case, when it becomes larger due to salt, and when freezing, the ice masses partially reject salt almost at the molecular level, then the difference in densities becomes much more significant. And it is no longer ten percent, but reaches almost twenty. That is, if you take the same iceberg, then 20% of its mass will be above the water, and 80% will be under water.
Since so much depends on the composition of the water, it is not always possible to quickly and objectively say how much lighter the volume of ice is. But even without a thorough study, we can safely say that moisture is always heavier, otherwise underwater icebergs would often come across in the Arctic today.
A liter is a unit of volume for liquid substances. It is also permissible to measure bulk solids with a sufficiently fine fraction in liters. For other solids, the concept of a cubic meter (decimeter, centimeter) is used. The definition of the term and concept of a liter was formulated by the General Conference on Weights and Measures in 1901. The definition is as follows: 1 liter is the volume of one kilogram of pure fresh water at an atmospheric pressure of 760 mm Hg and a temperature of +3.98 ° C. At this temperature, water reaches its highest density.
Steam, water and ice are states of the same substance, the molecule of which contains two hydrogen atoms and one oxygen atom. The difference between liquid water and solid water lies in the features of intermolecular constructions. Water has a higher density in a liquid than in a solid.
Having crossed the temperature threshold of +3.98°C, the density of water begins to decrease again, and at +8°C it again reaches the same values as at zero.
What's harder?
If, for example, water is poured into a vessel, it will have a volume equal to one liter. If you freeze this water, then with the same mass of 1 kg, the water, freezing, will tend to take up more space in the vessel. A closed vessel, limited to a capacity of 1 sq. dm (1 liter), the ice will break. It turns out that with the same mass of liquid and frozen water, the ice will have a larger volume, which will violate the original condition.
If we initially proceed from the equality of volumes, and limit frozen water - a piece of ice - to the size of a cube with a side equal to 1 dm (1 l), then its mass will become less than the original kilogram. How could it be otherwise if you cut and remove some of the ice, fitting the cube to a given volume. Therefore, water in the volume of a liter is heavier than ice in the same volume.
If you freeze a liter with 1,000 ml of water (1 liter), then approximately 80 ml of water will pour out of it during the hardening process. And to get 1 liter of ice, it is enough to freeze 920 ml of water.
Freeze and Restore
Today it is more and more difficult to find pure natural water. Especially in the conditions of the city, where, before entering the apartment, it is filtered, chlorinated, and subjected to other types of physical and chemical treatment. Clean water is becoming scarce, the cost of water produced from artesian wells is rising. However, water, it turns out, restores its original structure and energy after freezing - it is purified. Therefore: drink melt water! No wonder all plants react so well to it in spring and animals drink with pleasure.
The amazing ability of ice to float and float on the surface of the water is explained by nothing more than elementary physical properties, which are studied in the course of middle and high school. It is known for certain that substances tend to expand when heated, such as mercury in a thermometer, and water also freezes and increases in volume when the temperature drops, forming a crust of ice on the surface of reservoirs.
The increase in the volume of frozen water often plays a cruel joke on those who forget containers of liquid in the cold. Water literally breaks the container.
The opinion that microscopic pores filled with air appear in the newly formed ice layer is not erroneous, but it cannot properly explain the fact of ascent. In accordance with the principles derived and formulated by the ancient Greek scientist, later called the law of Archimedes, bodies that are immersed in a liquid are pushed out of it with a force that is equal to the weight characteristics of the liquid displaced by this body.
water physics
It is known for certain that ice is about one-tenth lighter than water, which is why giant icebergs are submerged in the ocean by about nine-tenths of their total volume and are only visible to a small fraction. These weights are explained by the properties of the crystal lattice, which, as is known, does not have an ordered structure in water and is characterized by constant movement and collision of molecules. This explains the higher density of water compared to ice, whose molecules under the influence of low temperatures show low mobility and a small energy component and, accordingly, a lower density.
It is also known that water has the maximum density and weight at a temperature equal to 4 ° C, a further decrease leads to expansion and a decrease in the density index, which explains the properties of ice. That is why in reservoirs, heavy four-degree water sinks to the bottom, allowing cooler water to rise and turn into non-sinking ice.
Ice has specific properties, for example, it is resistant to foreign elements, has low reactivity, is distinguished by the mobility of hydrogen atoms, and therefore has a low yield strength.
It is clear that this property is fundamental for the preservation of life on Earth, because if ice had the ability to sink under the water column, over time, after a decrease in temperature, all the water bodies of the Earth could be filled with layers constantly formed on the surface of the ice, which would lead to a natural disaster and the complete disappearance of the flora and fauna of water bodies from the equator itself to the opposite poles.
and how it differs from easy.
Many have heard about the existence of some kind of “heavy water”, but few people know why it is called heavy, and where this fabulous substance is located in general. The purpose of this material is to clarify the situation, and same way explain that nothing dangerous and fabulous in heavy water No , and that it is present in small amounts in almost all ordinary waters, including those that we drink every day.
"Heavy water" is really heavy in relation to ordinary water. Not much, about one-tenth by weight, but enough to change the properties of this water. And its “gravity” lies in the fact that instead of “light hydrogen”, or protium, 1H, the molecules of this water contain a heavy isotope hydrogen 2H, or deuterium (D), in the nucleus of which, in addition to the proton, there is also one more neutron. From the point of view of chemistry, the formula of heavy water is the same as that of simple, H2O, but physicists have made adjustments, and therefore it is customary to write the formula as - D2O or 2H2O. There is another version of heavy, or it is also called "superheavy" water - T2O is tritium oxide, an isotope of hydrogen withtwo neutrons in the nucleus (and there are three nucleons in total, hence "tritium"). But three t ii is radioactive, and the military use it as raw material for hydrogen bombs(and correspondingly, secret everything related to it - just in case), so we will not talk about superheavy water in this material.
Why is heavy water so valuable that it is not only isolated from simple water (and this, believe me, is a whole thing), but also worn like with a written sack?
And the whole point is in the additional neutrons that have joined the nuclei of protium. If a consider not a water molecule as a whole, but hydrogen atoms separately , it turns out that they have become twice as heavy! Not one tenth, but two! I.e, " fatter" they became, tsmarter. And since they are fatter, like all obese people, they do not want to move much. They are "lazy", not very active compared to protium, and exactly this they explain all the differences in properties between light and heavy water.
Let's start with a list of these properties.
Heavy water has no smell or color;by this parameterlight and heavy water not distinguish.
Its melting point is higher, heavy water ice begins to form already at a temperature of 3.813 ° C
boils it is at a higher temperature - 101.43°C
The viscosity of heavy water is 20% higher than the viscosity of ordinary
Density - 1, 1042 g/cm3 at 25°C, which is also not much, but higher than the density of ordinary water.
That is, they can be distinguished even at a primitive, everyday level. But heavy water also has properties that are difficult to define "at home in the kitchen." For example:
Heavy water, unlike light water, absorbs neutrons very poorly. And therefore it is an ideal moderator for nuclear reactions on slow, "thermal" neutrons.
There are other specific properties of it, but they go beyond the scope of philistine perception and are of interest mainly to narrow specialists., so we won't talk about them either.
Well, where is it located, this "heavy water"? Where is this magical source of valuable content? Valuable, because a kilogram of heavy water costs more than a thousand euros.
But there is none, a magical source! It is located… Everywhere.
On average, the ratio of heavy and ordinary water molecules in nature is 1:5500. However, this value is "hospital average"; in sea water, the content of heavy isotopes is higher, in river and rain water it is noticeably lower. (1:3000-3500 vs 1:7000-7500). There is also a strong variation in concentrations depending on the region and locality. There are also separate sources (separate regions) where the concentration of heavy water goes off scale and is comparable to the concentration of ordinary protium , but these are exceptional cases.
On the one hand, the abundance of heavy water is a blessing. It can be found literally everywhere, in any glass. On the other hand, the low concentration does not contribute isolating it in its pure form, separately from protium . Hence the high cost of obtaining it.
Interesting but true: scientists who discovered heavy water treated it as a scientific incident, something insignificant, side and entertaining. Hdid not see great opportunities in its application(in other words, let's be objective, such a situation, with scientific discoveries at every step). And only some time later, by completely different researchers, its scientific and industrial potential was discovered.
"Heavy water" is used:
In nuclear technologies;
In nuclear reactors, for slowing down neutrons and as a coolant;
As an isotope tracer in chemistry, physics, biology and hydrology;
As a detector of some elementary particles;
It is quite likely that inforeseeable futureheavy water will endless source of energy scientists are seriously considering how to use deuterium and as a fuel forcontrolled thermonuclear fusion.But this is still from the realm of fantasy, although success is given field are undeniable.
Chemists are interested in heavy water becausethe deuterium obtained from it is easily determined by simple laboratory methods. And if you synthesize the given substances with its help, completely replacing protium with deuterium, and combine them with other, “normal” substances, you can track which hydrogen atomduring the reactionentered the composition of that molecule, and which - another. That is, with the help of deuterium, chemists “mark” molecules and see how the mechanism of a particular reaction proceeds. And believe me, this method is worth calling it revolutionary - at one time it turned the knowledge of many theorists who knew “how it should be”, forcing them to revise the laws of nature again and again, finding new and new causalinvestigative links, build new hypotheses and theories, which, of course, greatly advanced chemistry as a science.
It is more interesting for a simple layman far from theoretical chemistry, but how does heavy water affect a person, and in general, biological systems, as such? And this is a very correct interest. For heavy water for living organisms is a POISON!
Heavy water, unlike mild, depresses vitality processes at all levels. Biologists call it “dead water” . In her presencechemical reactions are slowed downbiological processes… TO at least slow down. Including, for example, the reproduction of microbes and bacteria slows down and stops.
Experiments on mammals have shown that the replacement of 25% of hydrogen in tissues with deuterium leads to sterility, higher concentrations lead to rapid death of the animal. H some microorganisms are able to live in 70% heavy water) (protozoa) and even in pure heavy water (bacteria), but these are exceptions. A person can drink a glass of heavy water without visible harm to health, all deuterium will be removed from the body in a few days, but with constant prolonged exposure, water replacement in the tissues begins, after which negative consequences appear.
As an experiment, scientists tried to drink heavy water mice with malignant tumors. Well, remember the tale of vividly th and dead water, where the dead heals wounds? And they succeeded - the water turned out to be truly dead, the tumors destroyed! True, along with mice. Also, heavy waterut negatively on plants. Experimental dogs, rats and mice were given water, a third of which was replaced with heavy water., h after a short timethey havestarted metabolic disorder, kidney failure. With an increase in the proportion of heavy water, the animals died.
But there is also the other side of the coin: vice versa, decrease the deuterium content 25% below the norm in the water that was given to animals had a beneficial effect on their development: pigs, rats and mice gave birth to offspring many times more numerous and larger than usual, and egg production chickens have doubled.That is, in addition to "dead water", scientists discovered "living" water, and the children's fairy tale became a reality.
How to avoid contact with "dead" water and increase the use of "live"? Probably not. Both that and that will turn out on an industrial scale and cost crazy money. However, in everyday life, although we are not strong, we can influence the quality of the water we use. For example, rainwater contains noticeably more heavy water than snow. So in the "mystical »experiments with melt water and its effect on the body is not so much mystical. There is also a higher content of heavy water insea, and in the process of desalination by reverse osmosis, it only accumulates, which should be taken into account when designing desalination plants. Cases when the whole regions became victims of ignorance of this fact are known. People living in these regions regularly used desalinated sea water with a high content of deuterium, as a result of which many residents fell ill with serious illnesses.
However there is nothing superfluous in nature,And don't be too hard on heavy water., branding her with poison or calling her "useless". She is requires from us a special adequate attitude, attention andfurther study, and that doesn't make much of a difference. from the great multitudesubstances that require more attention. Chemistry is a science, so you need to approach the issue with the whole arsenal of its capabilities.
M. ADZHIEV
Heavy water is very expensive and scarce. However, if it is possible to find a cheap and practical way to obtain it, then the scope of this rare resource will expand noticeably. New pages may be opened in chemistry, biology, and these are new materials, unknown compounds, and perhaps unexpected forms of life.
Rice. one.
Water molecules are firmly bound to each other and form a stable molecular structure that resists any external influences, in particular thermal ones. (This is why it takes a lot of heat to turn water into steam.) The molecular structure of water is held together by a framework of special quantum-mechanical bonds, named in 1920 by two American chemists Latimer and Rodebush as hydrogen bonds. All the anomalous properties of water, including unusual freezing behavior, are explained in terms of the concept of hydrogen bonds.
Water in nature comes in several varieties. Plain, or protium (H 2 O). Heavy, or deuterium (D 2 O). Superheavy, or tritium (T 2 O), but it is almost absent in nature. Water also differs in the isotopic composition of oxygen. In total, there are at least 18 of its isotopic varieties.
If we open the water tap and fill the kettle, then there will be not homogeneous water, but its mixture. At the same time, there will be very few deuterium "inclusions" - about 150 grams per ton. It turns out that heavy water is everywhere - in every drop! The problem is how to take it. Nowadays, all over the world, its extraction is associated with huge energy costs and very complex equipment.
However, there is an assumption that such natural situations are possible on planet Earth when heavy and ordinary water separate from one another for some time - D 2 O from a dispersed, “dissolved” state passes into a concentrated one. So, maybe there are deposits of heavy water? So far, there is no unequivocal answer: none of the researchers has dealt with this issue before.
And at the same time, it is known that the physicochemical properties of D 2 O are completely different from those of H 2 0, its constant companion. Thus, the boiling point of heavy water is +101.4°C, and it freezes at +3.81°C. Its density is 10 percent greater than that of ordinary.
It should also be noted that the origin of heavy water, apparently, is purely terrestrial - no traces of it have been found in space. Deuterium is formed from protium due to the capture of a neutron from cosmic radiation. The oceans, glaciers, atmospheric moisture - these are the natural "factories" of heavy water.
Rice. 2. The dependence of the density of ordinary and heavy water on temperature. The difference in the density of one and the other varieties of water exceeds 10%, and therefore conditions are possible when the transition to a solid state upon cooling occurs first in heavy water, and then in ordinary water. In any case, physics does not prohibit the appearance of areas of the solid phase with a high content of deuterium. This "heavy" ice in the diagram corresponds to the shaded area. If water were a "normal" rather than an anomalous liquid, then the dependence of density on temperature would have the form shown by the dotted line.
So, since there is a noticeable difference in density between D 2 O and H 2 O, then it is the density, as well as the state of aggregation, that can serve as the most sensitive criteria in the search for possible heavy water deposits - after all, these criteria are associated with ambient temperature. And as you know, the environment is most "contrast" in the high latitudes of the planet.
But by now the opinion has been formed that the waters of high latitudes are poor in deuterium. The reason for this was the results of studies of water and ice samples from the Great Bear Lake in Canada and from other northern reservoirs. There were also fluctuations in the content of deuterium according to the seasons of the year - in winter, for example, in the Columbia River it is less than in summer. These deviations from the norm were associated with the peculiarities of the distribution of precipitation, which, as is commonly assumed, “carry” deuterium around the planet.
It seems that none of the researchers immediately noticed the hidden contradiction in this statement. Yes, precipitation affects the distribution of deuterium in the water bodies of the planet, but they do not affect the global process of deuterium formation!
When autumn comes in the North, a rapid cooling of the water mass begins in the rivers, which accelerates under the influence of permafrost, at the same time there is an association of H 2 O molecules. Finally, the critical moment of maximum density comes - the water temperature is everywhere a little below + 4 ° С. And then in the near-bottom zone in some areas loose underwater ice is intensively frozen.
Unlike ordinary ice, it does not have a regular crystal lattice, it has a different structure. The centers of its crystallization are different: stones, snags and various irregularities, and not necessarily lying on the bottom and associated with frozen ground. Loose ice appears on deep rivers, with a calm - laminar - flow.
Underwater ice formation usually ends with ice floes floating to the surface, although there is no other ice at this time. Underwater ice sometimes appears in summer. The question arises: what is this “water in water” that changes its state of aggregation when the established temperature in the river is too high for ordinary H 2 O to turn into ice, so that, as physicists say, a phase transition occurs?
It can be assumed that loose ice represents enriched concentrations of heavy water. By the way, if this is the case, then you need to remember that heavy water is indistinguishable from ordinary water, but its consumption inside the body can cause severe poisoning. By the way, local residents of high latitudes do not use river ice for cooking - only lake ice or snow.
The "mechanism" of the D 2 O phase transition in a river is very similar to that used by chemists in the so-called crystallization columns. Only in the northern river, the "column" stretches for hundreds of kilometers and is not so contrasting in temperature.
If we keep in mind that hundreds and thousands of cubic meters of water pass through the crystallization centers in a river in a short time, from which it turns into ice - it freezes - even a thousandth of a percent, then this is enough to talk about the ability of heavy water to concentrate, then is to form deposits.
Only the presence of such concentrations can explain the proven fact that in winter the percentage of deuterium in northern water bodies decreases markedly. Yes, and polar waters, as samples show, are also poor in deuterium, and in the Arctic, it is likely that there are areas where only ice floes enriched with deuterium float, because loose bottom ice appears first and melts last.
Moreover, studies have shown that glaciers and ice at high latitudes are generally richer in heavy isotopes than the waters surrounding the ice. For example, in South Greenland, in the vicinity of the Dai-3 station, isotope anomalies have been identified on the surface of glaciers, and the origin of such anomalies has not yet been explained. This means that ice floes enriched with deuterium can also be encountered. The point, as they say, is small - you need to find these still hypothetical deposits of heavy water.
M. ADZHIEV, geographer.
Information sources:
- L. Kulsky, V. Dahl, L. Lenchina. The water is familiar and mysterious.
- K .: "Radyansk school", 1982. - Science and Life No. 10, 1988.
