Heavy water contains heavy hydrogen, or deuterium, instead
of normal hydrogen. Deuterium is the
stable, nonradioactive isotope of hydrogen with atomic weight 2.01363 and
symbol D, or 2H. It is commonly called heavy hydrogen because its atomic weight
is approximately double that of ordinary hydrogen, but it has identical
chemical properties. Deuterium has about twice the atomic weight of normal
hydrogen because its nucleus contains a proton and a neutron, instead of just a
proton. Hydrogen as it occurs in nature contains approximately 0.02 percent of
deuterium. The boiling point of deuterium is -249.49° C (-417.08° F), or 3.28°
C (5.90° F) higher than that of ordinary hydrogen. Heavy water (deuterium
oxide, D2O) boils at 101.42° C (214.56° F) as compared to 100° C (212° F), the
boiling point of ordinary water. It freezes at 3.81° C (38.86° F) as compared
to 0° C (32° F) for ordinary water. Its density at room temperature is 10.79
percent greater than that of ordinary water.
Deuterium, which was discovered by the American chemist
Harold Urey and his associates in 1932, was the first isotope to be separated
in a pure form from an element. Several methods have been used to separate the
isotope from natural hydrogen. The two processes that have been most successful
have been fractional distillation of water and a catalytic exchange process
between hydrogen and water. In the latter system, when water and hydrogen are
brought together in the presence of a suitable catalyst, about three times as
much deuterium appears in the water as in hydrogen. Deuterium has also been
concentrated by electrolysis, centrifuging, and fractional distillation of
liquid hydrogen.
The nuclei of deuterium atoms, called deuterons, are much
used in research in physics because they can be readily accelerated by
cyclotrons and similar machines and used as “atomic bullets” to transform an
atom of one element into another element. Deuterium also has important uses in
biological research as a tracer element for studying problems of metabolism.
Regular hydrogen and deuterium are not normally metallic,
meaning they are not shiny or malleable. Scientists have used pressure and
heat, however, to force deuterium to act like a metal, making it shinier and
easier to compress. In 1998, scientists announced that they had used lasers to
shock a sample of deuterium, compressing it and heating it enough that it
behaved like a metal. Studying deuterium in these conditions can help
scientists understand how hydrogen behaves in the hot, heavily pressurized
interiors of planets such as Jupiter and Saturn and in the interiors of stars
such as our Sun.
The use of heavy water as a moderator in atomic piles was
suggested during World War II but in the first U.S. piles, graphite was
employed instead. Deuterium, either in deuterium oxide or in lithium deuteride
(LiD), and tritium are essential components of nuclear fusion weapons, or hydrogen
bombs. (Encarta Encyclopedia)
