spore: profile
id: tungsten-trioxide
spore_version: 0.2
family: oxide-ceramics
name: Tungsten trioxide
abbreviation: WO3
role: electrochromic and gas-sensing oxide
category: ceramics
type: oxides
summary: |
  Tungsten trioxide (WO3, tungsten(VI) oxide) is a yellow oxide that melts at 1472 °C. Supplier and chemical-database data give a density of 7.16 to 7.2 g/cm3. Laboratory films of WO3 switch colour in a few seconds: a Fe-doped mesoporous film reached a coloration efficiency of 71.1 cm2/C, and WO3 with about 5 wt% reduced graphene oxide reached about 386 cm2/C. A review reports WO3 gas sensors that detect NO2 at 10 ppb. No flight or space-environment test of WO3 was found in the sources opened for this profile. Tungsten is on both the USGS and the EU critical lists, and China produced 67000 of the 85000 t of tungsten mined in 2025.
best_for: Electrochromic films that switch in seconds, and resistive gas sensors for NO2 and NH3 at ppb levels (laboratory results)
weakest_at: 'Cycling stability and humidity tolerance: a bare WO3 film lost about 25% of its optical transparency over cycling in one study, and the sensor review lists humidity tolerance as a limit'
identity:
  formula: WO3
  cas: 1314-35-8
  crystal_system: monoclinic
  source: pmc-gas-review
  where: 'Monoclinic phase: the phases paragraph of the sensing section of the review, which compares monoclinic and hexagonal WO3. Formula O3W and CAS 1314-35-8: PubChem CID 14811 (Names and Identifiers)'
tags:
  environments: []
  stresses: []
  applications:
    - optics-and-cameras
    - habitats-and-suits
properties:
  - benchmark: molar_mass
    label: Molar mass
    value: 231.84
    unit: g/mol
    scope: material
    conditions:
      basis: molecular weight computed in the PubChem record for WO3
    method: Molecular weight printed in a chemical database (the Materion SDS prints 231.85 g/mol)
    status: calculated
    source: pubchem-wo3
    where: Chemical and Physical Properties, Molecular Weight (CID 14811)
  - benchmark: density
    label: Density, estimated (Materion SDS)
    value: 7.2
    unit: g/cm3
    scope: material
    conditions:
      grade: tungsten oxide powder, Materion product, SDS revision 07-27-2015
      basis: estimated, as printed
    method: Value printed in a supplier safety data sheet and marked as an estimate
    status: ground
    note: The SDS marks this as an estimate. The nano-powder SDS below gives 7.160 g/cm3.
    source: materion-sds
    where: Section 9, Other information, Density
  - benchmark: density
    label: Relative density, nano powder (Stanford Advanced Materials SDS)
    value: 7.16
    unit: g/cm3
    scope: material
    conditions:
      grade: Nano Tungsten Trioxide Powder, SDS version 3.0
      temperature: not stated
    method: Value printed in a supplier safety data sheet
    status: ground
    source: sam-sds
    where: Section 9.1, item m, Relative density
  - benchmark: melting_point
    label: Melting point (PubChem experimental record)
    value: 1472
    unit: °C
    scope: material
    conditions:
      basis: experimental value in the PubChem record; sample and grade not stated
    method: Experimental property quoted in a chemical database
    status: ground
    note: PubChem also prints 1473 °C as a second experimental entry. The first is used here.
    source: pubchem-wo3
    where: Chemical and Physical Properties, Experimental Properties, Melting Point (first entry)
  - benchmark: melting_point
    label: Melting point (nano powder SDS)
    value: 1472
    unit: °C
    scope: material
    conditions:
      grade: Nano Tungsten Trioxide Powder, Stanford Advanced Materials
    method: Value printed in a supplier safety data sheet
    status: ground
    source: sam-sds
    where: Section 9.1, item e, Melting point/freezing point
  - benchmark: boiling_point
    label: Boiling point at 1013 hPa (nano powder SDS)
    value: 1837
    unit: °C
    scope: material
    conditions:
      pressure: 1013 hPa (760 mmHg)
      grade: Nano Tungsten Trioxide Powder, Stanford Advanced Materials
    method: Value printed in a supplier safety data sheet
    status: ground
    note: Printed in the SDS only; no second source for this boiling value was opened.
    source: sam-sds
    where: Section 9.1, item f, Initial boiling point and boiling range
  - benchmark: coloration_efficiency
    label: Coloration efficiency, Fe-doped mesoporous WO3 film
    value: 71.1
    unit: cm2/C
    scope: material
    conditions:
      film: Fe-doped WO3 film with mesopores and oxygen vacancy defects
      device: electrochromic device, as described in the abstract
      paper: Switching electrochromic performance improvement enabled by highly developed mesopores and oxygen vacancy defects of Fe-doped WO3 films, Applied Surface Science 453 (2018)
    method: Value printed in the paper's abstract
    status: ground
    source: ass-2018-fe
    where: Abstract, high CE (71.1 cm2/C)
  - benchmark: coloration_time
    label: Coloration time, Fe-doped mesoporous WO3 film
    value: 2.8
    unit: s
    scope: material
    conditions:
      film: Fe-doped WO3 film with mesopores and oxygen vacancy defects
      device: electrochromic device, as described in the abstract
    method: Value printed in the paper's abstract as the coloration speed
    status: ground
    source: ass-2018-fe
    where: Abstract, 2.8 s for the coloration speed
  - benchmark: bleaching_time
    label: Bleaching time, Fe-doped mesoporous WO3 film
    value: 0.3
    unit: s
    scope: material
    conditions:
      film: Fe-doped WO3 film with mesopores and oxygen vacancy defects
      device: electrochromic device, as described in the abstract
    method: Value printed in the paper's abstract as the bleaching speed
    status: ground
    source: ass-2018-fe
    where: Abstract, 0.3 s for the bleaching speed
  - benchmark: coloration_efficiency
    label: Coloration efficiency, WO3 with reduced graphene oxide
    value: 386
    unit: cm2/C
    scope: material
    conditions:
      film: WO3 film with 5 wt% reduced graphene oxide
      comparison: pristine WO3 about 81 cm2/C in the same abstract
      paper: Study on the role of rGO in enhancing the electrochromic performance of WO3 film, Electrochimica Acta 427 (2022)
    method: Value printed in the paper's abstract as similar to 386 cm(2)/C
    status: ground
    note: The abstract gives about 81 for the pristine film and about 386 for the 5 wt% rGO film.
    source: rgo-2022
    where: Abstract, coloration efficiency rising from similar to 81 to similar to 386 cm(2)/C
  - benchmark: coloration_time
    label: Coloration time, WO3 with reduced graphene oxide
    value: 5.3
    unit: s
    scope: material
    conditions:
      film: WO3 film with 5 wt% reduced graphene oxide
      comparison: pristine film about 9.6 s in the same abstract
    method: Value printed in the paper's abstract as similar to 5.3 s
    status: ground
    source: rgo-2022
    where: Abstract, coloration time tc
  - benchmark: bleaching_time
    label: Bleaching time, WO3 with reduced graphene oxide
    value: 6.2
    unit: s
    scope: material
    conditions:
      film: WO3 film with 5 wt% reduced graphene oxide
      comparison: pristine film about 10.4 s in the same abstract
    method: Value printed in the paper's abstract as similar to 6.2 s
    status: ground
    source: rgo-2022
    where: Abstract, bleaching time tb
  - benchmark: optical_modulation
    label: Optical modulation, WO3 with reduced graphene oxide
    value: 50
    unit: '%'
    scope: material
    conditions:
      film: WO3 film with 5 wt% reduced graphene oxide
      basis: printed as similar to 50%
    method: Value printed in the paper's abstract
    status: ground
    source: rgo-2022
    where: Abstract, optical modulation
  - benchmark: detection_limit
    label: NO2 detection limit, doped WO3 hollow nanosphere sensor (cited in the review)
    value: 10
    unit: ppb
    scope: material
    conditions:
      gas: NO2
      detection_range: 10 to 1000 ppb
      material: mesoporous WO3 hollow nanospheres with a dopant, reference 95 in the review
      temperature: not stated in the sentence
    method: Value stated in a review of WO3 gas sensors; the primary paper was not opened
    status: ground
    note: Taken from the review, so the test conditions are not confirmed.
    source: pmc-gas-review
    where: Doping section, sentence beginning 'Enabling the detection of NO2 at concentrations as low as 10 ppb', citing reference 95
  - benchmark: operating_temperature
    label: Typical operating temperature range for WO3 gas response
    value: 100
    value_high: 400
    bound: range
    unit: °C
    scope: material
    conditions:
      basis: statement that the optimal temperature for WO3 gas sensors is typically in this range
    method: Range stated in a review
    status: ground
    source: pmc-gas-review
    where: Operating temperature paragraph, sentence on the optimal temperature for WO3, citing reference 37
  - benchmark: visible_absorption_limit
    label: Visible-light absorption, upper wavelength
    value: 480
    unit: nm
    scope: material
    conditions:
      basis: statement about WO3 as a visible-light-driven photocatalyst
    method: Value stated in a review abstract
    status: ground
    note: Only the wavelength is printed in the abstract. No band gap in eV was read in a fetched source.
    source: dutta-2021
    where: Abstract, high absorption of visible light (up to 480nm)
corrosion:
  - environment: Caustic alkali solutions and hydrofluoric acid
    headline: WO3 is soluble in caustic alkalies and slightly soluble in hydrofluoric acid.
    effect: PubChem's experimental solubility entries say insoluble in water, soluble in caustic alkalies, very slightly soluble in acids, and slightly soluble in hydrofluoric acid. No dissolution rate or test duration is given.
    rating: moderate
    conditions:
      basis: qualitative solubility statements in a chemical database; the rating is assigned from those words
      temperature: not stated
    source: pubchem-wo3
    where: Chemical and Physical Properties, Solubility (two entries)
  - environment: Repeated electrochromic switching in an electrolyte cell
    headline: A bare WO3 film lost about 25% of its optical transparency over cycling, and the rGO composite lost under 10%.
    effect: The abstract says the bare WO3 film showed a deterioration in optical transparency similar to 25%, while the film with reduced graphene oxide showed a deterioration of under 10%.
    rating: moderate
    conditions:
      film: bare WO3 and WO3 with 5 wt% reduced graphene oxide
      cycles: not stated in the abstract
      electrolyte: not stated in the abstract
    source: rgo-2022
    where: Abstract, cyclic stability
  - environment: Gas-sensing operation over time, in humid air
    headline: The sensor review lists stability, humidity tolerance and baseline drift as intrinsic limits of WO3 gas sensors.
    effect: The review names these limits and mitigation strategies in its critical assessment. The passage read does not quantify drift or humidity effects.
    rating: unknown
    conditions:
      basis: review text only; no quantified test was read
    source: pmc-gas-review
    where: Introduction, list of review aims, item iv
risks:
  hazards:
    - text: PubChem's aggregated record says the substance does not meet GHS hazard criteria in 41.5% (333 of 803) of company reports. The other reports use the signal word Warning and give H302 (58.5%), H315 (57.3%), H319 (57.3%) and H335 (57.3%).
      ghs:
        - H302
        - H315
        - H319
        - H335
      source: pubchem-wo3
      where: GHS Classification, aggregated notifications (CID 14811)
    - text: The Materion SDS (product T-MSDS0050, revision 07-27-2015) states that the substance does not meet the criteria for classification and has no signal word.
      ghs: []
      source: materion-sds
      where: Section 2, Hazard(s) identification
    - text: The Stanford Advanced Materials SDS for a nano powder states that the product is not a hazardous substance or mixture.
      ghs: []
      source: sam-sds
      where: Sections 2.1 and 2.2
  failure_risks:
    - mode: Loss of optical transparency after cycling
      trigger: Repeated colour switching of a bare WO3 film
      consequence: In the rGO study the bare film lost about 25% of its optical transparency, against under 10% for the rGO composite, so the cycling loss depends on the film.
      severity: moderate
      source: rgo-2022
      where: Abstract, cyclic stability
    - mode: Drift and loss of stability in gas sensors
      trigger: Long operation at the sensing temperature, including humid air
      consequence: The review lists stability, humidity tolerance, baseline drift and power consumption as intrinsic limits of WO3 gas sensors.
      severity: moderate
      source: pmc-gas-review
      where: Introduction, list of review aims, item iv
    - mode: Dissolution in strong alkali
      trigger: Contact with caustic alkali solutions
      consequence: WO3 is soluble in caustic alkalies, so a part or film left in an alkaline solution can lose material.
      severity: moderate
      source: pubchem-wo3
      where: Chemical and Physical Properties, Solubility
  side_effects: []
  handling:
    - text: Minimize dust generation and accumulation, provide exhaust ventilation where dust is formed, and practice good housekeeping. Store in a tightly closed container in a well-ventilated place, away from incompatible materials.
      source: materion-sds
      where: Section 7, Precautions for safe handling and Conditions for safe storage
    - text: The ACGIH threshold limit values for tungsten oxide are 10 mg/m3 as a short-term limit (STEL) and 5 mg/m3 as a time-weighted average (TWA).
      source: materion-sds
      where: Section 8, US ACGIH Threshold Limit Values
    - text: The SDS says that gases hazardous to health may form in a fire, and asks users to wash hands after handling.
      source: materion-sds
      where: Section 5, Specific hazards arising from the chemical; Section 2, Response
  mitigations:
    - text: Wear safety glasses with side shields, or goggles, as the SDS specifies for eye protection.
      source: materion-sds
      where: Section 8, Eye/face protection
uses:
  - application: optics-and-cameras
    device: Electrochromic smart-window film (laboratory device)
    example: A Fe-doped mesoporous WO3 film in an electrochromic device switched to colour in 2.8 s and bleached in 0.3 s, with a coloration efficiency of 71.1 cm2/C.
    source: ass-2018-fe
    where: Abstract
  - application: optics-and-cameras
    device: Electrochromic film with reduced graphene oxide (laboratory device)
    example: Adding about 5 wt% reduced graphene oxide raised coloration efficiency from about 81 to about 386 cm2/C, with optical modulation of about 50%.
    source: rgo-2022
    where: Abstract
  - application: habitats-and-suits
    device: Resistive gas sensors for NO2, NH3 and VOCs (air monitoring)
    example: The review reports WO3 sensors that detect NO2 at concentrations as low as 10 ppb, and describes WO3 as used for environmental monitoring of NO2, SO2 and VOCs.
    source: pmc-gas-review
    where: Introduction (applications paragraph) and doping section
  - application: habitats-and-suits
    device: Visible-light photocatalyst for environmental remediation
    example: The review describes WO3 as a visible-light-driven photocatalyst for environmental remediation, absorbing visible light up to 480 nm.
    source: dutta-2021
    where: Abstract
supply:
  - subject: Tungsten (feedstock for WO3)
    producers:
      - country: China
        share_percent: 78.8
        year: 2025
      - country: Vietnam
        share_percent: 4
        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:
      - list: USGS 2025 List of Critical Minerals (tungsten listed)
        listed: true
      - list: EU critical raw materials list (fifth list of 34 critical raw materials, as shown on the European Commission page)
        listed: true
    recycling: 'USGS: the quantity of secondary tungsten produced and consumed from secondary sources in 2025 was withheld to avoid disclosing company proprietary data.'
    substitutes:
      - 'USGS: potential substitutes for cemented tungsten carbides include molybdenum, niobium or titanium carbides, ceramics and cermets. No substitute is named for WO3 itself.'
    source: usgs-mcs2026-tungsten
    where: 'World Mine Production and Reserves, 2025 column. World total 85000 t (rounded). Shares calculated by Space Mushroom by dividing each 2025 figure by 85000 t: China 67000 t, Vietnam 3400 t, Kazakhstan 2400 t, Russia 2000 t, Korea, North 2000 t. Salient Statistics: net import reliance above 50% (2025e). Price, Rotterdam, tungsten trioxide, 380 dollars per dry metric ton unit (2025e). Critical lists: usgs-crit2025 page and ec-crm page.'
documents:
  - title: 'PubChem: Tungsten oxide (WO3), CID 14811, GHS classification and experimental properties'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/14811
    year: 2026
  - title: 'Materion Advanced Chemicals safety data sheet: Tungsten oxide, SDS T-MSDS0050 (revision 07-27-2015)'
    type: sds
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/SDS/tungsten%20(VI)%20oxide%20%20-%20Materion.pdf
    year: 2015
  - title: 'Stanford Advanced Materials safety data sheet: Nano Tungsten Trioxide Powder (version 3.0)'
    type: sds
    url: https://samaterials.com/tds/sc/1727405467-NN1589.pdf
    year: 2017
  - title: 'USGS Mineral Commodity Summaries 2026: Tungsten'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-tungsten.pdf
    year: 2026
  - title: 'Innovations in WO3 gas sensors: Nanostructure engineering, functionalization, and future perspectives (Heliyon 2024, open access)'
    type: paper
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC10955316/
    year: 2024
  - title: Switching electrochromic performance improvement enabled by highly developed mesopores and oxygen vacancy defects of Fe-doped WO3 films (Applied Surface Science 453, 2018)
    type: paper
    url: https://pure.seoultech.ac.kr/en/publications/switching-electrochromic-performance-improvement-enabled-by-highl/
    year: 2018
  - title: Study on the role of rGO in enhancing the electrochromic performance of WO3 film (Electrochimica Acta 427, 2022)
    type: paper
    url: https://cgcri.csircentral.net/5420/
    year: 2022
  - title: An Overview on WO3 based photocatalyst for environmental remediation (Journal of Environmental Chemical Engineering 9, 2021)
    type: paper
    url: https://pure.sruc.ac.uk/en/publications/an-overview-on-wo3-based-photocatalyst-for-environmental-remediat/
    year: 2021
  - title: 'USGS: About the 2025 List of Critical Minerals'
    type: report
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
  - title: 'European Commission: Critical raw materials'
    type: report
    url: https://single-market-economy.ec.europa.eu/sectors/raw-materials/areas-specific-interest/critical-raw-materials_en
    year: 2024
gaps:
  - No vacuum, radiation, thermal-vacuum or flight result for WO3 was found in any source opened for this profile.
  - Band gap in eV was not read in a fetched source. Search snippets gave a range of about 2.4 to 2.8 eV, which was not used because the snippets were not opened.
  - Density in PubChem (7.2 at 25 °C) is printed without a unit, so it is left out. The Materion SDS value of 7.2 g/cm3 is used instead.
  - Crustal abundance of tungsten was not found. The USGS PP 1802-A Table A1 we opened has no tungsten row.
  - Space group is not read in a fetched primary source. Wikipedia gives P121/n1 (No. 14) in the infobox and P21/n in the text, and the page conflicts with itself, so it is not used.
  - The electrochromic values come from single films with different electrolytes, thicknesses and dopants, so they are not directly comparable. The MDPI Coatings 2025 review and the RSC Materials Advances 2021 review returned HTTP 403 and were not read.
  - The NO2 detection limit is taken from a review and the primary paper was not opened, so its test temperature is not confirmed.
  - 'Hazard classifications conflict: PubChem''s aggregate reports H302, H315, H319 and H335 in most notifications, while the Materion SDS and the Stanford nano-powder SDS do not classify the material. The Stanford SDS is for a nano powder.'
  - Atomic weights were not read in a fetched source, so the recipe parts carry no atoms or atomic_weight.
  - Corrosion ratings are qualitative assignments made by the author from the wording of the sources.
  - Coloration, bleaching, modulation and cycling values use the wording of the abstracts (similar to, under) and are not checked against the full papers.
  - 'Properties not in the property canon use short snake_case names: molar_mass, coloration_efficiency, coloration_time, bleaching_time, optical_modulation, detection_limit, operating_temperature and visible_absorption_limit.'
sources:
  pubchem-wo3:
    title: PubChem compound record, Tungsten oxide (WO3), CID 14811
    id: CID 14811; CAS 1314-35-8; molecular formula O3W
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/14811/JSON
    year: 2026
    kind: database
    license: public domain (NCBI)
  materion-sds:
    title: 'Materion Advanced Chemicals safety data sheet: Tungsten oxide (SDS T-MSDS0050)'
    id: revision 07-27-2015; issue 10-14-2013
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/SDS/tungsten%20(VI)%20oxide%20%20-%20Materion.pdf
    year: 2015
    kind: datasheet
    license: supplier document, linked not reproduced
  sam-sds:
    title: 'Stanford Advanced Materials safety data sheet: Nano Tungsten Trioxide Powder'
    id: version 3.0, revision 09/04/2017; CAS 1314-35-8
    url: https://samaterials.com/tds/sc/1727405467-NN1589.pdf
    year: 2017
    kind: datasheet
    license: supplier document, linked not reproduced
  usgs-mcs2026-tungsten:
    title: Mineral Commodity Summaries 2026, Tungsten
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-tungsten.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-crit2025:
    title: About the 2025 List of Critical Minerals (USGS, final list)
    id: Final 2025 List of Critical Minerals, November 2025
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
    kind: web
    license: public domain (USGS)
  ec-crm:
    title: Critical raw materials (European Commission, fifth list of 34 critical raw materials)
    id: EU critical raw materials list
    url: https://single-market-economy.ec.europa.eu/sectors/raw-materials/areas-specific-interest/critical-raw-materials_en
    year: 2024
    kind: web
    license: European Commission web page
  pmc-gas-review:
    title: 'Innovations in WO3 gas sensors: Nanostructure engineering, functionalization, and future perspectives'
    id: doi:10.1016/j.heliyon.2024.e27740 (Heliyon 10(6), PMC10955316)
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC10955316/
    year: 2024
    kind: paper
    license: open access (PMC)
  ass-2018-fe:
    title: Switching electrochromic performance improvement enabled by highly developed mesopores and oxygen vacancy defects of Fe-doped WO3 films
    id: Applied Surface Science 453, 238-244 (2018)
    url: https://pure.seoultech.ac.kr/en/publications/switching-electrochromic-performance-improvement-enabled-by-highl/
    year: 2018
    kind: paper
    license: publisher abstract, linked not reproduced
  rgo-2022:
    title: Study on the role of rGO in enhancing the electrochromic performance of WO3 film
    id: Electrochimica Acta 427, 140820 (2022)
    url: https://cgcri.csircentral.net/5420/
    year: 2022
    kind: paper
    license: publisher abstract, linked not reproduced
  dutta-2021:
    title: An Overview on WO3 based photocatalyst for environmental remediation
    id: Journal of Environmental Chemical Engineering 9(1), 105018 (2021)
    url: https://pure.sruc.ac.uk/en/publications/an-overview-on-wo3-based-photocatalyst-for-environmental-remediat/
    year: 2021
    kind: paper
    license: publisher abstract, linked not reproduced
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 16
  unreachable: 2
  caveats: 5
  note: 'Read by an AI assistant on 2026-10-26 from the PubChem JSON record, the USGS MCS 2026 tungsten PDF, two supplier SDS PDFs, the PMC gas-sensor review, and three paper abstracts. The MDPI and RSC full texts and the DOAJ page returned HTTP 403 and were not read. Caveats: the PubChem and SDS hazard data conflict; the electrochromic values come from different films; the NO2 limit and the abstract wording are second-hand; no space data was found.'
story:
  recipe:
    line: WO3 is one tungsten and three oxygen. Tungsten(VI) oxide is a yellow powder that does not dissolve in water, and it is used as the starting material for making tungstates.
    parts:
      - name: Tungsten
        symbol: W
        role: The metal in the oxide, in its highest oxidation state.
      - name: Oxygen
        symbol: O
        role: Three oxygen per tungsten, bonded into the WO3 framework.
  risk_groups:
    - title: For people
      level: 1
      verdict: Hazard data conflict across sources
      lead: PubChem's aggregated record lists irritant and harmful-if-swallowed hazards, but the Materion SDS does not classify the powder, so the data conflict.
      points:
        - label: Hazard data
          line: PubChem reports H302, H315, H319 and H335 in 57.3 to 58.5 percent of its company reports. The Materion SDS and the Stanford nano-powder SDS do not classify the material.
        - label: Exposure limit
          line: The Materion SDS lists an ACGIH limit of 10 mg/m3 as a short-term limit and 5 mg/m3 as a time-weighted average for tungsten oxide.
        - label: Dust
          line: Minimize dust and provide exhaust ventilation where dust forms.
    - title: If it fails
      lead: These results come from laboratory film and sensor tests, not from field failures.
      points:
        - label: Cycling
          line: In one study the bare WO3 film lost about 25% of its transparency over cycling, against under 10% for the rGO composite.
        - label: Sensors
          line: The review lists stability, humidity tolerance and baseline drift as the main limits of WO3 gas sensors.
    - title: Handling and storage
      points:
        - label: Storage
          line: Store in a tightly closed container, away from incompatible materials.
        - label: Alkali
          line: Keep it out of caustic alkali solutions, which dissolve WO3.
  why: 'Tungsten trioxide (WO3) is a dense yellow oxide with a density of 7.2 g/cm3 and a melting point of 1472 °C. It is studied for two uses: electrochromic films that change colour when a small voltage is applied, and resistive gas sensors. Its laboratory films switch in a few seconds, and its sensors respond to ppb levels of NO2. Its limits are cycling loss, sensitivity to humidity, and hazard data that do not agree across suppliers.'
  uses:
    - where: Electrochromic smart windows
      line: A Fe-doped WO3 film switched to colour in 2.8 s and bleached in 0.3 s in one laboratory device. Adding 5 wt% reduced graphene oxide raised coloration efficiency from about 81 to about 386 cm2/C.
    - where: Gas sensors
      line: A review reports WO3 sensors that detect NO2 at 10 ppb, and describes WO3 as used for monitoring NO2, SO2 and VOCs in air.
    - where: Photocatalyst
      line: WO3 absorbs visible light up to 480 nm, so it is studied for environmental cleanup under sunlight.
  can_do:
    - label: Colour switching
      value: 2.8 s to colour
      line: The Fe-doped mesoporous film switched to colour in 2.8 s and bleached in 0.3 s, with a coloration efficiency of 71.1 cm2/C.
    - label: Coloration efficiency
      value: 386 cm2/C
      line: Adding about 5 wt% reduced graphene oxide raised the coloration efficiency from about 81 to about 386 cm2/C.
    - label: Gas detection
      value: 10 ppb NO2
      line: A doped WO3 sensor cited in the review detects NO2 at 10 ppb, within a range of 10 to 1000 ppb.
    - label: Visible light
      value: Up to 480 nm
      line: WO3 absorbs visible light up to 480 nm, which is why it is studied as a photocatalyst.
  compare: WO3 is a powder-based oxide whose strengths lie in optics and sensing, not in structure. Its density is about 7.2 g/cm3 and its melting point is 1472 °C. Its films show coloration efficiencies from 71.1 to 386 cm2/C, which depend on the dopant and on whether a graphene additive is present.
  compare_rows:
    - label: Melting point
      benchmark: melting_point
    - label: Density
      benchmark: density
    - label: Colour efficiency
      benchmark: coloration_efficiency
  handling:
    - Minimize dust, use exhaust ventilation where dust forms, and practice good housekeeping.
    - Store in a tightly closed container, away from incompatible materials.
    - Wear safety glasses with side shields or goggles.
    - Keep it out of caustic alkali solutions, which dissolve WO3.
  good_for:
    - Fast electrochromic films. The Fe-doped film colours in 2.8 s and bleaches in 0.3 s in a laboratory device.
    - Low-level gas sensing. The review cites detection of NO2 at 10 ppb.
  watch_out:
    - Cycling loss. A bare film lost about 25% of its transparency over cycling in one study.
    - Humidity and drift. The sensor review lists humidity tolerance and baseline drift as limits.
    - Conflicting hazard data. PubChem reports H302, H315, H319 and H335, while the Materion SDS does not classify the powder.
  verdict: WO3 is a promising laboratory material for fast electrochromic films and low-level gas sensors. Its hazard data conflict, its cycling and humidity stability are the main limits, and no space test was found.