spore: profile
id: potassium
spore_version: 0.2
family: alkali-and-alkaline-earth-metals
name: Potassium metal and NaK eutectic
abbreviation: K
role: liquid-metal coolant
category: metals
type: heavy-metals
summary: |
  Potassium is a soft silvery alkali metal that melts at 63.5 degC and boils at 759 degC. Mixed with sodium as the eutectic NaK-78 (22% sodium and 78% potassium by weight), it stays liquid down to -12.6 degC, which made it a working coolant for space fission reactors. The metal reacts violently with water, and that is the main hazard in handling and in any loop leak.
best_for: Liquid-metal heat transport in space fission reactor loops, where NaK stays liquid at room temperature
weakest_at: 'Any contact with water or oxygen: it reacts violently with water and forms a surface crust in air'
identity:
  formula: K
  cas: 7440-09-7
  source: pubchem-k
  where: Names and Identifiers > Other Identifiers > CAS (7440-09-7). NaK-78 composition (22% Na and 78% K by weight) from the 1973 NASA and AEC summary report, Introduction.
tags:
  environments: []
  stresses: []
  applications:
    - thermal-control
properties:
  - benchmark: melting_point
    label: Melting point, potassium metal
    value: 63.5
    unit: degC
    scope: material
    conditions:
      form: potassium metal, pure element as listed in PubChem
    method: Experimental value listed in the PubChem compound record
    status: ground
    source: pubchem-k
    where: Chemical and Physical Properties > Experimental Properties > Melting Point (63.5 degC entry)
  - benchmark: boiling_point
    label: Boiling point, potassium metal
    value: 759
    unit: degC
    scope: material
    conditions:
      pressure: 760 mmHg
    method: Experimental value listed in the PubChem compound record
    status: ground
    note: A supplier SDS gives 774 degC at 1013 hPa. Both values are kept as printed; see the supplier SDS rows.
    source: pubchem-k
    where: Chemical and Physical Properties > Experimental Properties > Boiling Point (759 degC at 760 mmHg)
  - benchmark: density
    label: Density, potassium metal
    value: 0.856
    unit: g/cm3
    scope: material
    conditions:
      temperature: not stated in the record
    method: Experimental value listed in the PubChem compound record
    status: ground
    source: pubchem-k
    where: Chemical and Physical Properties > Experimental Properties > Density (0.856 g/cm3 entry)
  - benchmark: specific_heat
    label: Specific heat at 0 degC, potassium metal
    value: 0.176
    unit: cal/(g deg)
    scope: material
    conditions:
      temperature: 0 degC
      unit_in_source: cal/g deg
    method: Experimental value listed in PubChem, kept in the unit it prints (not converted to J/(kg K))
    status: ground
    source: pubchem-k
    where: Chemical and Physical Properties > Experimental Properties > Other Experimental Properties (specific heat, 0 degC)
  - benchmark: thermal_conductivity
    label: Thermal conductivity at 21 degC, potassium metal
    value: 0.23
    unit: cal/(sec degC cm)
    scope: material
    conditions:
      temperature: 21 degC
      unit_in_source: cal/(sec degC cm)
    method: Experimental value listed in PubChem, kept in the unit it prints (not converted to W/(m K))
    status: ground
    source: pubchem-k
    where: Chemical and Physical Properties > Experimental Properties > Other Experimental Properties (thermal conductivity, 21 degC entry)
  - benchmark: thermal_conductivity
    label: Thermal conductivity at 400 degC, potassium metal
    value: 0.956
    unit: cal/(sec degC cm)
    scope: material
    conditions:
      temperature: 400 degC
      unit_in_source: cal/(sec degC cm)
    method: Experimental value listed in PubChem, kept in the unit it prints (not converted to W/(m K))
    status: ground
    source: pubchem-k
    where: Chemical and Physical Properties > Experimental Properties > Other Experimental Properties (thermal conductivity, 400 degC entry)
  - benchmark: vapor_pressure
    label: Vapor pressure at 432 degC, potassium metal
    value: 8
    unit: mm Hg
    scope: material
    conditions:
      temperature: 432 degC
    method: Experimental value listed in the PubChem compound record
    status: ground
    source: pubchem-k
    where: Chemical and Physical Properties > Experimental Properties > Vapor Pressure (8 mm Hg at 432 degC)
  - benchmark: melting_point
    label: Melting point, supplier SDS (potassium metal)
    value: 64
    unit: degC
    scope: material
    conditions:
      form: potassium metal, supplier SDS
    method: Value printed in the supplier safety data sheet, Section 9
    status: ground
    note: Rounded value. PubChem gives 63.5 degC.
    source: sa-k
    where: Section 9, Melting point/freezing point
  - benchmark: boiling_point
    label: Boiling point, supplier SDS (potassium metal)
    value: 774
    unit: degC
    scope: material
    conditions:
      pressure: 1013 hPa (760 mmHg)
    method: Value printed in the supplier safety data sheet, Section 9
    status: ground
    note: Differs from the PubChem value of 759 degC. Both are kept as printed.
    source: sa-k
    where: Section 9, Initial boiling point and boiling range
  - benchmark: density
    label: Relative density, supplier SDS (potassium metal)
    value: 0.86
    unit: g/cm3
    scope: material
    conditions:
      temperature: not stated in the SDS
    method: Value printed in the supplier safety data sheet, Section 9
    status: ground
    source: sa-k
    where: Section 9, Relative density (0.860 g/cm3)
  - benchmark: vapor_pressure
    label: Vapor pressure at 260 degC, supplier SDS (potassium metal)
    value: 0.12
    unit: hPa
    scope: material
    conditions:
      temperature: 260 degC
    method: Value printed in the supplier safety data sheet, Section 9
    status: ground
    source: sa-k
    where: Section 9, Vapor pressure (0.12 hPa at 260 degC)
  - benchmark: melting_point
    label: Melting point, NaK-78 eutectic
    value: -12.6
    unit: degC
    scope: material
    conditions:
      material: NaK-78 eutectic, 22% Na and 78% K by weight
    method: Value stated in a NASA paper on a NaK-cooled circuit
    status: ground
    source: nasa-2006
    where: Introduction, paragraph on liquid metals for space reactors (melting point of -12.6 degC)
  - benchmark: boiling_point
    label: Boiling point, NaK-78 eutectic
    value: 785
    unit: degC
    scope: material
    conditions:
      material: NaK-78 eutectic, 22% Na and 78% K by weight
    method: Value stated in a NASA paper on a NaK-cooled circuit
    status: ground
    source: nasa-2006
    where: Introduction, paragraph on liquid metals for space reactors (boiling point of 785 degC)
  - benchmark: volume_expansion
    label: Volume increase of NaK heated from 25 degC to 650 degC
    value: 17
    unit: '%'
    scope: material
    conditions:
      material: NaK
      from_temperature: 25 degC
      to_temperature: 650 degC
    method: Value stated in a NASA paper on the fission surface power test circuit
    status: ground
    source: nasa-2007
    where: Circuit design section, paragraph on expansion reservoir (NaK expands to 17% above its volume at 25 degC)
corrosion:
  - environment: Liquid water and wet air
    headline: Potassium reacts violently with water, releasing hydrogen and forming a caustic hydroxide.
    effect: NOAA CAMEO Chemicals records that potassium reacts violently or explosively with water. The PubChem entry for the alloy form says the reaction forms potassium hydroxide, a corrosive material, and hydrogen, a flammable gas that the heat may ignite.
    rating: severe
    conditions:
      exposure: contact with liquid or moist air
      form: potassium metal
    source: cameo-k
    where: Reactivity profile, water entry
  - environment: Oxygen in air (NaK in a loop)
    headline: NaK forms a crust of potassium oxide, peroxide and superoxide on its surface.
    effect: Exposure to oxygen makes NaK form potassium oxide, potassium peroxide and potassium superoxide, which create a crust on the surface of the liquid metal. NASA lists this as a disadvantage of NaK.
    rating: moderate
    conditions:
      form: NaK-78 eutectic
      temperature: not stated in the paper
    source: nasa-2006
    where: Introduction, paragraph on the disadvantages of NaK
  - environment: Stainless steel in NaK up to 650 degC
    headline: NaK has shown good compatibility with stainless steel up to 650 degC.
    effect: NASA reports good compatibility between NaK and stainless steel over the temperature range tested, with a maximum of 650 degC. The paper gives no corrosion rate.
    rating: low
    conditions:
      temperature: up to 650 degC
      material: stainless steel
    source: nasa-2007
    where: Introduction, paragraph on NaK properties
risks:
  hazards:
    - text: Classified Danger. In contact with water it releases flammable gases which may ignite spontaneously (H260), as reported in PubChem and the supplier SDS.
      ghs:
        - H260
      source: pubchem-k
      where: Safety and Hazards > GHS Classification (H260)
    - text: Causes severe skin burns and eye damage (H314), as reported in PubChem and the supplier SDS.
      ghs:
        - H314
      source: sa-k
      where: Section 2, Hazards identification (H314)
    - text: UN number 2257 (potassium) appears in the PubChem record.
      ghs: []
      source: pubchem-k
      where: Names and Identifiers > Other Identifiers > UN Number
  failure_risks:
    - mode: Water entering the metal or the loop
      trigger: Leak, wet surface, or moisture during storage, handling or filling
      consequence: Violent reaction releases hydrogen, which may ignite spontaneously. The SDS warns of possible flash fire.
      severity: high
      source: sa-k
      where: Section 2 (precautionary statement P223) and Section 10 (reacts violently with water)
    - mode: Crust formation on the NaK surface
      trigger: Exposure of NaK to oxygen
      consequence: Potassium oxide, peroxide and superoxide form a crust on the liquid surface, which NASA lists as a disadvantage of NaK.
      severity: moderate
      source: nasa-2006
      where: Introduction, paragraph on the disadvantages of NaK
  side_effects:
    - text: Reaction with water forms hydrogen gas and potassium hydroxide, a corrosive solution.
      affects: Anything the reaction products contact, including the loop or enclosure
      source: pubchem-k
      where: Chemical and Physical Properties > Physical Description (alloy entry)
  handling:
    - text: Handle under inert gas and protect from moisture. Keep away from any possible contact with water.
      source: sa-k
      where: Section 2 (P223, P231 plus P232) and Section 7
    - text: Never allow the product to contact water during storage. Handle and store under inert gas.
      source: sa-k
      where: Section 7, Conditions for safe storage
  mitigations:
    - text: Use stainless steel, which NASA found compatible with NaK up to 650 degC in its test circuit.
      source: nasa-2007
      where: Introduction, paragraph on NaK properties
    - text: Fight fires with dry sand, dry chemical or alcohol-resistant foam, as the SDS directs.
      source: sa-k
      where: Section 2 (P370 plus P378) and Section 5 (dry powder)
uses:
  - application: thermal-control
    device: Liquid-metal reactor coolant loop for a space fission power system
    example: The 1973 NASA and AEC summary describes a 5-kWe thermoelectric system in which reactor heat was carried by NaK, a eutectic of 22% Na and 78% K by weight, to a radiator.
    source: nasa-1973
    where: Description of the 5-kWe system, text near Figure 1
  - application: thermal-control
    device: Primary test circuit for fission surface power (ground test)
    example: NASA Marshall selected NaK as the primary coolant for its fission surface power primary test circuit, because NaK was the coolant of the SNAP-10A fission reactor.
    source: nasa-2007
    where: Abstract
supply:
  - subject: Potassium (as potash, K2O equivalent)
    producers:
      - country: Canada
        share_percent: 30.6
        year: 2025
      - country: Russia
        share_percent: 20.4
        year: 2025
      - country: China
        share_percent: 12.9
        year: 2025
      - country: Belarus
        share_percent: 12.2
        year: 2025
      - country: Germany
        share_percent: 6.1
        year: 2025
      - country: Laos
        share_percent: 4.9
        year: 2025
    critical_lists:
      - list: U.S. Final 2025 List of Critical Minerals (potash added in 2025)
        listed: true
    substitutes: []
    source: usgs-mcs2026-potash
    where: World Mine Production and Reserves table, 2025e, K2O equivalent, world total 49,000 thousand t (shares calculated by Space Mushroom as country production divided by the world total); critical minerals paragraph
documents:
  - title: 'Stanford Advanced Materials safety data sheet: potassium metal (revised 19 January 2023)'
    type: sds
    url: https://samaterials.com/tds/1697120713-1699-potassium-k-metal-sds.pdf
    year: 2023
  - title: 'PubChem: Potassium (CID 5462222), GHS classification and experimental properties'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/Potassium
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Potash'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-potash.pdf
    year: 2026
  - title: 'NASA: Design, Fabrication and Integration of a NaK-Cooled Circuit'
    type: paper
    url: https://ntrs.nasa.gov/citations/20060025550
    year: 2006
  - title: 'NASA: Capabilities and Testing of the Fission Surface Power Primary Test Circuit'
    type: paper
    url: https://ntrs.nasa.gov/citations/20070031971
    year: 2007
  - title: 'AEC and NASA: Space Nuclear System Thermoelectric NaK Pump Development, Summary Report (NASA-CR-121231)'
    type: report
    url: https://ntrs.nasa.gov/citations/19730016794
    year: 1973
  - title: 'NOAA CAMEO Chemicals: Potassium'
    type: database
    url: https://cameochemicals.noaa.gov/chemical/4316
  - title: 'NIST: Atomic Weights and Isotopic Compositions for Potassium'
    type: database
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=K
gaps:
  - No crustal abundance for potassium was read in a source for this profile, so the abundance field is left out.
  - The density of NaK-78 at 20 degC was not read in a source opened for this run. Wikipedia and a mirror give 0.866 g/cm3, but Wikipedia is used here only for composition and history, and the 1972 NaK handbook was not found.
  - Thermal conductivity, specific heat and electrical resistivity of NaK-78 were not found in a source opened for this run.
  - Electrical resistivity of potassium metal was not found. The flash point is not applicable in PubChem (combustible solid) and reads No data available in the supplier SDS.
  - Vapor pressure and volume_expansion are not canonical names in spores/property-canon.yaml. They are used here as short snake_case names.
  - No alkali-metal type exists under the metals category in src/data/taxonomy.ts. The type heavy-metals is the nearest available choice and should be reviewed.
  - The EU critical raw materials list was not checked for potassium or potash.
  - Producer shares are calculated from potash K2O-equivalent mine production, not from elemental potassium. The USGS world total is rounded.
  - No recycling or substitute data for potassium were read in a source for this run.
  - Boiling point differs between PubChem (759 degC) and the supplier SDS (774 degC). Both are kept as printed.
  - Radiation, vacuum and flight-result data for NaK-78 were not found beyond the 1973 summary report and the 2006 and 2007 NASA papers. No NaK-specific corrosion rate was found; NASA reports compatibility only.
sources:
  pubchem-k:
    title: PubChem compound record, Potassium (CID 5462222)
    id: CID 5462222; CAS 7440-09-7
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/5462222/JSON
    year: 2026
    kind: database
    license: public domain (NCBI)
  sa-k:
    title: 'Safety data sheet: Potassium metal (Stanford Advanced Materials)'
    id: revised 19 January 2023
    url: https://samaterials.com/tds/1697120713-1699-potassium-k-metal-sds.pdf
    year: 2023
    kind: datasheet
    license: supplier document, linked not reproduced
  usgs-mcs2026-potash:
    title: Mineral Commodity Summaries 2026, Potash
    id: USGS MCS, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-potash.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  nasa-2006:
    title: Design, Fabrication and Integration of a NaK-Cooled Circuit (NASA Marshall Space Flight Center, Paper 6389, 2006)
    id: NTRS 20060025550
    url: https://ntrs.nasa.gov/citations/20060025550
    year: 2006
    kind: paper
    license: public domain (NASA)
  nasa-2007:
    title: Capabilities and Testing of the Fission Surface Power Primary Test Circuit (FSP-PTC), Space Nuclear Conference 2007, Paper 2030
    id: NTRS 20070031971
    url: https://ntrs.nasa.gov/citations/20070031971
    year: 2007
    kind: paper
    license: public domain (NASA)
  nasa-1973:
    title: Space Nuclear System Thermoelectric NaK Pump Development, Summary Report (AEC and NASA-CR-121231)
    id: NTRS 19730016794; AEC-AI-13091
    url: https://ntrs.nasa.gov/citations/19730016794
    year: 1973
    kind: report
    license: public domain (NASA)
  cameo-k:
    title: 'NOAA CAMEO Chemicals: Potassium'
    id: CAMEO chemical record 4316
    url: https://cameochemicals.noaa.gov/chemical/4316
    kind: database
    license: public domain (NOAA)
  nist-k:
    title: Atomic Weights and Isotopic Compositions for Potassium (NIST Physical Measurement Laboratory)
    id: NIST standard atomic weight 39.0983(1)
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=K
    kind: database
    license: public domain (NIST)
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 14
  unreachable: 0
  caveats: 3
  note: Read by an AI assistant on 2026-10-26 from the cited pages. Three values differ between sources (boiling point, melting point rounding, density) and both are kept with notes.
story:
  recipe:
    line: Potassium is the element K, with one atom per formula unit. The NaK-78 eutectic is a liquid alloy of 22% sodium and 78% potassium by weight, as printed in the 1973 NASA and AEC summary report.
    parts:
      - name: Potassium
        symbol: K
        atoms: 1
        atomic_weight: 39.0983
        role: The only element in potassium metal. In NaK-78 it is the majority component (78% by weight), which sets the eutectic melting point.
        source: nist-k
        where: Standard atomic weight 39.0983(1)
  why: 'Potassium is a soft alkali metal. It is used as a metal and, as the eutectic NaK-78, as a liquid-metal coolant in space fission reactors, where the liquid metal carries reactor heat to a radiator or a converter. NaK stays liquid down to -12.6 °C, so a loop can be filled and circulated without first heating the metal, and it boils at 785 °C. Its difficulty is chemistry: it reacts violently with water and forms an oxide crust in air. NASA used NaK in the SNAP-10A space reactor and in thermoelectric power systems, which is why it has a service record in space that most metals lack.'
  uses:
    - where: Space fission power
      line: NaK was the coolant of the SNAP-10A space reactor. A 1973 NASA and AEC summary describes a 5-kWe thermoelectric system in which reactor heat was carried by NaK to a radiator. The NaK in that system was a 22% sodium and 78% potassium eutectic.
    - where: Ground test circuits
      line: NASA Marshall chose NaK as the primary coolant for its fission surface power primary test circuit, and the stainless steel circuit was tested at NaK temperatures up to 650 °C.
  can_do:
    - label: Melting point
      value: 63.5 °C
      line: Potassium melts at 63.5 °C, which is close to the temperature at which it can be handled as a liquid with mild heating. The supplier SDS gives 64 °C.
    - label: Liquid at low temperature
      value: '-12.6 °C'
      line: The NaK-78 eutectic stays liquid down to -12.6 °C. NASA notes that the low melting point helps ground testing, because the liquid metal does not need to be heated before it can be circulated.
    - label: Heat carrying
      value: 0.23 cal/(sec degC cm) at 21 °C
      line: Thermal conductivity is 0.23 at 21 °C and 0.956 at 400 °C, in the unit PubChem prints. The rise with temperature matters for a coolant that operates hot.
    - label: Vapor pressure
      value: 8 mm Hg at 432 °C
      line: The vapor pressure reaches 8 mm Hg at 432 °C, which is the figure to check when a loop runs hot.
  compare: Potassium is compared here with the NaK-78 eutectic as a coolant. Potassium melts at 63.5 °C and boils at 759 °C, while NaK-78 stays liquid down to -12.6 °C and boils at 785 °C. Potassium is less dense than water (0.856 g/cm3), so it floats, and both metals react violently with water. The choice of NaK is mainly about keeping the coolant liquid at room temperature.
  compare_rows:
    - label: Melting point
      benchmark: melting_point
    - label: Boiling point
      benchmark: boiling_point
    - label: Density
      benchmark: density
  handling:
    - Handle under inert gas and protect from moisture. The safety data sheet calls for this in its handling section.
    - Keep it away from any contact with water. Never let it contact water during storage.
    - Store in a dry place in a closed container.
  good_for:
    - Liquid-metal heat transport in space reactor loops, where NaK stays liquid at room temperature.
    - A coolant with a service record in NASA space-reactor systems, including SNAP-10A.
  watch_out:
    - Water. The reaction releases hydrogen, which may ignite spontaneously, and the SDS warns of a possible flash fire.
    - Oxygen. A crust of potassium oxide, peroxide and superoxide forms on the surface of NaK.
  verdict: Potassium and NaK are proven coolants in space fission systems. Their usefulness depends on keeping water and oxygen out of the loop.
  risk_groups:
    - title: For people
      level: 4
      verdict: Violently reactive with water and corrosive
      lead: Potassium metal is classified Danger. It reacts violently with water and causes severe skin burns and eye damage.
      points:
        - label: Classification
          line: The GHS classification is H260, which covers flammable gas release on contact with water, and H314, severe skin burns and eye damage. PubChem and the supplier SDS both report them.
        - label: Corrosion
          line: It is corrosive to skin and eyes. Its reaction with water forms potassium hydroxide, a caustic solution, and hydrogen.
        - label: Fire
          line: Keep it away from any contact with water, because of violent reaction and possible flash fire, the SDS warns. Dry sand, dry chemical or alcohol-resistant foam are the listed extinguishing media.
    - title: If a loop leaks
      level: 3
      verdict: Water leaks and oxide crust are the risks
      lead: These risks come from the chemistry of the metal and from NASA test reports, not from field incidents.
      points:
        - label: Water
          line: Water contact releases hydrogen, which may ignite. NASA's loop reports treat water as the main risk for a NaK system.
        - label: Oxide crust
          line: Oxygen forms a crust of potassium oxide, peroxide and superoxide on the NaK surface, which NASA lists as a disadvantage of NaK.
        - label: Stainless steel
          line: NaK has shown good compatibility with stainless steel up to 650 °C in NASA's test, but no corrosion rate is given.
    - title: Handling and storage
      points:
        - label: Storage
          line: Store and handle under inert gas in a dry, closed container, away from water. The SDS asks for protection from moisture.
        - label: Fire
          line: The SDS lists dry sand, dry chemical or alcohol-resistant foam for a fire, and notes that potassium oxides are formed in a fire.