Boron carbide B4C

spore: profile
id: boron-carbide
spore_version: 0.2
family: carbide-nitride-boride-ceramics
name: Boron carbide
abbreviation: B4C
role: extremely hard ceramic for armor, wear parts and neutron shielding
category: ceramics
type: carbides
summary: |
  Boron carbide is a boron-carbon ceramic, nominally B4C, and one of the hardest materials known. Saint-Gobain's hot-pressed Norbide datasheet gives a density of 2.50 gm/cm3, a Knoop hardness of 2800 kg/mm2, a four-point flexural strength of 425 MPa and an elastic modulus of 440 GPa, with a thermal conductivity of 90 W/mK at 20 °C. NIST's JANAF table gives a standard enthalpy of formation of -62.676 kJ/mol at 298.15 K. CoorsTek's table gives wider ranges for its hot-pressed grade, so the ranges are kept.
best_for: Hard, wear-resistant parts such as blast nozzles and armor tiles, and neutron shielding where boron content matters (Saint-Gobain datasheet; NASA 2023 composite study)
weakest_at: 'Brittleness: flexural strength of 425 MPa and fracture toughness of 3.1 MPa x m1/2 (Saint-Gobain), and loss of quality and hardness in hot air with traces of nitrogen (Varadachari et al. 2018)'
identity:
  formula: B4C, a boron-carbon compound; the material is a family of compositions from boron-rich to carbon-rich (Wikipedia)
  cas: 12069-32-8
  source: pubchem-b4c
  where: 'Names and Identifiers of PubChem CID 123279: CAS 12069-32-8 and molecular formula CB4; the supplier SDS gives the same CAS'
tags:
  environments: []
  stresses:
    - extreme-heat
  applications:
    - radiation-shielding
    - structures
    - mechanisms
properties:
  - benchmark: density
    label: Density, hot-pressed B4C (Norbide)
    value: 2.5
    unit: gm/cm3
    scope: material
    conditions:
      material: Norbide hot pressed boron carbide
    method: Typical physical properties table of the Saint-Gobain datasheet (method not stated)
    status: ground
    source: sg-norbide-hp
    where: Norbide Hot Pressed B4C Typical Physical Properties table, Density row
  - benchmark: knoop_hardness
    label: Knoop hardness, hot-pressed B4C
    value: 2800
    unit: kg/mm2
    scope: material
    conditions:
      load: Knoop 0.1 kg
      material: Norbide hot pressed
    method: Knoop hardness as printed; Knoop is not Vickers, so it is not comparable with Vickers values
    status: ground
    source: sg-norbide-hp
    where: Typical Physical Properties table, Hardness (Knoop) row, footnote 2
  - benchmark: flexural_strength
    label: Flexural strength, 4-point, hot-pressed B4C (Saint-Gobain)
    value: 425
    unit: MPa
    scope: material
    conditions:
      temperature: room temperature
      test_bar: 3 x 4 x 45 mm
      material: Norbide hot pressed
    method: Four-point bend on the test bar size given in the datasheet footnote
    status: ground
    source: sg-norbide-hp
    where: Typical Physical Properties table, Flexural Strength 4pt @ RT row, footnote 3
  - benchmark: compressive_strength
    label: Compressive strength, hot-pressed B4C
    value: 2900
    unit: MPa
    scope: material
    conditions:
      temperature: room temperature
      material: Norbide hot pressed
    method: Compressive strength as printed in the datasheet (method not stated)
    status: ground
    source: sg-norbide-hp
    where: Typical Physical Properties table, Compressive Strength @ RT row
  - benchmark: elastic_modulus
    label: Elastic modulus, hot-pressed B4C
    value: 440
    unit: GPa
    scope: material
    conditions:
      temperature: room temperature
      material: Norbide hot pressed
    method: Modulus of elasticity as printed in the datasheet (method not stated)
    status: ground
    source: sg-norbide-hp
    where: Typical Physical Properties table, Modulus of Elasticity @ RT row
  - benchmark: poissons_ratio
    label: Poisson's ratio, hot-pressed B4C
    value: 0.18
    unit: '-'
    scope: material
    conditions:
      material: Norbide hot pressed
    method: Poisson's ratio as printed in the datasheet
    status: ground
    source: sg-norbide-hp
    where: Typical Physical Properties table, Poisson's Ratio row
  - benchmark: fracture_toughness
    label: Fracture toughness, indentation, hot-pressed B4C (Saint-Gobain)
    value: 3.1
    unit: MPa x m1/2
    scope: material
    conditions:
      temperature: room temperature
      method_detail: indentation
    method: Indentation fracture toughness as printed in the datasheet
    status: ground
    source: sg-norbide-hp
    where: Typical Physical Properties table, Fracture Toughness @ RT (Indentation) row
  - benchmark: cte
    label: Coefficient of thermal expansion, hot-pressed B4C (Saint-Gobain)
    value: 5
    unit: x10-6 mm/mmK
    scope: material
    conditions:
      material: Norbide hot pressed
      temperature: not stated in the table
    method: CTE as printed; the datasheet unit is x10-6 mm/mmK, kept as printed
    status: ground
    source: sg-norbide-hp
    where: Typical Physical Properties table, Coefficient of Thermal Expansion row
  - benchmark: thermal_conductivity
    label: Thermal conductivity, hot-pressed B4C (Saint-Gobain)
    value: 90
    unit: W/mK
    scope: material
    conditions:
      temperature: 20 °C
      material: Norbide hot pressed
    method: Thermal conductivity as printed in the datasheet
    status: ground
    source: sg-norbide-hp
    where: Typical Physical Properties table, Thermal Conductivity @20°C row
  - benchmark: flexural_strength
    label: Flexural strength (MOR), hot-pressed B4C (CoorsTek)
    value: 320
    value_high: 450
    bound: range
    unit: MPa
    scope: material
    conditions:
      temperature: 20 °C
      grade: hot pressed boron carbide
    method: Flexural Strength, MOR (20 °C) row, Hot Pressed column; printed as 320 - 450
    status: ground
    source: coors-b4c
    where: Boron carbide properties table, Flexural Strength MOR (20 °C) row, Hot Pressed column
  - benchmark: fracture_toughness
    label: Fracture toughness K Ic, hot-pressed B4C (CoorsTek)
    value: 3
    value_high: 4
    bound: range
    unit: MPa m 1/2
    scope: material
    conditions:
      grade: hot pressed boron carbide
      method_detail: K Ic
    method: Fracture Toughness K Ic row, Hot Pressed column; printed as 3.0 - 4.0
    status: ground
    source: coors-b4c
    where: Boron carbide properties table, Fracture Toughness K Ic row, Hot Pressed column
  - benchmark: thermal_conductivity
    label: Thermal conductivity, hot-pressed B4C (CoorsTek)
    value: 45
    value_high: 100
    bound: range
    unit: W/m K
    scope: material
    conditions:
      temperature: 20 °C
      grade: hot pressed boron carbide
    method: Thermal Conductivity (20 °C) row, Hot Pressed column; printed as 45 - 100
    status: ground
    source: coors-b4c
    where: Boron carbide properties table, Thermal Conductivity (20 °C) row, Hot Pressed column
  - benchmark: cte
    label: Coefficient of thermal expansion, hot-pressed B4C (CoorsTek)
    value: 4.5
    value_high: 4.9
    bound: range
    unit: 1x10 -6 /°C
    scope: material
    conditions:
      grade: hot pressed boron carbide
    method: Coefficient of Thermal Expansion row, Hot Pressed column; printed as 4.5 - 4.9 under a unit header of 1x10 -6 /°C
    status: ground
    source: coors-b4c
    where: Boron carbide properties table, Coefficient of Thermal Expansion row, Hot Pressed column
  - benchmark: molar_heat_capacity
    label: Molar heat capacity Cp, B4C, 298.15 K
    value: 53.764
    unit: J K-1 mol-1
    scope: material
    conditions:
      temperature: 298.15 K
      reference_state: standard state pressure 0.1 MPa
      phase: crystalline (cr)
    method: JANAF table value at 298.15 K; the column headings in the fetched page are partly garbled, so the column is mapped from the table layout
    status: ground
    source: janaf-b4c
    where: Boron Carbide (B4C) table, row 298.15 K, Cp column
  - benchmark: standard_molar_entropy
    label: Standard molar entropy S, B4C, 298.15 K
    value: 27.175
    unit: J K-1 mol-1
    scope: material
    conditions:
      temperature: 298.15 K
      reference_state: standard state pressure 0.1 MPa
      phase: crystalline (cr)
    method: JANAF table value at 298.15 K; column mapped from the table layout, as for Cp
    status: ground
    source: janaf-b4c
    where: Boron Carbide (B4C) table, row 298.15 K, S column
  - benchmark: standard_enthalpy_of_formation
    label: Standard enthalpy of formation, B4C, 298.15 K
    value: -62.676
    unit: kJ mol-1
    scope: material
    conditions:
      temperature: 298.15 K
      reference_state: standard state pressure 0.1 MPa
      phase: crystalline (cr)
    method: JANAF table value at 298.15 K; column mapped from the table layout, as for Cp
    status: ground
    source: janaf-b4c
    where: Boron Carbide (B4C) table, row 298.15 K, Delta fH column
corrosion:
  - environment: Air or oxygen at elevated temperature
    headline: A B2O3 surface layer forms first and shields the carbide from catastrophic oxidation, according to a 2018 thermodynamic study
    effect: Varadachari, Bhowmick and Ghosh (2018) say the B2O3 that forms first acts as a protective shield, that oxidation reactions with O2 have positive log k values, and that the trioxide-producing reactions are the most energetically favoured. The region covered is 273 to 2300 K. The abstract gives no oxidation rates.
    rating: unknown
    conditions:
      temperature: 273 to 2300 K, as the study gives it
      atmosphere: O2 and N2
    source: zenodo-b4c-oxidation
    where: Abstract, Description section
  - environment: Air containing traces of nitrogen
    headline: Oxidation and nitrogen reactions affect the quality and hardness of the product
    effect: The abstract says oxidative processes and reaction with traces of nitrogen in air affect the quality and hardness of the product. BN forms at the lowest temperatures and is stable at higher temperatures, according to the same study.
    rating: unknown
    conditions:
      atmosphere: air with traces of nitrogen
    source: zenodo-b4c-oxidation
    where: Abstract, Description section
  - environment: Very low oxygen pressure and high concentrations of gaseous components
    headline: B4C is stable only under extremely low O2 pressures in the study's conditions
    effect: The abstract says B4C is stable only at extremely low O2 pressures and under high concentrations of gaseous components. No numeric pressure boundary is given.
    rating: unknown
    conditions:
      atmosphere: extremely low O2 pressure, high concentration of gaseous components
    source: zenodo-b4c-oxidation
    where: Abstract, Description section
risks:
  hazards:
    - text: 'PubChem aggregated GHS for boron carbide (CID 123279, signal word Danger): H360 and H360FD, reproductive toxicity, each notified by 19.5 percent of 185 company reports. 77.8 percent of reports (144 of 185) say it does not meet GHS criteria.'
      ghs:
        - H360
        - H360FD
      source: pubchem-b4c
      where: Safety and Hazards, GHS Classification
    - text: 'Supplier SDS (Stanford Advanced Materials, revised 10/11/2022): signal word Warning, with H332 harmful if inhaled, H315 causes skin irritation, H319 causes serious eye irritation and H335 may cause respiratory irritation.'
      ghs:
        - H332
        - H315
        - H319
        - H335
      source: sds-stanford-b4c
      where: Section 2, Hazards identification, Label elements
  failure_risks:
    - mode: Brittle fracture under tensile or bending load
      trigger: Mechanical load on a flaw or machining damage
      consequence: Four-point flexural strength of 425 MPa and indentation fracture toughness of 3.1 MPa x m1/2 for hot-pressed B4C
      severity: moderate
      source: sg-norbide-hp
      where: Typical Physical Properties table, Flexural Strength and Fracture Toughness rows
    - mode: Loss of quality and hardness from oxidation and nitrogen reactions in hot air
      trigger: Heating in air, including traces of nitrogen
      consequence: The 2018 study says oxidative processes and reaction with traces of nitrogen in air affect the quality and hardness of the product
      severity: moderate
      source: zenodo-b4c-oxidation
      where: Abstract, Description section
  side_effects: []
  handling:
    - text: 'Dust: PubChem''s reproductive-toxicity entries (H360 and H360FD) and the supplier''s inhalation statements (H332, H335) mean fine dust from grinding or machining should be controlled.'
      source: sds-stanford-b4c
      where: Section 2, Hazards identification (H332, H335)
    - text: 'Storage and disposal: the SDS gives P405, store locked up, and P501, dispose of contents under local regulations.'
      source: sds-stanford-b4c
      where: Section 2, Precautionary statements
  mitigations: []
uses:
  - application: radiation-shielding
    device: B4C particles in an aluminium alloy 6061 metal matrix composite for neutron shielding
    example: NASA's 2023 Langley study reports that 50 vol percent B4C in Al6061 raised neutron shielding effectiveness more than 110 times over pristine Al6061. The abstract says tensile strength rose up to 20 vol percent and thermal conductivity fell as B4C content rose.
    source: ntrs-20230003044
    where: Abstract
  - application: structures
    device: Hot-pressed B4C ballistic armor tiles
    example: Saint-Gobain lists ballistic armor tiles and wear-resistant components among the applications of Norbide hot-pressed boron carbide, and calls the material one of the hardest known.
    source: sg-norbide-hp
    where: Product Description and Applications list
  - application: mechanisms
    device: Wear-resistant nozzles, including grit-blast slurry nozzles
    example: Saint-Gobain lists blast nozzles, monument nozzles and nozzles for grit blasting slurry among the applications of Norbide hot-pressed boron carbide.
    source: sg-norbide-hp
    where: Product Description and Applications list
supply:
  - subject: Boron (feedstock for the boron half of B4C)
    abundance: 'USGS 2026: boron does not occur in nature as an element. It is sold as borates and boric oxide. The production table lists Turkey at 1,800 (2024) and 1,500 (2025) for refined borates, with units as printed. US imports of all boron forms were 90 percent from Turkey in 2021 to 2024.'
    producers: []
    critical_lists:
      - list: USGS 2025 Final List of Critical Minerals (boron added in the 2025 list)
        listed: true
    recycling: Not stated in the USGS boron chapter read.
    substitutes:
      - 'USGS: the substitution of other materials for boron is possible in detergents, enamels, insulation and soaps. This applies to boron in general, not to B4C.'
    source: usgs-mcs2026-boron
    where: Events, Trends and Issues (critical minerals paragraph; import sources, All forms 2021 to 2024); World Production and Reserves table; Substitutes
media: []
documents:
  - title: PubChem compound record CID 123279, Boron carbide
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/123279
  - title: NIST-JANAF Thermochemical Tables, Boron Carbide (B4C), table C-010
    type: database
    url: https://janaf.nist.gov/tables/C-010.html
  - title: Saint-Gobain Norbide Hot Pressed Boron Carbide technical data (Form No. B-1050)
    type: datasheet
    url: https://www.ceramicsrefractories.saint-gobain.com/fr/files/3956/view
  - title: CoorsTek boron carbide properties table
    type: datasheet
    url: https://coorstek.com/en/materials/boron-carbide/
  - title: Stanford Advanced Materials safety data sheet, Boron Carbide, CAS 12069-32-8
    type: sds
    url: https://samaterials.com/tds/1721380172-bc3503.pdf
  - title: USGS Mineral Commodity Summaries 2026, Boron
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-boron.pdf
  - title: NASA NTRS 20230003044, B4C-Al Metal Matrix Composites for Extreme Space Environments
    type: report
    url: https://ntrs.nasa.gov/citations/20230003044
  - title: Varadachari, Bhowmick and Ghosh 2018, Thermodynamics of oxidation and nitridation reactions of boron carbide
    type: paper
    url: https://zenodo.org/records/5642712
gaps:
  - 'NIST Structural Ceramics Database: no boron carbide entry was located. The searches returned SiC and TiB2 entries only, so no NIST B4C mechanical values are used.'
  - Vickers hardness and elastic modulus from Wikipedia (38 GPa and 460 GPa) are not used, because the brief limits Wikipedia to composition and history.
  - 'PubChem density (2.5 @25 °C) is not used: the record prints no unit, and the brief forbids inferring one.'
  - 'PubChem melting point (2350 °C) is not used: the source check cannot match it, because stripping tags from the PubChem JSON removes the Experimental Properties section. The value was read in the record but is left out of the file.'
  - 'Neutron absorption cross section and boron-10 content: not read in a fetched page. The EPJ Nuclear Sciences 2015 review and the MDPI Materials 2020 review both returned HTTP 403 and were not read.'
  - 'Ballistic performance and amorphization under high-velocity impact: no fetched source. A search snippet gave an impact threshold near 850 m/s, which is not used.'
  - 'Ageing under neutron irradiation (helium build-up, swelling, B4C degradation): no source read in this run.'
  - 'Oxidation onset temperature and rates: the 2018 study gives a temperature range of 273 to 2300 K and no rates. Onset temperatures in search snippets (about 600 and 700 °C) were not read in a fetched page and are not used.'
  - Hazard classifications differ. PubChem gives Danger with H360 and H360FD from 41 of 185 reports (aggregated ECHA notifications). The supplier SDS gives Warning with H332, H315, H319 and H335. Both are recorded; no SDS from a manufacturer was read.
  - 'Atomic weights of boron and carbon: not read in a fetched page, so the recipe parts carry no atomic_weight. PubChem gives a computed molecular weight of 55.3, which is not used as a part weight.'
  - 'Production shares of boron carbide: not found. The USGS boron table prints the world total as XX, so no share is calculated. The USGS 2026 abrasives chapter excerpt returned by search does not name boron carbide, and that chapter was not read in full.'
  - 'Recycling of boron carbide: not stated in any source read.'
  - 'Names not in property-canon.yaml: molar_heat_capacity, standard_molar_entropy, standard_enthalpy_of_formation, knoop_hardness, compressive_strength and fracture_toughness. The JANAF values are molar and cannot be converted to the canonical specific_heat unit without a molar mass.'
  - Grades and test methods differ between the Saint-Gobain datasheet (2004, Knoop and indentation toughness) and the CoorsTek table (K Ic and MOR). The two are kept side by side and not merged onto one scale.
  - Saint-Gobain datasheet is dated 2004 (Form No. B-1050, 11/04). It is the only source here with a full property table.
  - The 2018 oxidation study and the PubChem record are the only sources for the corrosion section. No manufacturer or NASA source on B4C corrosion was read.
sources:
  pubchem-b4c:
    title: PubChem compound CID 123279, Boron carbide (experimental properties, GHS classification, uses), read from the PubChem REST record
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/123279/JSON
    kind: database
    license: PubChem public database
  janaf-b4c:
    title: NIST-JANAF Thermochemical Tables, Boron Carbide (B4C), table C-010
    url: https://janaf.nist.gov/tables/C-010.html
    kind: database
    license: NIST public data
  sg-norbide-hp:
    title: Saint-Gobain Ceramics, Norbide Hot Pressed Boron Carbide Technical Data (Form No. B-1050, 11/04)
    url: https://www.ceramicsrefractories.saint-gobain.com/fr/files/3956/view
    kind: datasheet
    license: vendor datasheet, cited not reproduced
  coors-b4c:
    title: CoorsTek, Boron Carbide material properties table (reaction bonded, hot pressed, sintered)
    url: https://coorstek.com/en/materials/boron-carbide/
    kind: web
    license: vendor web page, cited not reproduced
  sds-stanford-b4c:
    title: Stanford Advanced Materials, Safety Data Sheet, Boron Carbide (CAS 12069-32-8), revised 10/11/2022
    url: https://samaterials.com/tds/1721380172-bc3503.pdf
    kind: datasheet
    license: vendor safety data sheet, cited not reproduced
  usgs-mcs2026-boron:
    title: USGS Mineral Commodity Summaries 2026, Boron
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-boron.pdf
    kind: report
    license: US government work, public domain
  ntrs-20230003044:
    title: Chu et al. 2023, B4C-Al Metal Matrix Composites for Extreme Space Environments, NASA NTRS 20230003044
    url: https://ntrs.nasa.gov/citations/20230003044
    kind: report
    license: NASA public document
  zenodo-b4c-oxidation:
    title: Varadachari, Bhowmick and Ghosh 2018, Thermodynamics of oxidation and nitridation reactions of boron carbide (Zenodo record 5642712)
    url: https://zenodo.org/records/5642712
    kind: paper
    license: open access record
  wikipedia-b4c:
    title: Wikipedia, Boron carbide (composition, history and uses only)
    url: https://en.wikipedia.org/wiki/Boron_carbide
    kind: web
    license: CC-BY-SA 4.0
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 16
  unreachable: 3
  caveats: 4
  note: 'Written in this run from pages read in this run: the PubChem REST record, the NIST JANAF table, the Saint-Gobain datasheet, the CoorsTek table, the Stanford SDS, the USGS boron chapter 2026, the NASA NTRS abstract, the 2018 Zenodo abstract and Wikipedia for composition and history. The PubChem HTML page showed a browser check, the EPJ 2015 review and the MDPI 2020 review returned HTTP 403, and none of the three was read.'
story:
  recipe:
    line: 'Boron carbide is a family of boron-carbon compounds, nominally B4C at the carbon-rich end, with a rhombohedral icosahedron-based structure (Wikipedia). CoorsTek makes it in three forms: reaction bonded, hot pressed and sintered (CoorsTek table). Hot-pressed grades are sold by Saint-Gobain as Norbide (Saint-Gobain datasheet). Henri Moissan first synthesized it (Wikipedia, Preparation).'
    parts:
      - name: Boron
        symbol: B
        role: Makes up most of the compound. NASA's 2023 study credits the boron in B4C for the neutron shielding gain.
      - name: Carbon
        symbol: C
        role: Forms the icosahedral boron-carbon network with the boron, giving the very high hardness.
  risk_groups:
    - title: For people
      level: 0
      verdict: PubChem lists H360 (reproductive); SDS lists irritation.
      lead: The two hazard sources disagree on the classification. Treat the material as a dust hazard until a manufacturer's SDS is read.
      points:
        - label: Dust
          line: Grinding or machining B4C makes fine dust. Control it with extraction and check the supplier's safety data sheet before handling powder or parts.
        - label: Inhalation
          line: The SDS gives H332 (harmful if inhaled) and H335 (may cause respiratory irritation). PubChem's notifications give H360 and H360FD (reproductive toxicity). 77.8 percent of company reports say the material does not meet GHS criteria.
    - title: If a part fails
      lead: These numbers come from the Saint-Gobain and CoorsTek tables.
      points:
        - label: Brittleness
          line: Hot-pressed B4C has a four-point flexural strength of 425 MPa (Saint-Gobain), and an indentation fracture toughness of 3.1 MPa x m1/2. It breaks rather than bends under a flaw.
  why: Boron carbide is used where hardness, low density and neutron capture matter. The Saint-Gobain datasheet gives a density of 2.50 gm/cm3 and a Knoop hardness of 2800 kg/mm2 for the hot-pressed grade. NASA's 2023 study credits the boron in B4C for the neutron shielding gain when it is added to aluminium alloy 6061.
  uses:
    - where: Neutron shielding in aluminium composites
      line: NASA's 2023 Langley study reports that 50 vol percent B4C in Al6061 raised neutron shielding effectiveness more than 110 times over pristine Al6061. The abstract says tensile strength rose up to 20 vol percent.
    - where: Armor tiles and wear parts
      line: Saint-Gobain lists ballistic armor tiles, blast nozzles and wear-resistant components among the applications of Norbide hot-pressed boron carbide.
  can_do:
    - label: Hardness
      benchmark: knoop_hardness
      line: The hot-pressed grade has a Knoop hardness of 2800 kg/mm2 at a 0.1 kg load (Saint-Gobain). Knoop values are not comparable with Vickers values.
    - label: Stiffness
      benchmark: elastic_modulus
      line: The hot-pressed grade has an elastic modulus of 440 GPa at room temperature (Saint-Gobain).
  compare: Across the hot-pressed range in CoorsTek's table, flexural strength is 320 to 450 MPa and thermal conductivity is 45 to 100 W/m K at 20 °C. The Saint-Gobain hot-pressed grade's flexural strength (425 MPa) and thermal conductivity (90 W/mK) sit inside those ranges, so the spread reflects grades and test methods rather than one material.
  compare_rows:
    - label: Flexural strength
      benchmark: flexural_strength
    - label: Thermal conductivity
      benchmark: thermal_conductivity
    - label: Coefficient of thermal expansion
      benchmark: cte
  handling:
    - Brittle material. Design for tension and bending loads with a safety margin.
    - 'Dust: the SDS lists H332 and H335 and PubChem lists H360. Control dust when grinding or machining, and check the supplier SDS.'
    - 'Oxidation: the 2018 study says B2O3 forms first and shields the surface in air, but traces of nitrogen can affect quality and hardness.'
  good_for:
    - Hard, wear-resistant parts. Saint-Gobain gives a Knoop hardness of 2800 kg/mm2 for the hot-pressed grade.
    - Neutron shielding in composites. NASA reports a more than 110-fold gain in shielding effectiveness at 50 vol percent B4C in Al6061.
  watch_out:
    - Brittleness. Hot-pressed B4C has a flexural strength of 425 MPa and an indentation fracture toughness of 3.1 MPa x m1/2 (Saint-Gobain).
    - The hazard classifications disagree. PubChem lists H360 and the supplier SDS lists H332, H315, H319 and H335. Read a manufacturer's SDS before handling.
    - Neutron-irradiation ageing, Vickers hardness, production shares and armor performance were not sourced in this run.
  verdict: Boron carbide is a very hard, low-density ceramic (2.50 gm/cm3 for the hot-pressed grade). Its datasheet values, its neutron-shielding and armor uses, and its oxidation behaviour are sourced here. Brittleness and the disagreeing hazard classifications need attention. Ageing under neutron irradiation, Vickers hardness and production shares are not yet sourced.