|Molecular formula||D 2 O ( 2 H 2 O)|
|External identifiers / databases|
|Molar mass||20.0286 g mol −1|
1.107 g cm −3
3.8 ° C
101.4 ° C
1.328 (20 ° C)
|As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C|
From a chemical point of view, heavy water ( deuterium oxide ) is water with the empirical formula D 2 O. It differs from “normal” water H 2 O, which is also referred to as “light water” in this context, in that the “normal” hydrogen atoms des Isotope protium (symbol H) have been replaced by heavy hydrogen atoms of the isotope deuterium (symbol D). Protium has only one proton in the atomic nucleus , while deuterium has one proton and one neutron . Accordingly, the molecular weight and density of heavy water are higher than those of ordinary water.
Semi-heavy water (hydrodeuterium oxide) with the empirical formula HDO, on the other hand, contains one normal and one heavy hydrogen atom. Statistically speaking, it occurs much more frequently in nature than heavy water. On earth there is about one deuterium atom for every 7000 hydrogen atoms (in snow or rainwater 1: 9000, in seawater with a high salt content 1: 5500).
Heavy water is obtained through enrichment from conventional water, in which it occurs in small quantities. If water is electrolyzed , the heavy water tends to remain undecomposed ( kinetic isotope effect ), while light water is split into hydrogen and oxygen . The Girdler sulfide process is also an enrichment .
Another process involves the distillation of ammonia or hydrogen sulfide . The starting material is preferably waste water from electroplating plants and the production of hydrogen by electrolysis, as this is already significantly enriched with HDO due to the preferred electrolysis of light water.
Heavy water is less reactive than normal water and has a lower solubility. The cause is the higher nuclear mass of the deuterium. As a result, the molecular vibrations have a lower frequency and the zero point energies of these vibrations are lower than in light water. With a stretching vibration , the effect is about 125 m eV or 5 k B T at room temperature. As a result, the dissociation of heavy water, which is a prerequisite for many biochemical reactions, requires more energy and can be greatly slowed. In addition to dissociation, the formation of hydrogen bonds , which are also of essential importance in biochemical systems, is influenced. Due to the “dynamic isotope effect ”, the translational and rotational mobility of the heavy water molecules in the liquid is somewhat lower than that of the light water molecules. At 25 ° C z. B. the self-diffusion coefficient of heavy water by 23% lower than that of light water.
Due to these different properties, heavy water is slightly toxic to most organisms. Experiments with mice showed that cell division ( mitosis ) is suppressed. As a result, tissue that needs to be replaced quickly (e.g. stomach wall) is affected by continued ingestion of heavy water. These effects became apparent when mice were replaced with heavy water for about 50 percent of their body water. Aggressive cancers should also be slowed down; however, the benefits of heavy water therapy would likely not outweigh the side effects.
(H 2 O)
(D 2 O)
(T 2 O)
|H 2 17 O||H 2 18 O|
|Molar mass (g / mol)||18.0153||19.017||20.0286||22.031||19.015||20.015|
|Melting point temperature||0.00 ° C||2.04 ° C||3.82 ° C||4.49 ° C||0.28 ° C|
|Boiling point (at normal pressure )||99.97 ° C||100.74 ° C||101.40 ° C||101.51 ° C||100.08 ° C||100.15 ° C|
|Maximum density at||3.98 ° C||2.04 ° C||11.24 ° C||13.40 ° C||4.30 ° C|
|Maximum density (g / cm³)||0.999975||1.1053||1.21501||1.111249|
|pK w value at 25 ° C||13,995||14,869||15.216|
|Neutral point||pH 7.00||pH 7.43||pH 7.61|
The higher density of ice from heavy water causes a heavy water ice cube to sink in normal water (liquid). In water (H 2 O) of e.g. B. 2 ° C a D 2 O ice cube does not melt , but can be dissolved by diffusion in the liquid phase.
Heavy water is used in heavy water reactors (for example reactors of the Candu type ) as a moderator and coolant , since it absorbs considerably fewer neutrons than normal water with a similar moderating effect. This means that natural uranium can be used in the reactor and the otherwise necessary enrichment can be dispensed with.
The deuteron is active in NMR , but does not appear in the H-NMR spectra because of the roughly different frequency. The addition of a little heavy water therefore causes lines in the spectrum of a sample that originate from hydrogen atoms that are exchanged with the solvent many times within the relaxation time to disappear.
Correspondingly, because of the different vibration frequencies, heavy water can advantageously be used in vibration spectroscopy of hydrogen-containing substances in aqueous solution.
Furthermore, heavy water is used for the targeted chemical synthesis of compounds, either to introduce deuterium into the product or to weaken a competitive reaction in which H or D is transferred.
Since lower organisms can also survive in pure heavy water, it is possible to isolate highly complex natural substances from such organisms in which all hydrogen atoms are replaced by deuterium.
Battle for heavy water in World War II
During the war years from 1942 to 1945, Rjukan in southern Norway in the Telemark province was the scene of an explosive conflict. Since 1934, the chemical and hydropower plant in Vemork has been the only European factory ( Norsk Hydro ) that could produce heavy water in significant quantities thanks to its immense energy surplus. With a clever move, the French got ahead of the Germans and initially secured the entire inventory of over 160 kg, which was brought to the United States by the French nuclear physicist Hans von Halban via Great Britain after the invasion of France by the French nuclear physicist Hans von Halban .
At the end of the 1930s, Otto Hahn , Fritz Straßmann and Lise Meitner discovered the principle of the nuclear chain reaction , from which a race with the Allies for control of the factory developed after the outbreak of World War II . For the German uranium project , the use of heavy water was intended as a moderator of a test reactor with which, among other things, weapons- grade plutonium could have been produced.
Thus, the Allies' attention turned to the facility in Rjukan, the elimination of which German nuclear research was able to neutralize in one fell swoop: After several setbacks, twelve Norwegian resistance fighters (supported by the Special Operations Executive ), who had kept hidden on the plateau of Hardangervidda , carried out the demolition at the high concentration plant for heavy water of the Norsk Hydro Werke . Just a few weeks later, however, the damage was repaired, and the German occupiers let production start up again. The Norwegian-French co-production Battle for Heavy Water ( Kampen om tungtvannet , 1948), the British feature film “Schweres Wasser” ( The Heroes of Telemark , 1965) and the Norwegian-Danish-British television miniseries Saboteurs im Eis - Operation Schweres Wasser ( Kampen om tungtvannet , 2015) deal with these events.
Several Allied bombing raids on the power plant and the rebuilt facility followed, until the German occupiers decided to give up the factory and take 50 barrels of heavy water that had already been produced. The concentration of the deuterium oxide fluctuated between 1% and 99%; it was identified by a two-digit number on the barrels, which did not allow outsiders to draw any conclusions about the concentration.
The Rjukanbanen railway ferry called Hydro , loaded with heavy water, was sabotaged on February 20, 1944 by an explosive device in the engine room. The ferry sank within a few minutes on the 460 meter deep Tinnsjø ( Norwegian for 'lake near Tinn '). Barrels with a highly concentrated content, which were only partially filled, floated on the water surface after sinking. They were recovered by the Germans and sent to Germany three weeks after the sinking and later used in the Haigerloch research reactor . When the ferry went down, four German soldiers and 14 civilians were killed.
The underwater archaeologist Brett Phaneuf was awarded with a Norwegian-American research team 60 years after the sinking of the hydraulic permission to a diving trip to the hydro, but with the requirement to raise just exactly a barrel since the wreck officially considered a war grave is true.
The very well-preserved barrel no.26 could be opened effortlessly after it had been recovered, as the rubber sealing ring of the bunghole was still intact after more than 60 years. During investigations on board and later in London an enrichment level of 1.1 percent ± 0.2 was determined. According to the secret loading list from 1944, this barrel contained a distillate of 1.64% heavy water.
From 1945 the Girdler sulphide process was used on an industrial scale in the United States , and the first heavy water reactors went into operation in 1953. The enrichment systems were initially operated by DuPont and taken over by Westinghouse Electric in 1989 .
One of the world's largest producers of heavy water is currently India . Technical development began as early as the 1960s as part of the Indian nuclear program . The country operates seven production plants. 22 of the total of 27 nuclear reactors, some of which are still under construction, are operated with heavy water as moderator.
In Iran, a plant for the extraction of heavy water had been under construction in Khonbad near Arak since 1996 . The capacity was designed for 8 tons per year. The production facility was completed in 2003, and a second expansion stage was announced at the same time, so that production would double to 16 tons per year. The heavy water is required to operate the 40 MW natural uranium reactor IR-40 .
Until 2015 Romania was the largest producer in Europe. Heavy water is also produced in Argentina, Norway, Canada, Pakistan, and Russia.
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