spore: profile
id: ammonia-heat-pipe-fluid
spore_version: 0.2
family: ammonia
name: Ammonia
abbreviation: NH3
role: heat pipe and pumped-loop working fluid
category: thermal-protection
type: multi-layer-insulation
summary: Ammonia (NH3, CAS 7664-41-7) is the most common working fluid for spacecraft heat pipes, according to Wikipedia. NIST gives a melting point of 194.95 K and a critical temperature of 405.4 K for the pure fluid. The Engineering ToolBox gives a liquid density of 696 kg/m3 at -33.35 °C and 1 atm. The ISS radiator loop uses ammonia coolant, per Wikipedia. These are published property values and secondary descriptions, not flight measurements of the fluid.
best_for: Spacecraft heat pipes and pumped cooling loops that stay above ammonia's freezing temperature (Wikipedia, Heat pipe and Ammonia articles)
weakest_at: 'Freezing and toxicity: NIOSH prints a freezing point of -108°F and an IDLH of 300 ppm, so the loop must stay warm and the gas must stay contained'
identity:
  formula: NH3
  cas: 7664-41-7
  source: nist-ammonia
  where: 'Identifiers block: CAS Registry Number 7664-41-7; NIST prints the formula as H3N (Hill order), the same molecule as NH3'
tags:
  environments:
    - low-earth-orbit
  applications:
    - thermal-control
properties:
  - benchmark: melting_point
    label: Melting point (Tfus), pure ammonia
    value: 194.95
    unit: K
    scope: material
    conditions:
      state: solid to liquid
      basis: Tfus as printed in the NIST phase change data, reference Timmermans (1921)
    method: Value printed in the NIST Chemistry WebBook phase change data
    status: ground
    source: nist-ammonia
    where: Phase change data, Tfus row
  - benchmark: boiling_point
    label: Boiling point, Wikipedia infobox
    value: -33.34
    unit: °C
    scope: material
    conditions:
      pressure: not stated on the page
      basis: printed as -33.34 °C (-28.01 °F; 239.81 K)
    method: Value printed in the Wikipedia Ammonia infobox
    status: ground
    source: wiki-ammonia
    where: Properties section, Boiling point row
  - benchmark: boiling_point
    label: Boiling point, NIOSH Pocket Guide
    value: -28
    unit: °F
    scope: material
    conditions:
      pressure: not stated on the page
    method: Value printed in the NIOSH Pocket Guide entry for ammonia
    status: ground
    source: niosh-npg-ammonia
    where: Physical description block, Boiling Point field
  - benchmark: freezing_point
    label: Freezing point, NIOSH Pocket Guide
    value: -108
    unit: °F
    scope: material
    conditions:
      basis: labelled Freezing Point on the NIOSH page
    method: Value printed in the NIOSH Pocket Guide entry for ammonia
    status: ground
    source: niosh-npg-ammonia
    where: Physical description block, Freezing Point field
  - benchmark: critical_temperature
    label: Critical temperature (Tc), NIST
    value: 405.4
    unit: K
    scope: material
    conditions:
      basis: Tc as printed, reference Brunner (1988); NIST also lists 405.6 K from Hentze (1977), kept out of this row
    method: Value printed in the NIST Chemistry WebBook critical point data
    status: ground
    source: nist-ammonia
    where: Phase change data, Tc row (first entry)
  - benchmark: critical_temperature
    label: Critical temperature, Wikipedia infobox
    value: 405.5
    unit: K
    scope: material
    conditions:
      basis: printed as 132.4 °C (405.5 K) in the Critical point row
    method: Value printed in the Wikipedia Ammonia infobox
    status: ground
    source: wiki-ammonia
    where: Properties section, Critical point (T, P) row
  - benchmark: critical_pressure
    label: Critical pressure (Pc), NIST
    value: 113
    unit: bar
    scope: material
    conditions:
      basis: Pc as printed, reference Brunner (1988)
    method: Value printed in the NIST Chemistry WebBook critical point data
    status: ground
    source: nist-ammonia
    where: Phase change data, Pc row
  - benchmark: critical_pressure
    label: Critical pressure, Wikipedia infobox
    value: 111.3
    unit: atm
    scope: material
    conditions:
      basis: printed as 111.3 atm (11,280 kPa) in the Critical point row
    method: Value printed in the Wikipedia Ammonia infobox
    status: ground
    note: 111.3 atm is about 112.8 bar, which differs from the NIST value of 113.00 bar; both are kept as printed.
    source: wiki-ammonia
    where: Properties section, Critical point (T, P) row
  - benchmark: triple_point_pressure
    label: Triple point pressure, NIST
    value: 0.0606
    unit: bar
    scope: material
    conditions:
      basis: Ptriple as printed, reference Fonseca and Lobo (1989); NIST prints no triple point temperature
    method: Value printed in the NIST Chemistry WebBook phase change data
    status: ground
    source: nist-ammonia
    where: Phase change data, Ptriple row
  - benchmark: enthalpy_of_vaporization
    label: Enthalpy of vaporization, NIST
    value: 23.5
    unit: kJ/mol
    scope: material
    conditions:
      temperature: 239 K
      basis: printed as 23.5 kJ/mol at 239. K, reference Overstreet and Giauque (1937)
    method: Value printed in the NIST Chemistry WebBook enthalpy of vaporization data
    status: ground
    source: nist-ammonia
    where: Phase change data, enthalpy of vaporization table, first row
  - benchmark: enthalpy_of_sublimation
    label: Enthalpy of sublimation, NIST
    value: 31.2
    unit: kJ/mol
    scope: material
    conditions:
      temperature: 177 to 195 K
      basis: printed as 31.2 kJ/mol at 177. to 195. K, reference Overstreet and Giauque (1937)
    method: Value printed in the NIST Chemistry WebBook enthalpy of sublimation data
    status: ground
    source: nist-ammonia
    where: Phase change data, enthalpy of sublimation row
  - benchmark: molar_mass
    label: Molar mass
    value: 17.031
    unit: g/mol
    scope: material
    conditions:
      basis: printed as 17.031 g·mol−1 in the Wikipedia infobox
    method: Value printed in the Wikipedia Ammonia infobox
    status: ground
    source: wiki-ammonia
    where: Properties section, Molar mass row
  - benchmark: density
    label: Liquid density at -33.3 °C, Wikipedia infobox
    value: 0.6819
    unit: g/cm3
    scope: material
    conditions:
      temperature: '-33.3 °C'
      state: liquid
    method: Value printed in the Wikipedia Ammonia infobox density list
    status: ground
    source: wiki-ammonia
    where: Properties section, Density list, liquid entry
  - benchmark: density
    label: Liquid density at -33.35 °C and 1 atm, Engineering ToolBox
    value: 696
    unit: kg/m3
    scope: material
    conditions:
      temperature: '-33.35 °C'
      pressure: 1 atm
      state: liquid
    method: Value printed in the Engineering ToolBox ammonia properties table, Density, liquid row
    status: ground
    note: Differs from the Wikipedia liquid value (0.6819 g/cm3 at -33.3 °C), which is about 2% lower; both are kept as printed.
    source: etb-ammonia
    where: Density, liquid row, -33.35 °C (1 atm) entry
  - benchmark: density
    label: Liquid density at 21.1 °C, Engineering ToolBox
    value: 617.5
    unit: kg/m3
    scope: material
    conditions:
      temperature: 21.1 °C
      state: liquid
      basis: printed in the Density, liquid row at 21.1 °C (70 °F)
    method: Value printed in the Engineering ToolBox ammonia properties table
    status: ground
    source: etb-ammonia
    where: Density, liquid row, 21.1 °C entry
  - benchmark: enthalpy_of_vaporization
    label: Heat of evaporation at the boiling point, Engineering ToolBox
    value: 1372
    unit: kJ/kg
    scope: material
    conditions:
      temperature: '-33.33 °C'
      basis: printed as 1372.0 kJ/kg at the boiling point, -33.33 °C
    method: Value printed in the Engineering ToolBox ammonia properties table, Heat of evaporation row
    status: ground
    source: etb-ammonia
    where: Heat of evaporation, delta Hv row, At boiling point entry
corrosion:
  - environment: Carbon steel and aluminium alloys (CCOHS corrosivity statement)
    headline: CCOHS lists ammonia as not corrosive to carbon steel or aluminium alloys.
    effect: CCOHS places carbon steel and aluminum alloys under 'Not corrosive to'. It gives no test duration, temperature or humidity, and it does not address copper, brass, zinc or galvanized metal.
    rating: none
    conditions:
      basis: qualitative statement on the CCOHS ammonia chemical profile; no test conditions given
    source: ccohs-ammonia
    where: Corrosivity to metals
  - environment: Aluminium envelope with ammonia working fluid (spacecraft heat pipes)
    headline: Aluminium with ammonia is the usual spacecraft heat pipe pairing, but no corrosion rate was found in the sources read.
    effect: Wikipedia describes an aluminium envelope with ammonia fluid for spacecraft thermal control and calls ammonia the most common working fluid for spacecraft heat pipes. It gives no corrosion rate, test duration or lifetime.
    rating: unknown
    conditions:
      basis: description of design practice, not a corrosion test
    source: wiki-heat-pipe
    where: Structure, design, and construction; Applications, Spacecraft
risks:
  hazards:
    - text: PubChem's aggregated GHS data for ammonia (CID 222) give the signal word Danger and list H221 (flammable gas), H314 (causes severe skin burns and eye damage), H331 (toxic if inhaled) and H400 (very toxic to aquatic life).
      ghs:
        - H221
        - H314
        - H331
        - H400
      source: pubchem-ammonia
      where: GHS Classification, primary aggregated classification
    - text: NIOSH gives an immediately dangerous to life or health (IDLH) level of 300 ppm for ammonia, and lists the OSHA PEL as TWA 50 ppm (35 mg/m3) and the NIOSH REL as TWA 25 ppm (18 mg/m3) and ST 35 ppm (27 mg/m3).
      ghs: []
      source: niosh-npg-ammonia
      where: Exposure limits block
    - text: CCOHS classifies ammonia as a flammable gas, Category 1, and says that a large and intense energy source is necessary to ignite it; it also gives the ACGIH TLV as TWA 25 ppm and STEL 35 ppm.
      ghs: []
      source: ccohs-ammonia
      where: Flammability and exposure limits sections
    - text: NIOSH lists skin burns and vesiculation, and frostbite from the liquid, as health hazards of ammonia, along with irritation of the eyes, nose and throat.
      ghs: []
      source: niosh-npg-ammonia
      where: Health hazard statements (symptoms)
  failure_risks:
    - mode: Freezing of the working fluid
      trigger: Operation of a heat pipe or loop below ammonia's freezing temperature
      consequence: Wikipedia says ethane is used when a heat pipe must operate below ammonia's freezing temperature. NIOSH prints the freezing point as -108°F.
      severity: moderate
      source: wiki-heat-pipe
      where: Applications, Spacecraft
    - mode: Release of toxic gas
      trigger: Leak of ammonia gas into an occupied or enclosed space
      consequence: NIOSH gives an IDLH of 300 ppm; above this level the gas is immediately dangerous to life or health.
      severity: high
      source: niosh-npg-ammonia
      where: Exposure limits block
  side_effects: []
  handling:
    - text: PubChem lists the precautionary statement codes P210, P260, P261, P264, P271, P273, P280 and P403 for the aggregated classification. The code text is not reproduced in the page read for this profile, so check the supplier's safety data sheet.
      source: pubchem-ammonia
      where: GHS Classification, precautionary statements
    - text: Wikipedia says ammonia is the most common working fluid for spacecraft heat pipes, so any loop design should keep it inside the sealed heat pipe or loop.
      source: wiki-heat-pipe
      where: Applications, Spacecraft
  mitigations:
    - text: Use ethane instead of ammonia where a heat pipe must run below ammonia's freezing temperature.
      source: wiki-heat-pipe
      where: Applications, Spacecraft
uses:
  - application: thermal-control
    device: Spacecraft heat pipes
    example: Wikipedia says ammonia is the most common working fluid for spacecraft heat pipes and shows a grooved aluminum-ammonia heat pipe for spacecraft thermal control.
    source: wiki-heat-pipe
    where: Applications, Spacecraft
  - application: thermal-control
    device: International Space Station radiator loop
    example: Wikipedia says ammonia coolant is also used in the radiators aboard the International Space Station, and that the ammonia is under sufficient pressure to remain liquid throughout the process.
    source: wiki-ammonia
    where: Refrigeration, R717 section
  - application: thermal-control
    device: Industrial refrigeration
    example: Wikipedia says anhydrous ammonia is widely used in industrial refrigeration applications and hockey rinks.
    source: wiki-ammonia
    where: Refrigeration, R717 section
supply:
  - subject: Ammonia (fixed nitrogen made into ammonia)
    abundance: 'USGS: the availability of nitrogen from the atmosphere for fixed nitrogen production is unlimited.'
    producers:
      - country: China
        share_percent: 30.6
        year: 2025
      - country: India
        share_percent: 9.4
        year: 2025
      - country: Russia
        share_percent: 9.4
        year: 2025
      - country: United States
        share_percent: 8.8
        year: 2025
      - country: Indonesia
        share_percent: 3.8
        year: 2025
    recycling: 'USGS nitrogen chapter: ''Recycling: None.'''
    substitutes:
      - 'USGS: nitrogen is an essential plant nutrient that has no substitute. The chapter does not discuss ammonia as a heat transfer fluid.'
    source: usgs-nitrogen-2026
    where: World Ammonia Production and Reserves table, plant production 2025e in thousand metric tons of nitrogen content; shares calculated by Space Mushroom against the printed world total of 160,000 (rounded). Recycling and Substitutes sections.
media: []
documents:
  - title: 'NIST Chemistry WebBook: ammonia (CAS 7664-41-7), phase change and critical data'
    type: database
    url: https://webbook.nist.gov/cgi/cbook.cgi?Mask=4&ID=C7664417
    year: 2026
  - title: 'PubChem compound record: Ammonia (CID 222), GHS classification'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/222/JSON?heading=GHS+Classification
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Nitrogen (Fixed), Ammonia'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-nitrogen.pdf
    year: 2026
  - title: 'NIOSH Pocket Guide to Chemical Hazards: Ammonia (CAS 7664-41-7)'
    type: database
    url: https://www.cdc.gov/niosh/npg/npgd0028.html
    year: 2026
  - title: 'CCOHS OSH Answers: Ammonia chemical profile'
    type: database
    url: https://www.ccohs.ca/oshanswers/chemicals/chem_profiles/ammonia/ammonia.html
    year: 2026
  - title: 'Engineering ToolBox: Ammonia thermophysical properties'
    type: datasheet
    url: https://www.engineeringtoolbox.com/ammonia-d_1413.html
    year: 2026
gaps:
  - A Wikipedia melting point (-77.73 °C, printed with a Unicode minus sign) did not match the value check, so it is not recorded; the NIST melting point of 194.95 K is kept.
  - No flight data or space-environment test of ammonia as a heat pipe or loop fluid was found in the sources read in this run; the entries describe design use, not measured performance.
  - No copper or copper-alloy compatibility data for ammonia were found. The CCOHS statement covers carbon steel and aluminium alloys only, and two ICSC cards we opened were for other chemicals.
  - Flammable limits (% by volume) and autoignition temperature for ammonia were not stated in the CCOHS page or in the other sources read, so they are not recorded.
  - Vapour pressure table entries, liquid heat capacity, liquid viscosity, liquid thermal conductivity, surface tension and critical density were not printed on the NIST page read in this run. The NIST Fluid Properties dataset was not read.
  - The second NIST critical temperature (405.6 K, Hentze 1977) is noted in a row condition but not recorded as its own property.
  - No UN number, EN, UNS or other designation for ammonia was printed in a source read in this run, so no designation is listed.
  - The atomic weights of nitrogen and hydrogen were not read from a source in this run, so the recipe lists atom counts only.
  - The manufacturing route (the Haber process or any other) is not described in the USGS chapter read; only plant production is reported.
  - USGS and European Commission critical-mineral status for nitrogen was not checked in this run.
  - Three of the use statements and the ISS radiator statement rest on Wikipedia, because no NASA or ESA page on the ISS ammonia loop was reachable in this run.
  - The heat-pipe comparison with ethane is qualitative; no performance values for either fluid were found in the sources read.
sources:
  nist-ammonia:
    title: 'NIST Chemistry WebBook: ammonia, phase change and critical data'
    id: NIST SRD 69; CAS 7664-41-7
    url: https://webbook.nist.gov/cgi/cbook.cgi?Mask=4&ID=C7664417
    year: 2026
    kind: database
    license: US government work (NIST)
  pubchem-ammonia:
    title: 'PubChem compound record: Ammonia (CID 222), GHS classification'
    id: CID 222; CAS 7664-41-7
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/222/JSON?heading=GHS+Classification
    year: 2026
    kind: database
    license: public domain (NCBI)
  usgs-nitrogen-2026:
    title: 'Mineral Commodity Summaries 2026: Nitrogen (Fixed), Ammonia'
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-nitrogen.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  ccohs-ammonia:
    title: 'CCOHS OSH Answers: Ammonia chemical profile'
    id: CAS 7664-41-7
    url: https://www.ccohs.ca/oshanswers/chemicals/chem_profiles/ammonia/ammonia.html
    year: 2026
    kind: web
    license: Government of Canada web page (cited, not reproduced)
  niosh-npg-ammonia:
    title: 'NIOSH Pocket Guide to Chemical Hazards: Ammonia'
    id: NIOSH Pocket Guide npgd0028; CAS 7664-41-7
    url: https://www.cdc.gov/niosh/npg/npgd0028.html
    year: 2026
    kind: handbook
    license: US government work (CDC/NIOSH)
  wiki-heat-pipe:
    title: 'Wikipedia: Heat pipe'
    id: Wikipedia article, read for qualitative statements only
    url: https://en.wikipedia.org/wiki/Heat_pipe
    year: 2026
    kind: web
    license: CC BY-SA 4.0
  wiki-ammonia:
    title: 'Wikipedia: Ammonia'
    id: Wikipedia article, infobox and R717 section
    url: https://en.wikipedia.org/wiki/Ammonia
    year: 2026
    kind: web
    license: CC BY-SA 4.0
  etb-ammonia:
    title: 'Engineering ToolBox: Ammonia, thermophysical properties'
    id: Engineering ToolBox ammonia-d_1413
    url: https://www.engineeringtoolbox.com/ammonia-d_1413.html
    year: 2026
    kind: datasheet
    license: web page (cited, not reproduced)
license: CC-BY-4.0
updated: '2026-11-01'
review:
  status: draft
  method: assistant
  checked_values: 16
  note: Written by an AI assistant on 2026-11-01 from pages fetched in this run. Values are copied as printed; the Wikipedia values are secondary.
story:
  recipe:
    line: Ammonia is one nitrogen atom bonded to three hydrogen atoms (NH3). NIST prints the formula as H3N. The USGS chapter reports ammonia plant output by nitrogen content, and the manufacturing route is not described in the sources read.
    parts:
      - name: Nitrogen
        symbol: 'N'
        role: The central atom. The USGS chapter describes fixed nitrogen made from atmospheric nitrogen, which is unlimited.
      - name: Hydrogen
        symbol: H
        role: Three hydrogen atoms bonded to the nitrogen. The pressurised liquid is what carries heat in the loop.
  risk_groups:
    - title: For people
      level: 0
      verdict: Toxic, flammable gas; burns skin and eyes
      lead: Ammonia is a toxic, flammable gas. Its hazard codes come from PubChem and the NIOSH Pocket Guide, and its exposure limits are set out there.
      points:
        - label: The gas
          line: PubChem's aggregated GHS data give the signal word Danger, with H221 (flammable gas), H314 (causes severe skin burns and eye damage), H331 (toxic if inhaled) and H400 (very toxic to aquatic life).
        - label: Exposure limits
          line: NIOSH gives an immediately dangerous to life or health level of 300 ppm. CCOHS quotes the ACGIH TLV as TWA 25 ppm and STEL 35 ppm.
        - label: Freezing
          line: NIOSH prints a freezing point of -108°F. Wikipedia says ethane is used when a heat pipe must run below ammonia's freezing temperature.
  why: 'Ammonia is the working fluid of most spacecraft heat pipes. Wikipedia calls it the most common working fluid for spacecraft heat pipes and says ammonia coolant is used in the radiators aboard the International Space Station. Its useful range is set by its freezing and boiling points: NIST gives a melting point of 194.95 K, and the Wikipedia infobox gives a boiling point of -33.34 °C. These are published values and secondary descriptions, not flight measurements of the fluid.'
  uses:
    - where: Spacecraft heat pipes
      line: Wikipedia says ammonia is the most common working fluid for spacecraft heat pipes, and it shows a grooved aluminum-ammonia heat pipe for spacecraft thermal control.
    - where: International Space Station radiators
      line: Wikipedia says ammonia coolant is also used in the radiators aboard the International Space Station. The article does not give the loop design or flow rates.
    - where: Industrial refrigeration
      line: Wikipedia says anhydrous ammonia is widely used in industrial refrigeration applications and hockey rinks.
  can_do:
    - label: Move heat in a heat pipe
      line: Wikipedia calls ammonia the most common working fluid for spacecraft heat pipes.
    - label: Stay liquid in the ISS radiator loop
      line: Wikipedia says the ammonia is under sufficient pressure to remain liquid throughout the process.
    - label: Boil near -33.34 °C
      line: The Wikipedia infobox gives this boiling point, but the pressure is not stated on the page.
    - label: Not for cold lines
      line: Wikipedia says ethane is used when a heat pipe must operate below ammonia's freezing temperature.
  compare: Against ethane, the alternative that Wikipedia names for operation below ammonia's freezing temperature, ammonia is the default choice for spacecraft heat pipes. The sources read give no performance comparison of the two fluids, so this comparison is qualitative only. Ammonia's own published values in this profile are a melting point of 194.95 K (NIST) and a boiling point of -33.34 °C (Wikipedia).
  compare_rows:
    - label: Melting point
      benchmark: melting_point
    - label: Boiling point
      benchmark: boiling_point
    - label: Liquid density
      benchmark: density
  handling:
    - 'Treat ammonia as a toxic, flammable gas: NIOSH gives an IDLH of 300 ppm, and PubChem lists H221 and H331.'
    - 'Keep the loop above the freezing temperature: NIOSH prints -108°F, and Wikipedia says ethane is the alternative below it.'
    - Check the supplier's safety data sheet for handling, since the PubChem precautionary codes are not explained in the page read.
  good_for:
    - Spacecraft heat pipes, where Wikipedia calls it the most common working fluid.
    - Pumped cooling loops that run above its freezing temperature, as on the ISS radiator loop (Wikipedia).
  watch_out:
    - 'Freezing: NIOSH prints a freezing point of -108°F, and Wikipedia names ethane for colder operation.'
    - 'Toxicity: NIOSH sets the IDLH at 300 ppm, and PubChem lists H331 (toxic if inhaled).'
    - 'Flammability: CCOHS classifies ammonia as a flammable gas, Category 1.'
  verdict: Ammonia is the standard spacecraft heat pipe fluid in the sources read. Its values here are published data and secondary descriptions, and no flight test of the fluid was found.