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D2O, an isotopic species of water in which the light hydrogen atom 1H is replaced by its heavy isotope 2H, which is called deuterium (D).
Heavy water was first discovered in natural water by H. Urey and E. F. Osborn (USA) in 1932; the species was isolated by G. N. Lewis and R. MacDonald (USA) in 1933. The density of heavy water is greater than that of ordinary water, hence the name. Heavy water is found in natural water and in atmospheric precipitation in the ratio of one D atom to 5,000–7,000 H atoms. The techniques of mass spectrometry, densimetry, and infrared spectroscopy are used in determining the content of heavy water.
The physical properties of D2O differ markedly from those of H2O. Heavy water boils at 101.43°C and freezes at 3.82°C; its density is 1.104 g/cm3. The chemical properties of heavy water are very close to those of H2O, although certain reactions occurring in a D2O medium are retarded or accelerated, sometimes by a factor between 2 and 3. The principal industrial methods for producing heavy water are the isotopic exchange of water and hydrogen sulfide, the distillation of hydrogen, and multistep electrolysis.
Heavy water is used in nuclear physics and power engineering as a neutron moderator and heat-transfer agent in nuclear reactors; it also serves as a starting material in the production of deuterium. Heavy water is used in chemistry, biology, and hydrology as an isotope tracer. In organisms, even a small amount of heavy water has an inhibitory effect, while larger doses are lethal.
The term “heavy water” is also used for water containing heavy oxygen, where 16O has been replaced by the heavy isotopes 17O and 18O. It likewise applies to HDO, to tritiated water (T2O), and to HTO and DTO. In superheavy water, ‘H is replaced by the radioisotope 3H, known as tritium (T).
REFERENCESKirshenbaum, I. Tiazhelaia voda. Moscow, 1953. (Translated from English.)
Kirshenbaum, I. Proizvodstvo tiazheloi vody. Moscow, 1961. (Translated from English.)
Kratkaia khimicheskaia entsiklopediia, vol. 1. Moscow, 1961. Pages 614–17.
Brodskii, A. I. Khimiia izotopov, 2nd ed. Moscow, 1957.
V. S. PARBUZIN