Neptunium(VI) fluoride
chemical compound
Neptunium(VI) fluoride (NpF6) is the highest fluoride of neptunium, and is also one of seventeen known binary hexafluorides. It is a volatile orange crystalline solid. It is relatively hard to handle, being very corrosive, volatile and radioactive. Neptunium hexafluoride is stable in dry air but reacts vigorously with water.
At normal pressure, it melts at 54.4 °C and boils at 55.18 °C. It is the only neptunium compound that boils at a low temperature. Due to these properties, it is possible to easily separate neptunium from spent fuel.
Preparation
Neptunium hexafluoride was first prepared in 1943 by American chemist Alan E. Florin, who heated a sample of neptunium(III) fluoride on a nickel filament in a stream of fluorine and condensed the product in a glass capillary tube. Methods of preparation from both neptunium(III) fluoride and neptunium(IV) fluoride were later patented by Glenn T. Seaborg and Harrison S. Brown.
Standard method
The usual method of preparation is by fluorination of neptunium(IV) fluoride (NpF4) by elemental fluorine (F2) at 500 °C.
NpF4 + F2 → NpF6
In comparison, uranium hexafluoride (UF6) is formed relatively rapidly from uranium tetrafluoride (UF4) and F2 at 300 °C, while plutonium hexafluoride (PuF6) only begins forming from plutonium tetrafluoride (PuF4) and F2 at 750 °C. This difference allows uranium, neptunium and plutonium to be effectively separated.
Other methods
Using a different starting material
Neptunium hexafluoride can also be obtained by fluorination of neptunium(III) fluoride or neptunium(IV) oxide.
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