Boron B

spore: profile
id: boron
spore_version: 0.2
family: semiconductor-materials
name: Boron
abbreviation: B
role: neutron absorber, hard amorphous powder and reinforcing fibre
category: semiconductors
type: silicon
summary: |
  Boron is element 5. Free boron is not found in nature; USGS says it occurs only in combined form, as borates. Elemental boron is made as an amorphous powder or as a fibre. The element melts at 2,075 degC (CRC value, reproduced on PubChem), and the fibre is boron deposited on a tungsten core. The boron-10 isotope captures thermal neutrons strongly: NIST gives 3835 barns for 10B and 767 barns for natural boron at 2200 m/s, so the enriched isotope is the useful absorber. NASA's 1995 shielding study called boron the best light-weight material for thermal-neutron absorption in spacecraft.
best_for: Thermal-neutron absorption where boron-10 content matters (NIST cross sections; NASA 1995 shielding report) and boron fibre for stiff composite plies (Specialty Materials datasheet)
weakest_at: 'Oxidation and reactivity: amorphous boron powder can ignite spontaneously as dust and reacts violently with steam at red heat (Materion; PubChem, citing Bretherick)'
identity:
  formula: B, elemental boron (crystalline and amorphous forms; PubChem lists amorphous, alpha-rhombohedral, alpha-tetragonal and beta-rhombohedral densities)
  cas: 7440-42-8
  source: pubchem-boron
  where: Chemical and Physical Properties, Density section (polymorph list); Materion MSDS Section I (reference number 7440-42-8, formula B)
tags:
  environments: []
  stresses: []
  applications:
    - structures
    - radiation-shielding
    - electronics-and-chips
properties:
  - benchmark: density
    label: Density, amorphous boron
    value: 2.35
    unit: g/cm3
    scope: material
    conditions:
      form: amorphous
      basis: value as printed in the Merck Index entry that PubChem reproduces
    method: Density listed in a handbook entry reproduced on the PubChem record
    status: ground
    source: pubchem-density
    where: Chemical and Physical Properties, Density section, first value (Merck Index 13th ed., p. 225, as cited)
  - benchmark: density
    label: Density, alpha-rhombohedral boron
    value: 2.46
    unit: g/cm3
    scope: material
    conditions:
      form: alpha-rhombohedral crystal
      basis: value as printed in the Merck Index entry that PubChem reproduces
    method: Density listed in a handbook entry reproduced on the PubChem record
    status: ground
    source: pubchem-density
    where: Chemical and Physical Properties, Density section, first value (Merck Index 13th ed., p. 225, as cited)
  - benchmark: density
    label: Density of solid boron (WebElements)
    value: 2460
    unit: kg/m3
    scope: material
    conditions:
      form: solid, polymorph not stated on the page
    method: Value printed on a periodic-table reference site
    status: ground
    source: webelements-boron
    where: Physical properties page, Density properties, Density of solid
  - benchmark: melting_point
    value: 2075
    unit: degC
    scope: material
    conditions:
      pressure: atmospheric
      basis: value as printed in the CRC Handbook 81st ed. entry that PubChem reproduces
    method: Melting point listed in a handbook entry reproduced on the PubChem record
    status: ground
    source: pubchem-melting
    where: Melting Point section, first value (CRC Handbook of Chemistry and Physics, 81st ed., p. 4-47, as cited)
  - benchmark: boiling_point
    value: 4000
    unit: degC
    scope: material
    conditions:
      pressure: 760 mmHg
      basis: value as printed in the CRC Handbook 81st ed. entry that PubChem reproduces
    method: Boiling point listed in a handbook entry reproduced on the PubChem record
    status: ground
    source: pubchem-boiling
    where: Boiling Point section, first value (CRC Handbook, 81st ed., p. 4-47, as cited)
  - benchmark: thermal_conductivity
    value: 27
    unit: W/(m·K)
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a periodic-table reference site
    status: ground
    source: webelements-boron
    where: Physical properties page, Heat and conduction, Thermal conductivity
  - benchmark: cte
    label: Coefficient of linear thermal expansion
    value: 6
    unit: ppm/K
    scope: material
    conditions:
      printed_as: 6 x 10^-6 K^-1
      temperature: not stated on the page
    method: Value printed on a periodic-table reference site
    status: ground
    source: webelements-boron
    where: Physical properties page, Heat and conduction, Coefficient of linear thermal expansion
  - benchmark: bulk_modulus
    value: 320
    unit: GPa
    scope: material
    conditions:
      note: The same page gives no data for Young's modulus, so this is the only elastic value sourced here
    method: Value printed on a periodic-table reference site
    status: ground
    source: webelements-boron
    where: Physical properties page, Elastic properties, Bulk modulus
  - benchmark: vickers_hardness
    label: Vickers hardness
    value: 49000
    unit: MN/m2
    scope: material
    conditions:
      printed_as: 49000 MN m-2 (about 49 GPa)
      form: elemental boron, form not stated
    method: Value printed on a periodic-table reference site
    status: ground
    note: Not a canonical property name; kept as a snake_case name and listed in gaps.
    source: webelements-boron
    where: Physical properties page, Hardnesses, Vickers hardness
  - benchmark: mineral_hardness
    label: Mineral hardness (Mohs scale)
    value: 9.3
    unit: '-'
    scope: material
    conditions:
      scale: mineral hardness as printed
    method: Value printed on a periodic-table reference site
    status: ground
    note: Not a canonical property name; kept as a snake_case name and listed in gaps.
    source: webelements-boron
    where: Physical properties page, Hardnesses, Mineral hardness
  - benchmark: neutron_absorption_cross_section
    label: Thermal-neutron absorption cross section, 10B
    value: 3835
    unit: barn
    scope: material
    conditions:
      isotope: 10B
      neutron_energy: 2200 m/s
      uncertainty: 9 barn, printed as 3835.(9.)
    method: Absorption cross section tabulated by NIST (from the 1992 Neutron News compilation, as the table states)
    status: ground
    note: Not a canonical property name; kept as a snake_case name and listed in gaps.
    source: nist-neutron
    where: Neutron scattering lengths and cross sections table, row 10B, column 8 (absorption cross section for 2200 m/s neutrons)
  - benchmark: neutron_absorption_cross_section
    label: Thermal-neutron absorption cross section, natural boron
    value: 767
    unit: barn
    scope: material
    conditions:
      isotope: natural boron (10B and 11B)
      neutron_energy: 2200 m/s
      uncertainty: 8 barn, printed as 767.(8.)
    method: Absorption cross section tabulated by NIST (from the 1992 Neutron News compilation, as the table states)
    status: ground
    note: Not a canonical property name; kept as a snake_case name and listed in gaps.
    source: nist-neutron
    where: Neutron scattering lengths and cross sections table, row B (natural), column 8
  - benchmark: isotope_abundance
    label: Natural abundance of 10B
    value: 20
    unit: '%'
    scope: material
    conditions:
      isotope: 10B
      note: NIST prints the abundance as a whole number; 11B is printed as 80
    method: Natural abundance printed in a neutron data table
    status: ground
    note: Not a canonical property name; kept as a snake_case name and listed in gaps.
    source: nist-neutron
    where: Neutron scattering lengths and cross sections table, row 10B, column 2 (Natural abundance)
  - benchmark: fibre_diameter
    label: Boron fibre diameter, 4.0-mil product
    value: 102
    unit: um
    scope: material
    conditions:
      product: 4.0-mil boron fibre on a tungsten substrate
      basis: typical value on the datasheet
    method: Typical value on a manufacturer datasheet
    status: ground
    note: Not a canonical property name; kept as a snake_case name and listed in gaps.
    source: specmat-boron-fiber
    where: Boron fiber properties table, Diameter row, 4-mil column (the page also lists 142 and 76 um)
  - benchmark: density
    label: Boron fibre density, 4.0-mil product
    value: 2.61
    unit: g/cc
    scope: material
    conditions:
      product: 4.0-mil boron fibre
      basis: typical value on the datasheet
    method: Typical value on a manufacturer datasheet
    status: ground
    source: specmat-boron-fiber
    where: Boron fiber properties table, Density row, 4-mil column
  - benchmark: ultimate_tensile_strength
    label: Boron fibre tensile strength, 4.0-mil product
    value: 4000
    unit: MPa
    scope: material
    conditions:
      product: 4.0-mil boron fibre
      basis: typical value on the datasheet
    method: Typical value on a manufacturer datasheet
    status: ground
    source: specmat-boron-fiber
    where: Boron fiber properties table, Tensile Strength row, 4-mil column (the 5.6-mil column also gives 4,000 MPa)
  - benchmark: elastic_modulus
    label: Boron fibre tensile modulus, 4.0-mil product
    value: 428
    unit: GPa
    scope: material
    conditions:
      product: 4.0-mil boron fibre
      basis: typical value on the datasheet
    method: Typical value on a manufacturer datasheet
    status: ground
    source: specmat-boron-fiber
    where: Boron fiber properties table, Tensile Modulus row, 4-mil column
  - benchmark: cte
    label: Boron fibre thermal expansion, 4.0-mil product
    value: 4.5
    unit: ppm/degC
    scope: material
    conditions:
      product: 4.0-mil boron fibre
      printed_as: PPM/degC 4.5
    method: Typical value on a manufacturer datasheet
    status: ground
    source: specmat-boron-fiber
    where: Boron fiber properties table, Thermal Expansion row, 4-mil column
  - benchmark: oxidation_activation_energy
    label: Activation energy, early-stage oxidation of amorphous boron
    value: 148
    unit: kJ/mol
    scope: material
    conditions:
      uncertainty: 6 kJ/mol
      material: 95% pure amorphous boron powder, pre-treated to thin the hydrated oxide layer
      atmosphere: oxygen-argon mixture, non-isothermal thermogravimetry
      model: core-shell particle model
    method: Kinetic parameter from a thermogravimetric study, reported in the abstract
    status: ground
    note: Not a canonical property name; kept as a snake_case name and listed in gaps.
    source: njit-boron-oxidation
    where: Abstract, final paragraph of the abstract text
corrosion:
  - environment: Room-temperature air, amorphous boron powder
    headline: The powder oxidizes slowly at room temperature, and dust can ignite spontaneously in air.
    effect: Materion's safety data sheet says boron metal powder is highly reactive, oxidizes slowly at room temperature and that dust may ignite spontaneously in air. The sheet does not give a rate or an oxide thickness, so the risk is the fine powder rather than bulk surface attack.
    rating: low
    conditions:
      form: amorphous powder
      exposure: room temperature air; exposure time not stated
    source: materion-msds-boron
    where: Section IV, Unusual fire and explosion hazards
  - environment: Oxygen at high temperature (thermogravimetric test, amorphous boron powder)
    headline: Early oxidation of amorphous boron has an activation energy of 148 kJ/mol.
    effect: Non-isothermal thermogravimetric tests of 95% pure amorphous boron in oxygen-argon, at several heating rates, were fitted with a core-shell particle model. The early stage of oxidation has an activation energy of 148 plus or minus 6 kJ/mol. The abstract gives no onset temperature, so the temperature at which oxidation becomes significant is not stated here.
    rating: moderate
    conditions:
      material: 95% pure amorphous boron, pre-treated with acetonitrile and water
      atmosphere: oxygen-argon mixture
      method: non-isothermal thermogravimetry
    source: njit-boron-oxidation
    where: Abstract
  - environment: Steam or water at red heat (powdered boron)
    headline: Powdered boron and steam may react violently at red heat.
    effect: PubChem, citing Bretherick's Handbook of Reactive Chemical Hazards, says the interaction of powdered boron and steam may become violent at red heat, and that highly exothermic reactions with water might become combustive or explosive at sufficiently high temperatures and pressures.
    rating: severe
    conditions:
      temperature: red heat (not given as a number on the page)
      medium: steam or water
    source: pubchem-boron
    where: Firefighting Hazards section
  - environment: Gaseous chlorine or fluorine at room temperature
    headline: Boron powder may ignite on contact with gaseous chlorine or fluorine at room temperature.
    effect: Materion's sheet lists chlorine and fluorine gas as ignition risks at room temperature, and says boron may react exothermically with metals above 900 degC.
    rating: severe
    conditions:
      form: powder
      reagent: gaseous Cl2 or F2
    source: materion-msds-boron
    where: Section IV, Unusual fire and explosion hazards
risks:
  hazards:
    - text: 'PubChem: 52.2% (253 of 485) of company reports say the substance does not meet GHS hazard criteria. The statements it lists for the other reports are H302, H332, H335 and H412, with the Warning signal word. The percentages are as PubChem prints them.'
      ghs:
        - H302
        - H332
        - H335
        - H412
      source: pubchem-boron
      where: Safety and Hazards, GHS Classification
    - text: 'Höganäs grade sheet PD-4031: Grade I is not classified under EU Regulation 1272/2008. Grades II and III are classified Repr. 1B, with H360FD (may damage fertility; may damage the unborn child) and the signal word Danger.'
      ghs:
        - H360FD
      source: hoganas-pd4031
      where: Hazards identification in Advertising, one entry per grade
  failure_risks:
    - mode: Spontaneous ignition of boron dust
      trigger: Fine boron powder dispersed or dusting in air
      consequence: Materion says dust may ignite spontaneously in air, and that the powder is highly reactive.
      severity: high
      source: materion-msds-boron
      where: Section IV, Unusual fire and explosion hazards
    - mode: Violent reaction with steam or water
      trigger: Powdered boron at red heat with steam, or water at high temperature and pressure
      consequence: Reaction may become violent at red heat; exothermic reactions with water may become combustive or explosive at high temperature and pressure.
      severity: high
      source: pubchem-boron
      where: Firefighting Hazards section
    - mode: Ignition with halogen gas
      trigger: Contact with gaseous chlorine or fluorine at room temperature
      consequence: Boron powder may ignite; Materion also lists bromine, chlorine, nitric acid and copper oxide among materials to avoid.
      severity: high
      source: materion-msds-boron
      where: Section IV and Section V, incompatible materials
  side_effects:
    - text: Boron metal may emit toxic fumes if involved in a fire; the hazardous combustion product named is boron oxide.
      affects: Firefighters and anyone downwind of a fire
      source: materion-msds-boron
      where: Section IV, Hazardous combustion products; Section V, decomposition products
  handling:
    - text: Store in a closed container, as the Höganäs grade sheet directs.
      source: hoganas-pd4031
      where: Storage and Handling section
    - text: Use a Class D or other suitable metal extinguishing agent for boron powder fires.
      source: materion-msds-boron
      where: Section IV, Extinguishing media
    - text: Keep away from the materials Materion lists as incompatible, including chlorine, bromine, fluorine compounds, nitric acid, potassium chlorate and potassium nitrate.
      source: materion-msds-boron
      where: Section V, Incompatibility
uses:
  - application: structures
    device: Boron fibre epoxy composites (stiffening plies)
    example: The Specialty Materials datasheet says adding boron fibre to composites with standard and intermediate-modulus fibres increases tensile and compression modulus, which allows fewer plies or less thickness for the same stiffness.
    source: specmat-boron-fiber
    where: Boron fiber product page, bullet list under the properties table
  - application: radiation-shielding
    device: Spacecraft thermal-neutron shielding (ground study with boron powder in polymer films)
    example: NASA-funded work at the College of William and Mary (1995) concluded that boron is the best light-weight material for thermal-neutron absorption in spacecraft, because 10B captures neutrons and gives stable products. In a 600 MeV/amu iron-ion test, adding boron powder to a polyetherimide film did not significantly change its cosmic-ray shielding.
    source: nasa-cr-199720
    where: Introduction, paragraph on thermal-neutron absorption; Computer design and results on boron-containing polyetherimide
  - application: electronics-and-chips
    device: Semiconductor manufacturing
    example: The USGS says that boron was used in abrasives, cleaning products, insecticides, insulation and the production of semiconductors, and that glass and ceramics were the leading domestic users in 2025.
    source: usgs-mcs2026-boron
    where: Domestic Production and Use paragraph
supply:
  - subject: Boron (produced as borates; USGS says elemental boron has limited commercial applications and does not occur in nature in elemental form)
    abundance: Not found in a fetched source
    producers:
      - country: Turkey
        share_percent: 51.4
        year: 2025
      - country: Bolivia
        share_percent: 13
        year: 2025
      - country: Chile
        share_percent: 10.3
        year: 2025
      - country: China
        share_percent: 7.9
        year: 2025
      - country: Peru
        share_percent: 7.5
        year: 2025
      - country: Argentina
        share_percent: 5.8
        year: 2025
      - country: Russia
        share_percent: 2.7
        year: 2025
      - country: Germany
        share_percent: 1.4
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (boron added in the final 2025 list)
        listed: true
    recycling: 'USGS: insignificant.'
    substitutes:
      - 'USGS: substitution is possible in detergents, enamels, insulation and soaps. The chapter does not discuss neutron-absorbing or electronic uses.'
    source: usgs-mcs2026-boron
    where: 'World Production and Reserves table, 2025 column (thousand metric tons, as printed; the table lists boric oxide equivalent for China and crude or refined forms for other countries, so the shares are not on one basis). Shares calculated by Space Mushroom against the 2,920 thousand t total of the listed countries, because the USGS world total is not given (XX). US production is withheld (W). US imports 2021-24: Turkey 90%, Bolivia 6%, other 4%. Reserves (thousand t): Turkey 950,000; Russia 40,000; United States 48,000; Chile 35,000; China 9,100; Peru 4,000.'
story:
  recipe:
    line: 'Elemental boron, symbol B. Natural boron is a mix of two isotopes: 10B, which absorbs thermal neutrons strongly, and 11B. Specialty Materials says its boron fibre is deposited on a fine tungsten wire by chemical vapor deposition.'
    parts:
      - name: Boron-10
        symbol: 10B
        share_percent: 20
        role: The neutron absorber. Its capture cross section is about 3835 barns at 2200 m/s, against 767 barns for natural boron.
      - name: Boron-11
        symbol: 11B
        share_percent: 80
        role: The main isotope of natural boron. It has a much smaller thermal-neutron capture cross section, so it contributes little to shielding.
      - name: Boron
        symbol: B
        atoms: 1
        atomic_weight: 10.81
        role: Element as a whole. The Materion sheet gives its molecular weight.
  risk_groups:
    - title: For people
      level: 0
      verdict: Hazard depends on the grade
      lead: The grades differ. Some suppliers list no hazard for the powder, and others classify it as a reproductive toxicant.
      points:
        - label: Grade I powder
          line: Höganäs lists no hazard classification under EU Regulation 1272/2008 for amorphous boron Grade I. Its specification is at least 95% boron.
        - label: Grades II and III
          line: The same sheet classifies Grades II and III as Repr. 1B with H360FD and the signal word Danger. PubChem's summary records H302 and H332 for the reports that do classify the substance.
        - label: Dust
          line: Materion says dust can ignite spontaneously in air, so the fine powder is the main hazard in handling.
    - title: In a fire
      lead: Boron powder is the fire hazard. Water, steam and halogen gases are the reactions to avoid.
      points:
        - label: Extinguishing
          line: Materion says to use a Class D or other suitable metal extinguishing agent.
        - label: Reaction with steam
          line: PubChem, citing Bretherick, says powdered boron and steam may react violently at red heat.
        - label: Halogens
          line: Materion says boron powder may ignite on contact with gaseous chlorine or fluorine at room temperature.
    - title: Handling and storage
      points:
        - label: Container
          line: Store the powder in a closed container, as the Höganäs grade sheet directs.
        - label: Incompatible materials
          line: Materion lists chlorine, bromine, fluorine compounds, nitric acid, potassium chlorate and potassium nitrate among the materials to avoid.
  why: 'Elemental boron is a metalloid, and the USGS states that it has limited commercial use in its elemental form. It is used in two forms in the sources read here: an amorphous powder whose boron content depends on grade (Höganäs'' grade sheet), and a fibre that Specialty Materials makes by depositing boron on a tungsten wire. Its main value in space work is its neutron capture, which comes almost entirely from the 10B isotope.'
  uses:
    - where: Neutron shielding in spacecraft
      line: NASA-funded work at the College of William and Mary (1995) called boron the best light-weight material for absorbing thermal neutrons in a spacecraft. This was a shielding study and ground test, not a flight result.
    - where: Stiffening composite plies
      line: Specialty Materials' boron fibre is 102 micrometres in its 4-mil form, with a tensile modulus of 428 GPa and a tensile strength of 4000 MPa. The datasheet says it is used to stiffen composites that already use standard or intermediate-modulus fibres.
    - where: Semiconductor manufacturing
      line: The USGS lists boron among the uses in semiconductor production. The chapter does not give the size of that use.
  can_do:
    - label: Neutron absorption
      benchmark: neutron_absorption_cross_section
      value: 3835 barn
      line: NIST gives an absorption cross section of 3835 barns for 10B at 2200 m/s neutrons, against 767 barns for natural boron. Enriched boron is therefore worth far more as an absorber than the natural mix.
    - label: Stiffness of the fibre
      benchmark: elastic_modulus
      value: 428 GPa
      line: The 4-mil boron fibre has a tensile modulus of 428 GPa on Specialty Materials' datasheet, with a density of 2.61 g/cc.
    - label: Melting point
      benchmark: melting_point
      value: 2075 degC
      line: The CRC Handbook value, reproduced on PubChem, is 2,075 degC for the element.
    - label: Oxidation
      benchmark: oxidation_activation_energy
      value: 148 kJ/mol
      line: Early oxidation of 95% pure amorphous boron in oxygen has an activation energy of 148 plus or minus 6 kJ/mol. The abstract gives no onset temperature.
  compare: 'Boron is a light solid, with a density of 2.35 to 2.46 g/cm3, and it melts at 2,075 degC. Its strongest engineering property is its neutron capture, which depends on the isotope: the 10B isotope has a cross section about five times that of natural boron. Its weak point is its reactivity. Amorphous powder can ignite as dust, and the powder reacts with steam and halogen gases, so it needs more care in handling than a stable structural solid. The table compares boron with the other entries in this collection on its main properties.'
  compare_rows:
    - label: Density
      benchmark: density
    - label: Melting point
      benchmark: melting_point
    - label: Thermal conductivity
      benchmark: thermal_conductivity
  handling:
    - Store in a closed container. The powder can ignite as dust, so keep dust out of the air.
    - Keep it away from chlorine, bromine, fluorine compounds, nitric acid and potassium nitrate or chlorate.
    - Use a Class D or other suitable metal extinguishing agent on a fire.
    - Check the grade's hazard classification before use, because Grades II and III carry a reproductive-toxicity classification.
  good_for:
    - Neutron absorption where the 10B isotope is enriched. NIST gives 3835 barns for 10B against 767 barns for natural boron.
    - Stiff fibre for composites. Specialty Materials gives a tensile modulus of 428 GPa for the 4-mil fibre.
  watch_out:
    - Dust and reactive powder. Materion says dust can ignite spontaneously in air.
    - Steam and halogen gases. PubChem and Materion both name reactions that can turn violent at high temperature.
    - Hazard data differ by grade. Grade I shows no classification, while Grades II and III are classified as Repr. 1B.
  verdict: Elemental boron is a strong neutron absorber when enriched in 10B, and it is a stiff fibre. Its powder is reactive and needs careful handling, and the hazard classification depends on the grade.
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 19
  unreachable: 0
  caveats: 3
  note: 'Written by an AI assistant on 2026-10-26 from pages fetched in this run. verify-values finds all 19 values in their cited sources. Caveats: non-canonical property names (7 values), grade-dependent hazard data, and a melting point on one supplier sheet that conflicts with the CRC value.'
gaps:
  - Specific heat of boron not found in a fetched source (WebElements gives no value on the physical-properties page).
  - Young's modulus of crystalline boron not found (WebElements prints no data). The only elastic value here is the bulk modulus.
  - No neutron-absorber use in reactor control rods was sourced. The only spacecraft shielding source is the NASA-funded 1995 report.
  - Crustal abundance of boron not found in a fetched source (the WebElements abundance page did not return a value).
  - The European Commission critical raw materials list was not checked for boron.
  - ChemicalBook and Strem safety sheets returned HTML, not PDF, so their hazard entries (H228, H302, H332, H335) are not used here.
  - Materion's sheet prints a melting point of 2300 degC and a boiling point of 2550 degC. These conflict with the CRC values from PubChem, so the CRC values are used and the Materion figures are left out.
  - The Knoop hardness of the boron fibre (3,200) is printed without a unit on the datasheet, so it is left out.
  - WebElements prints the electrical resistivity as a garbled expression (> 10 12 x 10-8 ohm m). It is left out.
  - The boron fibre core diameter and the tungsten-core structure are not taken from a fetched datasheet value; the Specialty Materials page describes the core but gives no number.
  - Hazard data differ by grade and by supplier. The PubChem GHS percentages are as printed and rest on company notifications, not a single test.
  - Oxidation onset temperature for amorphous boron not found in the fetched abstract.
  - The NIST table prints the 10B abundance as a whole number (20). A more precise natural abundance was not taken from a fetched source.
sources:
  pubchem-boron:
    title: 'PubChem compound record, Boron (CID 5462311): chemical and physical properties, safety and hazards'
    id: CID 5462311
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/5462311/JSON
    year: 2026
    kind: database
    license: public domain (NCBI)
  nist-neutron:
    title: 'NIST Center for Neutron Research: Neutron scattering lengths and cross sections (table of elements and isotopes)'
    id: NIST NCNR, from Neutron News 3(3), 1992
    url: https://www.ncnr.nist.gov/resources/n-lengths/list.html
    year: 1992
    kind: database
    license: public domain (NIST)
  webelements-boron:
    title: 'WebElements: Boron, physical properties'
    id: WebElements, Mark Winter
    url: https://www.webelements.com/boron/physics.html
    year: 2026
    kind: database
    license: site terms (cited, not reproduced)
  usgs-mcs2026-boron:
    title: Mineral Commodity Summaries 2026, Boron
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-boron.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  specmat-boron-fiber:
    title: 'Specialty Materials: Boron fiber, properties table and product description'
    id: Specialty Materials boron fiber product page
    url: https://www.specmaterials.com/boron-fiber-test-page
    year: 2026
    kind: datasheet
    license: supplier document, linked not reproduced
  njit-boron-oxidation:
    title: Heterogeneous reaction kinetics for oxidation and combustion of boron
    id: NJIT Digital Commons, faculty publications 7148 (publication date 2019-12-01)
    url: https://digitalcommons.njit.edu/fac_pubs/7148
    year: 2019
    kind: paper
    license: repository record (abstract read)
  nasa-cr-199720:
    title: Shielding Materials for Highly Penetrating Space Radiations (NASA-CR-199720, final technical report, NCC-1-151)
    id: NTRS 19960007435; NASA-CR-199720; November 1995
    url: https://ntrs.nasa.gov/api/citations/19960007435/downloads/19960007435.pdf
    year: 1995
    kind: report
    license: public domain (NASA)
  materion-msds-boron:
    title: 'Materion Advanced Chemicals: Material Safety Data Sheet, Boron, powder (product B-MSDS0070)'
    id: Materion MSDS, reference 7440-42-8 (revision 05/03/2001, generated 2011)
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/Retired%20SDS%20and%20MSDS/2017%20removed%20safety%20sheets/MSDS%20updated%20to%20SDS/boron%20powder%20%20-%20Materion.pdf
    year: 2001
    kind: datasheet
    license: supplier document, linked not reproduced
  hoganas-pd4031:
    title: 'Höganäs: Powders for special applications, Amorphous boron grades I, II and III (PD-4031, issue 3, 2025)'
    id: Hoganas PD-4031, issue 3-08.08.2025
    url: https://chinafytarget.hoganas.com/globalassets/downloads/stc/pd-4031.pdf
    year: 2025
    kind: datasheet
    license: supplier document, linked not reproduced
  pubchem-density:
    title: 'PubChem compound record, Boron (CID 5462311): Density section'
    id: CID 5462311, pug_view heading Density
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/5462311/JSON?heading=Density
    year: 2026
    kind: database
    license: public domain (NCBI)
  pubchem-melting:
    title: 'PubChem compound record, Boron (CID 5462311): Melting Point section'
    id: CID 5462311, pug_view heading Melting Point
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/5462311/JSON?heading=Melting+Point
    year: 2026
    kind: database
    license: public domain (NCBI)
  pubchem-boiling:
    title: 'PubChem compound record, Boron (CID 5462311): Boiling Point section'
    id: CID 5462311, pug_view heading Boiling Point
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/5462311/JSON?heading=Boiling+Point
    year: 2026
    kind: database
    license: public domain (NCBI)
license: CC-BY-4.0
documents:
  - title: 'PubChem: Boron (CID 5462311), chemical and physical properties and GHS classification'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/5462311
    year: 2026
  - title: 'NIST: Neutron scattering lengths and cross sections'
    type: database
    url: https://www.ncnr.nist.gov/resources/n-lengths/list.html
    year: 1992
  - title: 'WebElements: Boron physical properties'
    type: database
    url: https://www.webelements.com/boron/physics.html
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Boron'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-boron.pdf
    year: 2026
  - title: 'Specialty Materials: Boron fiber datasheet'
    type: datasheet
    url: https://www.specmaterials.com/boron-fiber-test-page
    year: 2026
  - title: Heterogeneous reaction kinetics for oxidation and combustion of boron (NJIT)
    type: paper
    url: https://digitalcommons.njit.edu/fac_pubs/7148
    year: 2019
  - title: 'NASA-CR-199720: Shielding Materials for Highly Penetrating Space Radiations'
    type: report
    url: https://ntrs.nasa.gov/api/citations/19960007435/downloads/19960007435.pdf
    year: 1995
  - title: Materion boron powder MSDS
    type: sds
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/Retired%20SDS%20and%20MSDS/2017%20removed%20safety%20sheets/MSDS%20updated%20to%20SDS/boron%20powder%20%20-%20Materion.pdf
    year: 2001
  - title: 'Höganäs PD-4031: Amorphous boron grades'
    type: datasheet
    url: https://chinafytarget.hoganas.com/globalassets/downloads/stc/pd-4031.pdf
    year: 2025