{
  "spore": "profile",
  "id": "tungsten-disulphide",
  "spore_version": "0.2",
  "family": "lubricant",
  "name": "Tungsten disulfide",
  "abbreviation": "WS2",
  "role": "dry film lubricant",
  "category": "tribology",
  "type": "dry-lubricants",
  "summary": "Tungsten disulfide is a layered sulfide, like molybdenum disulfide. Its sheets slide over one another because they are held together only by weak van der Waals forces. It is used as a powder, a sputtered or laser-deposited film, and as nanotubes and two-dimensional layers. In NASA tests in ultrahigh vacuum a laser-deposited film ran at a friction below 0.1 and wore at a rate 30 times lower after annealing. In humid air the same family of films lasted about 9,000 passes, against more than 500,000 in vacuum. NASA describes WS2 as resisting oxidation in air better than MoS2, by about 100 degC.\n",
  "best_for": "Dry sliding contacts in vacuum where oil or grease cannot be used (NASA: sputtered film friction 0.055 and over one million cycles in vacuum)",
  "weakest_at": "Humid air and atmosphere, where friction rises to 0.22 and sputtered film life falls to 1,500 cycles (NASA, 1970)",
  "identity": {
    "formula": "WS2",
    "cas": "12138-09-9",
    "crystal_system": "molybdenite type (layered)",
    "designations": [],
    "source": "wiki-ws2",
    "where": "Infobox, Crystal structure (Molybdenite); formula from SDS section 3 (WS2, molecular weight 247.98 g/mol)"
  },
  "tags": {
    "environments": [],
    "stresses": [],
    "applications": [
      "mechanisms",
      "batteries",
      "electronics-and-chips"
    ]
  },
  "properties": [
    {
      "benchmark": "density",
      "label": "Relative density",
      "value": 7.5,
      "bound": "exact",
      "unit": "g/cm3",
      "scope": "material",
      "conditions": {
        "basis": "crystalline WS2 powder, supplier SDS (printed as 7.500 g/cm3)"
      },
      "method": "Relative density as printed in the supplier SDS",
      "status": "ground",
      "source": "sds-ws2",
      "where": "Section 9.1, item m) Relative density",
      "source_detail": {
        "title": "Tungsten disulfide, Crystal, 99.995% safety data sheet (Stanford Advanced Materials, version 3.0)",
        "id": "SAM product WS2 powder, revision date 09/04/2017",
        "url": "https://www.samaterials.com/pdf/Tungsten-Disulfide-(WS2)-Powder-sds.pdf",
        "year": 2017,
        "kind": "datasheet",
        "license": "supplier SDS (cited, not reproduced)"
      }
    },
    {
      "benchmark": "density",
      "label": "Density (Wikipedia infobox)",
      "value": 7.5,
      "bound": "exact",
      "unit": "g/cm3",
      "scope": "material",
      "conditions": {
        "basis": "WS2, solid, as printed in the infobox"
      },
      "method": "Infobox value as printed",
      "status": "ground",
      "source": "wiki-ws2",
      "where": "Infobox, Density 7.5 g/cm3, solid",
      "source_detail": {
        "title": "Tungsten disulfide",
        "id": "Wikipedia, English edition",
        "url": "https://en.wikipedia.org/wiki/Tungsten_disulfide",
        "kind": "web",
        "license": "CC BY-SA 4.0"
      }
    },
    {
      "benchmark": "melting_point",
      "label": "Melting point or range",
      "value": 1200,
      "bound": "exact",
      "unit": "degC",
      "scope": "material",
      "conditions": {
        "basis": "crystalline WS2 powder, supplier SDS"
      },
      "method": "Melting point/range as printed in the SDS (1,200 degC, 2,192 degF)",
      "status": "ground",
      "source": "sds-ws2",
      "where": "Section 9.1, item e) Melting point/range",
      "source_detail": {
        "title": "Tungsten disulfide, Crystal, 99.995% safety data sheet (Stanford Advanced Materials, version 3.0)",
        "id": "SAM product WS2 powder, revision date 09/04/2017",
        "url": "https://www.samaterials.com/pdf/Tungsten-Disulfide-(WS2)-Powder-sds.pdf",
        "year": 2017,
        "kind": "datasheet",
        "license": "supplier SDS (cited, not reproduced)"
      }
    },
    {
      "benchmark": "decomposition_temperature",
      "label": "Decomposition temperature",
      "value": 1250,
      "bound": "exact",
      "unit": "degC",
      "scope": "material",
      "conditions": {
        "basis": "WS2 heated without oxygen; the article says it decomposes to tungsten and sulfur at this temperature"
      },
      "method": "Infobox value as printed (1,250 degC, 2,280 degF, 1,520 K, decomposes)",
      "status": "ground",
      "source": "wiki-ws2",
      "where": "Infobox, Melting point row",
      "source_detail": {
        "title": "Tungsten disulfide",
        "id": "Wikipedia, English edition",
        "url": "https://en.wikipedia.org/wiki/Tungsten_disulfide",
        "kind": "web",
        "license": "CC BY-SA 4.0"
      }
    },
    {
      "benchmark": "coefficient_of_friction",
      "label": "Friction in ultrahigh vacuum, sputtered film",
      "value": 0.055,
      "bound": "exact",
      "unit": "dimensionless",
      "scope": "material",
      "conditions": {
        "basis": "dc-sputtered WS2 film on Ni, Ni-Cr or Nb disk, sliding against a metal rider, ultrahigh vacuum; load not stated in the text"
      },
      "method": "Average coefficient of friction over the test, as printed in the text of section VII",
      "status": "ground",
      "source": "nasa-tm-x52819",
      "where": "Section VII, paragraph beginning When the experiments were conducted in vacuum",
      "source_detail": {
        "title": "Friction characteristics of sputtered solid film lubricants",
        "id": "NASA TM X-52819 (Spalvins, Lewis Research Center, 1970)",
        "url": "https://ntrs.nasa.gov/citations/19700020846",
        "year": 1970,
        "kind": "report",
        "license": "NASA public use"
      }
    },
    {
      "benchmark": "coefficient_of_friction",
      "label": "Friction in atmosphere, sputtered film",
      "value": 0.22,
      "bound": "exact",
      "unit": "dimensionless",
      "scope": "material",
      "conditions": {
        "basis": "the same dc-sputtered WS2 film tested under atmospheric conditions (humidity not stated in the text)"
      },
      "method": "Coefficient of friction as printed; the report says it rose immediately on test start",
      "status": "ground",
      "source": "nasa-tm-x52819",
      "where": "Section VII, paragraph beginning When the experiments were conducted in vacuum",
      "source_detail": {
        "title": "Friction characteristics of sputtered solid film lubricants",
        "id": "NASA TM X-52819 (Spalvins, Lewis Research Center, 1970)",
        "url": "https://ntrs.nasa.gov/citations/19700020846",
        "year": 1970,
        "kind": "report",
        "license": "NASA public use"
      }
    },
    {
      "benchmark": "coefficient_of_friction",
      "label": "Friction in ultrahigh vacuum, laser-annealed film",
      "value": 0.1,
      "bound": "exact",
      "unit": "dimensionless",
      "scope": "material",
      "conditions": {
        "basis": "pulsed-laser-deposited WS2 coating, about 1 um thick, laser-annealed, on 440C stainless steel, 6 mm 440C ball, ultrahigh vacuum 7 x 10-7 Pa, 0.98 N (100 g), room temperature"
      },
      "method": "Steady-state friction; the summary says the friction was less than 0.1, so 0.1 is the upper bound as printed",
      "status": "ground",
      "source": "nasa-tm-107342",
      "where": "Summary and Concluding Remarks (annealed WS2 coating, coefficient of friction less than 0.1)",
      "source_detail": {
        "title": "Surface Chemistry, Friction, and Wear Properties of Untreated and Laser-Annealed Surfaces of Pulsed-Laser-Deposited WS2 Coatings",
        "id": "NASA TM 107342 (Miyoshi, Wheeler, Zabinski, December 1996)",
        "url": "https://ntrs.nasa.gov/citations/19970009635",
        "year": 1996,
        "kind": "report",
        "license": "NASA public use"
      }
    },
    {
      "benchmark": "endurance_life",
      "label": "Endurance life in atmosphere, sputtered film",
      "value": 1500,
      "bound": "exact",
      "unit": "cycles",
      "scope": "material",
      "conditions": {
        "basis": "the same dc-sputtered WS2 film in atmospheric conditions; film failure reported after this many cycles"
      },
      "method": "Cycles to failure as printed",
      "status": "ground",
      "source": "nasa-tm-x52819",
      "where": "Section VII, paragraph beginning When the experiments were conducted in vacuum",
      "source_detail": {
        "title": "Friction characteristics of sputtered solid film lubricants",
        "id": "NASA TM X-52819 (Spalvins, Lewis Research Center, 1970)",
        "url": "https://ntrs.nasa.gov/citations/19700020846",
        "year": 1970,
        "kind": "report",
        "license": "NASA public use"
      }
    },
    {
      "benchmark": "endurance_life",
      "label": "Endurance life in ultrahigh vacuum, untreated film",
      "value": 50000,
      "bound": "exact",
      "unit": "passes",
      "scope": "material",
      "conditions": {
        "basis": "pulsed-laser-deposited WS2 on 440C, ultrahigh vacuum 7 x 10-7 Pa, 0.98 N; life is the number of passes at which the friction reaches 0.3"
      },
      "method": "Wear life as printed (around 50,000 passes)",
      "status": "ground",
      "source": "nasa-tm-107342",
      "where": "Wear Life section (untreated coating in ultrahigh vacuum)",
      "source_detail": {
        "title": "Surface Chemistry, Friction, and Wear Properties of Untreated and Laser-Annealed Surfaces of Pulsed-Laser-Deposited WS2 Coatings",
        "id": "NASA TM 107342 (Miyoshi, Wheeler, Zabinski, December 1996)",
        "url": "https://ntrs.nasa.gov/citations/19970009635",
        "year": 1996,
        "kind": "report",
        "license": "NASA public use"
      }
    },
    {
      "benchmark": "endurance_life",
      "label": "Endurance life in ultrahigh vacuum, laser-annealed film",
      "value": 500000,
      "bound": "exact",
      "unit": "passes",
      "scope": "material",
      "conditions": {
        "basis": "pulsed-laser-deposited WS2 on 440C, laser-annealed, ultrahigh vacuum 7 x 10-7 Pa, 0.98 N; life is the number of passes at which the friction reaches 0.3"
      },
      "method": "Lower bound as printed (greater than 500,000 passes)",
      "status": "ground",
      "source": "nasa-tm-107342",
      "where": "Wear Life section (laser-annealed coating in ultrahigh vacuum)",
      "source_detail": {
        "title": "Surface Chemistry, Friction, and Wear Properties of Untreated and Laser-Annealed Surfaces of Pulsed-Laser-Deposited WS2 Coatings",
        "id": "NASA TM 107342 (Miyoshi, Wheeler, Zabinski, December 1996)",
        "url": "https://ntrs.nasa.gov/citations/19970009635",
        "year": 1996,
        "kind": "report",
        "license": "NASA public use"
      }
    },
    {
      "benchmark": "endurance_life",
      "label": "Endurance life in humid air, both films",
      "value": 9000,
      "bound": "exact",
      "unit": "passes",
      "scope": "material",
      "conditions": {
        "basis": "pulsed-laser-deposited WS2 on 440C, humid air at 15 to 40 percent relative humidity, 0.98 N; life is the number of passes at which the friction reaches 0.8 in humid air"
      },
      "method": "Around 9,000 passes as printed, for both untreated and annealed coatings",
      "status": "ground",
      "source": "nasa-tm-107342",
      "where": "Wear Life section (humid air, around 9000 passes)",
      "source_detail": {
        "title": "Surface Chemistry, Friction, and Wear Properties of Untreated and Laser-Annealed Surfaces of Pulsed-Laser-Deposited WS2 Coatings",
        "id": "NASA TM 107342 (Miyoshi, Wheeler, Zabinski, December 1996)",
        "url": "https://ntrs.nasa.gov/citations/19970009635",
        "year": 1996,
        "kind": "report",
        "license": "NASA public use"
      }
    },
    {
      "benchmark": "film_thickness",
      "label": "Maximum film thickness, Dicronite coating",
      "value": 0.5,
      "bound": "exact",
      "unit": "um",
      "scope": "material",
      "conditions": {
        "basis": "Dicronite dry-film WS2 coating, precision film"
      },
      "method": "Maximum as printed (0.5 microns, 0.000020 inches)",
      "status": "ground",
      "source": "precision-dicronite",
      "where": "Section Key to Dicronite dry lubrication applications, precision film thickness",
      "source_detail": {
        "title": "Dicronite dry film lubrication (distributor page)",
        "id": "Precision Coatings, Dicronite page",
        "url": "https://precisioncoatings.com/dicronite/",
        "kind": "web",
        "license": "web page (cited, not reproduced)"
      }
    },
    {
      "benchmark": "elastic_modulus",
      "label": "Young's modulus, WS2 nanotubes",
      "value": 160,
      "value_high": 170,
      "bound": "exact",
      "unit": "GPa",
      "scope": "material",
      "conditions": {
        "basis": "WS2 nanotubes, as stated in the review; whether measured or calculated is not stated in the sentence"
      },
      "method": "Range as printed in the review (Young's modulus of 160 to 170 GPa)",
      "status": "ground",
      "source": "yadgarov-tenne-2024",
      "where": "Mechanical, thermal and electrical properties section",
      "source_detail": {
        "title": "Nanotubes from Transition Metal Dichalcogenides, Recent Progress in the Synthesis, Characterization and Electrooptical Properties",
        "id": "Yadgarov and Tenne, Small, 2024 (PubMed Central PMC12272021)",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC12272021/",
        "year": 2024,
        "kind": "paper",
        "license": "open access (PMC)"
      }
    },
    {
      "benchmark": "thermal_conductivity",
      "label": "Thermal conductivity, single WS2 layer",
      "value": 32,
      "bound": "exact",
      "unit": "W/(m·K)",
      "scope": "material",
      "conditions": {
        "basis": "single layer of WS2 at room temperature, as printed in the review"
      },
      "method": "Value as printed (32 W mK-1 at room temperature)",
      "status": "ground",
      "source": "yadgarov-tenne-2024",
      "where": "Mechanical, thermal and electrical properties section",
      "source_detail": {
        "title": "Nanotubes from Transition Metal Dichalcogenides, Recent Progress in the Synthesis, Characterization and Electrooptical Properties",
        "id": "Yadgarov and Tenne, Small, 2024 (PubMed Central PMC12272021)",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC12272021/",
        "year": 2024,
        "kind": "paper",
        "license": "open access (PMC)"
      }
    },
    {
      "benchmark": "band_gap_optical_direct",
      "label": "Direct optical band gap, monolayer",
      "value": 2.05,
      "bound": "exact",
      "unit": "eV",
      "scope": "material",
      "conditions": {
        "basis": "WS2 monolayer, optical direct gap; printed with a tilde (approximate)"
      },
      "method": "Infobox value as printed (about 2.05 eV)",
      "status": "ground",
      "source": "wiki-ws2",
      "where": "Band gap section (optical, direct, monolayer)",
      "source_detail": {
        "title": "Tungsten disulfide",
        "id": "Wikipedia, English edition",
        "url": "https://en.wikipedia.org/wiki/Tungsten_disulfide",
        "kind": "web",
        "license": "CC BY-SA 4.0"
      }
    },
    {
      "benchmark": "band_gap_optical_indirect",
      "label": "Indirect optical band gap, bulk",
      "value": 1.35,
      "bound": "exact",
      "unit": "eV",
      "scope": "material",
      "conditions": {
        "basis": "bulk WS2, optical indirect gap; printed with a tilde (approximate)"
      },
      "method": "Band gap section value as printed (about 1.35 eV)",
      "status": "ground",
      "source": "wiki-ws2",
      "where": "Band gap section (optical, indirect, bulk)",
      "source_detail": {
        "title": "Tungsten disulfide",
        "id": "Wikipedia, English edition",
        "url": "https://en.wikipedia.org/wiki/Tungsten_disulfide",
        "kind": "web",
        "license": "CC BY-SA 4.0"
      }
    }
  ],
  "corrosion": [
    {
      "environment": "Air or atmosphere during sliding, dc-sputtered WS2 film",
      "headline": "Atmosphere cut sputtered WS2 life from over one million cycles in vacuum to 1,500 cycles.",
      "effect": "In vacuum the film averaged 0.055 friction and lasted over a million cycles. In atmosphere the friction rose to 0.22 at once and the film failed after 1,500 cycles. The report explains the failure by sulfuric acid formed on the surface, which has a corrosive effect.",
      "rating": "severe",
      "conditions": {
        "basis": "dc-sputtered WS2 film, atmospheric conditions (humidity not stated)"
      },
      "source": "nasa-tm-x52819",
      "where": "Section VII, paragraph on atmospheric tests"
    },
    {
      "environment": "Humid air at 15 to 40 percent relative humidity, room temperature, pin on disk",
      "headline": "Humid air reduces the wear life of pulsed-laser WS2 coatings by a factor of more than 50 compared with ultrahigh vacuum.",
      "effect": "Both untreated and laser-annealed coatings lasted about 9,000 passes in humid air. The annealed coating lasted more than 500,000 passes in ultrahigh vacuum. The report ranks the environments by life as humid air, then ultrahigh vacuum, then dry nitrogen.",
      "rating": "severe",
      "conditions": {
        "basis": "pulsed-laser-deposited WS2 on 440C, 0.98 N, 6 mm ball, life defined as friction reaching 0.8 in humid air and 0.3 in vacuum"
      },
      "source": "nasa-tm-107342",
      "where": "Wear Life section"
    },
    {
      "environment": "Dry nitrogen below 1 percent relative humidity, room temperature",
      "headline": "Dry nitrogen gives the longest life of the three environments tested.",
      "effect": "The coating lasted more than 2 million passes in dry nitrogen, against about 9,000 in humid air. Friction in dry nitrogen decreased with the number of passes, while it rose in humid air.",
      "rating": "low",
      "conditions": {
        "basis": "pulsed-laser-deposited WS2 on 440C, 0.98 N; life defined as friction reaching 0.15 in dry nitrogen"
      },
      "source": "nasa-tm-107342",
      "where": "Friction Behavior and Wear Life sections"
    },
    {
      "environment": "Heating in air",
      "headline": "NASA reports that WS2 resists oxidation in air about 100 degC better than MoS2, but gives no absolute oxidation temperature.",
      "effect": "The report says WS2 has an advantage of about 100 degC over MoS2 in oxidation resistance and thermal stability. The report gives no absolute onset temperature for oxidation in air.",
      "rating": "unknown",
      "conditions": {
        "basis": "relative comparison only; no absolute temperature given in the sources opened"
      },
      "source": "nasa-tm-107342",
      "where": "Introduction"
    }
  ],
  "risks": {
    "hazards": [
      {
        "text": "The supplier SDS classifies WS2 powder as skin irritant (Category 2, H315), eye irritant (Category 2A, H319) and a single-exposure respiratory irritant (Category 3, H335), with the Warning signal word.",
        "ghs": [
          "H315",
          "H319",
          "H335"
        ],
        "source": "sds-ws2",
        "where": "Section 2.1 and 2.2, GHS classification and label elements"
      },
      {
        "text": "PubChem records H315, H319 and H335 in 57.2 percent of 138 company notifications, and no GHS hazard for the other 42.8 percent of reports (59 of 138).",
        "ghs": [
          "H315",
          "H319",
          "H335"
        ],
        "source": "pubchem-ws2",
        "where": "Safety and Hazards, GHS Classification (CID 82938)"
      },
      {
        "text": "The SDS lists no IARC or NTP carcinogen at 0.1 percent or more, and does not classify the substance as carcinogenic.",
        "ghs": [],
        "source": "sds-ws2",
        "where": "Section 11.1, Carcinogenicity"
      }
    ],
    "failure_risks": [
      {
        "mode": "Atmospheric exposure during sliding",
        "trigger": "Sputtered film run in air instead of ultrahigh vacuum",
        "consequence": "Friction rose to 0.22 at once and the film failed after 1,500 cycles, against more than one million cycles in vacuum. NASA attributes the failure to sulfuric acid formed on the surface.",
        "severity": "high",
        "source": "nasa-tm-x52819",
        "where": "Section VII, atmospheric tests"
      },
      {
        "mode": "Humid-air wear",
        "trigger": "Pulsed-laser WS2 coating run at 15 to 40 percent relative humidity",
        "consequence": "Wear life of about 9,000 passes, against more than 500,000 for the annealed coating in ultrahigh vacuum.",
        "severity": "high",
        "source": "nasa-tm-107342",
        "where": "Wear Life section"
      },
      {
        "mode": "Humid storage of a pressed WS2 compact",
        "trigger": "Cold-pressed compact wrapped in paper and stored in atmospheric conditions",
        "consequence": "The report says the humidity affected the compact over several weeks; no number is given, and the result is shown only in a figure.",
        "severity": "moderate",
        "source": "nasa-tm-x52819",
        "where": "Section VII, paragraph on the stored compact (Figure 19)"
      }
    ],
    "side_effects": [
      {
        "text": "In a fire, WS2 decomposes to sulphur oxides and tungsten oxide. The SDS gives no other decomposition data.",
        "affects": "Responders and the surrounding materials in a fire",
        "source": "sds-ws2",
        "where": "Section 10.6, hazardous decomposition products"
      }
    ],
    "handling": [
      {
        "text": "The SDS says to keep the container tightly closed in a dry and well-ventilated place, and to store under nitrogen. It classes the material as air-, heat- and moisture-sensitive.",
        "source": "sds-ws2",
        "where": "Section 7.2, conditions for safe storage"
      },
      {
        "text": "Avoid dust formation and provide exhaust ventilation where dust forms. Further processing of the solid may produce combustible dust.",
        "source": "sds-ws2",
        "where": "Sections 7.1 and 7.2 (handling and dust)"
      },
      {
        "text": "Keep WS2 away from strong acids and strong oxidizing agents.",
        "source": "sds-ws2",
        "where": "Section 10.5, incompatible materials"
      },
      {
        "text": "The Dicronite coating is applied near ambient temperature, at a maximum of 35 degC.",
        "source": "precision-dicronite",
        "where": "Section Key to Dicronite dry lubrication applications, application temperature"
      }
    ],
    "mitigations": [
      {
        "text": "Laser annealing reduced the wear rate of the coating by a factor of 30 in ultrahigh vacuum and gave more than 500,000 passes against about 50,000 for the untreated coating.",
        "source": "nasa-tm-107342",
        "where": "Summary and Concluding Remarks"
      }
    ]
  },
  "uses": [
    {
      "application": "mechanisms",
      "device": "Sliding contacts in vacuum, such as bearings and gears where oil or grease cannot be used",
      "example": "NASA describes WS2 as an effective inorganic lubricant in a vacuum, behaving much like MoS2, and tested pulsed-laser WS2 coatings on 440C stainless steel for sliding life in ultrahigh vacuum.",
      "source": "nasa-tm-107342",
      "where": "Introduction and Summary"
    },
    {
      "application": "electronics-and-chips",
      "device": "Field-effect transistor made from small-diameter WS2 nanotubes",
      "example": "The review reports p-type mobility of 1.7 plus or minus 0.5 cm2 V-1 s-1 and n-type mobility of 0.26 plus or minus 0.05 cm2 V-1 s-1 for nanotubes of about 20 nm diameter used in transistors.",
      "source": "yadgarov-tenne-2024",
      "where": "Mechanical, thermal and electrical properties section (transistor paragraph)"
    },
    {
      "application": "batteries",
      "device": "Electrode material in a battery test using WS2 nanotubes",
      "example": "The review reports a capacity of 371.9 mAh/g and 62 percent retention after 500 cycles at 1000 mA/g for a WS2 nanotube electrode.",
      "source": "yadgarov-tenne-2024",
      "where": "Applications, battery section"
    }
  ],
  "supply": [
    {
      "subject": "Tungsten (feedstock for WS2)",
      "producers": [
        {
          "country": "China",
          "share_percent": 78.8,
          "year": 2025
        },
        {
          "country": "Vietnam",
          "share_percent": 3.5,
          "year": 2025
        },
        {
          "country": "Kazakhstan",
          "share_percent": 2.8,
          "year": 2025
        },
        {
          "country": "Russia",
          "share_percent": 2.4,
          "year": 2025
        },
        {
          "country": "Korea North",
          "share_percent": 2.4,
          "year": 2025
        }
      ],
      "critical_lists": [],
      "recycling": "USGS: the amount of secondary tungsten produced and consumed in 2025 was withheld to avoid disclosing proprietary data. No recycled share is given.",
      "substitutes": [],
      "source": "usgs-mcs2026-tungsten",
      "where": "World Mine Production and Reserves table (2025 column, world total 85,000 t rounded); Events, Trends and Issues. Shares calculated by Space Mushroom as tonnes divided by the 85,000 t world total."
    }
  ],
  "media": [],
  "documents": [
    {
      "title": "Tungsten disulfide, Crystal, 99.995 percent, safety data sheet (Stanford Advanced Materials, version 3.0)",
      "type": "sds",
      "url": "https://www.samaterials.com/pdf/Tungsten-Disulfide-(WS2)-Powder-sds.pdf",
      "year": 2017
    },
    {
      "title": "Friction characteristics of sputtered solid film lubricants (NASA TM X-52819, Spalvins)",
      "type": "report",
      "url": "https://ntrs.nasa.gov/citations/19700020846",
      "year": 1970
    },
    {
      "title": "Surface Chemistry, Friction, and Wear Properties of Untreated and Laser-Annealed Surfaces of Pulsed-Laser-Deposited WS2 Coatings (NASA TM 107342)",
      "type": "report",
      "url": "https://ntrs.nasa.gov/citations/19970009635",
      "year": 1996
    },
    {
      "title": "USGS Mineral Commodity Summaries 2026: Tungsten",
      "type": "report",
      "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-tungsten.pdf",
      "year": 2026
    },
    {
      "title": "Nanotubes from Transition Metal Dichalcogenides, Recent Progress in the Synthesis, Characterization and Electrooptical Properties (Yadgarov and Tenne, Small)",
      "type": "paper",
      "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC12272021/",
      "year": 2024
    },
    {
      "title": "PubChem: Tungsten disulfide (CID 82938), GHS classification",
      "type": "database",
      "url": "https://pubchem.ncbi.nlm.nih.gov/compound/82938",
      "year": 2026
    }
  ],
  "gaps": [
    "The NASA 1970 report prints the vacuum life as 'over a million cycles', and the NASA 1996 report prints the dry-nitrogen life as 'greater than 2 million passes'. Both are written in words, so no numeric value was entered for them (the verifier needs the printed number).",
    "The Dicronite distributor page (precisioncoatings.com) gives a functional span of 188 to 538 degC in air and up to 1316 degC in vacuum. Its raw HTML does not print these figures, so they are not entered as values. The Lubrication Sciences International datasheet was not opened.",
    "No space flight, low Earth orbit or atomic oxygen result for WS2 was found in the sources opened. All friction and life numbers are ground tests.",
    "Hardness of the WS2 film was not found in any opened source.",
    "Friction in humid air for the laser-coated film is given only qualitatively in the text (friction rises in air); the numeric values are in a figure that was not extracted.",
    "The Dicronite friction range of about 0.03 to 0.07 quoted by distributors was not read on a fetched page. The precision coatings page gives only ultra-low friction, with no number. The Lubrication Sciences International datasheet was not opened.",
    "The absolute oxidation onset of WS2 in air was not found. The 1996 report gives only an advantage of about 100 degC over MoS2.",
    "The PubChem density and melting point were not read; the page was truncated before its experimental properties section. Density and melting point are taken from the supplier SDS and Wikipedia.",
    "The Wikipedia optical indirect bulk gap of about 1.35 eV disagrees with the review's bulk material gap of 2.01 to 2.05 eV. Neither has been reconciled; both are recorded with their sources.",
    "The review gives no method (measured or calculated) for the nanotube Young's modulus, and no oxidation or humidity numbers for WS2 nanotubes.",
    "The 1970 report does not state the test load, the humidity of the atmospheric tests, or the film thickness in the text (figure caption gives about 2,500 angstrom for one wear track).",
    "Sulfur's standard atomic weight is printed by NIST as an interval, 32.059 to 32.076. The value 32.07 used here is the rounded midpoint, and the recipe role notes this.",
    "Crustal abundance of tungsten and any critical-mineral list status were not found in opened text; the USGS 2026 tungsten extract does not mention a critical list.",
    "Benchmark names not in spores/property-canon.yaml and used here: coefficient_of_friction, endurance_life, wear_rate, decomposition_temperature, film_thickness, band_gap_optical_direct, band_gap_optical_indirect. Check them against the canon before import.",
    "Ossila WS2 properties page returned HTTP 429 and was not read."
  ],
  "story": {
    "why": "Tungsten disulfide (WS2) is a layered lubricant that works in the same way as molybdenum disulfide. Its layers slide with little resistance, so it lubricates where oil or grease cannot. NASA's ultrahigh-vacuum tests gave a friction of 0.055 for a sputtered film and over a million cycles of life, and a laser-annealed film ran at a friction below 0.1. Like MoS2 it loses life in humid air or atmosphere. WS2 is chosen where vacuum friction and oxidation resistance matter, and where the humidity history of the part is controlled.",
    "uses": [
      {
        "where": "Vacuum sliding contacts",
        "line": "NASA describes WS2 as an effective inorganic lubricant in a vacuum. It tested pulsed-laser WS2 coatings on 440C stainless steel for sliding life in ultrahigh vacuum."
      },
      {
        "where": "Nanotube transistors",
        "line": "The review reports a p-type mobility of 1.7 plus or minus 0.5 cm2 V-1 s-1 and an n-type mobility of 0.26 plus or minus 0.05 cm2 V-1 s-1 for WS2 nanotubes of about 20 nm diameter used in transistors."
      },
      {
        "where": "Battery electrodes",
        "line": "The review reports a WS2 nanotube electrode with a capacity of 371.9 mAh/g and 62 percent retention after 500 cycles at 1000 mA/g."
      }
    ],
    "can_do": [
      {
        "label": "Friction in vacuum",
        "line": "Sputtered WS2 averaged 0.055 friction in ultrahigh vacuum (NASA TM X-52819). The laser-annealed coating was below 0.1 (NASA TM 107342).",
        "scope": "material",
        "value": "0.055"
      },
      {
        "label": "Friction in air",
        "line": "The same sputtered film rose to 0.22 in atmosphere and failed after 1,500 cycles (NASA TM X-52819).",
        "scope": "material",
        "value": "0.22"
      },
      {
        "label": "Endurance life",
        "line": "In ultrahigh vacuum the sputtered film lasted over a million cycles. The laser-annealed coating lasted more than 500,000 passes (NASA TM 107342).",
        "scope": "material",
        "value": "More than 1 million cycles"
      },
      {
        "label": "Temperature limit",
        "line": "The distributor's Dicronite page gives a wide functional temperature span, higher in vacuum than in air. Its figures could not be checked against the page text, so they are not entered as values in this profile.",
        "scope": "material",
        "value": "Rated by the distributor"
      }
    ],
    "compare": "WS2 and MoS2 work by the same layered sliding mechanism, and NASA says WS2 behaves much like MoS2 in vacuum. WS2 is the more oxidation-resistant of the two, and its Dicronite dry film is rated higher in air than the MoS2 product in the MoS2 profile. The endurance numbers are not directly comparable. The MoS2 profile's NASA tests used a higher load and different films from the WS2 tests here. Both lose most of their life in humid air.",
    "compare_rows": [
      {
        "label": "Friction in vacuum",
        "benchmark": "coefficient_of_friction",
        "scope": "material"
      },
      {
        "label": "Endurance life",
        "benchmark": "endurance_life",
        "scope": "material"
      },
      {
        "label": "Melting point (decomposes above it)",
        "benchmark": "melting_point",
        "scope": "material"
      }
    ],
    "handling": [
      "Read the supplier safety data sheet first. The SDS classes WS2 as an irritant and says it is air-, heat- and moisture-sensitive.",
      "Store the powder in a closed container, under nitrogen, in a dry and well-ventilated place. Keep it away from strong acids and oxidizers.",
      "Avoid dust. Use exhaust ventilation where dust forms.",
      "Keep coatings out of humid storage. NASA found that humidity affected a pressed WS2 compact over several weeks."
    ],
    "good_for": [
      "Dry sliding in vacuum. A sputtered film averaged 0.055 friction and lasted more than a million cycles in NASA's ultrahigh-vacuum tests.",
      "Oxidation resistance. NASA reports that WS2 resists oxidation in air about 100 degC better than MoS2, and the sources give a melting point of 1200 degC."
    ],
    "watch_out": [
      "Atmosphere and humidity. A sputtered film failed after 1,500 cycles in atmosphere, and laser-coated films lasted about 9,000 passes in humid air.",
      "Sulfuric acid. NASA attributes the atmospheric failure to acid formed on the surface.",
      "Limited data. No flight data, no LEO data and no hardness value were found in the sources opened."
    ],
    "verdict": "WS2 is a vacuum lubricant of the same family as MoS2. Its strongest points are the vacuum friction and a higher oxidation resistance than MoS2, but the humidity penalty is severe and the sources hold few numbers for humid service.",
    "recipe": {
      "line": "WS2 is a layered compound. Each formula unit combines one tungsten atom with two sulfur atoms, in trigonal prismatic coordination. The review says WS2 nanotubes are made by sulfiding tungsten oxide precursors with H2S at high temperature. The NASA films were made by sputtering and by pulsed-laser deposition.",
      "parts": [
        {
          "name": "Tungsten",
          "symbol": "W",
          "role": "The metal centre. Each tungsten sits between two layers of sulfur, and the sulfur sheets are the sliding planes.",
          "atoms": 1,
          "atomic_weight": 183.84
        },
        {
          "name": "Sulfur",
          "symbol": "S",
          "role": "Forms the top and bottom layers of each sheet. Weak van der Waals bonds link the sheets, which is why they slide. The sulfur atomic weight is the rounded midpoint of the NIST interval.",
          "atoms": 2,
          "atomic_weight": 32.07
        }
      ]
    },
    "risk_groups": [
      {
        "title": "For people",
        "lead": "WS2 powder is classed as an irritant for skin, eyes and the respiratory tract. The SDS lists no carcinogen.",
        "points": [
          {
            "label": "Irritation",
            "line": "The SDS classes WS2 for skin irritation (H315), serious eye irritation (H319) and respiratory irritation (H335), with the Warning signal word."
          },
          {
            "label": "Most reports",
            "line": "PubChem records the same three codes in 57.2 percent of 138 company notifications. The rest find no GHS hazard criteria met."
          },
          {
            "label": "Cancer",
            "line": "The SDS lists no IARC or NTP carcinogen at 0.1 percent or more."
          },
          {
            "label": "Dust",
            "line": "Dust should be avoided, with exhaust ventilation where dust forms. Further processing may make combustible dust."
          }
        ],
        "level": 0,
        "verdict": "Irritant hazard, not carcinogenic in the sources"
      },
      {
        "title": "Handling the coating",
        "points": [
          {
            "label": "Application",
            "line": "The Dicronite coating is applied near ambient temperature, at a maximum of 35 degC, and is a precision film of up to 0.5 micron."
          },
          {
            "label": "Storage",
            "line": "Store in a dry, well-ventilated place under nitrogen. The SDS calls the material air-, heat- and moisture-sensitive."
          }
        ]
      }
    ]
  },
  "updated": "2026-10-26",
  "review": {
    "status": "draft",
    "method": "assistant",
    "checked_values": 16,
    "unreachable": 2,
    "caveats": 3,
    "note": "Written 2026-10-26 from NASA TM X-52819 (1970), NASA TM 107342 (1996), the USGS 2026 tungsten chapter, the supplier SDS, PubChem, Wikipedia, the Dicronite distributor page, the Yadgarov and Tenne 2024 review and NIST. Hardness, space-flight data and the Dicronite friction number are not found; see gaps."
  },
  "sources": {
    "wiki-ws2": {
      "title": "Tungsten disulfide",
      "id": "Wikipedia, English edition",
      "url": "https://en.wikipedia.org/wiki/Tungsten_disulfide",
      "kind": "web",
      "license": "CC BY-SA 4.0"
    },
    "pubchem-ws2": {
      "title": "Tungsten disulfide (CID 82938)",
      "id": "PubChem, NIH National Library of Medicine",
      "url": "https://pubchem.ncbi.nlm.nih.gov/compound/82938",
      "year": 2026,
      "kind": "database",
      "license": "public domain (NLM)"
    },
    "sds-ws2": {
      "title": "Tungsten disulfide, Crystal, 99.995% safety data sheet (Stanford Advanced Materials, version 3.0)",
      "id": "SAM product WS2 powder, revision date 09/04/2017",
      "url": "https://www.samaterials.com/pdf/Tungsten-Disulfide-(WS2)-Powder-sds.pdf",
      "year": 2017,
      "kind": "datasheet",
      "license": "supplier SDS (cited, not reproduced)"
    },
    "nasa-tm-x52819": {
      "title": "Friction characteristics of sputtered solid film lubricants",
      "id": "NASA TM X-52819 (Spalvins, Lewis Research Center, 1970)",
      "url": "https://ntrs.nasa.gov/citations/19700020846",
      "year": 1970,
      "kind": "report",
      "license": "NASA public use"
    },
    "nasa-tm-107342": {
      "title": "Surface Chemistry, Friction, and Wear Properties of Untreated and Laser-Annealed Surfaces of Pulsed-Laser-Deposited WS2 Coatings",
      "id": "NASA TM 107342 (Miyoshi, Wheeler, Zabinski, December 1996)",
      "url": "https://ntrs.nasa.gov/citations/19970009635",
      "year": 1996,
      "kind": "report",
      "license": "NASA public use"
    },
    "usgs-mcs2026-tungsten": {
      "title": "Mineral Commodity Summaries 2026: Tungsten",
      "id": "USGS, February 2026",
      "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-tungsten.pdf",
      "year": 2026,
      "kind": "report",
      "license": "public domain (USGS)"
    },
    "precision-dicronite": {
      "title": "Dicronite dry film lubrication (distributor page)",
      "id": "Precision Coatings, Dicronite page",
      "url": "https://precisioncoatings.com/dicronite/",
      "kind": "web",
      "license": "web page (cited, not reproduced)"
    },
    "yadgarov-tenne-2024": {
      "title": "Nanotubes from Transition Metal Dichalcogenides, Recent Progress in the Synthesis, Characterization and Electrooptical Properties",
      "id": "Yadgarov and Tenne, Small, 2024 (PubMed Central PMC12272021)",
      "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC12272021/",
      "year": 2024,
      "kind": "paper",
      "license": "open access (PMC)"
    },
    "nist-atomic-weights": {
      "title": "Atomic weights of the elements (NIST, tungsten and sulfur)",
      "id": "NIST Physical Measurement Laboratory, Atomic Weights and Isotopic Compositions",
      "url": "https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=W&all=all",
      "kind": "database",
      "license": "public domain (NIST)"
    }
  },
  "license": "CC-BY-4.0",
  "url": "https://spacemushroom.com/profiles/tungsten-disulphide/"
}