Molybdenum disulfide MoS2

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.
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)
  source: wiki-mos2
  where: Infobox and Structure section
tags:
  environments:
    - low-earth-orbit
  stresses: []
  applications:
    - mechanisms
properties:
  - benchmark: density
    value: 5.06
    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)
  - benchmark: coefficient_of_friction
    value: 0.045
    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
  - benchmark: coefficient_of_friction
    value: 0.07
    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
  - benchmark: coefficient_of_friction
    value: 0.06
    value_high: 0.09
    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)
  - benchmark: coefficient_of_friction
    value: 0.14
    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
  - benchmark: coefficient_of_friction
    value: 0.1
    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)
  - benchmark: coefficient_of_friction
    value: 0.04
    value_high: 0.15
    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
  - benchmark: endurance_life
    value: 1000000
    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)
  - benchmark: endurance_life
    value: 274130
    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
  - benchmark: endurance_life
    value: 113570
    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)
  - benchmark: endurance_life
    value: 277377
    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)
  - benchmark: endurance_life
    value: 100200
    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)
  - benchmark: endurance_life
    value: 64900
    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)
  - benchmark: max_service_temp
    value: 600
    value_high: 700
    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)
  - benchmark: max_service_temp
    value: 400
    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)
  - benchmark: max_service_temp
    value: 450
    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)
  - benchmark: min_service_temp
    value: -180
    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)
  - benchmark: load_carrying_capacity_falex
    value: 12500
    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)
  - benchmark: load_carrying_capacity_lfw
    value: 2860
    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)
  - benchmark: film_thickness
    value: 5
    value_high: 20
    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
  - benchmark: film_thickness
    value: 2000
    value_high: 3000
    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
  - benchmark: film_thickness
    value: 10
    value_high: 14
    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
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
        tonnes: 97000
        share_percent: 37.3
        year: 2025
      - country: Chile
        tonnes: 42000
        share_percent: 16.2
        year: 2025
      - country: United States
        tonnes: 40000
        share_percent: 15.4
        year: 2025
      - country: Peru
        tonnes: 39000
        share_percent: 15
        year: 2025
      - country: Mexico
        tonnes: 17000
        share_percent: 6.5
        year: 2025
    reserves: 'USGS 2026: reserves of 7,800 thousand t (China), 2,600 (Chile), 3,500 (United States), 1,000 (Peru) and 130 (Mexico). World total mine production 2025e: 260,000 t, molybdenum content.'
    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.'
    export_controls: 'USGS: China imposed export controls on molybdenum powders in February 2025, which prompted other countries to seek alternative sources. Powder is the form used for MoS2 feedstock in this profile''s chain.'
    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.
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
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.
story:
  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
        atoms: 1
        atomic_weight: 95.95
        role: Sits between two sulfur layers in each sheet; the sheets are the sliding planes.
      - name: Sulfur
        symbol: S
        atoms: 2
        atomic_weight: 32.07
        role: Forms the top and bottom layers of each sheet; weak van der Waals bonds link the sheets to one another.
  risk_groups:
    - title: For people
      level: 0
      verdict: Not classified hazardous in most reports
      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.
    - 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.
  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
      value: '0.045'
      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).
    - label: Friction in humid air
      value: '0.14'
      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.
    - label: Endurance life
      value: More than 1 million passes
      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.
    - label: Temperature limit
      value: 450 degC
      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.
  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:
    - scope: material
      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
  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.