| 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 100°C |
| Melting point |
-11°C (12°F) [2] |
| Boiling point |
785°C (1445°F) |
| Solubility in water | Reacts violently |
| Thermal conductivity | 23 W·m−1·K−1[1] |
| Hazards | |
| Main hazards | Highly Reactive, Corrosive and Flammable |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
NaK, or sodium-potassium alloy, an alloy, of potassium (K), and sodium (Na), is usually liquid at room temperature.[3] 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.[2]
Contents |
NaK containing 40% to 90% potassium by weight is liquid at room temperature. 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.[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 on December 8, 1999, being cleaned up after an accidental spill and inappropriately treated with mineral oil was scratched with a metal tool.[4] 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]
NaK has been used 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.
The Soviet RORSAT radar satellites were powered by a NaK-cooled reactor.[6][7] 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.[8]
Both sodium and potassium are used as desiccants in drying solvents prior to distillation.
Industrially, NaK is produced in a reactive distillation.[9] 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.