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Hydrogen has three isotopes ( [link] ) and unlike other elements these are given special names to differentiate then from the most abundant isotope. Tritium is radioactive with a half life of about 10 years.

Summary of isotopes of hydrogen.
Isotope Hydrogen-1 Hydrogen-2 Hydrogen-3
Special name Hydrogen Deuterium Tritium
Symbol H D T
Atomic number 1 1 1
Number of neutrons 0 1 2
Mass number 1 2 3
Natural abundance 99.9844% 0.0156% very small

Synthesis of deuterium compounds

Electrolysis of water

The electrolysis of hydrogen-1 water (H 2 O) in the presence of an alkali results in the formation of hydrogen and oxygen.

In a similar manner the hydrolysis of deuterated water (D 2 O) yields deuterium and oxygen.

However, the rate of electrolysis of D 2 O is slightly slower than that of H 2 O. Thus, the partial hydrolysis of water with a mixture of natural isotopes results in the slight enrichment of the water with D 2 O. The level of enrichment in one step is less than 1%. In order to obtain high levels of D 2 O (e.g., ca. 30%) it is necessary to reduce the original volume of water by 1/100,000 th .

Chemical equilibrium

Proton exchange reactions can be used to enrich compounds in deuterium. For example, the reaction of HSD with water shown in [link] has a slight preference for the formation of H 2 S, i.e., K eq = 1.012. Thus, bubbling HSD through water results in the enrichment of the water in HOD. However, about 30% enrichment is about the best that can be achieved by this method.

Fractional distillation

The boiling point of H 2 O is (by definition) 100 °C, in contrast the boiling point of D 2 O is 101.4 °C. Thus, it is possible to separate H 2 O from D 2 O by fractional distillation. This method provides the most suitable route to high isotopic enrichment and D 2 O of 99.8% can be produced this way.

The term heavy water is used for D 2 O of greater than 99.8% enrichment.

Uses of deuterium compounds

Possible nuclear fusion

The largest use of D 2 O is as a moderator and heat exchanger for fission nuclear reactors, however, the biggest potential application will be if nuclear fusion is realized as a commercial process.

The fusion of two deuterium atoms to form a helium atom and energy would be one source of energy, [link] , however, deuterium-tritium fusion is the most promising, [link] .

The deuterium part of the fuel does not pose a great problem because about 1 part in 5000 of the hydrogen in seawater is deuterium. This amounts to an estimate that there is over 10 15 tons of deuterium in the oceans. The tritium part of the fuel is more problematic since there is no significant natural source ( [link] ), and the tritium would have to be obtained by breeding the tritium from lithium.

Since a gallon of seawater could produce as much energy as 300 gallons of gasoline, there is clearly a large amount of energy that can potentially be realized through nuclear fusion. Unfortunately, this advantage is also a disadvantage since the temperatures attained are similar to the surface of the sun, which would vaporize any conventional container. Fusion experiments therefore use a magnetic field to contain the reaction. The shape of the field is like a bottle, hence the term “magnetic bottle”.

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Source:  OpenStax, Hydrogen. OpenStax CNX. Sep 28, 2009 Download for free at http://cnx.org/content/col10984/1.4
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