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NaK
Identifiers
CAS number 11135-81-2
Properties
Molecular formula Na + K
Molar mass N/A
Appearance Liquid metal
Density 0.855 g/mL at 100Cº
Melting point

-11 Cº (12Fº) [2]

Boiling point

785 Cº (1445Fº)

Solubility in water Reacts violently
Thermal conductivity 23 W·m−1·K−1[1]
Hazards
Main hazards Highly Reactive, Corrosive and Flammable
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

NaK (pronounced /ˈnæk/, rhyming with "sack") is a sodium (Na) - potassium (K) alloy usually liquid at room temperature.[3] Various commercial grades are available. NaK is highly reactive with air or water and must be handled with special precautions. Quantities as small as one gram can be a fire or explosion risk.[4]

Contents

Physical properties

NaK containing 40% to 90% potassium by weight is liquid at room temperature. The eutectic mix consists of 78% potassium and 22% sodium, is liquid from −12.6 to 785 °C, and has a density of 866 kg/m³ at 21°C and 855 kg/m³ at 100°C, making it less dense than water.[3] It reacts explosively with water and is stored under dry nitrogen for safety reasons.

When stored in air, it forms a yellow potassium superoxide coating and may ignite. This superoxide reacts explosively with organics. NaK is not dense enough to sink in most hydrocarbons but will sink in lighter mineral oil. It is unsafe to store in this manner if the superoxide has formed. A large explosion took place at the Oak Ridge Y-12 facility in 2000 when NaK stored under mineral oil was scratched. [5] It also attacks Teflon.

NaK has a very high surface tension which makes large amounts of it pull into a bun-like shape. Its specific heat capacity is 982 J/kg which is roughly one-fourth of that for water.[1]

Usage

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Coolant

One notable use is as the coolant in experimental fast neutron nuclear reactors. Unlike commercial plants, these are frequently shut down and defuelled. Use of lead or pure sodium, the other materials used in practical reactors, would require continual heating to maintain the coolant as a liquid. Use of NaK overcomes this. NaK is used in many other heat transfer applications for similar reasons.[citation needed]

The Soviet RORSAT radar satellites were powered by a NaK-cooled reactor.[6] Apart from the wide liquid temperature range, NaK has a very low vapor pressure which is important in the vacuum of space.

The Danish computer cooling company Danamics use NaK in their CPU coolers.[7]

Catalysis

NaK is also used as a catalyst for many reactions, including precursors of ibuprofen.[citation needed]

Desiccant

Both sodium and potassium are used as desiccants in drying solvents prior to distillation. However, without heating, the solid metal is only able to react at the surface. Formation of oxide crusts also reduces the reactivity. As a liquid metal alloy at room temperature, the use of NaK as a desiccant helps to avoid these problems.[citation needed]

Synthesis and production

Industrially, NaK is produced in a reactive distillation.[8] In this continuous process a distillation column is fed with potassium chloride and sodium. In the reaction zone potassium chloride reacts with sodium to sodium chloride and potassium. The lighter boiling potassium is enriched in an upper fractionating zone and drawn at the column head while sodium chloride is withdrawn from the bottom.

See also

References

  1. ^ a b "Danamics LM10 - Liquid metal put to the test". http://www.nordichardware.com/Reviews/?page=2&skrivelse=549.  2010-01-10 nordichardware.com
  2. ^ "MSDS". http://www.youngshin.com/wwwboard/data/3/NaK-MSDS.pdf.  youngshin.com/../NaK-MSDS.pdf 2009-05-19
  3. ^ a b "Sodium-Potassium Alloy (NaK)". BASF. http://www.basf.com/inorganics/pdfs/tech_datasheet/NaK.pdf. Retrieved 2009-03-05. 
  4. ^ Material Safety Data Sheet
  5. ^ Oak Ridge Explosion NaK Cleanup 2000
  6. ^ Space.com article about RORSATs leaking NaK after jettisoning their reactor core. Retrieved 03/10/2009.
  7. ^ Danamics Liquid Metal Technology Retrieved 10/28/2009.
  8. ^ The Manufacture of Potassium and NaK], Jackson, C.B.; Werner, R.C.; January 1, 1957

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