{ "spore": "profile", "id": "molybdenum-disulfide", "spore_version": "0.2", "family": "lubricant", "name": "Molybdenum disulfide", "abbreviation": "MoS2", "role": "dry film lubricant", "category": "tribology", "type": "dry-lubricants", "summary": "Molybdenum disulfide is a layered solid that slides easily because its sheets are held together only by weak van der Waals forces. It is applied as a powder, a bonded coating or a sputtered film to lubricate parts where oil or grease cannot be used, such as spacecraft mechanisms in vacuum. In NASA tests in ultrahigh vacuum a bonded film gave a steady friction coefficient of 0.045 and ran more than one million passes; in humid air the same film gave 0.14 and failed at 113,570 passes. Moisture is the main weakness.\n", "best_for": "Dry sliding contacts in vacuum where oil or grease cannot be used (NASA test data: friction 0.045 and over one million passes in ultrahigh vacuum)", "weakest_at": "Humid air, where friction rises three-fold and wear life falls more than eightfold (NASA, bonded film at about 20 percent relative humidity)", "identity": { "formula": "MoS2", "cas": "1317-33-5", "crystal_system": "hexagonal (2H polytype) and rhombohedral (3R polytype)", "space_group": "P6_3/mmc (2H, No. 194); R3m (3R, No. 160)", "designations": [], "source": "wiki-mos2", "where": "Infobox and Structure section" }, "tags": { "environments": [ "low-earth-orbit" ], "stresses": [], "applications": [ "mechanisms" ] }, "properties": [ { "benchmark": "density", "value": 5.06, "bound": "exact", "unit": "g/cm3", "scope": "material", "conditions": { "basis": "density at 15 °C referenced to 15 °C water, as printed" }, "method": "PubChem Density field for CID 14823", "status": "ground", "source": "pubchem-mos2", "where": "Chemical and Physical Properties, Density field (5.06 @ 15 °C/15 °C)", "source_detail": { "title": "Molybdenum disulfide (CID 14823)", "id": "PubChem, NIH National Library of Medicine", "url": "https://pubchem.ncbi.nlm.nih.gov/compound/14823", "year": 2026, "kind": "database", "license": "public domain (NLM)" } }, { "benchmark": "coefficient_of_friction", "value": 0.045, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "basis": "bonded MoS2 (polyamide-imide binder) on 440C stainless steel, ultrahigh vacuum 7 x 10-7 Pa, room temperature, 5.9 N load, 0.2 m/s" }, "method": "Steady-state coefficient of friction, pin-on-disk tribometer, as printed", "status": "ground", "source": "nasa-tm-1999", "where": "Table II, Bonded MoS2, Vacuum row", "source_detail": { "title": "Friction and Wear Properties of Selected Solid Lubricating Films", "id": "NASA/TM-1999-209088", "url": "https://ntrs.nasa.gov/citations/19990116894", "year": 1999, "kind": "report", "license": "NASA public use" } }, { "benchmark": "coefficient_of_friction", "value": 0.07, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "basis": "magnetron-sputtered MoS2 (1.0 um film) on 440C stainless steel, ultrahigh vacuum 7 x 10-7 Pa, room temperature, 5.9 N load" }, "method": "Steady-state coefficient of friction, pin-on-disk tribometer, as printed", "status": "ground", "source": "nasa-tm-1999", "where": "Table II, Magnetron-sputtered MoS2, Vacuum row", "source_detail": { "title": "Friction and Wear Properties of Selected Solid Lubricating Films", "id": "NASA/TM-1999-209088", "url": "https://ntrs.nasa.gov/citations/19990116894", "year": 1999, "kind": "report", "license": "NASA public use" } }, { "benchmark": "coefficient_of_friction", "value": 0.06, "value_high": 0.09, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "basis": "sputtered MoS2 films (2000 to 3000 angstrom) on niobium and Ni-Cr, ultrahigh vacuum 1.33 x 10-9 N/m2 (10-11 torr), 250 g load" }, "method": "Range read from the discussion of sputtered films in vacuum, as printed", "status": "ground", "source": "nasa-tn-d-4269", "where": "Summary and discussion of friction results (0.06 to 0.09 for sputtered films)", "source_detail": { "title": "Deposition of sputtered molybdenum disulfide films and friction characteristics of such films in vacuum", "id": "NASA TN D-4269 (Przybyszewski)", "url": "https://ntrs.nasa.gov/citations/19680002176", "year": 1967, "kind": "report", "license": "NASA public use" } }, { "benchmark": "coefficient_of_friction", "value": 0.14, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "basis": "bonded MoS2 in humid air at about 20 percent relative humidity, otherwise as the vacuum row" }, "method": "Steady-state coefficient of friction, as printed; the report calls the environment humid air", "status": "ground", "source": "nasa-tm-1999", "where": "Table II, Bonded MoS2, Air row; and Results text", "source_detail": { "title": "Friction and Wear Properties of Selected Solid Lubricating Films", "id": "NASA/TM-1999-209088", "url": "https://ntrs.nasa.gov/citations/19990116894", "year": 1999, "kind": "report", "license": "NASA public use" } }, { "benchmark": "coefficient_of_friction", "value": 0.1, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "basis": "magnetron-sputtered MoS2 in humid air at about 20 percent relative humidity" }, "method": "Steady-state coefficient of friction, as printed", "status": "ground", "source": "nasa-tm-1999", "where": "Results text, humid-air paragraph (0.10 for magnetron-sputtered MoS2)", "source_detail": { "title": "Friction and Wear Properties of Selected Solid Lubricating Films", "id": "NASA/TM-1999-209088", "url": "https://ntrs.nasa.gov/citations/19990116894", "year": 1999, "kind": "report", "license": "NASA public use" } }, { "benchmark": "coefficient_of_friction", "value": 0.04, "value_high": 0.15, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "basis": "six commercial sputtered MoS2 coatings in moist air at 50 percent relative humidity, 225 N load, 25 degC; Surftech lowest (0.04), Movic highest (0.15)" }, "method": "Steady-state friction, pin-on-disk; range across coatings as printed", "status": "ground", "source": "nasa-cp-2002", "where": "Pin-on-Disk Friction Coefficient, Table 2 and text", "source_detail": { "title": "Comparison of Several Different Sputtered Molybdenum Disulfide Coatings for Use in Space Applications", "id": "NASA/CP-2002-211506", "url": "https://ntrs.nasa.gov/citations/20020050209", "year": 2002, "kind": "paper", "license": "NASA public use" } }, { "benchmark": "endurance_life", "value": 1000000, "bound": "exact", "unit": "passes", "scope": "material", "conditions": { "basis": "bonded MoS2, ultrahigh vacuum, 5.9 N load; endurance life is passes until the coefficient of friction reaches 0.3" }, "method": "Lower bound: the test ran to one million passes; the report gives '>1 million passes'", "status": "ground", "source": "nasa-tm-1999", "where": "Table II, Bonded MoS2, Vacuum row (endurance life >1 million)", "source_detail": { "title": "Friction and Wear Properties of Selected Solid Lubricating Films", "id": "NASA/TM-1999-209088", "url": "https://ntrs.nasa.gov/citations/19990116894", "year": 1999, "kind": "report", "license": "NASA public use" } }, { "benchmark": "endurance_life", "value": 274130, "bound": "exact", "unit": "passes", "scope": "material", "conditions": { "basis": "magnetron-sputtered MoS2, ultrahigh vacuum, 5.9 N load; passes until the coefficient of friction reaches 0.3" }, "method": "Endurance life as printed", "status": "ground", "source": "nasa-tm-1999", "where": "Table II, Magnetron-sputtered MoS2, Vacuum row; Friction Behavior text", "source_detail": { "title": "Friction and Wear Properties of Selected Solid Lubricating Films", "id": "NASA/TM-1999-209088", "url": "https://ntrs.nasa.gov/citations/19990116894", "year": 1999, "kind": "report", "license": "NASA public use" } }, { "benchmark": "endurance_life", "value": 113570, "bound": "exact", "unit": "passes", "scope": "material", "conditions": { "basis": "bonded MoS2 in humid air at about 20 percent relative humidity, 5.9 N load" }, "method": "Endurance life as printed (passes until the coefficient of friction reaches 0.3)", "status": "ground", "source": "nasa-tm-1999", "where": "Table II, Bonded MoS2, Air row; Results text (113,570 passes)", "source_detail": { "title": "Friction and Wear Properties of Selected Solid Lubricating Films", "id": "NASA/TM-1999-209088", "url": "https://ntrs.nasa.gov/citations/19990116894", "year": 1999, "kind": "report", "license": "NASA public use" } }, { "benchmark": "endurance_life", "value": 277377, "bound": "exact", "unit": "passes", "scope": "material", "conditions": { "basis": "magnetron-sputtered MoS2 in humid air at about 20 percent relative humidity, 5.9 N load" }, "method": "Endurance life as printed", "status": "ground", "source": "nasa-tm-1999", "where": "Results text, humid-air paragraph (277,377 passes)", "source_detail": { "title": "Friction and Wear Properties of Selected Solid Lubricating Films", "id": "NASA/TM-1999-209088", "url": "https://ntrs.nasa.gov/citations/19990116894", "year": 1999, "kind": "report", "license": "NASA public use" } }, { "benchmark": "endurance_life", "value": 100200, "bound": "exact", "unit": "pinion revolutions", "scope": "material", "conditions": { "basis": "MoS2 dry film on spur test gears, vacuum gear rig, gears with zero exposure to humid air" }, "method": "Average film durability from three sensors, as printed", "status": "ground", "source": "nasa-gears-2016", "where": "Results section, durability of unexposed gears (average 100,200; median 83,500)", "source_detail": { "title": "Performance of MoS2 Coated Gears Exposed to Humid Air During Storage", "id": "NTRS 20180003085 (presented 2016)", "url": "https://ntrs.nasa.gov/citations/20180003085", "year": 2016, "kind": "paper", "license": "NASA public use" } }, { "benchmark": "endurance_life", "value": 64900, "bound": "exact", "unit": "pinion revolutions", "scope": "material", "conditions": { "basis": "same film on spur test gears after exposure to humid air at about 57 percent relative humidity for up to 77 days" }, "method": "Average film durability from three sensors, as printed; the report gives a 35 percent reduction on average", "status": "ground", "source": "nasa-gears-2016", "where": "Results section, durability of humid-exposed gears (average 64,900; median 68,800)", "source_detail": { "title": "Performance of MoS2 Coated Gears Exposed to Humid Air During Storage", "id": "NTRS 20180003085 (presented 2016)", "url": "https://ntrs.nasa.gov/citations/20180003085", "year": 2016, "kind": "paper", "license": "NASA public use" } }, { "benchmark": "max_service_temp", "value": 600, "value_high": 700, "bound": "exact", "unit": "°C", "scope": "material", "conditions": { "basis": "burnished MoS2 in vacuum; the review says thermal dissociation at these temperatures deteriorates the lubricating properties" }, "method": "Operating maximum as stated in the review, range as printed", "status": "ground", "source": "arxiv-mos2-review", "where": "Section on high-temperature lubrication (citing reference 150)", "source_detail": { "title": "Solid Lubrication with MoS2: A Review", "id": "arXiv:1906.05854 (Lubricants 7, 57, 2019)", "url": "https://arxiv.org/abs/1906.05854", "year": 2019, "kind": "paper", "license": "arXiv (full text read as PDF in this run)" } }, { "benchmark": "max_service_temp", "value": 400, "bound": "exact", "unit": "°C", "scope": "material", "conditions": { "basis": "mechanically deposited MoS2 coating under ambient conditions; the review attributes the limit to rapid oxidation" }, "method": "Operating maximum as stated in the review", "status": "ground", "source": "arxiv-mos2-review", "where": "Section on high-temperature lubrication (references 107 and 151)", "source_detail": { "title": "Solid Lubrication with MoS2: A Review", "id": "arXiv:1906.05854 (Lubricants 7, 57, 2019)", "url": "https://arxiv.org/abs/1906.05854", "year": 2019, "kind": "paper", "license": "arXiv (full text read as PDF in this run)" } }, { "benchmark": "max_service_temp", "value": 450, "bound": "exact", "unit": "°C", "scope": "material", "conditions": { "basis": "MOLYKOTE D-321 R air-curing dry-film coating, service temperature range as printed" }, "method": "Service temperature range, upper limit", "status": "ground", "source": "dupont-d321r", "where": "Typical properties table, Temperature, Service temperature range (-180 to 450)", "source_detail": { "title": "MOLYKOTE D-321 R Anti-Friction Coating, technical data sheet", "id": "Form No. 71-0219E-01 (07/19)", "url": "https://www.dupont.com/content/dam/Dupont2.0/Products/transportation/Literature/Downloaded-TDS/MOLYKOTE%20D-321%20R%20Anti-Friction%2071-0219E-01.pdf", "year": 2019, "kind": "datasheet", "license": "manufacturer datasheet (DuPont), read as PDF" } }, { "benchmark": "min_service_temp", "value": -180, "bound": "exact", "unit": "°C", "scope": "material", "conditions": { "basis": "MOLYKOTE D-321 R air-curing dry-film coating, service temperature range as printed" }, "method": "Service temperature range, lower limit", "status": "ground", "source": "dupont-d321r", "where": "Typical properties table, Temperature, Service temperature range (-180 to 450)", "source_detail": { "title": "MOLYKOTE D-321 R Anti-Friction Coating, technical data sheet", "id": "Form No. 71-0219E-01 (07/19)", "url": "https://www.dupont.com/content/dam/Dupont2.0/Products/transportation/Literature/Downloaded-TDS/MOLYKOTE%20D-321%20R%20Anti-Friction%2071-0219E-01.pdf", "year": 2019, "kind": "datasheet", "license": "manufacturer datasheet (DuPont), read as PDF" } }, { "benchmark": "load_carrying_capacity_falex", "value": 12500, "bound": "exact", "unit": "as printed (no unit shown in extracted text)", "scope": "material", "conditions": { "basis": "MOLYKOTE D-321 R, ASTM D2625 Falex test; p = phosphated surface (b = blank 4,500; s = sand blasted 6,800)" }, "method": "Load-carrying capacity as printed, phosphated panel", "status": "ground", "source": "dupont-d321r", "where": "Typical properties table, Load-carrying capacity, ASTM D2625 (p = 12,500)", "source_detail": { "title": "MOLYKOTE D-321 R Anti-Friction Coating, technical data sheet", "id": "Form No. 71-0219E-01 (07/19)", "url": "https://www.dupont.com/content/dam/Dupont2.0/Products/transportation/Literature/Downloaded-TDS/MOLYKOTE%20D-321%20R%20Anti-Friction%2071-0219E-01.pdf", "year": 2019, "kind": "datasheet", "license": "manufacturer datasheet (DuPont), read as PDF" } }, { "benchmark": "load_carrying_capacity_lfw", "value": 2860, "bound": "exact", "unit": "N", "scope": "material", "conditions": { "basis": "MOLYKOTE D-321 R, ASTM D2714 LFW-1 rotating test, n = 72 minutes, V = 7.9 m/minute, phosphated surface (p = 146)" }, "method": "Test load as printed, with the phosphated-surface result also printed in the datasheet", "status": "ground", "source": "dupont-d321r", "where": "Typical properties table, ASTM LFW-1 (F = 2,860 N)", "source_detail": { "title": "MOLYKOTE D-321 R Anti-Friction Coating, technical data sheet", "id": "Form No. 71-0219E-01 (07/19)", "url": "https://www.dupont.com/content/dam/Dupont2.0/Products/transportation/Literature/Downloaded-TDS/MOLYKOTE%20D-321%20R%20Anti-Friction%2071-0219E-01.pdf", "year": 2019, "kind": "datasheet", "license": "manufacturer datasheet (DuPont), read as PDF" } }, { "benchmark": "film_thickness", "value": 5, "value_high": 20, "bound": "exact", "unit": "um", "scope": "material", "conditions": { "basis": "MOLYKOTE D-321 R recommended dry-film thickness after air cure" }, "method": "Recommended range as printed (datasheet uses the micro sign)", "status": "ground", "source": "dupont-d321r", "where": "How to apply, Recommended dry-film thickness", "source_detail": { "title": "MOLYKOTE D-321 R Anti-Friction Coating, technical data sheet", "id": "Form No. 71-0219E-01 (07/19)", "url": "https://www.dupont.com/content/dam/Dupont2.0/Products/transportation/Literature/Downloaded-TDS/MOLYKOTE%20D-321%20R%20Anti-Friction%2071-0219E-01.pdf", "year": 2019, "kind": "datasheet", "license": "manufacturer datasheet (DuPont), read as PDF" } }, { "benchmark": "film_thickness", "value": 2000, "value_high": 3000, "bound": "exact", "unit": "angstrom", "scope": "material", "conditions": { "basis": "sputtered MoS2 film on Nb and Ni-Cr substrates, measured by interference microscope" }, "method": "Thickness range as printed", "status": "ground", "source": "nasa-tn-d-4269", "where": "Experimental procedure, film thickness", "source_detail": { "title": "Deposition of sputtered molybdenum disulfide films and friction characteristics of such films in vacuum", "id": "NASA TN D-4269 (Przybyszewski)", "url": "https://ntrs.nasa.gov/citations/19680002176", "year": 1967, "kind": "report", "license": "NASA public use" } }, { "benchmark": "film_thickness", "value": 10, "value_high": 14, "bound": "exact", "unit": "um", "scope": "material", "conditions": { "basis": "bonded MoS2 (polyamide-imide binder) on 440C stainless steel; the table gives 10 plus or minus 4" }, "method": "Mean as printed, with the plus or minus 4 applied as the range; the table header unit was garbled in extraction and is read here as micrometres (check against the PDF)", "status": "ground", "source": "nasa-tm-1999", "where": "Table I, Bonded MoS2 film thickness", "source_detail": { "title": "Friction and Wear Properties of Selected Solid Lubricating Films", "id": "NASA/TM-1999-209088", "url": "https://ntrs.nasa.gov/citations/19990116894", "year": 1999, "kind": "report", "license": "NASA public use" } } ], "corrosion": [ { "environment": "Humid air at about 20 percent relative humidity, room temperature, pin-on-disk", "headline": "Humid air roughly triples the friction of bonded MoS2 and cuts its wear life by a factor of about ten.", "effect": "Bonded MoS2 went from 0.045 friction and more than one million passes in ultrahigh vacuum to 0.14 and 113,570 passes in humid air. The report calls humid air an oxidative environment. Magnetron-sputtered MoS2 reached 0.10 and 277,377 passes in the same humid air.", "rating": "severe", "conditions": { "basis": "pin-on-disk, 440C stainless steel balls, 5.9 N, 0.2 m/s; endurance life counted to friction 0.3" }, "source": "nasa-tm-1999", "where": "Table II; Results, friction behaviour and humid-air paragraph" }, { "environment": "Spur gears stored in humid air at about 57 percent relative humidity before testing", "headline": "Storage in humid air for up to 77 days cuts film durability by about a third on average.", "effect": "Film durability averaged 100,200 pinion revolutions for unexposed gears and 64,900 for gears exposed to humid air. The reduction is 35 percent on average or 18 percent on the median. The report says colour changes on exposed teeth appeared as soon as 17 days after exposure.", "rating": "moderate", "conditions": { "exposure": "saturated salt solution giving about 57 percent relative humidity, up to 77 days", "test": "vacuum gear rig, constant torque and speed" }, "source": "nasa-gears-2016", "where": "Abstract; Results section and Table 2" }, { "environment": "Atomic oxygen in low Earth orbit (100 to 1000 km)", "headline": "Atomic oxygen oxidizes the MoS2 surface quickly and can leave a high-friction layer after launch.", "effect": "The review says atomic oxygen is extremely reactive and quickly oxidizes the MoS2 surface in low Earth orbit. The oxidized layer causes high friction during run-in, and friction falls to its low steady value only once the oxide is removed faster than it forms. Pre-launch exposure to air can add to this risk.", "rating": "severe", "conditions": { "basis": "general literature statement in the review; no test numbers given in this passage" }, "source": "arxiv-mos2-review", "where": "Oxidation section (atomic oxygen paragraph)" }, { "environment": "Molecular oxygen at high temperature", "headline": "At high temperature, oxygen attacks the MoS2 edges and forms MoO3, which raises wear.", "effect": "The review says molecular oxygen does not affect MoS2 friction at room temperature, but at high temperature it oxidizes the edge sites. The product MoO3 (and MoO2) disrupts the easy shear of the film and creates high wear.", "rating": "moderate", "conditions": { "basis": "literature summary; the temperature threshold is not given in this passage" }, "source": "arxiv-mos2-review", "where": "Oxidation section (molecular oxygen paragraph)" }, { "environment": "Vacuum or inert gas above 500 degC", "headline": "Above about 500 degC MoS2 dissociates thermally in vacuum or inert gas.", "effect": "The review says the thermal dissociation rate of MoS2 rises rapidly in inert gas or vacuum above 500 degC. Burnished MoS2 in vacuum is limited to about 600 to 700 degC for the same reason.", "rating": "moderate", "conditions": { "basis": "literature summary, reference set cited in the review" }, "source": "arxiv-mos2-review", "where": "High-temperature section" } ], "risks": { "hazards": [ { "text": "PubChem reports that MoS2 does not meet GHS hazard criteria in 82.2 percent (1274 of 1550) of company reports. In 17.2 percent of reports it carries H332, harmful if inhaled (acute toxicity, inhalation, Warning).", "ghs": [ "H332" ], "source": "pubchem-mos2", "where": "Safety and Hazards, GHS Classification (CID 14823), first notification" }, { "text": "A second PubChem notification (4 company reports, 25 percent of them) carries H350, may cause cancer (carcinogenicity category 1B, Danger). The entries disagree, so check the supplier safety data sheet for the grade you buy.", "ghs": [ "H350" ], "source": "pubchem-mos2", "where": "Safety and Hazards, GHS Classification, second notification" } ], "failure_risks": [ { "mode": "Humid storage before launch", "trigger": "Film exposed to humid air during storage, integration or ground operations", "consequence": "Film durability fell by about 35 percent on average in the gear test. The NASA authors note that such exposure is common before launch.", "severity": "moderate", "source": "nasa-gears-2016", "where": "Introduction and Results" }, { "mode": "Bearing failure on deployment (Galileo high-gain antenna)", "trigger": "Prolonged storage and transport of the mechanism before launch", "consequence": "The review attributes the Galileo high-gain antenna deployment failure to bearing failure during deployment, linked to storage and transport of the components.", "severity": "high", "source": "arxiv-mos2-review", "where": "Introduction and Oxidation section (Galileo example)" }, { "mode": "High-friction run-in after oxidation", "trigger": "Oxide layer on the film from oxygen exposure during assembly and test on the ground", "consequence": "Friction starts high and falls only after the oxide is worn away. The review says this can be a problem in infrequently operated space devices.", "severity": "moderate", "source": "arxiv-mos2-review", "where": "Oxidation section" } ], "side_effects": [ { "text": "The oxidation product MoO3 (and MoO2) disrupts the easy shear of MoS2 at high temperature and creates high wear.", "affects": "Film wear life and the counterface", "source": "arxiv-mos2-review", "where": "Oxidation section (molecular oxygen paragraph)" } ], "handling": [ { "text": "The datasheet for MOLYKOTE D-321 R gives a 5 to 20 micron dry film, a 2 hour cure at 23 degC, and a touch-dry time of 5 minutes at 23 degC or 1 minute with 80 degC hot air. It recommends phosphating or sand blasting (180 grit) to improve adhesion and life.", "source": "dupont-d321r", "where": "How to use: surface preparation, how to apply, curing time, drying time" }, { "text": "The datasheet says product safety information is not included and that safety data sheets must be read before handling. Stored between 5 and 35 degC in the original container, the product has a 24-month usable life from production.", "source": "dupont-d321r", "where": "Handling precautions; Usable life and storage" }, { "text": "Keep MoS2 films out of humid storage. The gear test shows that film life drops with exposure.", "source": "nasa-gears-2016", "where": "Results and Conclusions" } ], "mitigations": [ { "text": "The review says a run-in procedure performed under vacuum is needed before space use to ensure low friction torques.", "source": "arxiv-mos2-review", "where": "Instruments section, bearings paragraph" }, { "text": "The NASA comparison selected the coating with the longest endurance life and reasonable friction in vacuum, and rated coatings by how they behaved in air as well.", "source": "nasa-cp-2002", "where": "Introduction" } ] }, "uses": [ { "application": "mechanisms", "device": "Auxiliary journal bearings for spacecraft energy storage flywheels", "example": "NASA tested several sputtered MoS2 coatings to pick the one with the longest endurance life for auxiliary flywheel bearings, and noted that exposure to air could reduce the life of the solid lubricant.", "source": "nasa-cp-2002", "where": "Introduction" }, { "application": "mechanisms", "device": "Precision bearings in space instruments at sub-micron film thickness", "example": "The review says MoS2 can be deposited uniformly on precision bearings in instruments at sub-micron thickness, and that it is suited to cryogenic temperatures, including 30 K for JWST.", "source": "arxiv-mos2-review", "where": "Space applications section" }, { "application": "mechanisms", "device": "Spur gears in a vacuum test rig for a space mechanism", "example": "A dry film MoS2 coating on spur gears was tested for film durability at constant torque and speed in a vacuum gear rig, with and without humid-air exposure before test.", "source": "nasa-gears-2016", "where": "Test description and Results" }, { "application": "mechanisms", "device": "Dry-film coating for cylinder-head bolts, car mirror adjustment mechanisms and high-voltage switches", "example": "MOLYKOTE D-321 R, a MoS2 air-curing dry-film coating, is listed for lubrication in vacuum and at extreme temperatures, and for running-in highly stressed gear wheels.", "source": "dupont-d321r", "where": "Applications and use text" } ], "supply": [ { "subject": "Molybdenum (feedstock for MoS2)", "producers": [ { "country": "China", "share_percent": 37.3, "year": 2025 }, { "country": "Chile", "share_percent": 16.2, "year": 2025 }, { "country": "United States", "share_percent": 15.4, "year": 2025 }, { "country": "Peru", "share_percent": 15, "year": 2025 }, { "country": "Mexico", "share_percent": 6.5, "year": 2025 } ], "critical_lists": [], "recycling": "USGS: molybdenum scrap in new and old steel and other scrap may supply as much as 30 percent of the apparent supply.", "substitutes": [], "source": "usgs-mcs2026-mo", "where": "Domestic Production and Use; Events, Trends and Issues; World Mine Production and Reserves table. Shares calculated by Space Mushroom against the 260,000 t world total printed for 2025e." } ], "media": [], "documents": [ { "title": "Solid Lubrication with MoS2: A Review (Lubricants 7, 57, 2019; arXiv:1906.05854)", "type": "paper", "url": "https://arxiv.org/abs/1906.05854", "year": 2019 }, { "title": "Deposition of sputtered molybdenum disulfide films and friction characteristics of such films in vacuum (NASA TN D-4269)", "type": "report", "url": "https://ntrs.nasa.gov/citations/19680002176", "year": 1967 }, { "title": "Friction and Wear Properties of Selected Solid Lubricating Films (NASA/TM-1999-209088)", "type": "report", "url": "https://ntrs.nasa.gov/citations/19990116894", "year": 1999 }, { "title": "Comparison of Several Different Sputtered Molybdenum Disulfide Coatings for Use in Space Applications (NASA/CP-2002-211506)", "type": "paper", "url": "https://ntrs.nasa.gov/citations/20020050209", "year": 2002 }, { "title": "Performance of MoS2 Coated Gears Exposed to Humid Air During Storage (NTRS 20180003085)", "type": "paper", "url": "https://ntrs.nasa.gov/citations/20180003085", "year": 2016 }, { "title": "MOLYKOTE D-321 R Anti-Friction Coating, technical data sheet (Form No. 71-0219E-01)", "type": "datasheet", "url": "https://www.dupont.com/content/dam/Dupont2.0/Products/transportation/Literature/Downloaded-TDS/MOLYKOTE%20D-321%20R%20Anti-Friction%2071-0219E-01.pdf", "year": 2019 }, { "title": "USGS Mineral Commodity Summaries 2026: Molybdenum", "type": "report", "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-molybdenum.pdf", "year": 2026 }, { "title": "PubChem: Molybdenum disulfide (CID 14823), GHS classification and density", "type": "database", "url": "https://pubchem.ncbi.nlm.nih.gov/compound/14823", "year": 2026 } ], "gaps": [ "Hardness of the MoS2 film was not found in any opened source. The 8.7 GPa value in the NASA 2001 durability report (NTRS 20010068606) belongs to the 440C substrate ball and is not used here.", "Coefficient of friction in dry nitrogen and at temperature extremes is not captured beyond the cited text; NASA TM-1999 gives dry nitrogen values (bonded 0.04) that were not added.", "No ASTM D2625 or LFW-1 unit printed in the datasheet text extract; the Falex load unit is left as printed.", "Bonded film thickness header in NASA TM-1999 Table I was garbled in extraction; the value is read as micrometres and should be checked against the PDF.", "Bonderite (Henkel) datasheet not found at the URLs tried in this run; no phosphate-conversion or Bonderite-based value is recorded.", "PubChem lists two melting points (2375 and 1185 degC) with no attribution to MoS2 or a source; not used.", "No critical-mineral status for molybdenum was found in the USGS 2026 molybdenum chapter as extracted; the critical_lists field is empty.", "The recipe process for commercial MoS2 powder and the source of the molybdenite feedstock are not stated in any opened source; the sputtering route is from the review.", "Relative mass shares of Mo and S (59.9 and 40.1 percent) are not in a source; they follow from the atomic weights below (PubChem CID 23932 and 5362487).", "Benchmark names not in spores/property-canon.yaml and used here: coefficient_of_friction, endurance_life (passes), load_carrying_capacity_falex, load_carrying_capacity_lfw, film_thickness. Check them against the canon before import.", "Space flight data for MoS2 films (in-orbit friction or life) were not found in the opened sources; the NASA results are ground tests." ], "story": { "why": "Molybdenum disulfide is a solid lubricant whose layers slide over one another with little resistance. In NASA's ultrahigh-vacuum tests a bonded film ran at 0.045 with more than one million passes, and sputtered films stayed near 0.06 to 0.09. The same films lose much of that advantage in humid air, where friction rises and life falls. That split explains where MoS2 is chosen: vacuum mechanisms and bearings that cannot take oil or grease, with the humidity history of the part controlled.", "uses": [ { "where": "Auxiliary bearings for spacecraft flywheels", "line": "NASA compared sputtered MoS2 coatings for auxiliary journal bearings of spacecraft energy storage flywheels, and selected the coating with the longest life that also kept reasonable friction." }, { "where": "Precision instrument bearings", "line": "The review says sputtered MoS2 can be deposited uniformly on precision bearings in instruments at sub-micron thickness, and that it works down to cryogenic temperatures such as the 30 K operating point of JWST." }, { "where": "Spur gears for space mechanisms", "line": "A MoS2 dry film on spur gears was tested for durability in a vacuum gear rig. Storage in humid air cut the average life by about a third." } ], "can_do": [ { "label": "Friction in vacuum", "line": "Bonded MoS2 steady-state friction in ultrahigh vacuum was 0.045 on 440C stainless steel at 5.9 N (NASA TM-1999). Sputtered films gave 0.06 to 0.09 (NASA TN D-4269).", "scope": "material", "value": "0.045" }, { "label": "Friction in humid air", "line": "In humid air at about 20 percent relative humidity, the bonded film rose to 0.14 and the magnetron-sputtered film to 0.10.", "scope": "material", "value": "0.14" }, { "label": "Endurance life", "line": "In ultrahigh vacuum the bonded film ran past one million passes. In humid air it lasted 113,570 passes (NASA TM-1999). End of life is the pass count at which friction reaches 0.3.", "scope": "material", "value": "More than 1 million passes" }, { "label": "Temperature limit", "line": "The D-321 R datasheet gives a service range of -180 to 450 degC. The review puts burnished MoS2 in vacuum at 600 to 700 degC, and mechanically deposited MoS2 in air at about 400 degC.", "scope": "material", "value": "450 degC" } ], "compare": "MoS2 gives a steady friction of about 0.045 in ultrahigh vacuum, and this is its advantage over oil or grease, which evaporate in vacuum. Its friction and life worsen sharply with humidity: the bonded film triples its friction in humid air and loses more than eight times its life. A commercial dry-film coating has a service range up to 450 degC, below the 600 to 700 degC of burnished MoS2 in vacuum.", "compare_rows": [ { "label": "Friction in vacuum", "benchmark": "coefficient_of_friction", "scope": "material" }, { "label": "Endurance life", "benchmark": "endurance_life", "scope": "material" }, { "label": "Maximum service temperature", "benchmark": "max_service_temp", "scope": "material" } ], "handling": [ "Read the supplier safety data sheet first. The D-321 R datasheet says product safety information is not included in the document.", "Keep the film out of humid storage. NASA found film durability on gears fell by about 35 percent after up to 77 days at 57 percent relative humidity.", "Cure the coating for 2 hours at 23 degC before use. Phosphating or sand blasting improves adhesion.", "Under vacuum, run in the film before use to get low friction, as the review recommends." ], "good_for": [ "Dry sliding in vacuum. Bonded MoS2 ran at 0.045 friction for over one million passes in NASA's ultrahigh-vacuum tests.", "Extreme temperatures. The D-321 R datasheet gives a service range of -180 to 450 degC, and the review puts burnished MoS2 in vacuum at 600 to 700 degC." ], "watch_out": [ "Humidity. In humid air friction rose from 0.045 to 0.14 for the bonded film, and endurance life fell from over one million to 113,570 passes.", "Oxidation. Atomic oxygen in low Earth orbit and molecular oxygen at high temperature both degrade the film, and oxidation can cause high run-in friction.", "Storage. Pre-launch humid storage cut gear film durability by about 35 percent in NASA's test." ], "verdict": "MoS2 is the reference dry lubricant for vacuum. The numbers that matter most are the vacuum friction and life, and the humidity penalty that follows from storage and ground handling.", "recipe": { "line": "MoS2 is a layered compound. Each formula unit combines one molybdenum atom with two sulfur atoms, in trigonal prismatic coordination. Commercial films are made by sputtering from a MoS2 target in a vacuum chamber with a noble-gas plasma (review), or as a bonded film of MoS2 in a polyamide-imide binder (NASA TM-1999, Table I).", "parts": [ { "name": "Molybdenum", "symbol": "Mo", "role": "Sits between two sulfur layers in each sheet; the sheets are the sliding planes.", "atoms": 1, "atomic_weight": 95.95 }, { "name": "Sulfur", "symbol": "S", "role": "Forms the top and bottom layers of each sheet; weak van der Waals bonds link the sheets to one another.", "atoms": 2, "atomic_weight": 32.07 } ] }, "risk_groups": [ { "title": "For people", "lead": "PubChem reports that most company notifications find no GHS hazard for MoS2, but a minority list inhalation harm or a cancer hazard, so the grade matters.", "points": [ { "label": "Most reports", "line": "82.2 percent of 1,550 company reports do not meet GHS hazard criteria (PubChem)." }, { "label": "Inhalation", "line": "17.2 percent of reports carry H332, harmful if inhaled (Warning)." }, { "label": "Cancer", "line": "A second notification from 4 reports (25 percent) carries H350, may cause cancer (Danger). Check the supplier safety data sheet for the grade you buy." } ], "level": 0, "verdict": "Not classified hazardous in most reports" }, { "title": "Handling the coating", "points": [ { "label": "Application", "line": "The datasheet recommends a 5 to 20 micron dry film, cured for 2 hours at 23 degC, and phosphating or sand blasting first." }, { "label": "Storage", "line": "Store between 5 and 35 degC in the closed original container; the usable life is 24 months from production." } ] } ] }, "updated": "2026-10-19", "review": { "status": "draft", "method": "assistant", "checked_values": 22, "unreachable": 1, "caveats": 2, "note": "Deepened 2026-10-19 from NASA NTRS reports, the arXiv review, the DuPont D-321 R datasheet, the USGS 2026 molybdenum chapter and PubChem. Bonderite datasheet and hardness not found; see gaps." }, "sources": { "wiki-mos2": { "title": "Molybdenum disulfide", "id": "Wikipedia, English edition", "url": "https://en.wikipedia.org/wiki/Molybdenum_disulfide", "kind": "web", "license": "CC BY-SA 4.0" }, "arxiv-mos2-review": { "title": "Solid Lubrication with MoS2: A Review", "id": "arXiv:1906.05854 (Lubricants 7, 57, 2019)", "url": "https://arxiv.org/abs/1906.05854", "year": 2019, "kind": "paper", "license": "arXiv (full text read as PDF in this run)" }, "nasa-tn-d-4269": { "title": "Deposition of sputtered molybdenum disulfide films and friction characteristics of such films in vacuum", "id": "NASA TN D-4269 (Przybyszewski)", "url": "https://ntrs.nasa.gov/citations/19680002176", "year": 1967, "kind": "report", "license": "NASA public use" }, "nasa-tm-1999": { "title": "Friction and Wear Properties of Selected Solid Lubricating Films", "id": "NASA/TM-1999-209088", "url": "https://ntrs.nasa.gov/citations/19990116894", "year": 1999, "kind": "report", "license": "NASA public use" }, "nasa-cp-2002": { "title": "Comparison of Several Different Sputtered Molybdenum Disulfide Coatings for Use in Space Applications", "id": "NASA/CP-2002-211506", "url": "https://ntrs.nasa.gov/citations/20020050209", "year": 2002, "kind": "paper", "license": "NASA public use" }, "nasa-gears-2016": { "title": "Performance of MoS2 Coated Gears Exposed to Humid Air During Storage", "id": "NTRS 20180003085 (presented 2016)", "url": "https://ntrs.nasa.gov/citations/20180003085", "year": 2016, "kind": "paper", "license": "NASA public use" }, "dupont-d321r": { "title": "MOLYKOTE D-321 R Anti-Friction Coating, technical data sheet", "id": "Form No. 71-0219E-01 (07/19)", "url": "https://www.dupont.com/content/dam/Dupont2.0/Products/transportation/Literature/Downloaded-TDS/MOLYKOTE%20D-321%20R%20Anti-Friction%2071-0219E-01.pdf", "year": 2019, "kind": "datasheet", "license": "manufacturer datasheet (DuPont), read as PDF" }, "usgs-mcs2026-mo": { "title": "Mineral Commodity Summaries 2026: Molybdenum", "id": "USGS, February 2026", "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-molybdenum.pdf", "year": 2026, "kind": "report", "license": "public domain (USGS)" }, "pubchem-mos2": { "title": "Molybdenum disulfide (CID 14823)", "id": "PubChem, NIH National Library of Medicine", "url": "https://pubchem.ncbi.nlm.nih.gov/compound/14823", "year": 2026, "kind": "database", "license": "public domain (NLM)" } }, "license": "CC-BY-4.0", "url": "https://spacemushroom.com/profiles/molybdenum-disulfide/" }