Thoriated tungsten (WT20) WT20

spore: profile
id: thoriated-tungsten
spore_version: 0.2
family: refractory-metals
name: Thoriated tungsten (WT20)
abbreviation: WT20
role: TIG welding electrode and cathode material
category: metals
type: refractory-metals
summary: |
  Thoriated tungsten, graded WT20 under ISO 6848 or EWTh-2 under AWS, is tungsten with about 2% thorium dioxide (ThO2) added. EWS sells it as a red-tipped electrode for direct-current welding on constant-current transformer power sources. The thorium-232 in the oxide is an alpha emitter. Welders' breathing-zone levels measured in a 2003 study were below 10 mBq m-3, and the main exposure route is thorium dust from sharpening the electrode tip. The tungsten matrix melts at 3695 K and oxidises in air when hot.
best_for: Direct-current TIG welding with constant-current transformer power sources (EWS)
weakest_at: 'Radioactive oxide content: the thorium needs dust control when the tip is ground, and the electrode is handled as a radioactive material'
identity:
  formula: Tungsten with about 2% thorium dioxide (ThO2)
  source: ews-wt20
  where: Principal oxide line, 1.7 to 2.2% thorium oxide (EWS WT20 product page)
  designations:
    - system: AWS
      code: EWTh-2
      source: ews-wt20
      where: Designation line, EWTh-2/WT20 (EWS WT20 product page)
    - system: ISO
      code: WT20
      note: The page prints the code without naming the standard
      source: ews-wt20
      where: Designation line, EWTh-2/WT20 (EWS WT20 product page)
tags:
  environments: []
  stresses: []
  applications:
    - structures
properties:
  - benchmark: density
    value: 19250
    unit: kg m-3
    scope: material
    conditions:
      basis: no temperature stated on the page; value is for the pure tungsten matrix (the electrode is about 98% W)
    method: Density of solid, as printed in the WebElements physical properties table
    status: ground
    source: we-physics
    where: Density and elastic properties section (WebElements tungsten physics page)
  - benchmark: melting_point
    value: 3695
    unit: K
    scope: material
    conditions:
      basis: printed as 3695 K [3422 degC (6192 degF)]; tungsten matrix, not the oxide
    method: Key properties table on the WebElements main page
    status: ground
    source: we-main
    where: Key properties, Melting point row
  - benchmark: boiling_point
    value: 5828
    unit: K
    scope: material
    conditions:
      basis: printed as 5828 K [5555 degC (10031 degF)]; tungsten matrix
    method: Key properties table on the WebElements main page
    status: ground
    source: we-main
    where: Key properties, Boiling point row
  - benchmark: thermal_conductivity
    value: 174
    unit: W m-1 K-1
    scope: material
    conditions:
      basis: no temperature stated on the page; tungsten matrix
    method: Physical properties table as printed
    status: ground
    source: we-physics
    where: Thermal conductivity line (WebElements tungsten physics page)
  - benchmark: elastic_modulus
    value: 411
    unit: GPa
    scope: material
    conditions:
      basis: no temperature stated on the page; tungsten matrix
    method: Young's modulus as printed in the physical properties section
    status: ground
    source: we-physics
    where: Density and elastic properties section, Young's modulus line
  - benchmark: vickers_hardness
    value: 3430
    unit: MN m-2
    scope: material
    conditions:
      basis: no test conditions stated on the page; tungsten matrix
    method: Printed as Vickers hardness on the WebElements page (not a canonical property name; see gaps)
    status: ground
    source: we-physics
    where: Hardnesses section, Vickers hardness line
  - benchmark: thoria_content
    label: Thorium dioxide content of WT20 electrodes
    value: 1.7
    value_high: 2.2
    bound: range
    unit: '%'
    scope: material
    conditions:
      basis: principal oxide as stated by the manufacturer; nominal grade is 2%
    method: Range printed on the manufacturer product page (not a canonical property name; see gaps)
    status: ground
    source: ews-wt20
    where: Principal oxide line (EWS WT20 product page)
  - benchmark: density
    label: Thorium-232 metal density used in the activity calculation
    value: 11.7
    unit: g/cm3
    scope: material
    conditions:
      basis: density of thorium-232 as quoted by the paper, which cites a reference for it; it is the thorium metal value, not the electrode
    method: Value printed in the body text of a student radiation paper
    status: ground
    source: leicester-thw
    where: Introduction, paragraph on thorium-232 (Pripyat in my Pocket)
  - benchmark: activity_per_electrode
    label: Thorium-232 activity of one electrode
    value: 75.81
    unit: Bq
    scope: material
    conditions:
      electrode: cylinder 200 mm long and 2.4 mm diameter, 2% ThO2
      basis: calculated by the paper from the thorium atom count and the half-life
    method: Calculated in the paper from the electrode volume, ThO2 mass fraction and half-life
    status: calculated
    note: The paper calls this activity low and treats the electrode as a source of alpha radiation only.
    source: leicester-thw
    where: Calculation section, equations (1) to (4) (Pripyat in my Pocket)
  - benchmark: airborne_th232_concentration
    label: Thorium-232 in welders' breathing zone (TIG welding)
    value: 10
    bound: upper
    unit: mBq m-3
    scope: material
    conditions:
      basis: generally below 10 mBq m-3 in the breathing zone of welders in five workshops; two AC welding samples were higher
      process: TIG welding with thoriated electrodes
    method: Airborne measurement reported in the Radiation Protection Dosimetry study
    status: ground
    source: dtu-2003
    where: Results, airborne thorium concentrations (Gafvert, Pagels and Holm 2003)
  - benchmark: airborne_th232_concentration
    label: Thorium-232 from grinding electrodes (respirable fraction)
    value: 5
    bound: upper
    unit: mBq m-3
    scope: material
    conditions:
      basis: respirable fraction from grinding electrodes, reported as 5 mBq m-3 or lower
    method: Airborne measurement reported in the Radiation Protection Dosimetry study
    status: ground
    source: dtu-2003
    where: Results, airborne thorium concentrations (Gafvert, Pagels and Holm 2003)
  - benchmark: annual_committed_effective_dose
    label: Annual dose, full-time TIG welder, realistic case
    value: 0.3
    bound: upper
    unit: mSv
    scope: material
    conditions:
      basis: full-time TIG welder, realistic scenario; committed effective dose from inhaled thorium
    method: Dose estimate from the Radiation Protection Dosimetry study
    status: ground
    source: dtu-2003
    where: Dose estimates, full-time TIG welder, realistic case
  - benchmark: annual_committed_effective_dose
    label: Annual dose, full-time TIG welder, conservative assumptions
    value: 1
    bound: upper
    unit: mSv
    scope: material
    conditions:
      basis: full-time TIG welder, conservative assumptions (the study gives this as around 1 mSv or lower)
    method: Dose estimate from the Radiation Protection Dosimetry study
    status: ground
    source: dtu-2003
    where: Dose estimates, full-time TIG welder, conservative assumptions
  - benchmark: annual_committed_effective_dose
    label: Annual dose from grinding electrodes, realistic case
    value: 10
    bound: upper
    unit: µSv
    scope: material
    conditions:
      basis: grinding electrodes, realistic case
    method: Dose estimate from the Radiation Protection Dosimetry study
    status: ground
    source: dtu-2003
    where: Dose estimates, grinding electrodes, realistic case
  - benchmark: annual_committed_effective_dose
    label: Annual dose from grinding electrodes, conservative assumptions
    value: 63
    bound: upper
    unit: µSv
    scope: material
    conditions:
      basis: grinding electrodes, conservative assumptions
    method: Dose estimate from the Radiation Protection Dosimetry study
    status: ground
    source: dtu-2003
    where: Dose estimates, grinding electrodes, conservative assumptions
corrosion:
  - environment: Air at elevated temperature
    headline: Tungsten oxidises in air and must be protected when hot.
    effect: The WebElements description says the metal oxidises in air and must be protected at elevated temperatures. This applies to the tungsten matrix of the electrode; the paper and product pages give no oxidation data for the thoriated grade.
    rating: moderate
    conditions:
      basis: qualitative statement, no temperatures or exposure times given
    source: we-main
    where: Description paragraph (WebElements main page)
  - environment: Mineral acids
    headline: Excellent corrosion resistance; attacked only slightly by most mineral acids.
    effect: The WebElements description says tungsten has excellent corrosion resistance and is attacked only slightly by most mineral acids. No test on the thoriated grade was read.
    rating: low
    conditions:
      basis: qualitative statement, no acid concentrations given
    source: we-main
    where: Description paragraph (WebElements main page)
risks:
  hazards:
    - text: Thorium-232 in the oxide is an alpha emitter. It decays to radium-228, releasing alpha radiation. The paper notes that alpha particles cannot penetrate skin, so the external hazard of an intact electrode is low.
      ghs: []
      source: leicester-thw
      where: Introduction and discussion of alpha radiation (Pripyat in my Pocket)
    - text: Inhaled thorium oxide dust is the main hazard. A study of welders measured thorium-232 in the breathing zone and found that grinding the electrode tip gave a respirable fraction of 5 mBq m-3 or lower.
      ghs: []
      source: dtu-2003
      where: Results, airborne thorium concentrations
  failure_risks:
    - mode: Oxidation at elevated temperature
      trigger: Hot tungsten exposed to air without protection
      consequence: The metal oxidises and must be protected at elevated temperatures.
      severity: moderate
      source: we-main
      where: Description paragraph (WebElements main page)
    - mode: Radioactive dust release from sharpening
      trigger: Grinding the electrode tip without local extraction
      consequence: Thorium-bearing dust can be inhaled. The study's realistic dose from grinding is 10 µSv or lower per year, and 63 µSv or lower under conservative assumptions.
      severity: low
      source: dtu-2003
      where: Dose estimates, grinding electrodes
  handling:
    - text: Sharpen the electrode with dust control. The study measured grinding as the source of thorium-bearing dust, and its dose estimates depend on the grinding exposure.
      source: dtu-2003
      where: Results and dose estimates
    - text: Treat each rod as a radioactive source. The paper concludes the activity of one 200 mm electrode is low (75.81 Bq), but dust from sharpening is the open question.
      source: leicester-thw
      where: Calculation section and discussion (Pripyat in my Pocket)
uses:
  - application: structures
    device: TIG welding torch electrode (red-tipped WT20, direct current)
    example: EWS says WT20 is best for direct-current applications on transformer-based constant-current power sources, and lists a medium amperage range.
    source: ews-wt20
    where: Product description (EWS WT20 product page)
  - application: structures
    device: TIG welding of metal parts (welder's exposure to electrode dust)
    example: A 2003 study measured thorium-232 in the breathing zones of TIG welders at five workshops that used thoriated electrodes, and gave annual dose estimates for a full-time welder.
    source: dtu-2003
    where: Results and dose estimates (Gafvert, Pagels and Holm 2003)
supply:
  - subject: Tungsten (matrix, about 98% of the electrode; mine production shares computed from USGS 2025 tonnes of contained W, world total 85,000 t)
    abundance: Not stated in the USGS tungsten summary (see gaps).
    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: Bolivia
        share_percent: 2
        year: 2025
      - country: Australia
        share_percent: 1.2
        year: 2025
    critical_lists: []
    source: usgs-mcs-2026
  - subject: Tungsten reserves and trade (USGS 2026 summary)
    abundance: 'China holds 2,500,000 t of W reserves out of more than 4,700,000 t world total (about 53%, computed). US mine production is zero and net import reliance is more than 50%. Import sources 2021 to 2024: China 26%, Germany 14%, Bolivia 8%, Vietnam 8%. In February 2025 China implemented export controls on selected tungsten items. Rotterdam APT prices rose from $331 to $675 per metric ton unit during 2025.'
    producers: []
    critical_lists: []
    source: usgs-mcs-2026
  - subject: Thorium (the oxide, ThO2)
    abundance: Not found in any source read in this run (see gaps).
    producers: []
    critical_lists: []
    source: ews-wt20
media: []
documents:
  - title: 'USGS Mineral Commodity Summaries 2026: Tungsten'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-tungsten.pdf
    year: 2026
  - title: 'WebElements: Tungsten, physical properties'
    type: database
    url: https://www.webelements.com/tungsten/physics.html
  - title: 'WebElements: Tungsten, key properties and description'
    type: database
    url: https://www.webelements.com/tungsten/
  - title: 'EWS: TIGZONE tungsten WT20 (red) product page'
    type: datasheet
    url: https://en.ewsgmbh.com/produkt/tigzone-tungsten-wt20-red/
  - title: 'Gafvert T, Pagels J, Holm E: Thorium exposure during tungsten inert gas welding with thoriated tungsten electrodes (Radiation Protection Dosimetry, 2003)'
    type: paper
    url: https://orbit.dtu.dk/en/publications/thorium-exposure-during-tungsten-inert-gas-welding-with-thoriated/
    year: 2003
  - title: Pripyat in my Pocket - Thoriated Tungsten (University of Leicester student paper)
    type: paper
    url: https://journals.le.ac.uk/index.php/pst/article/download/4799/4815/17325
gaps:
  - 'Electrical resistivity of the tungsten matrix (5.4 x 10-8 ohm m, WebElements) was removed: the page prints it with a superscript exponent that the value check cannot match.'
  - 'Half-life of thorium-232 (4.415 x 10^17 s, Leicester paper) was removed for the same reason: the PDF text loses the exponent superscript.'
  - No GHS classification for the thoriated electrode was read. PubChem returned a reCAPTCHA page in this run, and no supplier safety data sheet for WT20 was read.
  - 'Melting point, density and hardness were read for the tungsten matrix (WebElements). No WT20 datasheet value for density or melting point was found: the EWS page gives none, and the Midwest Tungsten and Strongwire pages were not readable or did not list values.'
  - No IARC or national radiation-protection classification of thorium-232 or thorium dioxide was read. The IARC monograph PDF and list page did not load in this run.
  - No space-flight, vacuum or radiation-environment use was found for thoriated tungsten. The uses above are welding uses, not flight hardware.
  - No thorium supply data (production shares, reserves, critical-mineral status) was read. The USGS tungsten summary does not name tungsten as a critical mineral and does not give crustal abundance.
  - Corrosion data are qualitative and come from the tungsten matrix; no oxidation or acid test on the thoriated grade was read.
  - Vickers hardness and ThO2 content are not canonical property names and were entered as snake_case names (vickers_hardness, thoria_content).
  - Only six sources were read in this run, short of the eight aimed for. The NRC and Birmingham safety documents were encrypted or returned 404.
  - Secondary (recycled) tungsten quantity for 2025 is withheld in the USGS summary, so recycling share is not given.
sources:
  usgs-mcs-2026:
    title: 'USGS Mineral Commodity Summaries 2026: Tungsten'
    id: USGS MCS 2026, tungsten
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-tungsten.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  we-physics:
    title: 'WebElements: Tungsten, physical properties'
    id: WebElements, tungsten physics page
    url: https://www.webelements.com/tungsten/physics.html
    kind: database
    license: WebElements terms of use (cited, not reproduced)
  we-main:
    title: 'WebElements: Tungsten, key properties and description'
    id: WebElements, tungsten main page
    url: https://www.webelements.com/tungsten/
    kind: database
    license: WebElements terms of use (cited, not reproduced)
  ews-wt20:
    title: 'EWS: TIGZONE tungsten WT20 (red) product page'
    id: EWS GmbH, TIGZONE tungsten WT20 (red)
    url: https://en.ewsgmbh.com/produkt/tigzone-tungsten-wt20-red/
    kind: web
    license: manufacturer web page (cited, not reproduced)
  dtu-2003:
    title: Thorium exposure during tungsten inert gas welding with thoriated tungsten electrodes
    id: Radiation Protection Dosimetry 103(4), 349-357, 2003 (Gafvert T, Pagels J, Holm E)
    url: https://orbit.dtu.dk/en/publications/thorium-exposure-during-tungsten-inert-gas-welding-with-thoriated/
    year: 2003
    kind: paper
    license: publisher abstract page (cited, not reproduced)
  leicester-thw:
    title: Pripyat in my Pocket - Thoriated Tungsten
    id: University of Leicester student paper, journal article 4799
    url: https://journals.le.ac.uk/index.php/pst/article/download/4799/4815/17325
    kind: paper
    license: open student paper (cited, not reproduced)
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 15
  unreachable: 3
  caveats: 4
  note: 'Read by an AI assistant on 2026-10-26: 17 properties read from WebElements, EWS, the 2003 dosimetry study and a student radiation paper. The IARC, PubChem, NRC and Birmingham sources were not readable in this run.'
story:
  recipe:
    line: Thoriated tungsten is tungsten with about 2% thorium dioxide (ThO2) mixed in. Thorium dioxide is the oxide of the radioactive element thorium-232 (the Leicester paper uses 2% ThO2 as its basis).
    parts:
      - name: Tungsten
        symbol: W
        share: about 98% by mass
        role: The matrix. It gives the electrode its high melting point and its rigid structure during welding.
      - name: Thorium dioxide
        symbol: ThO2
        share: about 2% by mass (EWS gives 1.7 to 2.2%)
        role: The minor oxide that makes the electrode a thoriated grade. It carries the thorium-232 that is the radiological hazard.
  risk_groups:
    - title: For people
      level: 0
      verdict: Low dose when the electrode is intact; dust is the concern
      lead: The welding dose estimates are small, but the thorium is a radioactive source that must be controlled.
      points:
        - label: The electrode
          line: The paper calls the activity of one electrode low (75.81 Bq for a 200 mm by 2.4 mm rod) and says the alpha particles cannot penetrate skin.
        - label: Dust from grinding
          line: The 2003 study measured a respirable thorium fraction of 5 mBq m-3 or lower when grinding electrodes. The realistic dose from grinding is 10 µSv or lower per year.
        - label: Welders
          line: Breathing-zone levels for TIG welders were generally below 10 mBq m-3. A full-time welder's realistic annual dose was below 0.3 mSv, and about 1 mSv under conservative assumptions.
    - title: Handling
      points:
        - label: Grinding
          line: The study points to grinding dust as the main route of exposure, so use local extraction when sharpening.
  why: Thoriated tungsten is the traditional TIG electrode for direct-current welding. The thorium dioxide is added to the tungsten matrix, which keeps the electrode stable at welding temperature. The tungsten part melts at 3695 K. The same oxide that makes the grade useful carries the thorium-232 that makes it radioactive.
  uses:
    - where: TIG welding electrodes
      line: EWS sells WT20 as a red-tipped electrode best suited to direct-current welding on constant-current transformer power sources, with a medium amperage range.
    - where: Welders' exposure
      line: The 2003 study measured thorium in the breathing zones of TIG welders in five workshops, and estimated annual doses for a full-time welder and for grinding electrodes.
  can_do:
    - label: Melting point of the matrix
      benchmark: melting_point
      value: 3695 K
      line: WebElements gives 3695 K, which it prints as 3422 degC. The value is for the tungsten matrix.
    - label: Density of the matrix
      benchmark: density
      value: 19250 kg m-3
      line: WebElements gives 19250 kg m-3 for tungsten. The electrode is about 98% tungsten, so its density is close to this.
    - label: Thorium dioxide content
      benchmark: thoria_content
      value: 1.7 to 2.2 %
      line: EWS gives a principal oxide range of 1.7 to 2.2% thorium oxide, against a nominal 2% grade.
    - label: Welder dose
      benchmark: annual_committed_effective_dose
      value: below 0.3 mSv
      line: The realistic annual dose for a full-time TIG welder is below 0.3 mSv, with about 1 mSv under conservative assumptions.
  compare: 'Thoriated tungsten shares the high melting point and density of pure tungsten, so it is well suited to the high temperature of the arc. Its radiological side is what sets it apart: the thorium oxide adds an alpha source that pure tungsten does not have. The table compares the melting point, density and thorium-232 activity of the electrode.'
  compare_rows:
    - label: Melting point
      benchmark: melting_point
    - label: Density
      benchmark: density
    - label: Thorium-232 activity of one electrode
      benchmark: activity_per_electrode
  handling:
    - Sharpen electrodes with local extraction, since grinding is the main exposure route in the study.
    - Keep the electrode from air when hot. The tungsten matrix oxidises in air above room temperature.
    - Treat the rods as radioactive material when storing or disposing of them. The source does not say how many rods are a hazard.
  good_for:
    - Direct-current TIG welding with constant-current transformer power sources (EWS).
    - Welding where the high melting point of the tungsten matrix is needed.
  watch_out:
    - Thorium-232 is an alpha emitter. Grinding dust is the main route into the body, and the study measured it at 5 mBq m-3 or lower.
    - The tungsten matrix oxidises in air when hot, and the electrode should be protected from air at high temperature.
    - 'Supply: no thorium supply data was read in this run, and the tungsten supply is concentrated in China (78.8% of 2025 mine output, computed).'
  verdict: Thoriated tungsten is a well-established TIG electrode with low measured radiation dose to welders. Its thorium oxide content makes it radioactive, so control dust when sharpening and check the supplier's safety data sheet before buying.