Wollaston wire (silver-clad platinum and Pt-10Rh microwire) Wollaston wire

spore: profile
id: wollaston-platinum-wire
spore_version: 0.2
family: precious-metals
name: Wollaston wire (silver-clad platinum and Pt-10Rh microwire)
abbreviation: Wollaston wire
role: Fine sensing wire for hot-wire anemometers and micro-thermocouples
category: metals
type: precious-metals
summary: |
  Wollaston wire is a platinum or platinum-rhodium core drawn inside a silver sheath until the core is only a few micrometres across. Goodfellow lists core diameters of 0.0006 mm to 0.01 mm for the platinum grade and 0.0025 mm to 0.006 mm for the Pt 90/Rh 10 grade. The silver is etched away with dilute nitric acid to leave the bare core.
best_for: Hot-wire anemometer sensing elements and micro-thermocouple legs; Goodfellow names hot-wire anemometry as the primary application
weakest_at: 'Fragility of the fine core: Goodfellow says it must be handled carefully to avoid kinking or breaking, and that cutting it needs microsurgical techniques or laser ablation'
identity:
  formula: Pt core (99.9% purity, 3N) or Pt 90/Rh 10 alloy core, both drawn in a silver sheath
  cas: 7440-06-4
  crystal_system: face centred cubic
  source: goodfellow-pt
  where: Identification table (Grade Wollaston, purity 99.9%, CAS 7440-06-4); Atomic Properties table (atomic number 78, atomic weight 195.08, face centred cubic)
  designations:
    - system: Trade name
      code: Wollaston
      note: grade name printed for the silver-sheathed fine wire; no UNS, EN or ASTM code is printed on the page
      source: goodfellow-pt
      where: Identification table, Grade
tags:
  environments: []
  stresses: []
  applications:
    - thermal-control
    - electronics-and-chips
properties:
  - benchmark: density
    label: Density of the platinum core
    value: 21.45
    unit: g/cm3
    scope: material
    conditions:
      grade: Pt core, 99.9% purity, as drawn
      temperature: 20 °C
    method: Printed in the Physical Properties table of the Goodfellow page as Density (gcm⁻³) 21.45 at 20°C
    status: ground
    source: goodfellow-pt
    where: Physical Properties table
  - benchmark: melting_point
    label: Melting point of the platinum core
    value: 1772
    unit: °C
    scope: material
    conditions:
      grade: Pt core, 99.9% purity, as drawn
    method: Printed in the Thermal Properties table of the Goodfellow page as Melting point (C) 1772
    status: ground
    source: goodfellow-pt
    where: Thermal Properties table
  - benchmark: boiling_point
    label: Boiling point of the platinum core
    value: 3827
    unit: °C
    scope: material
    conditions:
      grade: Pt core, 99.9% purity, as drawn
    method: Printed in the Physical Properties table of the Goodfellow page as Boiling point (C) 3827
    status: ground
    source: goodfellow-pt
    where: Physical Properties table
  - benchmark: electrical_resistivity
    label: Electrical resistivity of the platinum core
    value: 10.58
    unit: µOhmcm
    scope: material
    conditions:
      grade: Pt core, 99.9% purity, as drawn
      temperature: 20 °C
    method: Printed in the Electrical Properties table as 10.58 at 20°C; unit as printed
    status: ground
    source: goodfellow-pt
    where: Electrical Properties table
  - benchmark: temperature_coefficient_of_resistance
    label: Temperature coefficient of resistance of the platinum core
    value: 0.00392
    unit: K-1
    scope: material
    conditions:
      grade: Pt core, 99.9% purity
      temperature_range: 0 to 100 °C
    method: Printed in the Electrical Properties table as 0.00392 at 0-100°C; not a canonical property name, see gaps
    status: ground
    source: goodfellow-pt
    where: Electrical Properties table
  - benchmark: thermal_conductivity
    label: Thermal conductivity of the platinum core
    value: 71.6
    unit: W/(m·K)
    scope: material
    conditions:
      grade: Pt core, 99.9% purity
      temperature_range: 0 to 100 °C
    method: Printed in the Thermal Properties table as 71.6 at 0-100°C; unit as printed W m⁻¹ K⁻¹
    status: ground
    source: goodfellow-pt
    where: Thermal Properties table
  - benchmark: specific_heat
    label: Specific heat of the platinum core
    value: 133
    unit: J/(kg·K)
    scope: material
    conditions:
      grade: Pt core, 99.9% purity
      temperature: 25 °C (printed as 025°C)
    method: Printed in the Thermal Properties table as 133 at 025°C; unit as printed J K⁻¹ kg⁻¹
    status: ground
    source: goodfellow-pt
    where: Thermal Properties table
  - benchmark: cte
    label: Coefficient of thermal expansion of the platinum core
    value: 9
    unit: ppm/K
    scope: material
    conditions:
      grade: Pt core, 99.9% purity
      temperature_range: 0 to 100 °C
      unit_in_source: x10⁻⁶ K⁻¹ as printed
    method: Printed in the Thermal Properties table as 9 at 0-100 with the unit x10⁻⁶ K⁻¹; 10⁻⁶ K⁻¹ is the same as ppm/K
    status: ground
    source: goodfellow-pt
    where: Thermal Properties table
  - benchmark: elastic_modulus
    label: Tensile modulus of the platinum core
    value: 170
    unit: GPa
    scope: material
    conditions:
      grade: Pt core, 99.9% purity
      temper: hard and soft (the same value is printed for both)
    method: Printed in the Mechanical Properties table as Tensile modulus (GPa) 170 for both columns
    status: ground
    source: goodfellow-pt
    where: Mechanical Properties table
  - benchmark: poissons_ratio
    label: Poisson's ratio of the platinum core
    value: 0.39
    unit: '-'
    scope: material
    conditions:
      grade: Pt core, 99.9% purity
      temper: hard and soft (the same value is printed for both)
    method: Printed in the Mechanical Properties table as Poisson's ratio 0.39 for both columns
    status: ground
    source: goodfellow-pt
    where: Mechanical Properties table
  - benchmark: ultimate_tensile_strength
    label: Tensile strength of the platinum core, hard temper
    value: 200
    value_high: 300
    bound: range
    unit: MPa
    scope: material
    conditions:
      grade: Pt core, 99.9% purity
      temper: hard
    method: Printed in the Mechanical Properties table as Tensile strength (MPa) 200-300 in the Hard column
    status: ground
    source: goodfellow-pt
    where: Mechanical Properties table
  - benchmark: ultimate_tensile_strength
    label: Tensile strength of the platinum core, soft temper
    value: 125
    value_high: 150
    bound: range
    unit: MPa
    scope: material
    conditions:
      grade: Pt core, 99.9% purity
      temper: soft
    method: Printed in the Mechanical Properties table as Tensile strength (MPa) 125-150 in the Soft column
    status: ground
    source: goodfellow-pt
    where: Mechanical Properties table
  - benchmark: core_diameter
    label: Core diameter of the platinum wire
    value: 0.0006
    value_high: 0.01
    bound: range
    unit: mm
    scope: material
    conditions:
      grade: Pt core, 99.9% purity
      form: silver-clad spooled wire
    method: Printed in the Construction and dimensions table as Core Diameter 0.0006 mm to 0.01 mm; not a canonical property name, see gaps
    status: ground
    source: goodfellow-pt
    where: Construction and dimensions table
  - benchmark: outside_diameter
    label: Outside diameter of the silver-clad platinum wire
    value: 0.025
    value_high: 0.1
    bound: range
    unit: mm
    scope: material
    conditions:
      grade: Pt core, 99.9% purity
      form: silver-clad spooled wire
    method: Printed in the Construction and dimensions table as Outside Diameter 0.025 mm to 0.1 mm; not a canonical property name, see gaps
    status: ground
    source: goodfellow-pt
    where: Construction and dimensions table
  - benchmark: density
    label: Density of the Pt 90/Rh 10 core
    value: 19.97
    unit: g/cm3
    scope: material
    conditions:
      grade: Pt 90/Rh 10 core
      temperature: not stated in the table
    method: Printed in the Physical Properties table of the Goodfellow Pt-Rh page as Density (gcm⁻³) 19.97
    status: ground
    source: goodfellow-ptrh
    where: Physical Properties table
  - benchmark: melting_point
    label: Melting point of the Pt 90/Rh 10 core
    value: 1830
    value_high: 1855
    bound: range
    unit: °C
    scope: material
    conditions:
      grade: Pt 90/Rh 10 core
    method: Printed in the Thermal Properties table of the Goodfellow Pt-Rh page as Melting point (C) 1830-1855
    status: ground
    source: goodfellow-ptrh
    where: Thermal Properties table
  - benchmark: electrical_resistivity
    label: Electrical resistivity of the Pt 90/Rh 10 core
    value: 18.4
    value_high: 19.2
    bound: range
    unit: µOhmcm
    scope: material
    conditions:
      grade: Pt 90/Rh 10 core
      temperature: not stated in the table
    method: Printed in the Electrical Properties table of the Goodfellow Pt-Rh page as 18.4-19.2
    status: ground
    source: goodfellow-ptrh
    where: Electrical Properties table
  - benchmark: thermal_conductivity
    label: Thermal conductivity of the Pt 90/Rh 10 core
    value: 38
    unit: W/(m·K)
    scope: material
    conditions:
      grade: Pt 90/Rh 10 core
      temperature: 23 °C
    method: Printed in the Thermal Properties table of the Goodfellow Pt-Rh page as 38 at 23°C; unit as printed W m⁻¹ K⁻¹
    status: ground
    source: goodfellow-ptrh
    where: Thermal Properties table
  - benchmark: ultimate_tensile_strength
    label: Tensile strength of the Pt 90/Rh 10 core
    value: 320
    value_high: 620
    bound: range
    unit: MPa
    scope: material
    conditions:
      grade: Pt 90/Rh 10 core
      temper: not named in the table (the identification table lists As Drawn)
    method: Printed in the Mechanical Properties table of the Goodfellow Pt-Rh page as Tensile strength (MPa) 320-620
    status: ground
    source: goodfellow-ptrh
    where: Mechanical Properties table
  - benchmark: elongation
    label: Elongation at break of the Pt 90/Rh 10 core
    value: 35
    unit: '%'
    scope: material
    conditions:
      grade: Pt 90/Rh 10 core
      temper: not named in the table
    method: Printed in the Mechanical Properties table of the Goodfellow Pt-Rh page as Elongation at break (%) 35
    status: ground
    source: goodfellow-ptrh
    where: Mechanical Properties table
  - benchmark: core_diameter
    label: Core diameter of the Pt 90/Rh 10 wire
    value: 0.0025
    value_high: 0.006
    bound: range
    unit: mm
    scope: material
    conditions:
      grade: Pt 90/Rh 10 core
      form: silver-clad spooled wire
    method: Printed in the Dimensions section as Core diameter 0.0025 mm to 0.006 mm; not a canonical property name, see gaps
    status: ground
    source: goodfellow-ptrh
    where: Dimensions section
  - benchmark: outside_diameter
    label: Outside diameter of the silver-clad Pt 90/Rh 10 wire
    value: 0.025
    value_high: 0.1
    bound: range
    unit: mm
    scope: material
    conditions:
      grade: Pt 90/Rh 10 core
      form: silver-clad spooled wire
    method: Printed in the Dimensions section as Outside diameter 0.025 mm to 0.1 mm; not a canonical property name, see gaps
    status: ground
    source: goodfellow-ptrh
    where: Dimensions section
corrosion:
  - environment: Air and oxygen at high temperature (bulk platinum metal)
    headline: Platinum does not corrode in air, even at high temperatures.
    effect: Wikipedia says platinum does not corrode, even at high temperatures, and that heated metal wires lose weight faster in air or oxygen than in a vacuum. Goodfellow says the pure platinum core resists corrosion and oxidation.
    rating: none
    conditions:
      basis: statements about platinum metal in general and Goodfellow wording for the Wollaston core; no test on the drawn wire is given in these sources
    source: wiki-platinum
    where: Corrosion and oxidation in air section; Goodfellow Key Features (Wollaston platinum page)
  - environment: Hydrochloric and nitric acid (bulk platinum metal)
    headline: Platinum is insoluble in hydrochloric and nitric acid.
    effect: Wikipedia says platinum is insoluble in hydrochloric and nitric acid, and resistant to hydrochloric and sulfuric acids.
    rating: none
    conditions:
      basis: acids named alone; the same article says platinum dissolves in hot aqua regia (see next row)
    source: wiki-platinum
    where: Acids and aqua regia section
  - environment: Hot aqua regia (bulk platinum metal)
    headline: Hot aqua regia dissolves platinum.
    effect: Wikipedia says platinum dissolves in hot aqua regia to form aqueous chloroplatinic acid, H2PtCl6, and gives the reaction Pt + 4 HNO3 + 6 HCl gives H2PtCl6 + 4 NO2 + 4 H2O.
    rating: severe
    conditions:
      basis: hot aqua regia, a mixture of nitric and hydrochloric acid
    source: wiki-platinum
    where: Acids and aqua regia section
  - environment: Chlorine, bromine, iodine and sulfur (bulk platinum metal)
    headline: Chlorine, bromine, iodine and sulfur attack platinum.
    effect: Wikipedia says that although elemental platinum is generally unreactive, it is attacked by chlorine, bromine, iodine, and sulfur, and reacts vigorously with fluorine at 500 °C to form platinum tetrafluoride.
    rating: moderate
    conditions:
      basis: elemental halogens and sulfur; the source gives no test on the drawn wire
    source: wiki-platinum
    where: General chemical reactivity section
  - environment: Dilute nitric acid used to etch off the silver sheath
    headline: Dilute nitric acid removes the silver sheath and leaves the platinum core.
    effect: Goodfellow says the silver cladding is selectively etched away with dilute nitric acid over the active sensing length, which releases the core as a dimensionally precise, free-standing metallic element. The page reports no attack on the core itself.
    rating: none
    conditions:
      exposure: dilute nitric acid over the active sensing length, as described on the Pt-Rh page
      basis: the page describes silver removal; no core corrosion is reported
    source: goodfellow-ptrh
    where: Description section
risks:
  hazards:
    - text: PubChem's GHS record for the platinum element (CID 23939) lists H228 (flammable solid) for 10.7% of the reports, with the signal word Danger and pictogram GHS02 (flame). The record reports 410 of 504 company reports as not meeting GHS criteria. It does not state the physical form the H228 classification applies to, and it is for the element, not for drawn wire.
      ghs:
        - H228
      source: pubchem-pt
      where: GHS Classification section, ECHA C&L Notifications Summary
    - text: 'The same PubChem record says 94 of 504 reports gave hazard codes: H315 (skin irritation), H319 (serious eye irritation), H334 (may cause allergy or asthma symptoms or breathing difficulties if inhaled) and H335 (may cause respiratory irritation).'
      ghs:
        - H315
        - H319
        - H334
        - H335
      source: pubchem-pt
      where: GHS Classification section, GHS Hazard Statements
  failure_risks:
    - mode: Breakage or kinking of the ultra-fine core
      trigger: Handling the spooled wire, or cutting and terminating it
      consequence: Goodfellow says ultra-fine platinum wire is fragile and must be handled carefully to avoid kinking or breaking, and that cutting and termination typically need microsurgical techniques or laser ablation. The page gives no failure rate.
      severity: moderate
      source: goodfellow-pt
      where: Handling, fragility and breakage section
  side_effects:
    - text: Goodfellow says the catalytic activity of platinum is retained at ultra-fine gauge, so the bare core still acts as a catalytic surface.
      affects: Reactions at the wire surface
      source: goodfellow-pt
      where: FAQ answers
  handling:
    - text: Goodfellow says the silver sheath should be dissolved in dilute nitric acid rather than concentrated acid.
      source: goodfellow-pt
      where: Handling section
    - text: Goodfellow says connections to instrument leads are made by spot welding, ultrasonic bonding, or wrapping.
      source: goodfellow-pt
      where: Handling section
    - text: Goodfellow gives a wire diameter tolerance of ±10% and a length tolerance of +5% / -1%.
      source: goodfellow-pt
      where: Tolerances section
    - text: PubChem lists the precautionary codes P210, P240, P241, P280 and P370+P378 for the platinum element record, with the H228 flammable-solid classification.
      source: pubchem-pt
      where: Precautionary Statement Codes, GHS Classification section
uses:
  - application: thermal-control
    device: Hot-wire anemometer sensing element
    example: Goodfellow says hot-wire anemometry is the primary application of Wollaston platinum wire, and Wikipedia says the fastest-responding hot-wire anemometers still use it.
    source: goodfellow-pt
    where: Applications and uses section; FAQ answer The primary applications are hot-wire anemometry
  - application: thermal-control
    device: Ultra-miniaturized Type S thermocouple junction (Pt-10Rh positive leg)
    example: Goodfellow says the Pt-10%Rh wire is used to fabricate the positive leg of ultra-miniaturized Type S thermocouple junctions.
    source: goodfellow-ptrh
    where: Industrial Applications section
  - application: electronics-and-chips
    device: Early radio electrolytic detector
    example: Wikipedia says early radio detectors called electrolytic detectors used Wollaston wire.
    source: wiki-wollaston
    where: Applications list in the article
supply:
  - subject: Platinum
    producers:
      - country: South Africa
        share_percent: 70.6
        year: 2025
      - country: Russia
        share_percent: 11.8
        year: 2025
      - country: Zimbabwe
        share_percent: 10.6
        year: 2025
      - country: Canada
        share_percent: 2.9
        year: 2025
    critical_lists:
      - list: USGS Final 2025 List of Critical Minerals (platinum listed in Table 6; footnote 3 says it is included in the Platinum-Group Metals chapter)
        listed: true
    recycling: About 140,000 kilograms of palladium and platinum were recovered globally from new and old scrap in 2025, including about 50,000 kilograms of palladium and 8,600 kilograms of platinum recovered from automobile catalytic converters in the United States (USGS).
    substitutes:
      - 'USGS: palladium has been used as a substitute for platinum in most gasoline-engine catalytic converters, and about 25% of palladium can routinely be substituted for platinum in diesel catalytic converters.'
    source: usgs-mcs2026-pgm
    where: 'Platinum-Group Metals chapter: World Mine Production and Reserves table, platinum 2025e (South Africa 120,000 kg, Russia 20,000 kg, Zimbabwe 18,000 kg, Canada 5,000 kg, world total 170,000 kg rounded; shares calculated by Space Mushroom and rounded to one decimal place); Recycling; Substitutes. Critical-list status: USGS Final 2025 List of Critical Minerals page (usgs-crit2025)'
media: []
documents:
  - title: Goodfellow Wollaston platinum wire product page (Pt 99.9%)
    type: datasheet
    url: https://www.goodfellow.com/usa/wollaston-platinum-spooled-wire-group
    year: 2026
  - title: Goodfellow Wollaston platinum-rhodium wire product page (Pt 90/Rh 10)
    type: datasheet
    url: https://www.goodfellow.com/usa/wollaston-platinum-rhodium-alloy-spooled-wire-pt90-rh10-group
    year: 2026
  - title: Heraeus Precious Metals platinum datasheet (document 01, status 09/2021)
    type: datasheet
    url: https://pim.heraeus.com/datasheets/HPM/FM/Contact%20Materials/Pt_Datasheet_EN_(Heraeus_Precious_Metals).pdf
    year: 2021
  - title: PubChem compound record for platinum (CID 23939)
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/23939
    year: 2026
  - title: USGS Mineral Commodity Summaries 2026 (Platinum-Group Metals chapter)
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026.pdf
    year: 2026
gaps:
  - No flight, vacuum, radiation or space-environment result for Wollaston wire was found in the sources read; the uses are ground instruments.
  - Vickers hardness on the Goodfellow platinum page is listed as 40 and 100 in the Hard and Soft columns, but the Key Features text gives the reverse. Not recorded.
  - 'Yield strength on the Goodfellow platinum page is inconsistent: the soft yield value (185 MPa) is above the soft tensile range (125-150 MPa), and the hard yield range (14-35 MPa) is not checked. Not recorded.'
  - Brinell hardness of the Pt 90/Rh 10 core (90-165) is printed without a unit, so it is not recorded.
  - 'The California Fine Wire datasheet for Platinum 10% Rhodium Wire (item 100177) is not used for values: its page blocked automated access during verification, so its figures could not be checked against the page, and no supplier-to-supplier comparison is recorded.'
  - Wikipedia gives a final platinum core of 1.5 µm (0.00006 inches) and also says the wire is about 0.001 mm thick. The two do not match and the article does not explain why; the thickness is not recorded as a property.
  - Core diameter, outside diameter and temperature coefficient of resistance are not canonical property names; they are recorded with snake-case or descriptive names as printed.
  - The Pt 90/Rh 10 tensile strength (320-620 MPa) is not split by temper in the Goodfellow table.
  - The Heraeus platinum datasheet gives pure platinum values (density, melting point, thermal conductivity, Young's modulus) for bulk metal, not for this wire grade, so they are not recorded as properties.
  - The Wikipedia bulk-platinum density and melting point (21.452 g/cm3 and 1768.3 °C in the infobox) are for bulk metal, not for this grade, so they are not recorded as properties.
  - 'Rhodium supply is not covered: the USGS Platinum-Group Metals chapter gives rhodium only as imports, exports and prices, with no mine production by country, so no rhodium supplier row is recorded.'
  - Platinum crustal abundance and the EU critical raw materials status were not read for this profile.
  - The PubChem hazard data are for the platinum element, not the drawn wire. No supplier safety data sheet for the wire was consulted.
  - No peer-reviewed paper on Wollaston wire in hot-wire anemometers was read; the anemometer use rests on the Goodfellow page and the Wikipedia article.
  - Sensitivity of the wire to heating in air above the platinum core's melting point is not stated in the sources read; the heating and ageing behaviour of the fine core is not recorded.
sources:
  goodfellow-pt:
    title: Pure Wollaston Platinum Wire, Pt 99.9% (3N), spooled wire product page
    id: Goodfellow Metals product page, accessed 2026-11-01
    url: https://www.goodfellow.com/usa/wollaston-platinum-spooled-wire-group
    year: 2026
    kind: datasheet
    license: supplier product page, cited not reproduced
  goodfellow-ptrh:
    title: Wollaston Platinum-Rhodium Spooled Wire, Pt 90/Rh 10, product page
    id: Goodfellow Metals product page, accessed 2026-11-01
    url: https://www.goodfellow.com/usa/wollaston-platinum-rhodium-alloy-spooled-wire-pt90-rh10-group
    year: 2026
    kind: datasheet
    license: supplier product page, cited not reproduced
  heraeus-pt:
    title: Platinum datasheet, Heraeus Precious Metals (document 01, status 09/2021)
    id: Heraeus Precious Metals datasheet, document 01
    url: https://pim.heraeus.com/datasheets/HPM/FM/Contact%20Materials/Pt_Datasheet_EN_(Heraeus_Precious_Metals).pdf
    year: 2021
    kind: datasheet
    license: supplier datasheet, cited not reproduced
  wiki-wollaston:
    title: Wollaston wire, Wikipedia article
    id: Wikipedia, accessed 2026-11-01
    url: https://en.wikipedia.org/wiki/Wollaston_wire
    year: 2026
    kind: web
    license: CC BY-SA 4.0
  wiki-platinum:
    title: Platinum, Wikipedia article (corrosion, acids and reactivity sections)
    id: Wikipedia, accessed 2026-11-01
    url: https://en.wikipedia.org/wiki/Platinum
    year: 2026
    kind: web
    license: CC BY-SA 4.0
  pubchem-pt:
    title: PubChem compound record, Platinum (CID 23939), GHS classification and CAS number
    id: CID 23939; CAS 7440-06-4
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/23939/JSON
    year: 2026
    kind: database
    license: public domain (NCBI); classifications attributed to ECHA notifiers
  usgs-mcs2026-pgm:
    title: Mineral Commodity Summaries 2026, Platinum-Group Metals chapter
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-crit2025:
    title: About the 2025 List of Critical Minerals (USGS)
    id: Final 2025 List of Critical Minerals
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
    kind: web
    license: public domain (USGS)
license: CC-BY-4.0
updated: '2026-11-01'
review:
  status: draft
  method: assistant
  checked_values: 22
  unreachable: 1
  caveats: 4
  note: Values read by an AI assistant on 2026-11-01 from the Goodfellow product pages, the Wikipedia articles, PubChem, the USGS Mineral Commodity Summaries 2026 and the Heraeus platinum datasheet. The California Fine Wire datasheet was read but its values are not recorded, because its page blocks automated access.
story:
  recipe:
    line: Wollaston wire is a platinum or Pt 90/Rh 10 core drawn inside a silver sheath. Goodfellow says the silver sheath gives the mechanical support needed to draw the core to fine diameters, and the sheath is etched away with dilute nitric acid over the active sensing length.
    parts:
      - name: Platinum
        symbol: Pt
        atoms: 1
        atomic_weight: 195.08
        role: The core metal of the platinum grade (99.9% purity). Platinum has atomic number 78 and is a noble metal.
      - name: Rhodium
        symbol: Rh
        role: The alloying metal of the Pt 90/Rh 10 grade, at 10 per cent of the core by weight.
      - name: Silver
        symbol: Ag
        role: The sheath that carries the core through drawing and is etched off with dilute nitric acid.
  risk_groups:
    - title: For people
      level: 0
      verdict: Pure platinum is inert; the fine wire is fragile
      lead: The platinum element is not classed as hazardous in most PubChem reports, but a minority of reports give flammability and respiratory codes.
      points:
        - label: The metal
          line: PubChem reports that 410 of 504 company reports do not meet GHS criteria for the platinum element.
        - label: Flammable class
          line: PubChem lists H228 (flammable solid) for 10.7% of the reports, with the signal word Danger. The record does not say which physical form it applies to.
        - label: Respiratory and skin codes
          line: From 94 of 504 reports that gave codes, PubChem lists H315, H319, H334 and H335, which cover skin and eye irritation and sensitisation by inhalation.
    - title: Handling the wire
      level: 1
      lead: The main risk in handling Wollaston wire is mechanical, not toxic.
      points:
        - label: Fragility
          line: Goodfellow says ultra-fine platinum wire is fragile and must be handled carefully to avoid kinking or breaking.
        - label: Acid etching
          line: Goodfellow says the silver sheath should be dissolved in dilute nitric acid rather than concentrated acid.
        - label: Joining
          line: Goodfellow says leads are joined by spot welding, ultrasonic bonding, or wrapping.
  why: Wollaston wire is a fine core of platinum or Pt 90/Rh 10 alloy drawn inside a silver sheath. Goodfellow says the process extends the diameter range of platinum wire downward to sub-micrometre diameters, for specialized research applications. The platinum grade has a core diameter of 0.0006 mm to 0.01 mm, and the Pt 90/Rh 10 grade 0.0025 mm to 0.006 mm, with an outside diameter of 0.025 mm to 0.1 mm for both. The silver sheath is removed after drawing, so the bare core is what sensing elements use. Heraeus lists platinum wire among its platinum product forms.
  uses:
    - where: Hot-wire anemometers
      line: Goodfellow calls hot-wire anemometry the primary application of Wollaston platinum wire. Wikipedia says the fastest-responding hot-wire anemometers still use it.
    - where: Micro-thermocouples
      line: Goodfellow says the platinum grade is used for the negative leg of ultra-miniaturized Type R and Type S thermocouple junctions, and the Pt 90/Rh 10 grade for the positive leg of ultra-miniaturized Type S junctions.
    - where: Early radio detectors
      line: Wikipedia says early radio detectors called electrolytic detectors used Wollaston wire, and that it was also used in the hot-wire barretter.
  can_do:
    - label: Sense gas flow
      line: Goodfellow names hot-wire anemometry as its primary application.
    - label: Measure temperature
      line: Measure temperature in micro-thermocouples, where the platinum grade forms the negative leg of Type R and Type S junctions.
    - label: Heat and sense
      line: Act as a heater and a thermometer at once, since the wire can heat itself by Joule heating and read its own resistance, as Goodfellow says.
  compare: The platinum core has a higher density (21.45 g/cm3) and a lower melting point (1772 °C) than the Pt 90/Rh 10 core (19.97 g/cm3 and 1830 to 1855 °C per Goodfellow). Its electrical resistivity is lower, at 10.58 µOhmcm at 20 °C against 18.4 to 19.2 µOhmcm for the alloy. Both grades are sold as silver-clad spooled wire, and the table compares their key values.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Melting point
      benchmark: melting_point
    - label: Electrical resistivity
      benchmark: electrical_resistivity
  handling:
    - 'Keep the wire spooled and handle it with care: Goodfellow says it is fragile and can kink or break.'
    - Etch the silver sheath with dilute nitric acid, not concentrated acid (Goodfellow).
    - Join leads by spot welding, ultrasonic bonding or wrapping (Goodfellow).
    - Keep fine platinum away from heat and ignition sources, since PubChem gives the element the flammable-solid class H228 with precautionary codes P210 and P240.
  good_for:
    - Hot-wire anemometry, where Goodfellow names it as the primary application.
    - Micro-thermocouples, with the platinum grade as the negative leg of Type R and Type S junctions (Goodfellow).
  watch_out:
    - Fragility of the fine core, which Goodfellow says can kink or break.
    - Goodfellow gives the Pt 90/Rh 10 density and electrical resistivity without a stated temperature, so compare them only with that caveat.
    - The silver sheath gives mechanical support during drawing and is etched away for most uses (Wikipedia).
  verdict: Wollaston wire is the fine-core choice for hot-wire anemometry and micro-thermocouples, provided the fragile core is handled with care.