NaK
Encyclopedia
NaK, or sodium-potassium alloy, an alloy
, of potassium
(K), and sodium
(Na), is usually liquid at room temperature. Various commercial grades are available. NaK is highly reactive with water and may catch fire when exposed to air, so must be handled with special precautions. Quantities as small as one gram can be a fire or explosion risk.
. The eutectic mixture 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. 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 hydrocarbon
s, 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
on December 8, 1999, being cleaned up after an accidental spill and inappropriately treated with mineral oil was scratched with a metal tool. 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 , which is roughly one-fourth of that for water.
in experimental fast neutron nuclear reactor
s. 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.
The Soviet RORSAT
radar satellites were powered by a NaK-cooled reactor. As well as 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.
s in drying solvent
s prior to distillation
.
. In this continuous process, a distillation column is fed with potassium chloride and sodium. In the reaction zone, potassium chloride reacts with sodium to form 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boiling potassium is enriched in an upper fractionating zone and drawn at the column head while sodium chloride is withdrawn from the bottom.
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
, of potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
(K), and sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
(Na), is usually liquid at room temperature. Various commercial grades are available. NaK is highly reactive with water and may catch fire when exposed to air, so must be handled with special precautions. Quantities as small as one gram can be a fire or explosion risk.
Physical properties
NaK containing 40% to 90% potassium by weight is liquid at room temperatureRoom temperature
-Comfort levels:The American Society of Heating, Refrigerating and Air-Conditioning Engineers has listings for suggested temperatures and air flow rates in different types of buildings and different environmental circumstances. For example, a single office in a building has an occupancy ratio per...
. The eutectic mixture 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. It reacts explosively with water and is stored under dry nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
for safety reasons.
When stored in air, it forms a yellow potassium superoxide
Potassium superoxide
Potassium superoxide is the chemical compound with the formula KO2. This rare salt of the superoxide ion is produced by burning molten potassium in pure oxygen...
coating and may ignite. This superoxide reacts explosively with organics. NaK is not dense enough to sink in most hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
s, but will sink in lighter mineral oil
Mineral oil
A mineral oil is any of various colorless, odorless, light mixtures of alkanes in the C15 to C40 range from a non-vegetable source, particularly a distillate of petroleum....
. 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
Y-12 National Security Complex
The Y-12 National Security Complex is a United States Department of Energy National Nuclear Security Administration facility located in Oak Ridge, Tennessee, near the Oak Ridge National Laboratory...
on December 8, 1999, being cleaned up after an accidental spill and inappropriately treated with mineral oil was scratched with a metal tool. It also attacks Teflon.
NaK has a very high surface tension
Surface tension
Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...
, which makes large amounts of it pull into a bun
Bun
A bun is a small, usually sweet, bread. Commonly they are hand-sized or smaller, domed in shape, with a flat bottom. A bun can also be a savory bread roll similar to a bap or barmcake....
-like shape. Its specific heat capacity is , which is roughly one-fourth of that for water.
Coolant
NaK has been used as the coolantCoolant
A coolant is a fluid which flows through a device to prevent its overheating, transferring the heat produced by the device to other devices that use or dissipate it. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, and chemically inert, neither causing nor...
in experimental fast neutron nuclear reactor
Fast neutron reactor
A fast neutron reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons...
s. Unlike commercial plants, these are frequently shut down and defuelled. Use of lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
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.
The Soviet RORSAT
RORSAT
Radar Ocean Reconnaissance SATellite or RORSAT is the western name given to the Soviet Upravlyaemyj Sputnik Aktivnyj satellites. These satellites were launched between 1967 and 1988 to monitor NATO and merchant vessels using active radar...
radar satellites were powered by a NaK-cooled reactor. As well as the wide liquid temperature range, NaK has a very low vapor pressure
Vapor pressure
Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...
, which is important in the vacuum of space
Outer space
Outer space is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos....
.
The Danish computer cooling
Computer cooling
Computer cooling is required to remove the waste heat produced by computer components, to keep components within their safe operating temperature limits.Various cooling methods help to improve processor performance or reduce the noise of cooling fans....
company Danamics use NaK in their CPU coolers.
Desiccant
Both sodium and potassium are used as desiccantDesiccant
A desiccant is a hygroscopic substance that induces or sustains a state of dryness in its local vicinity in a moderately well-sealed container....
s in drying solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
s prior to distillation
Distillation
Distillation is a method of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
.
Synthesis and production
Industrially, NaK is produced in a reactive distillationReactive distillation
Reactive distillation is a process where the chemical reactor is also the still. Separation of the product from the reaction mixture does not need a separate distillation step, which saves energy and materials....
. In this continuous process, a distillation column is fed with potassium chloride and sodium. In the reaction zone, potassium chloride reacts with sodium to form 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
- Air-free techniqueAir-free techniqueAir-free techniques refer to a range of manipulations in the chemistry laboratory for the handling of compounds that are air-sensitive. These techniques prevent the compounds from reacting with components of air, usually water and oxygen; less commonly carbon dioxide and nitrogen...
- Perkin trianglePerkin triangleA Perkin triangle is a specialized apparatus for the distillation of air-sensitive materials. It is named after William Henry Perkin Jr., whose design was approximately triangular in shape. The image opposite shows a more modern version in which the glass taps have been replaced with more air-tight...
- PyrophoricityPyrophoricityA pyrophoric substance is a substance that will ignite spontaneously in air. Examples are iron sulfide and many reactive metals including uranium, when powdered or sliced thin. Pyrophoric materials are often water-reactive as well and will ignite when they contact water or humid air...
- Schlenk lineSchlenk line225px|thumb|Vacuum gas manifold set up: 1 inert gas in, 2 inert gas out , 3 vacuum 4 reaction line, 5 Teflon tap to gas, 6 Teflon tap to vacuum 225px|thumb| Vacuum gas manifold set up: 1 inert gas in, 2 inert gas out , 3 vacuum , 4 reaction line, 5 double oblique stopcock...
, Schlenk flaskSchlenk flaskA Schlenk flask, or Schlenk tube is a reaction vessel typically used in air sensitive chemistry, invented by Wilhelm Schlenk. It has a side arm fitted with a PTFE or ground glass stopcock which allows the vessel to be evacuated or filled with gases... - List of desiccants
- SodiumSodiumSodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
- PotassiumPotassiumPotassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
- GalinstanGalinstanGalinstan is a family of eutectic alloys mainly consisting of gallium, indium, and tin, which are liquids at room temperature, typically freezing at . Due to the low toxicity and low reactivity of its component metals, it finds use as a replacement for many applications that previously employed...