spore: profile
id: hafnium
spore_version: 0.2
family: refractory-metals
name: Hafnium
abbreviation: Hf
role: nuclear control rod material and superalloy additive
category: metals
type: refractory-metals
summary: |
  Hafnium is the element Hf (atomic number 72), a heavy metal with a density of 13.3 g/cm3 that melts at 2233 °C. It occurs naturally with zirconium at about 1:50 and is produced as a co-product of nuclear-grade zirconium. Its biggest use is as control rod material in nuclear reactors, where its thermal neutron cross-section is 104 barns. Small additions strengthen the grain boundaries of nickel superalloys used in jet engine hot sections. The C103 niobium alloy, which contains 10 % hafnium, has been used for liquid-rocket thruster nozzles, including the Apollo Lunar Module engine.
best_for: Absorbing neutrons in reactor control rods (104 barns thermal neutron cross-section) and strengthening nickel superalloys (ATI)
weakest_at: Fine powder and chips, which ignite in air (ATI, ESPI), and strength that depends strongly on oxygen, nitrogen and carbon pickup (ATI)
identity:
  formula: Hf (element, atomic number 72); grades R1 and R3 are unalloyed hafnium, and the alloy-addition product has up to 4.5 % zirconium (ATI)
  cas: 7440-58-6
  source: pubchem-hf
  where: Other Identifiers, CAS entry (PubChem CID 23986)
  designations:
    - system: UNS
      code: R02001
      note: alloy-addition hafnium with zirconium up to 4.5 %
      source: ati-hf-tds
      where: Title block, Hafnium Alloy Addition (UNS R02001)
    - system: ASTM
      code: B776
      note: strip, sheet and plate, grades R1 and R3
      source: ati-hf-tds
      where: Chemical Properties paragraph, Mill products conform to ASTM B776
    - system: Trade name
      code: Crystal Bar Hafnium
      note: iodide crystal bar form
      source: ucsb-espi-msds
      where: Section I Product Identification, Synonyms
tags:
  applications:
    - propulsion-and-tanks
    - structures
    - radiation-shielding
properties:
  - benchmark: density
    label: Density, hafnium alloy-addition data sheet
    value: 13.3
    unit: g/cm3
    scope: material
    conditions:
      temperature: not stated in the table
      unit_in_source: 13.3 g/cm3 (0.481 lbs / in3)
    method: Typical value printed in a manufacturer technical data sheet, which says the data are typical and not maximum or minimum values
    status: ground
    source: ati-hf-tds
    where: Table 2 Physical Properties of Hafnium, row Density
  - benchmark: density
    label: Density, hafnium foil (Goodfellow)
    value: 13.1
    unit: g/cm3
    scope: material
    conditions:
      temperature: 20 °C
      form: hafnium foil
    method: Value printed in a supplier product datasheet
    status: ground
    note: The same supplier page gives melting point 2227 and a different density from ATI's 13.3, so the sources differ by about 0.2 g/cm3.
    source: goodfellow-hf-foil
    where: Physical properties table, row Density (13.1@20°C)
  - benchmark: melting_point
    label: Melting point, hafnium
    value: 2233
    unit: °C
    scope: material
    conditions:
      unit_in_source: 2233°C (4051°F)
      pressure: not stated
    method: Value printed in a manufacturer technical data sheet
    status: ground
    source: ati-hf-tds
    where: Table 2 Physical Properties of Hafnium, row Melting Point
  - benchmark: boiling_point
    label: Boiling point, hafnium
    value: 4603
    unit: °C
    scope: material
    conditions:
      pressure: not stated in the infobox
      unit_in_source: 4876 K (4603 °C, 8317 °F)
    method: Value printed in the Wikipedia infobox; PubChem's Experimental Properties also list 4603 °C at 760 mmHg
    status: ground
    note: ATI prints 4690 °C in its data sheet, and PubChem gives 4602 °C in one entry. The sources differ by about 90 °C, so this profile records the Wikipedia infobox value.
    source: wikipedia-hf
    where: Infobox, Boiling point row, 4876 K (4603 °C, 8317 °F)
  - benchmark: thermal_conductivity
    label: Thermal conductivity, hafnium
    value: 23
    unit: W/(m·K)
    scope: material
    conditions:
      temperature: 298 K
      unit_in_source: 23.0 W/m • K @298K
    method: Value printed in a manufacturer technical data sheet
    status: ground
    source: ati-hf-tds
    where: Table 2 Physical Properties of Hafnium, row Thermal Conductivity
  - benchmark: specific_heat
    label: Specific heat capacity, hafnium
    value: 25.69
    unit: J/(g·K)
    scope: material
    conditions:
      temperature: not stated in the table
      unit_in_source: 25.69 J/g • K
    method: Value printed in a manufacturer technical data sheet
    status: ground
    source: ati-hf-tds
    where: Table 2 Physical Properties of Hafnium, row Specific Heat
  - benchmark: cte
    label: Coefficient of thermal expansion, hafnium
    value: 5.9
    unit: ppm/K
    scope: material
    conditions:
      temperature: not stated in the table
      unit_in_source: 5.9 X 10-6 m/m • K-1
    method: Value printed in a manufacturer technical data sheet; 10-6 m/m per K is the same unit as ppm/K
    status: ground
    source: ati-hf-tds
    where: Table 2 Physical Properties of Hafnium, row Thermal Expansion
  - benchmark: elastic_modulus
    label: Young's modulus, hafnium at room temperature
    value: 137
    unit: GPa
    scope: material
    conditions:
      temperature: room temperature
      form: not stated
    method: Value printed in a manufacturer technical data sheet, typical values
    status: ground
    note: Goodfellow's foil page prints a tensile modulus of 141 GPa, close to ATI's 137 GPa. American Elements prints 78 GPa as a theoretical value, which was not opened.
    source: ati-hf-tds
    where: Table 5 Other Mechanical Properties, row Young's Modulus
  - benchmark: shear_modulus
    label: Shear modulus, hafnium at room temperature
    value: 54.2
    unit: GPa
    scope: material
    conditions:
      temperature: room temperature
    method: Value printed in a manufacturer technical data sheet, typical values
    status: ground
    source: ati-hf-tds
    where: Table 5 Other Mechanical Properties, row Shear Modulus
  - benchmark: poissons_ratio
    label: Poisson's ratio, hafnium
    value: 0.29
    unit: '-'
    scope: material
    conditions:
      temperature: not stated in the table
    method: Value printed in a manufacturer technical data sheet
    status: ground
    source: ati-hf-tds
    where: Table 5 Other Mechanical Properties, row Poisson's Ratio
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, annealed, longitudinal, room temperature, grade R1
    value: 400
    bound: lower
    unit: MPa
    scope: material
    conditions:
      grade: R1 (nuclear)
      temper: annealed
      direction: longitudinal
      temperature: room temperature
      unit_in_source: 58 ksi (400 MPa)
      product_form: strip, sheet and plate (ASTM B 776-07 Table 3)
    method: Minimum value printed in the mechanical property table of ASTM B 776-07
    status: ground
    note: ATI's data sheet gives the same 400 MPa minimum for rod and plate in the longitudinal direction.
    source: astm-b776-copy
    where: Table 3 Grade 1 Mechanical Properties, row Longitudinal, annealed, RT, column Tensile Strength
  - benchmark: yield_strength
    label: Yield strength Rp0.2, annealed, longitudinal, room temperature, grade R1
    value: 151
    bound: lower
    unit: MPa
    scope: material
    conditions:
      grade: R1 (nuclear)
      temper: annealed
      direction: longitudinal
      temperature: room temperature
      unit_in_source: 22 ksi (151 MPa)
      product_form: strip, sheet and plate (ASTM B 776-07 Table 3)
    method: Minimum value printed in the mechanical property table of ASTM B 776-07
    status: ground
    note: ATI prints 150 MPa for the same minimum yield strength in its rod and plate table, and this profile records the ASTM value.
    source: astm-b776-copy
    where: Table 3 Grade 1 Mechanical Properties, row Longitudinal, annealed, RT, column Yield Strength
  - benchmark: elongation
    label: Elongation, annealed, longitudinal, room temperature, grade R1
    value: 20
    bound: lower
    unit: '%'
    scope: material
    conditions:
      grade: R1 (nuclear)
      temper: annealed
      direction: longitudinal
      temperature: room temperature
      gauge_length: 2 in. (50 mm)
    method: Minimum value printed in the mechanical property table of ASTM B 776-07
    status: ground
    note: ATI prints a typical 25 to 30 % elongation at room temperature, dependent on purity, which is a different basis and is not used.
    source: astm-b776-copy
    where: Table 3 Grade 1 Mechanical Properties, row Longitudinal, annealed, RT, column Elongation (min %) in 2 in.
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, annealed, longitudinal, 315 °C, grade R1
    value: 172
    bound: lower
    unit: MPa
    scope: material
    conditions:
      grade: R1 (nuclear)
      temper: annealed
      direction: longitudinal
      temperature: 315 °C (600 °F)
      unit_in_source: 25 ksi (172 MPa)
    method: Minimum value printed in the mechanical property table of ASTM B 776-07
    status: ground
    source: astm-b776-copy
    where: Table 3 Grade 1 Mechanical Properties, row Longitudinal, annealed, 600°F (315°C), column Tensile Strength
  - benchmark: yield_strength
    label: Yield strength Rp0.2, annealed, longitudinal, 315 °C, grade R1
    value: 76
    bound: lower
    unit: MPa
    scope: material
    conditions:
      grade: R1 (nuclear)
      temper: annealed
      direction: longitudinal
      temperature: 315 °C (600 °F)
      unit_in_source: 11 ksi (76 MPa)
    method: Minimum value printed in the mechanical property table of ASTM B 776-07
    status: ground
    source: astm-b776-copy
    where: Table 3 Grade 1 Mechanical Properties, row Longitudinal, annealed, 600°F (315°C), column Yield Strength
  - benchmark: vickers_hardness
    label: Vickers hardness, hafnium
    value: 1760
    unit: MPa
    scope: material
    conditions:
      temperature: not stated in the table
      unit_in_source: 1760 MPa
    method: Value printed in a manufacturer technical data sheet; the unit is printed as MPa
    status: ground
    note: No canonical name exists for hardness in the property file, so vickers_hardness is a new name and is listed in gaps.
    source: ati-hf-tds
    where: Table 5 Other Mechanical Properties, row Hardness, Vickers
  - benchmark: thermal_neutron_cross_section
    label: Thermal neutron cross-section, hafnium
    value: 104
    unit: barn
    scope: material
    conditions:
      neutron: thermal
      unit_in_source: 104 Barns
    method: Value printed in a manufacturer technical data sheet
    status: ground
    note: No canonical name exists for this property in the property file, so thermal_neutron_cross_section is a new name and is listed in gaps.
    source: ati-hf-tds
    where: Table 2 Physical Properties of Hafnium, row Thermal Neutron Cross-section
corrosion:
  - environment: Hot water at 360 °C and 18.5 MPa
    headline: Grade R1 hafnium may gain no more than 10 mg/dm2 in 672 h of 360 °C water.
    effect: ASTM B 776 specifies a test in water at 680 °F (360 °C) and 2690 psi (18.5 MPa) for 672 h. Grade R1 coupons must show a weight gain of not more than 10 mg/dm2. Grade R3 is tested for information only.
    rating: low
    conditions:
      specimen: two random samples from each lot
      duration: 672 h
      temperature: 360 °C (680 °F)
      pressure: 18.5 MPa (2690 psi)
      grade: R1 (nuclear)
    source: astm-b776-copy
    where: Section 9.1.1 and 9.1.2 (Corrosion Properties)
  - environment: Mineral acids, alkalis and hydrogen fluoride
    headline: Hafnium resists nitric acid and dilute hydrochloric or sulfuric acid, but fluoride traces make mineral acids attack it.
    effect: PubChem summarises that hafnium is unaffected by nitric acid in all concentrations, resists dilute hydrochloric and sulfuric acid, is attacked by all mineral acids if traces of fluoride are present, is slowly attacked by concentrated sulfuric acid, and is very resistant to alkalis. It is soluble in hydrogen fluoride. ATI says its corrosion behaviour is very similar to zirconium.
    rating: moderate
    conditions:
      temperature: not stated
    source: pubchem-hf
    where: Chemical and Physical Properties, Experimental Properties, Solubility
  - environment: Hydrogen at about 700 °C
    headline: Hafnium absorbs hydrogen quickly at 700 °C, forming HfH.
    effect: PubChem records that hafnium rapidly absorbs hydrogen to form HfH at 700 °C. ATI notes that mechanical properties are strongly affected by interstitial contamination.
    rating: moderate
    conditions:
      temperature: 700 °C
      atmosphere: hydrogen
    source: pubchem-hf
    where: Chemical and Physical Properties, Experimental Properties, Other Experimental Properties
  - environment: Fine powder and chips in air or water
    headline: Fine hafnium ignites in air, while massive pieces can be worked without burning.
    effect: ATI says massive pieces can be heated and worked without burning, but sponge, fines, machine chips and foil can easily ignite and burn at very high temperature. ESPI says solid hafnium will not ignite and 10 micron powder may autoignite at room temperature.
    rating: severe
    conditions:
      form: powder, chips, turnings, sponge and foil
      particle_size: 10 micron powder (ESPI)
    source: ati-hf-tds
    where: Special Precautions paragraph
risks:
  hazards:
    - text: 'PubChem GHS summary, ECHA C&L notifications: H250 (50.6 %), catches fire spontaneously if exposed to air (Pyr. Sol. 1), signal word Danger. Of 360 company reports, 124 (34.4 %) say the substance does not meet GHS criteria, so classification depends on the form and notifier.'
      ghs:
        - H250
      source: pubchem-hf
      where: Safety and Hazards, Hazards Identification, GHS Classification
    - text: 'Samaterials hafnium foil data sheet (revised 2022): the foil is not classified as hazardous under CLP, which differs from the H250 notification for the powder form.'
      ghs: []
      source: samaterials-sds
      where: Section 2 Hazards Identification
    - text: 'ESPI safety data sheet (1996): hafnium metal has no known toxicity and is not corrosive; the OSHA exposure limit is 0.5 mg/m3 as a time-weighted average. PubChem gives the same OSHA and NIOSH limit, 0.5 mg/m3 (10 h TWA).'
      ghs: []
      source: ucsb-espi-msds
      where: Section II Hazardous Ingredients and Section V Health Hazard Information
  failure_risks:
    - mode: Fire in fines and chips
      trigger: Finely divided hafnium such as powder, chips, turnings or sponge exposed to air or to water
      consequence: Fines ignite and burn at extremely high temperatures (ATI). ESPI warns that water on burning fines can cause a violent explosion, and that hydrogen and steam from a wet mass can explode. Water and CO2 feed such fires (ATI).
      severity: critical
      source: ati-hf-tds
      where: Special Precautions paragraph
    - mode: Loss of ductility from interstitial gases
      trigger: Pickup of oxygen, nitrogen or carbon during melting, processing or service
      consequence: ATI says mechanical properties are strongly affected by interstitial contamination, and that a very low interstitial content may be needed for ductility. Crystal bar is made with oxygen of 60 ppm or less for critical applications.
      severity: moderate
      source: ati-hf-tds
      where: Introduction paragraph on interstitial contamination
    - mode: Hydrogen pickup at high temperature
      trigger: Hafnium exposed to hydrogen at about 700 °C
      consequence: Hafnium rapidly absorbs hydrogen to form HfH (PubChem). The source gives no embrittlement value.
      severity: moderate
      source: pubchem-hf
      where: Chemical and Physical Properties, Experimental Properties, Other Experimental Properties
    - mode: Corrosion above the grade R1 limit in hot water
      trigger: Exposure to 360 °C water at 18.5 MPa for 672 h
      consequence: A weight gain above 10 mg/dm2 fails the grade R1 corrosion requirement in ASTM B 776-07.
      severity: low
      source: astm-b776-copy
      where: Section 9.1.2 (Grade R1 coupons)
  side_effects:
    - text: Hafnium is hard to separate from zirconium. PubChem says zirconium and hafnium are two of the most difficult elements to separate, and that very pure hafnium has been made with zirconium as the main impurity.
      affects: Purity and grade of hafnium metal
      source: pubchem-hf
      where: Use and Manufacturing, Impurities
  handling:
    - text: Specify the grade, because the limits differ. Grade R1 (nuclear) maximum oxygen 0.040, nitrogen 0.010 and iron 0.050 weight %; grade R3 (commercial) oxygen 0.130, nitrogen 0.015 and iron 0.0750 weight %, with zirconium reported (ASTM B 776-07 Table 1).
      source: astm-b776-copy
      where: Table 1 Chemical Requirements
    - text: Keep chips and fines covered with water, or in nonflammable containers in isolated areas. The water must not be allowed to evaporate or the material to dry out (ATI).
      source: ati-hf-tds
      where: Special Precautions paragraph
    - text: Keep fine turnings completely dry or very wet. If wet, the water content should be more than 25 % by weight, and do not accumulate large quantities of fines (ESPI).
      source: ucsb-espi-msds
      where: Section IX Special Precautions
    - text: Fight small fires with salt, sand, metal or a Type D extinguisher. Never use water or CO2 (ATI).
      source: ati-hf-tds
      where: Special Precautions paragraph, last paragraph
  mitigations: []
uses:
  - application: radiation-shielding
    device: Control rods in nuclear reactors
    example: ATI says hafnium's biggest application is as control rod material in nuclear reactors, because of its relatively high thermal neutron cross-section of 104 barns. A few percent zirconium does not affect its performance there. Wikipedia gives about 600 times the neutron capture cross-section of zirconium.
    source: ati-hf-tds
    where: Introduction, second paragraph; Table 2 Thermal Neutron Cross-section
  - application: structures
    device: Nickel-based superalloys for hot-end parts of jet engines
    example: ATI says a small amount of hafnium strengthens the grain boundaries of nickel-based superalloys, improving creep ductility and rupture life. PubChem says the largest use is as a 1 to 2 % alloy addition in nickel superalloys for turbine vanes in jet aircraft engines.
    source: ati-hf-tds
    where: Introduction, third paragraph
  - application: propulsion-and-tanks
    device: Liquid-rocket thruster nozzles (C103 alloy)
    example: The C103 alloy is 89 % niobium, 10 % hafnium and 1 % titanium, and is used for liquid-rocket thruster nozzles, such as the Apollo Lunar Module main engine.
    source: wikipedia-hf
    where: Uses, Rocket subsection
supply:
  - subject: Hafnium abundance
    abundance: 3.0 to 4.8 ppm of Earth's upper crust by mass, occurring mainly in zircon, where 1 to 4 % of the zirconium is replaced by hafnium (Wikipedia)
    producers: []
    critical_lists: []
    source: wikipedia-hf
    where: Composition section, first paragraph
  - subject: Hafnium metal (U.S. imports of unwrought hafnium, import shares 2021 to 2024)
    producers:
      - country: Germany
        share_percent: 54
        year: 2024
      - country: China
        share_percent: 21
        year: 2024
      - country: France
        share_percent: 12
        year: 2024
      - country: United Kingdom
        share_percent: 8
        year: 2024
    critical_lists: []
    recycling: 'USGS: hafnium metal recycling was minimal. Two companies in Oregon and Utah produced zirconium and hafnium metal from zirconium intermediates in 2025.'
    substitutes:
      - 'USGS: boron or cadmium-silver-indium alloys can substitute for hafnium metal in nuclear control rods, and zirconium can be used interchangeably with hafnium in certain superalloys. Niobium, stainless steel and tantalum give some substitution in nuclear applications.'
    source: usgs-zr-hf
    where: Import Sources (2021 to 2024) paragraph; Recycling; Substitutes. U.S. imports of unwrought hafnium 72 t in 2025e (Salient Statistics). Shares are import shares, not production shares.
documents:
  - title: 'USGS Mineral Commodity Summaries 2026: Zirconium and Hafnium'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-zirconium-hafnium.pdf
    year: 2026
  - title: ATI Hafnium Alloy Addition Technical Data Sheet (UNS R02001), version 1, 2014
    type: datasheet
    url: https://www.atimaterials.com/Products/Documents/datasheets/niobium-hafnium-tantalum-vanadium/hafnium/hafnium_v1.pdf
    year: 2014
  - title: PubChem compound record for hafnium (CID 23986), including ECHA C&L Inventory classification
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/23986
  - title: 'Wikipedia: Hafnium'
    type: database
    url: https://en.wikipedia.org/wiki/Hafnium
    year: 2026
  - title: Goodfellow hafnium foil, light tight (product datasheet)
    type: datasheet
    url: https://www.goodfellow.com/usa/hafnium-foil-light-tight-1000071871
  - title: ASTM B 776-07 Standard Specification for Hafnium and Hafnium Alloy Strip, Sheet, and Plate (copy hosted by GS Alloy)
    type: standard
    url: https://gsalloy.com/wp-content/uploads/2024/05/ASTM-B776.pdf
    year: 2007
  - title: Hafnium material safety data sheet, Electronic Space Products International (1996), copy hosted by UCSB Nanofab
    type: sds
    url: https://wiki.nanofab.ucsb.edu/w/images/2/27/Hafnium_MSDS.pdf
    year: 1996
  - title: Safety data sheet, hafnium foil, Stanford Advanced Materials (revised 2022)
    type: sds
    url: https://samaterials.com/tds/1697119777-907-hafnium-foil-sds.pdf
    year: 2022
gaps:
  - 'World primary hafnium production and reserves: USGS says world production data and quantitative reserve estimates are not available, so no production shares are entered. The supply shares above are U.S. import shares.'
  - 'Critical-mineral listing: the USGS zirconium and hafnium summary read here does not state a critical-minerals listing for hafnium, so critical_lists is empty.'
  - 'Space use: the only flight use found in the sources read is the C103 nozzle of the Apollo Lunar Module main engine (Wikipedia). No satellite or spacecraft structure with hafnium was named, and no environment tags are set because no source ties hafnium to a specific environment.'
  - 'ASTM B 776 edition: the copy read is ASTM B 776-07. The ASTM store lists B 776-12 (reapproved 2019), and the current edition was not opened, so grade limits and minimums are from B 776-07.'
  - 'Elastic constants of pure hafnium: the ultrasonic study (Journal of Applied Physics 2016) and a first-principles paper were seen only in search results, and neither was opened. The room-temperature modulus from ATI is used.'
  - 'Goodfellow hard and soft tensile and yield values: the fetched table listed values by temper, but the column order was not clear, so they are not entered. Only ATI and ASTM values are used.'
  - 'Beta transus or hcp-to-bcc transition: ATI gives 1760 °C and Wikipedia gives 2388 K (2115 °C). The sources disagree, so neither is entered.'
  - 'Oxidation rate of hafnium in air at high temperature: no value from an opened source.'
  - 'Cold welding, atomic oxygen erosion and outgassing of hafnium in vacuum: not found in the sources read.'
  - Vickers hardness and thermal neutron cross-section are entered under new names (vickers_hardness, thermal_neutron_cross_section) because the property file has no canonical name for them. Vickers hardness is printed in MPa.
  - 'Boiling point: PubChem gives 4603 °C and ATI gives 4690 °C. The PubChem value is entered and the difference is not reconciled.'
  - 'Electrical resistivity: ATI prints 3.51 X 10-7 W • m at 298 K, but its exponent format could not be matched in the fetched text, so the value was removed. Goodfellow prints 32.2 µOhmcm at 20 °C, which was not entered as a property.'
  - 'Hazard classification: the PubChem ECHA summary gives H250 for the powder, and the Stanford Advanced Materials foil sheet does not classify the foil. Both are recorded, and the form-dependence is noted.'
  - Radiation effects, emissivity and crustal figures beyond Wikipedia's abundance range were not searched.
  - 'Process steps: the Kroll reduction and iodide (van Arkel) crystal bar process come from PubChem and ATI. No primary process reference was opened.'
  - The American Elements hafnium page returned HTTP 403 and was not read. The Upmet C103 page returned HTTP 403, and the Rembar search returned no Rembar hafnium datasheet.
sources:
  usgs-zr-hf:
    title: 'Mineral Commodity Summaries 2026: Zirconium and Hafnium (USGS)'
    id: USGS MCS 2026, prepared by Shelby N. Johnston
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-zirconium-hafnium.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  ati-hf-tds:
    title: Hafnium Alloy Addition, Technical Data Sheet (Allegheny Technologies Incorporated, version 1, 2014)
    id: UNS R02001
    url: https://www.atimaterials.com/Products/Documents/datasheets/niobium-hafnium-tantalum-vanadium/hafnium/hafnium_v1.pdf
    year: 2014
    kind: datasheet
    license: manufacturer data sheet, typical values, cited not reproduced
  pubchem-hf:
    title: 'PubChem compound record: Hafnium (CID 23986), including ECHA C&L Inventory classification'
    id: CAS 7440-58-6
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/23986/JSON
    kind: database
    license: PubChem (NCBI), public domain; sections attributed to ECHA, NIOSH and others
  wikipedia-hf:
    title: Hafnium (Wikipedia)
    url: https://en.wikipedia.org/wiki/Hafnium
    year: 2026
    kind: web
    license: CC BY-SA 4.0 (cited, not reproduced)
  goodfellow-hf-foil:
    title: Hafnium foil, light tight (Goodfellow product datasheet)
    url: https://www.goodfellow.com/usa/hafnium-foil-light-tight-1000071871
    kind: datasheet
    license: supplier web page (cited, not reproduced)
  astm-b776-copy:
    title: ASTM B 776-07 Standard Specification for Hafnium and Hafnium Alloy Strip, Sheet, and Plate (copy hosted by GS Alloy)
    id: ASTM B 776-07
    url: https://gsalloy.com/wp-content/uploads/2024/05/ASTM-B776.pdf
    year: 2007
    kind: standard
    license: ASTM copyright, cited not reproduced
  ucsb-espi-msds:
    title: 'Material Safety Data Sheet: Hafnium (Electronic Space Products International, September 1996), copy hosted by UCSB Nanofab'
    id: Trade names Crystal Bar Hafnium and Iodide Bar Hafnium
    url: https://wiki.nanofab.ucsb.edu/w/images/2/27/Hafnium_MSDS.pdf
    year: 1996
    kind: datasheet
    license: supplier safety data sheet, cited not reproduced
  samaterials-sds:
    title: 'Safety Data Sheet: Hafnium Foil (Stanford Advanced Materials, revised 2022-12-08)'
    url: https://samaterials.com/tds/1697119777-907-hafnium-foil-sds.pdf
    year: 2022
    kind: datasheet
    license: supplier safety data sheet, cited not reproduced
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 17
  unreachable: 3
  caveats: 6
  note: 'Values were read by an AI assistant on 2026-10-26 from the pages and PDFs named in each entry. Unreachable: American Elements hafnium page (403), Upmet C103 page (403), NSF PAR elastic-constants paper (connection refused). Caveats: most physical values come from one manufacturer''s typical data (ATI, which covers alloy-addition hafnium); mechanical minimums are from ASTM B 776-07, a superseded edition; the boiling point and density differ between sources; the foil and powder hazard classifications differ; the supply shares are U.S. import shares, not world production.'
story:
  risk_groups:
    - title: For people
      lead: The hazard is in the fine form. Solid hafnium has no known toxicity, but fine powder and chips can catch fire, and the sources disagree on the classification.
      level: 1
      verdict: Form-dependent
      points:
        - label: Powder and chips
          line: PubChem lists H250, catches fire spontaneously if exposed to air, with signal word Danger, for the notifications it reports (50.6 % of reports). A 1996 supplier sheet says solid hafnium will not ignite, but 10 micron powder may autoignite at room temperature.
        - label: Foil
          line: A 2022 Stanford Advanced Materials sheet does not classify hafnium foil under CLP, which differs from the H250 entry for the powder.
        - label: Dust
          line: The OSHA and NIOSH exposure limit is 0.5 mg/m3 as a time-weighted average.
    - title: If it fails
      lead: 'The sources give three failure routes: a fire in fines, loss of ductility from interstitial gases, and weight gain above the grade limit in hot water.'
      points:
        - label: Fire in fines
          line: ATI says fines and chips ignite easily and burn at very high temperature, and ESPI warns that water on burning fines can cause a violent explosion.
        - label: Gas pickup
          line: ATI says mechanical properties depend strongly on interstitial contamination. PubChem says hafnium rapidly absorbs hydrogen at 700 °C to form HfH.
        - label: Hot water
          line: ASTM B 776-07 allows grade R1 a weight gain of no more than 10 mg/dm2 after 672 h in 360 °C water at 18.5 MPa.
    - title: Handling and storage
      points:
        - label: Keep fines wet or dry
          line: ATI says to keep chips covered with water and never let it dry out. ESPI says wet fines need more than 25 % water by weight.
        - label: Fire
          line: Use salt, sand, metal or a Type D extinguisher on small fires. Never use water or CO2 (ATI).
  why: Hafnium is a heavy metal that absorbs neutrons strongly, and that drives its main uses. ATI calls nuclear control rods its biggest application, where its thermal neutron cross-section is 104 barns. In small amounts it strengthens nickel superalloys used in jet engine hot sections. It is also the hafnium share of the C103 niobium alloy used for rocket nozzles, and USGS reports that unwrought hafnium is priced far above zirconium sponge.
  uses:
    - where: Nuclear control rods
      line: ATI calls control rods hafnium's biggest application. A few percent zirconium does not affect its performance there.
    - where: Jet engine superalloys
      line: Hafnium strengthens the grain boundaries of nickel superalloys, improving creep ductility and rupture life, in the hot end of jet engines.
    - where: Rocket nozzles
      line: The C103 alloy, 89 % niobium, 10 % hafnium and 1 % titanium, is used for liquid-rocket thruster nozzles, including the Apollo Lunar Module engine (Wikipedia).
  can_do:
    - label: Absorb neutrons
      value: 104 barns
      line: The thermal neutron cross-section is 104 barns (ATI Table 2).
    - label: Carry heat
      value: 23.0 W/(m·K)
      benchmark: thermal_conductivity
      line: Thermal conductivity is 23.0 W/(m·K) at 298 K (ATI Table 2).
    - label: Weight
      value: 13.3 g/cm3
      benchmark: density
      line: Density is 13.3 g/cm3 in ATI's data sheet and 13.1 g/cm3 at 20 °C in the Goodfellow foil sheet.
    - label: Melting
      value: 2233 °C
      benchmark: melting_point
      line: Melting point is 2233 °C (ATI). PubChem gives a boiling point of 4603 °C at 760 mmHg.
    - label: Strength when annealed
      value: 400 MPa
      line: ASTM B 776-07 grade R1 minimums for annealed strip, sheet or plate, longitudinal, at room temperature, are 400 MPa tensile, 151 MPa yield and 20 % elongation.
    - label: Stiffness
      value: 137 GPa
      benchmark: elastic_modulus
      line: Young's modulus is 137 GPa at room temperature, with a shear modulus of 54.2 GPa and Poisson's ratio of 0.29 (ATI Table 5).
  compare: PubChem says the density of zirconium is about half that of hafnium, and ATI says the two metals behave nearly alike in corrosive media. Hafnium and zirconium have nearly opposite nuclear properties, which is why hafnium is the control rod material and zirconium is not. The USGS says zirconium can replace hafnium in certain superalloys. This profile does not carry a zirconium profile, so read the rows as hafnium values only.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Melting point
      benchmark: melting_point
    - label: Thermal conductivity
      benchmark: thermal_conductivity
  recipe:
    line: Hafnium is a single-element metal (Hf) with a hexagonal close-packed structure at room temperature (ATI, Wikipedia). Most of it is made by reducing the tetrachloride with magnesium or sodium, the Kroll process. The iodide (van Arkel) route gives crystal bar with oxygen of 60 ppm or less (PubChem, ATI). ASTM B 776-07 Table 1 sets the impurity limits for each grade, and zirconium must be reported.
    parts:
      - name: Hafnium
        symbol: Hf
        atoms: 1
        atomic_weight: 178.49
        role: The whole material. Unalloyed grades R1 and R3 are hafnium with a balance; PubChem gives molecular weight 178.49 for the element. Impurity limits are in the risks section.
  handling:
    - 'Specify the grade: R1 (nuclear) and R3 (commercial) have different oxygen, nitrogen and iron limits (ASTM B 776-07).'
    - Keep chips and fines covered with water or in nonflammable containers, and do not let them dry out (ATI).
    - Use salt, sand or a Type D extinguisher on fires. Never use water or CO2 (ATI).
    - Wear a NIOSH-approved respirator and a heat-resistant suit when grinding or burning fine scrap (ESPI).
  good_for:
    - 'Neutron absorption: 104 barns thermal neutron cross-section in control rods (ATI).'
    - 'Superalloy additive: strengthens nickel superalloy grain boundaries and improves creep ductility (ATI).'
    - 'Rocket nozzles: the C103 alloy with 10 % hafnium, used in liquid-rocket thrusters (Wikipedia).'
  watch_out:
    - Fine powder and chips ignite in air, and water on burning fines can cause a violent explosion (ATI, ESPI).
    - Strength and ductility depend strongly on oxygen, nitrogen and carbon (ATI).
    - 'Supply data are thin: USGS gives no world production figures, and the 2021 to 2024 import shares are Germany 54 %, China 21 % and France 12 %.'
    - The foil and the powder carry different hazard classifications in the sources.
  verdict: Hafnium is a neutron absorber and a superalloy additive, with a density of 13.3 g/cm3 and a melting point of 2233 °C. Its strong neutron capture and high melting point are well documented, but its room-temperature strength is only a minimum from one standard, and its supply data are incomplete. Fine powder is pyrophoric, so fines need the handling steps above. The only rocket use read is the Apollo Lunar Module nozzle in C103 alloy.