{ "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", "designations": [], "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" ], "stresses": [], "applications": [ "thermal-control" ] }, "properties": [ { "benchmark": "melting_point", "label": "Melting point (Tfus), pure ammonia", "value": 194.95, "bound": "exact", "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", "source_detail": { "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)" } }, { "benchmark": "boiling_point", "label": "Boiling point, Wikipedia infobox", "value": -33.34, "bound": "exact", "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", "source_detail": { "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" } }, { "benchmark": "boiling_point", "label": "Boiling point, NIOSH Pocket Guide", "value": -28, "bound": "exact", "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", "source_detail": { "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)" } }, { "benchmark": "freezing_point", "label": "Freezing point, NIOSH Pocket Guide", "value": -108, "bound": "exact", "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", "source_detail": { "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)" } }, { "benchmark": "critical_temperature", "label": "Critical temperature (Tc), NIST", "value": 405.4, "bound": "exact", "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)", "source_detail": { "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)" } }, { "benchmark": "critical_temperature", "label": "Critical temperature, Wikipedia infobox", "value": 405.5, "bound": "exact", "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", "source_detail": { "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" } }, { "benchmark": "critical_pressure", "label": "Critical pressure (Pc), NIST", "value": 113, "bound": "exact", "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", "source_detail": { "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)" } }, { "benchmark": "critical_pressure", "label": "Critical pressure, Wikipedia infobox", "value": 111.3, "bound": "exact", "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", "source_detail": { "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" } }, { "benchmark": "triple_point_pressure", "label": "Triple point pressure, NIST", "value": 0.0606, "bound": "exact", "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", "source_detail": { "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)" } }, { "benchmark": "enthalpy_of_vaporization", "label": "Enthalpy of vaporization, NIST", "value": 23.5, "bound": "exact", "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", "source_detail": { "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)" } }, { "benchmark": "enthalpy_of_sublimation", "label": "Enthalpy of sublimation, NIST", "value": 31.2, "bound": "exact", "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", "source_detail": { "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)" } }, { "benchmark": "molar_mass", "label": "Molar mass", "value": 17.031, "bound": "exact", "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", "source_detail": { "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" } }, { "benchmark": "density", "label": "Liquid density at -33.3 °C, Wikipedia infobox", "value": 0.6819, "bound": "exact", "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", "source_detail": { "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" } }, { "benchmark": "density", "label": "Liquid density at -33.35 °C and 1 atm, Engineering ToolBox", "value": 696, "bound": "exact", "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", "source_detail": { "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)" } }, { "benchmark": "density", "label": "Liquid density at 21.1 °C, Engineering ToolBox", "value": 617.5, "bound": "exact", "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", "source_detail": { "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)" } }, { "benchmark": "enthalpy_of_vaporization", "label": "Heat of evaporation at the boiling point, Engineering ToolBox", "value": 1372, "bound": "exact", "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", "source_detail": { "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)" } } ], "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 } ], "critical_lists": [], "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." ], "story": { "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.", "scope": "material" }, { "label": "Stay liquid in the ISS radiator loop", "line": "Wikipedia says the ammonia is under sufficient pressure to remain liquid throughout the process.", "scope": "material" }, { "label": "Boil near -33.34 °C", "line": "The Wikipedia infobox gives this boiling point, but the pressure is not stated on the page.", "scope": "material" }, { "label": "Not for cold lines", "line": "Wikipedia says ethane is used when a heat pipe must operate below ammonia's freezing temperature.", "scope": "material" } ], "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", "scope": "material" }, { "label": "Boiling point", "benchmark": "boiling_point", "scope": "material" }, { "label": "Liquid density", "benchmark": "density", "scope": "material" } ], "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.", "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", "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." } ], "level": 0, "verdict": "Toxic, flammable gas; burns skin and eyes" } ] }, "updated": "2026-11-01", "review": { "status": "draft", "method": "assistant", "checked_values": 16, "unreachable": 0, "caveats": 0, "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." }, "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", "url": "https://spacemushroom.com/profiles/ammonia-heat-pipe-fluid/" }