Niobium Nb

spore: profile
id: niobium
spore_version: 0.2
family: refractory-metals
name: Niobium
abbreviation: Nb
role: refractory metal for high-temperature rocket nozzles, steel microalloying and superconducting wire
category: metals
type: refractory-metals
summary: |
  Niobium (Nb, atomic number 41) is a body-centred cubic refractory metal with a melting point of 2477 °C and a density of 8.582 g/cm3 at 20 °C (Wikipedia infobox). Its alloy C-103 (Nb-10Hf-1Ti, UNS R04295) is used for liquid-rocket thruster nozzles. The Smiths High Performance datasheet gives minimum tensile yield strengths for recrystallised C-103 of 276 MPa at room temperature and 124 MPa at 1093 °C in vacuum. Niobium begins to oxidise in air at 200 °C, and the Golden Sunbird technical guide says C-103 needs a protective coating for extended service above 800 °C in oxidising air.
best_for: 'Hot structures that must hold stress above 1000 °C: C-103 keeps a minimum yield strength of 124 MPa at 1093 °C in vacuum (Smiths datasheet, minimum values)'
weakest_at: 'Oxidation in air: niobium begins to oxidise at 200 °C, and unprotected C-103 needs a coating above 800 °C. C103 is expensive because of its hafnium content (NASA Glenn), and the USGS reports 100 % net import reliance for the United States.'
identity:
  formula: 'Nb (element, atomic number 41); C-103 alloy Nb-10Hf-1Ti in wt% (ASTM B654 limits: Hf 9.0 to 11.0, Ti 0.7 to 1.3, Zr max 0.7, Ta max 0.5, W max 0.5)'
  cas: 7440-03-1
  source: uvm-niobium-sds
  where: Section 3.1 Substances, row Niobium, CAS-No 7440-03-1, EC No. 231-113-5
  designations:
    - system: UNS
      code: R04295
      source: stainless-c103
      where: Header block, product title NIOBIUM C-103 with UNS R04295
    - system: Trade name
      code: C-103
      source: stainless-c103
      where: Header block, NIOBIUM C-103 registered mark; Trademarks line reads Niobium C-103 alloy
    - system: ASTM
      code: B654
      note: plate, sheet and strip
      source: stainless-c103
      where: 'Header block, standards list: ASTM B652, B654, B655'
    - system: ASTM
      code: B655
      note: bar and wire
      source: smiths-c103
      where: 'Related Specifications line: ASTM B652, B654, B655, AMS 7852, AMS 7857'
    - system: AMS
      code: '7852'
      note: sheet, strip and plate
      source: smiths-c103
      where: 'Related Specifications line: AMS 7852'
    - system: AMS
      code: '7857'
      note: bar, rod and wire
      source: smiths-c103
      where: 'Related Specifications line: AMS 7857'
tags:
  environments: []
  stresses: []
  applications:
    - propulsion-and-tanks
    - structures
    - in-space-manufacturing
properties:
  - benchmark: density
    label: Density, pure niobium
    value: 8.582
    unit: g/cm3
    scope: material
    conditions:
      form: pure unalloyed niobium
      temperature: 20 °C
    method: Value printed in the physical properties infobox of the Wikipedia article (cites a handbook)
    status: ground
    source: wikipedia-niobium
    where: Infobox, Physical properties, Density (at 20° C) row
  - benchmark: density
    label: Density, C-103 alloy
    value: 8.86
    unit: g/cm3
    scope: material
    conditions:
      grade: Niobium C-103 (Nb-10Hf-1Ti)
      temperature: 20 °C
      form: wrought
    method: Value printed in a supplier datasheet, Physical properties at 20 °C
    status: ground
    source: stainless-c103
    where: Physical properties at 20 °C, Density row
  - benchmark: melting_point
    label: Melting point, pure niobium
    value: 2477
    unit: °C
    scope: material
    conditions:
      form: pure unalloyed niobium
    method: Value printed in the infobox of the Wikipedia article, given as 2750 K (2477 °C, 4491 °F)
    status: ground
    source: wikipedia-niobium
    where: Infobox, Physical properties, Melting point row
  - benchmark: melting_point
    label: Melting point, C-103 alloy
    value: 2350
    unit: °C
    scope: material
    conditions:
      grade: Niobium C-103 (Nb-10Hf-1Ti)
      tolerance: plus or minus 50 °C as printed
    method: Value printed in a supplier datasheet, with a tolerance of plus or minus 50 °C
    status: ground
    note: The Smiths datasheet prints the same 2350 plus or minus 50 °C and the H.C. Starck datasheet prints 2350 °C.
    source: stainless-c103
    where: Physical properties at 20 °C, Melting point row
  - benchmark: boiling_point
    label: Boiling point, pure niobium
    value: 4744
    unit: °C
    scope: material
    conditions:
      form: pure unalloyed niobium
      unit_in_source: 5017 K (4744 °C, 8571 °F)
    method: Value printed in the infobox of the Wikipedia article
    status: ground
    note: The UVM Alfa Aesar niobium powder SDS prints 4927 °C for the boiling point, which differs from the 4744 °C in the infobox. The SDS value is not used here.
    source: wikipedia-niobium
    where: Infobox, Physical properties, Boiling point row
  - benchmark: specific_heat
    label: Specific heat capacity, pure niobium
    value: 264.784
    unit: J/(kg·K)
    scope: material
    conditions:
      form: pure unalloyed niobium
      temperature: not stated in the infobox
    method: Value printed in the infobox of the Wikipedia article
    status: ground
    source: wikipedia-niobium
    where: Infobox, Physical properties, Specific heat capacity row
  - benchmark: thermal_conductivity
    label: Thermal conductivity, pure niobium
    value: 53.7
    unit: W/(m·K)
    scope: material
    conditions:
      form: pure unalloyed niobium
      temperature: not stated in the infobox
    method: Value printed in the infobox of the Wikipedia article
    status: ground
    source: wikipedia-niobium
    where: Infobox, Physical properties, Thermal conductivity row
  - benchmark: thermal_conductivity
    label: Thermal conductivity, C-103 at 811 °C
    value: 38.1
    unit: W/(m·K)
    scope: material
    conditions:
      grade: Niobium C-103, fully recrystallised
      temperature: 811 °C (1600 °F)
      unit_in_source: W/m°C, printed in parentheses after the Btu/hr-ft2-°F/ft value of 22.0
    method: Value printed in a manufacturer datasheet; W/m°C is numerically the same as W/(m·K)
    status: ground
    source: smiths-c103
    where: Thermal Properties table, K column, row 1600°F (811°C)
  - benchmark: thermal_conductivity
    label: Thermal conductivity, C-103 at 1304 °C
    value: 44.7
    unit: W/(m·K)
    scope: material
    conditions:
      grade: Niobium C-103, fully recrystallised
      temperature: 1304 °C (2380 °F)
      unit_in_source: W/m°C, printed in parentheses after the value of 25.8
    method: Value printed in a manufacturer datasheet; W/m°C is numerically the same as W/(m·K)
    status: ground
    source: smiths-c103
    where: Thermal Properties table, K column, row 2380°F (1304°C)
  - benchmark: cte
    label: Coefficient of thermal expansion, pure niobium at 20 °C
    value: 7.07
    unit: ppm/K
    scope: material
    conditions:
      form: pure unalloyed niobium
      temperature: 20 °C
      unit_in_source: 7.07 × 10⁻⁶ /K
    method: Value printed in the infobox of the Wikipedia article
    status: ground
    source: wikipedia-niobium
    where: Infobox, Physical properties, Thermal expansion row
  - benchmark: elastic_modulus
    label: Young's modulus, pure niobium
    value: 105
    unit: GPa
    scope: material
    conditions:
      form: pure unalloyed niobium
      temperature: not stated in the infobox
    method: Value printed in the infobox of the Wikipedia article
    status: ground
    source: wikipedia-niobium
    where: Infobox, Physical properties, Young's modulus row
  - benchmark: elastic_modulus
    label: Young's modulus, C-103 at 20 °C
    value: 90
    unit: GPa
    scope: material
    conditions:
      grade: Niobium C-103
      temperature: 20 °C
      unit_in_source: 90 x 10 3 MPa
    method: Value printed in a manufacturer datasheet, Physical properties at 20 °C
    status: ground
    source: stainless-c103
    where: Physical properties at 20 °C, Young's modulus line
  - benchmark: yield_strength
    label: Yield strength, C-103 at room temperature (minimum)
    value: 276
    unit: MPa
    scope: material
    conditions:
      grade: Niobium C-103
      temper: fully recrystallised
      atmosphere: air
      product_form: bar, rod, sheet and plate (Smiths)
      basis: minimum value
      unit_in_source: 40 ksi (276)
    method: Minimum value printed in a manufacturer datasheet, for room and elevated temperature tensile testing when fully recrystallised
    status: ground
    source: smiths-c103
    where: Mechanical Properties (minimum) table, row RT, column YS ksi (MPa)
  - benchmark: yield_strength
    label: Yield strength, C-103 at 538 °C (minimum)
    value: 172
    unit: MPa
    scope: material
    conditions:
      grade: Niobium C-103
      temper: fully recrystallised
      atmosphere: vacuum
      temperature: 538 °C (1000 °F)
      basis: minimum value
      unit_in_source: 25 ksi (172)
    method: Minimum value printed in a manufacturer datasheet
    status: ground
    source: smiths-c103
    where: Mechanical Properties (minimum) table, row 1000°F (538°C), column YS ksi (MPa)
  - benchmark: yield_strength
    label: Yield strength, C-103 at 1093 °C (minimum)
    value: 124
    unit: MPa
    scope: material
    conditions:
      grade: Niobium C-103
      temper: fully recrystallised
      atmosphere: vacuum
      temperature: 1093 °C (2000 °F)
      basis: minimum value
      unit_in_source: 18 ksi (124)
    method: Minimum value printed in a manufacturer datasheet
    status: ground
    source: smiths-c103
    where: Mechanical Properties (minimum) table, row 2000°F (1093°C), column YS ksi (MPa)
  - benchmark: yield_strength
    label: Yield strength, C-103 at 1300 °C (laser powder bed fusion)
    value: 130
    unit: MPa
    scope: material
    conditions:
      grade: C103 (Nb-10Hf-1Ti), laser powder bed fusion
      form: as printed then stress relieved at 900 °C for 1 h in high vacuum
      temperature: 1300 °C
      test: uniaxial tension in high vacuum
    method: Value printed in a NASA Glenn Research Center presentation (TMS 2025), in the comparison table of C103 and Nb521
    status: ground
    note: This is an additive-manufactured lab result, not the wrought datasheet value, so it is not directly comparable with the rows above.
    source: nasa-c103-nb521
    where: Comparing Performance, Cost and Other Properties slide, row Yield Strength at 1300 °C [MPa], column C103
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, C-103 at room temperature (minimum)
    value: 386
    unit: MPa
    scope: material
    conditions:
      grade: Niobium C-103
      temper: fully recrystallised
      atmosphere: air
      basis: minimum value
      unit_in_source: 56 ksi (386)
    method: Minimum value printed in a manufacturer datasheet
    status: ground
    source: smiths-c103
    where: Mechanical Properties (minimum) table, row RT, column UTS ksi (MPa)
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, C-103 at 1093 °C (minimum)
    value: 172
    unit: MPa
    scope: material
    conditions:
      grade: Niobium C-103
      temper: fully recrystallised
      atmosphere: vacuum
      temperature: 1093 °C (2000 °F)
      basis: minimum value
      unit_in_source: 25 ksi (172)
    method: Minimum value printed in a manufacturer datasheet
    status: ground
    source: smiths-c103
    where: Mechanical Properties (minimum) table, row 2000°F (1093°C), column UTS ksi (MPa)
  - benchmark: elongation
    label: Elongation at room temperature, C-103 (minimum)
    value: 20
    unit: '%'
    scope: material
    conditions:
      grade: Niobium C-103
      temper: fully recrystallised
      atmosphere: air
      basis: minimum value
    method: Minimum value printed in a manufacturer datasheet
    status: ground
    source: smiths-c103
    where: Mechanical Properties (minimum) table, row RT, column Elongation (%)
  - benchmark: elongation
    label: Elongation at 1093 °C, C-103 (minimum)
    value: 30
    unit: '%'
    scope: material
    conditions:
      grade: Niobium C-103
      temper: fully recrystallised
      atmosphere: vacuum
      temperature: 1093 °C (2000 °F)
      basis: minimum value
    method: Minimum value printed in a manufacturer datasheet
    status: ground
    source: smiths-c103
    where: Mechanical Properties (minimum) table, row 2000°F (1093°C), column Elongation (%)
  - benchmark: yield_strength
    label: Yield strength, C-103 at 1371 °C (minimum)
    value: 55
    unit: MPa
    scope: material
    conditions:
      grade: Niobium C-103
      temper: fully recrystallised
      atmosphere: vacuum
      temperature: 1371 °C (2500 °F)
      basis: minimum value
      unit_in_source: 8 ksi (55)
    method: Minimum value printed in a manufacturer datasheet
    status: ground
    source: smiths-c103
    where: Mechanical Properties (minimum) table, row 2500°F (1371°C), column YS ksi (MPa)
corrosion:
  - environment: Air at high temperature, uncoated niobium and C-103
    headline: Niobium begins to oxidise in air at 200 °C, and unprotected C-103 needs a coating above 800 °C.
    effect: Wikipedia states that the metal begins to oxidise in air at 200 °C. The Golden Sunbird technical guide says the primary limitation of C-103 is its oxidation resistance in air at elevated temperatures, that its oxide at 800 °C is Nb2O5 followed by HfO2, and that extended service above 800 °C in oxidising environments requires protective coatings.
    rating: severe
    conditions:
      basis: air; no exposure duration printed for the 200 °C start
      alloy: C-103 and pure niobium
    source: wikipedia-niobium
    where: Chemical properties, Oxidation paragraph (the 200 °C statement); the 800 °C statement is in section 8.1 of the Golden Sunbird guide
  - environment: Air at high temperature, silicide-coated C-103
    headline: A silicide coating raises the usable temperature of C-103 to about 1400 °C.
    effect: A NASA Glenn presentation says C103 is typically used with a high-temperature oxidation-resistant silicide coating, Si-20Cr-20Fe with the tradename R512E, which enables operation up to 1400 °C. The same slide gives MoSi2 coatings as 1600 °C for Nb521.
    rating: moderate
    conditions:
      coating: R512E silicide, NbSi2 per NASA table
      basis: maximum operating temperature with coating, as printed
    source: nasa-c103-nb521
    where: Introduction slide, and Comparing Performance table row Maximum Operating Temp. with Coating
  - environment: Aqueous acids and hot chemical environments
    headline: Niobium resists several mineral acids but is attacked by hot concentrated sulfuric acid and by hydrofluoric acid.
    effect: Wikipedia states that niobium resists corrosion by aqua regia, hydrochloric, sulfuric, nitric and phosphoric acids, and is attacked by hot concentrated sulfuric acid, hydrofluoric acid and hydrofluoric/nitric acid mixtures.
    rating: low
    conditions:
      basis: general statement in the Wikipedia article; no concentration or temperature table read
    source: wikipedia-niobium
    where: Chemical properties, Corrosion paragraph
risks:
  hazards:
    - text: Niobium powder (Alfa Aesar product, UVM copy of the SDS) is classified as Flammable solids, Category 1 (H228), with signal word Danger and precautionary statement P210 (keep away from heat and ignition sources). The substance's CLP entry is Flam. Sol. 1 (H228).
      ghs:
        - H228
      source: uvm-niobium-sds
      where: Section 2.1 and 2.2 (Signal Word, Hazard Statements); Section 3.1 Substances table
    - text: 'PubChem aggregates ECHA C&L notifications for niobium: 34 % of 529 company reports give H228 (Flammable solid) with signal word Danger. Reports stating that the substance does not meet GHS criteria make up 58 % (307 of 529).'
      ghs:
        - H228
      source: pubchem-niobium
      where: GHS Classification section, aggregated information from 7 notifications to the ECHA C&L Inventory
    - text: The H.C. Starck datasheet for C-103 bar and rod gives the hazard statement under the EU advertising directives as None.
      ghs: []
      source: hcs-c103
      where: Physical Properties page, row Hazards identification in Advertising
  failure_risks:
    - mode: Air oxidation of unprotected niobium alloy at high temperature
      trigger: Exposure to air above 200 °C for pure niobium, and above about 800 °C for C-103 without a coating
      consequence: A non-protective oxide scale forms, Nb2O5 first and HfO2 later in C-103 (Golden Sunbird guide, citing Kathiravan et al.). The guide also reports internal oxidation along grain boundaries in the 800 to 850 °C range.
      severity: critical
      source: wikipedia-niobium
      where: Chemical properties, Oxidation statement at 200 °C; the rest from section 3.4 and 8.1 of the Golden Sunbird guide
    - mode: Interstitial contamination by hydrogen, nitrogen and oxygen
      trigger: Contact with hydrogen at 200 °C, nitrogen at 400 °C or residual oxygen in the melt
      consequence: Products are interstitial and nonstoichiometric (Wikipedia). The C-103 datasheet limits O to 225 ppm max, N to 150 ppm max and H to 10 ppm max, which are the limits that prevent this contamination in production.
      severity: moderate
      source: hcs-c103
      where: Chemical Characteristics table (O, N, H max rows); the reaction temperatures are in the Wikipedia article, Chemical properties section
    - mode: Fire from fine niobium powder
      trigger: Handling niobium powder in air, which the SDS classes as a flammable solid
      consequence: Flammable solid, Category 1 (H228); the SDS says to use approved Class D extinguishers and not water or foam.
      severity: moderate
      source: uvm-niobium-sds
      where: Section 5.1 Extinguishing media
  side_effects: []
  handling:
    - text: Keep niobium powder away from heat, hot surfaces, sparks and open flames, and extinguish fires with a Class D agent, not water or foam (UVM copy of the SDS, P210 and Section 5.1).
      source: uvm-niobium-sds
      where: Section 2.2 precautionary statement P210; Section 5.1
    - text: Specify the oxygen, nitrogen and hydrogen limits of C-103 on the order. The H.C. Starck datasheet gives max O 225 ppm, N 150 ppm and H 10 ppm.
      source: hcs-c103
      where: Chemical Characteristics table
  mitigations: []
uses:
  - application: propulsion-and-tanks
    device: Liquid-rocket thruster nozzle in C-103 alloy
    example: Wikipedia says C-103 is used for liquid-rocket thruster nozzles, such as the descent engine of the Apollo Lunar Modules. H.C. Starck lists rocket nozzle applications with temperatures up to 2700 °F (1482 °C).
    source: wikipedia-niobium
    where: Alloys section, paragraph on C-103 (Niobium-based alloys); also hcs-c103 Applications row
  - application: structures
    device: Steel microalloy (ferroniobium, high-strength low-alloy steel)
    example: The USGS 2026 summary estimates that steels took about 77 % of U.S. niobium consumption, and superalloys about 23 %.
    source: usgs-mcs2026-niobium
    where: Domestic Production and Use paragraph
  - application: in-space-manufacturing
    device: C103 parts made by laser powder bed fusion
    example: NASA Glenn printed C103 by laser powder bed fusion and tested it in high vacuum to 1500 °C; its yield at 1300 °C was 130 MPa.
    source: nasa-c103-nb521
    where: Laser Powder Bed Fusion and Elevated Temperature Uniaxial Tensile Testing slides; Comparing Performance table
supply:
  - subject: Niobium (mine production)
    producers:
      - country: Brazil
        share_percent: 93
        year: 2025
      - country: Canada
        share_percent: 5
        year: 2025
    critical_lists: []
    recycling: The USGS says niobium was recycled when niobium-bearing steels and superalloys were recycled, but scrap recovery for niobium content was negligible. It may have been as much as 20 % of apparent consumption.
    substitutes:
      - 'USGS: ceramic matrix composites, molybdenum, tantalum and tungsten in superalloys; molybdenum, tantalum and titanium in stainless and high-strength steels; molybdenum and vanadium in high-strength low-alloy steels. Performance loss or higher cost may follow.'
    source: usgs-mcs2026-niobium
    where: Events, Trends and Issues paragraph (Brazil about 93 %, Canada 5 %, 2025); World Mine Production and Reserves table (Brazil 104,000 t, Canada 6,000 t, Congo (Kinshasa) 970 t, world total 112,000 t, 2025e, niobium content); Recycling; Substitutes
  - subject: Niobium (United States import dependence and imports)
    abundance: 'USGS: world resources of niobium are more than adequate to supply projected needs, most identified resources are pyrochlore in carbonatite deposits outside the United States. World reserves are more than 21,000,000 t, and Brazil holds 14,000,000 t.'
    producers:
      - country: Brazil (imports of ferroniobium and niobium metal, 2021 to 2024)
        share_percent: 65
        year: 2024
      - country: Canada (imports of ferroniobium and niobium metal, 2021 to 2024)
        share_percent: 31
        year: 2024
    critical_lists: []
    source: usgs-mcs2026-niobium
    where: Salient Statistics table (net import reliance 100 % in 2025e; imports for consumption 10,000 t in 2025e; apparent consumption 9,900 t); Import Sources (2021 to 2024); World Resources paragraph
documents:
  - title: 'USGS Mineral Commodity Summaries 2026: Niobium (Columbium)'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-niobium.pdf
    year: 2026
  - title: 'Wikipedia: Niobium'
    type: database
    url: https://en.wikipedia.org/wiki/Niobium
    year: 2026
  - title: UVM copy of Alfa Aesar niobium powder safety data sheet (revision 2, 19 February 2021)
    type: sds
    url: https://www.uvm.edu/cosmolab/msds/niobiumpowdermsds.pdf
    year: 2021
  - title: PubChem compound record for niobium (CID 23936), GHS classification
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/23936/JSON?heading=GHS+Classification
  - title: H.C. Starck product data sheet PD-7054, Niobium C-103 alloy bar and rod (issue 15.05.2018)
    type: datasheet
    url: https://www.hcstarcksolutions.com/wp-content/uploads/PD-7054_0-Nb-C-103-Bar-Rod.pdf
    year: 2018
  - title: Smiths High Performance technical datasheet, Niobium C-103 (revision 18.02.2025)
    type: datasheet
    url: https://www.smithshp.com/assets/pdf/niobium/niobium-c-103-english.pdf
    year: 2025
  - title: Stainless SA datasheet, Niobium C-103 (UNS R04295)
    type: datasheet
    url: https://www.stainless.eu/wp-content/uploads/2024/11/Niobium-C103%C2%AE-EN.pdf
  - title: Golden Sunbird Metals technical guide, Niobium C-103 Alloy (UNS R04295/Nb-10Hf-1Ti)
    type: datasheet
    url: https://gsalloy.com/niobium-c-103-alloy-uns-r04295-nb-10hf-1ti-a-technical-guide/
  - title: Brizes and Milner, A Comparison of Niobium Alloys C103 and Nb521, NASA Glenn, TMS 2025
    type: report
    url: https://ntrs.nasa.gov/api/citations/20250002178/downloads/A%20Comparison%20of%20Nb%20Alloys%20C103%20and%20Nb521.pdf
    year: 2025
  - title: NIST Atomic Weights and Isotopic Compositions for All Elements, niobium row
    type: database
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Nb&all=all&ascii=html
gaps:
  - 'UNS R04200 and R04210 (unalloyed reactor and commercial grade niobium, ASTM B392): the ASTM B392 listing page opened did not print the grade numbers, and the MakeItFrom page could not be fetched, so these codes are not listed as designations.'
  - 'EN, EN name, DIN, JIS and W.Nr. designations for niobium or C-103: no page printing one for this grade was read in this run.'
  - 'Critical-mineral list status: the USGS 2026 niobium summary prints no critical-mineral list, and the EU critical raw materials list was not opened, so critical_lists is empty.'
  - No atomic-oxygen erosion yield, outgassing or total mass loss, and no radiation test was found for niobium or C-103 in space.
  - 'Electrical resistivity of pure niobium (152 nΩ·m at 0 °C, Wikipedia) is not entered: the unit nΩ·m is not in the site''s unit registry, so the value was left out.'
  - 'Pseudo-creep rate of L-PBF C103 (4.82 %/h at 1300 °C and 50 MPa, NASA) is not entered: no canonical property name or unit exists for it in the site''s property canon.'
  - Wrought C-103 tensile values at 2000 °F from the H.C. Starck datasheet (YS 16 ksi, UTS 21 ksi) and the Golden Sunbird sheet and plate minimums (UTS 385 MPa, YS 275 MPa, elongation 20 %) were read but not entered; the Smiths minimum table was used instead, and ksi values are not in the site's unit registry.
  - 'Coefficient of thermal expansion for C-103: the Stainless SA datasheet prints 6,84 x 10-6 m/m.°C with a decimal comma, and the H.C. Starck datasheet prints 3.8 to 4.5 x 10-6/°F; neither was entered because the unit or the number format could not be matched cleanly.'
  - 'Hardness, Mohs 6.0 and Vickers 870 to 1320 MPa for pure niobium (Wikipedia), were read but not entered: no canonical hardness property name exists in the property canon.'
  - Atomic weights of hafnium and titanium were not read from a NIST page, so the alloy recipe gives only shares for those two elements.
  - Golden Sunbird sheet minimums and the ASTM B654 composition limits are used in the identity and recipe text only, not as property values.
  - 'Niobium production process: Wikipedia says electron beam melting under vacuum is the method used by the two major distributors, and the USGS text gives no process steps, so the recipe line does not describe the reduction of ore to metal.'
  - 'Mine production process, smelting of niobium concentrates: not read from a primary source.'
sources:
  wikipedia-niobium:
    title: Niobium, Wikipedia (infobox physical properties, chemical properties, production, alloys, applications)
    url: https://en.wikipedia.org/wiki/Niobium
    year: 2026
    kind: web
    license: CC BY-SA 4.0 (cited, not reproduced)
  usgs-mcs2026-niobium:
    title: Mineral Commodity Summaries 2026, Niobium (Columbium), February 2026
    id: USGS MCS 2026, prepared by Chad A. Friedline
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-niobium.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  uvm-niobium-sds:
    title: Safety data sheet, niobium powder (Alfa Aesar product ALFAA40510), copy hosted by the University of Vermont, revision 2
    id: CAS 7440-03-1, EC 231-113-5, revision 19-Feb-2021
    url: https://www.uvm.edu/cosmolab/msds/niobiumpowdermsds.pdf
    year: 2021
    kind: datasheet
    license: supplier safety data sheet (cited, not reproduced)
  pubchem-niobium:
    title: 'PubChem compound record: Niobium (CID 23936), GHS Classification section'
    id: CID 23936, ECHA C&L Inventory aggregated notifications
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/23936/JSON?heading=GHS+Classification
    kind: database
    license: PubChem (NCBI), public domain; sections attributed to ECHA
  stainless-c103:
    title: Niobium C-103 (UNS R04295) technical datasheet, Stainless SA, Dannemarie-sur-Crete
    id: UNS R04295; ASTM B652, B654, B655; AMS 7852, AMS 7857
    url: https://www.stainless.eu/wp-content/uploads/2024/11/Niobium-C103%C2%AE-EN.pdf
    kind: datasheet
    license: manufacturer datasheet, general information (cited, not reproduced)
  smiths-c103:
    title: Niobium C-103 technical datasheet, Smiths High Performance, revision 18.02.2025
    id: Related specifications ASTM B652, B654, B655, AMS 7852, AMS 7857; C-103 a proprietary product of Materion
    url: https://www.smithshp.com/assets/pdf/niobium/niobium-c-103-english.pdf
    year: 2025
    kind: datasheet
    license: supplier datasheet (cited, not reproduced)
  hcs-c103:
    title: Niobium C-103 alloy bar and rod, product data sheet PD-7054, H.C. Starck Inc.
    id: PD-7054, issue 0-15.05.2018
    url: https://www.hcstarcksolutions.com/wp-content/uploads/PD-7054_0-Nb-C-103-Bar-Rod.pdf
    year: 2018
    kind: datasheet
    license: manufacturer datasheet (cited, not reproduced)
  golden-sunbird-c103:
    title: 'Niobium C-103 Alloy (UNS R04295/Nb-10Hf-1Ti): A Technical Guide, Golden Sunbird Metals'
    id: ASTM B654 composition limits; oxidation section 3.4; coatings section 8.1
    url: https://gsalloy.com/niobium-c-103-alloy-uns-r04295-nb-10hf-1ti-a-technical-guide/
    kind: web
    license: supplier web page (cited, not reproduced)
  nasa-c103-nb521:
    title: A Comparison of Niobium Alloys C103 and Nb521, Brizes and Milner, NASA Glenn Research Center, TMS 2025
    id: NASA NTRS 20250002178
    url: https://ntrs.nasa.gov/api/citations/20250002178/downloads/A%20Comparison%20of%20Nb%20Alloys%20C103%20and%20Nb521.pdf
    year: 2025
    kind: report
    license: NASA public document
  nist-atomic-weights-nb:
    title: NIST Atomic Weights and Isotopic Compositions for All Elements, niobium
    id: NIST standard atomic weight table, Nb 92.906
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Nb&all=all&ascii=html
    kind: database
    license: US government data
license: CC-BY-4.0
updated: '2026-10-25'
review:
  status: draft
  method: assistant
  checked_values: 21
  unreachable: 2
  caveats: 6
  note: 'Values were read by an AI assistant on 2026-10-25 from the pages and PDFs named in each entry (PDFs extracted with pdftotext; the USGS and NASA values from the PDF text). Unreachable: MatWeb C-103 pages (Cloudflare check) and the MakeItFrom R04200 page. Caveats: the C-103 mechanical values are minimums from one datasheet (Smiths), so they are not typical values; the 130 MPa yield at 1300 °C is an additive-manufactured lab result; the density of pure niobium is from Wikipedia while the SDS prints 8.57 g/cm3; the boiling point differs between the Wikipedia infobox (4744 °C) and the powder SDS (4927 °C); the 800 °C oxidation threshold comes from a supplier guide, not a test report.'
story:
  recipe:
    line: Niobium is a single-element metal (Nb, atomic number 41) with a body-centred cubic structure (Wikipedia). C-103 is a niobium base alloy with 9.0 to 11.0 wt% hafnium and 0.7 to 1.3 wt% titanium, and maximum 0.7 wt% zirconium, 0.5 wt% tantalum and 0.5 wt% tungsten, as printed in the H.C. Starck and Smiths datasheets. Electron beam melting under vacuum is the method used by the two major niobium distributors (Wikipedia), because niobium reacts with oxygen and must be worked in vacuum or inert gas.
    parts:
      - name: Niobium
        symbol: Nb
        atoms: 1
        atomic_weight: 92.906
        role: The base metal, the balance of the alloy. Pure niobium has a density of 8.582 g/cm3 and a melting point of 2477 °C (Wikipedia).
      - name: Hafnium
        symbol: Hf
        share_note: 9.0 to 11.0 wt% (ASTM B654 limit, H.C. Starck and Smiths)
        role: Solid-solution strengthener that raises the recrystallisation temperature and forms HfO2 scales that add some oxidation resistance (Golden Sunbird guide).
      - name: Titanium
        symbol: Ti
        share_note: 0.7 to 1.3 wt% (ASTM B654 limit, H.C. Starck and Smiths)
        role: The 1 wt% nominal alloying addition in C-103 (Wikipedia).
  risk_groups:
    - title: For people
      lead: The powder is a flammable solid in the supplier safety data sheet. The bulk alloy datasheet gives no hazard statement.
      level: 1
      verdict: Flammable as powder, not hazardous as bulk alloy
      points:
        - label: Niobium powder
          line: The UVM copy of the Alfa Aesar safety data sheet classifies niobium powder as Flammable solid, Category 1 (H228), with the signal word Danger. PubChem's ECHA aggregate shows H228 in 34 % of 529 reports.
        - label: C-103 bar and rod
          line: The H.C. Starck datasheet gives the hazard statement under the EU advertising directives as None.
    - title: If it fails
      lead: The failure routes here are oxidation in air and contamination by gases. The sources give no test of these in space.
      points:
        - label: Oxidation
          line: Niobium begins to oxidise in air at 200 °C, and unprotected C-103 needs a coating for extended service above 800 °C.
        - label: Gas pickup
          line: Hydrogen at 200 °C, nitrogen at 400 °C and oxygen all form interstitial products, so the C-103 datasheet sets maximum oxygen, nitrogen and hydrogen contents.
  why: 'Niobium is a refractory metal with a melting point of 2477 °C (pure) and a body-centred cubic structure. Its alloy C-103, with 10 wt% hafnium and 1 wt% titanium, keeps useful strength at high temperature, which is why it is used for liquid-rocket thruster nozzles. Smiths High Performance gives minimum tensile yield strengths of 276 MPa at room temperature and 124 MPa at 1093 °C in vacuum. Most niobium goes into steel: the USGS 2026 summary estimates steels at about 77 % of U.S. consumption.'
  uses:
    - where: Rocket nozzles
      line: C-103 is the thruster nozzle alloy for liquid-rocket engines, including the descent engine of the Apollo Lunar Modules (Wikipedia). H.C. Starck lists rocket nozzle applications up to 1482 °C.
    - where: Steel
      line: Niobium is an important addition to high-strength low-alloy steels, including pipeline steel (Wikipedia). The USGS 2026 summary estimates steels at about 77 % of U.S. consumption.
    - where: Additive manufacturing
      line: NASA Glenn printed C103 by laser powder bed fusion and reported a yield strength of 130 MPa at 1300 °C after stress relief.
  can_do:
    - label: Carry load when hot
      value: 124 MPa yield at 1093 °C
      benchmark: yield_strength
      line: The minimum yield strength of recrystallised C-103 in vacuum is 124 MPa at 1093 °C and 55 MPa at 1371 °C (Smiths datasheet).
    - label: Carry heat
      value: 38.1 W/(m·K) at 811 °C
      benchmark: thermal_conductivity
      line: C-103 has a thermal conductivity of 38.1 W/(m·K) at 811 °C and 44.7 W/(m·K) at 1304 °C (Smiths datasheet, W/m°C).
    - label: Weight
      value: 8.86 g/cm3
      benchmark: density
      line: C-103 has a density of 8.86 g/cm3 at 20 °C (Stainless SA datasheet). Pure niobium has a density of 8.582 g/cm3 (Wikipedia).
    - label: Melting
      value: 2350 °C
      benchmark: melting_point
      line: C-103 melts at 2350 plus or minus 50 °C (Stainless and Smiths datasheets). Pure niobium melts at 2477 °C (Wikipedia).
    - label: Stiffness
      value: 90 GPa
      benchmark: elastic_modulus
      line: C-103 has a Young's modulus of 90 GPa at 20 °C (Stainless SA datasheet). Pure niobium has 105 GPa (Wikipedia).
  compare: NASA Glenn reports that Nb521 (Nb-5W-2Mo-1Zr) has about 70 MPa higher yield strength than C103 across the tested temperature range, and about 100 times the creep resistance at 1300 °C and 50 MPa. Its estimated raw material cost is about 100 USD/kg against about 500 USD/kg for C103 (NASA slide table), so C103 is the costlier raw material. The three rows below compare density, melting point and thermal conductivity of niobium and C-103 only.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Melting point
      benchmark: melting_point
    - label: Thermal conductivity
      benchmark: thermal_conductivity
  handling:
    - Specify the oxygen, nitrogen and hydrogen limits on the order, as the C-103 datasheet does.
    - Keep niobium powder away from heat and ignition sources, and use a Class D extinguisher (UVM SDS).
    - Protect C-103 with a silicide coating for any service above 800 °C in air (Golden Sunbird guide).
  good_for:
    - 'High-temperature load in vacuum: 124 MPa minimum yield at 1093 °C for recrystallised C-103 (Smiths).'
    - 'Thruster nozzles: C-103 is the standard liquid-rocket nozzle alloy named in Wikipedia and the H.C. Starck datasheet.'
    - 'Heat conduction at temperature: 38.1 W/(m·K) at 811 °C for C-103 (Smiths).'
  watch_out:
    - 'Oxidation: niobium begins to oxidise in air at 200 °C, and C-103 needs a coating above 800 °C (Wikipedia, Golden Sunbird).'
    - 'Powder: niobium powder is a Category 1 flammable solid (H228) and needs a Class D extinguisher (UVM SDS).'
    - 'Supply: Brazil mines about 93 % of world niobium and the United States imports all of its niobium material (USGS 2026).'
    - No space outgassing, erosion yield or radiation data for niobium or C-103 were found in the sources read.
  verdict: Niobium is a dense refractory metal (8.582 g/cm3 pure, melting point 2477 °C) whose C-103 alloy holds a minimum 124 MPa yield strength at 1093 °C in vacuum and is the standard thruster nozzle alloy. It oxidises in air from 200 °C and needs a coating above 800 °C, and the metal powder is a flammable solid. Its supply is concentrated in Brazil, and this profile has no sourced space-environment test data.