spore: profile
id: zirconium-diboride
spore_version: 0.2
family: metal-borides
name: Zirconium diboride (ZrB2)
abbreviation: ZrB2
role: ultra-high-temperature ceramic
category: ceramics
type: ultra-high-temperature-ceramics
summary: |
  Zirconium diboride (ZrB2) is a hexagonal boride ceramic with an AlB2-type structure. Sani et al. (2016) tabulate a melting temperature of 3245 °C and a density of 6.119 g/cm3 for dense ZrB2, and a hardness of 23 GPa. Monolithic ZrB2 starts to oxidize in air at about 600 °C, so uncoated parts need additives or a cooler air limit. A PubChem record quotes "3000 °C" as the melting point, and a supplier oxidation range of 1200 to 1400 °C are in conflict with these figures, so both are reported with their sources.
best_for: Very high melting and hot-structure ceramic parts where the material stays out of air above about 600 °C, or carries oxidation-resistance additives
weakest_at: Oxidation in air above about 600 °C for monolithic material; sintering is difficult and needs high temperatures
identity:
  formula: ZrB2 (one zirconium atom and two boron atoms per formula unit; AlB2-type hexagonal structure)
  cas: 12045-64-6
  crystal_system: hexagonal
  space_group: P6/mmm
  source: sani2016
  where: Table 1, Crystal system space group and prototype structure rows (hexagonal, P6/mmm, AlB2 prototype). CAS number 12045-64-6 is printed in the PubChem record (CID 9812765). The Wikipedia infobox gives hP3 and No. 191 for the same space group; not used for values.
tags:
  environments:
    - re-entry
  applications:
    - heat-shields
    - propulsion-and-tanks
    - thermal-control
properties:
  - benchmark: density
    label: Density, dense ZrB2 (literature value)
    value: 6.119
    unit: g/cm3
    scope: material
    conditions:
      basis: literature value tabulated in Table 1 of Sani et al. (cited there to ref. 6); not the paper's own samples
      form: dense bulk ZrB2
    method: Literature value printed in a table of a peer-reviewed paper
    status: ground
    source: sani2016
    where: Table 1, Density row, ZrB2 column
  - benchmark: melting_point
    label: Melting temperature (literature value)
    value: 3245
    unit: degC
    scope: material
    conditions:
      basis: literature value tabulated in Table 1 (cited there to ref. 6); not the paper's own samples
    method: Literature value printed in a table of a peer-reviewed paper
    status: ground
    source: sani2016
    where: Table 1, Melting Temperature row, ZrB2 column
  - benchmark: enthalpy_of_formation
    label: Enthalpy of formation at 25 degC
    value: -322.6
    unit: kJ/mol
    scope: material
    conditions:
      temperature: 25 degC
      basis: literature value tabulated in Table 1 (cited there to ref. 6)
    method: Literature value printed in a table of a peer-reviewed paper
    status: ground
    source: sani2016
    where: Table 1, Enthalpy of formation row, ZrB2 column
  - benchmark: heat_capacity_molar
    label: Molar heat capacity at 25 degC
    value: 48.2
    unit: J/(mol·K)
    scope: material
    conditions:
      temperature: 25 degC
      basis: literature value tabulated in Table 1 (cited there to ref. 6)
    method: Literature value printed in a table of a peer-reviewed paper
    status: ground
    source: sani2016
    where: Table 1, Heat Capacity row, ZrB2 column
  - benchmark: thermal_conductivity
    label: Thermal conductivity (literature value)
    value: 60
    unit: W/(m·K)
    scope: material
    conditions:
      basis: literature value tabulated in Table 1 (cited there to ref. 6); temperature not stated in the table
    method: Literature value printed in a table of a peer-reviewed paper
    status: ground
    source: sani2016
    where: Table 1, Thermal conductivity row, ZrB2 column
  - benchmark: elastic_modulus
    label: Young's modulus (literature value)
    value: 489
    unit: GPa
    scope: material
    conditions:
      basis: literature value tabulated in Table 1 (cited there to ref. 6); test method not stated
    method: Literature value printed in a table of a peer-reviewed paper
    status: ground
    source: sani2016
    where: Table 1, Young's Modulus row, ZrB2 column
  - benchmark: hardness
    label: Hardness (literature value)
    value: 23
    unit: GPa
    scope: material
    conditions:
      basis: literature value tabulated in Table 1 (cited there to ref. 6); test method and load not stated
    method: Literature value printed in a table of a peer-reviewed paper
    status: ground
    source: sani2016
    where: Table 1, Hardness row, ZrB2 column
  - benchmark: lattice_parameter_a
    label: Lattice parameter a
    value: 3.17
    unit: Å
    scope: material
    conditions:
      structure: hexagonal, P6/mmm (AlB2 prototype)
      temperature: not stated in the table
    method: Value printed in a table of a peer-reviewed paper
    status: ground
    source: sani2016
    where: Table 1, a (Å) row, ZrB2 column
  - benchmark: lattice_parameter_c
    label: Lattice parameter c
    value: 3.53
    unit: Å
    scope: material
    conditions:
      structure: hexagonal, P6/mmm (AlB2 prototype)
      temperature: not stated in the table
    method: Value printed in a table of a peer-reviewed paper
    status: ground
    source: sani2016
    where: Table 1, c (Å) row, ZrB2 column
  - benchmark: elastic_modulus
    label: Elastic modulus, ZrB2 nanopowder product (supplier range)
    value: 340
    value_high: 500
    bound: range
    unit: GPa
    scope: material
    conditions:
      product: ZrB2 nanopowder, 99.5% purity, about 45 nm, product NG04CO2502
      basis: supplier product page; test method and sample density not stated
    method: Range printed on a supplier product page
    status: ground
    note: Second-hand supplier figure, not from a test report. It differs from the 489 GPa literature value in Sani et al.
    source: nanografi-zrb2
    where: Product description, material properties text
  - benchmark: hardness
    label: Hardness, ZrB2 nanopowder product (supplier range)
    value: 20
    value_high: 25
    bound: range
    unit: GPa
    scope: material
    conditions:
      product: ZrB2 nanopowder, 99.5% purity, about 45 nm, product NG04CO2502
      basis: supplier product page; test method not stated
    method: Range printed on a supplier product page
    status: ground
    note: Second-hand supplier figure. The literature value in Sani et al. is 23 GPa.
    source: nanografi-zrb2
    where: Product description, material properties text
  - benchmark: oxidation_onset_temperature
    label: Onset of oxidation in air, monolithic ZrB2
    value: 600
    unit: degC
    scope: material
    conditions:
      atmosphere: air (oxidative environment)
      material: monolithic ZrB2 without oxidation-resistance additives
      basis: approximate value stated by the authors, citing earlier work
    method: Statement in the conclusions of a peer-reviewed paper, citing earlier work
    status: ground
    note: Sani et al. write 'approximately 600 °C' for both ZrB2 and TaB2, and say that suitable additives are needed for more severe conditions.
    source: sani2016
    where: Conclusions, final paragraph before the acknowledgements
  - benchmark: oxidation_onset_temperature
    label: Oxidation resistance (supplier claim)
    value: 1200
    value_high: 1400
    bound: range
    unit: degC
    scope: material
    conditions:
      product: ZrB2 nanopowder, 99.5% purity, product NG04CO2502
      basis: supplier product page; no test atmosphere, time or sample state printed
    method: Range printed on a supplier product page
    status: ground
    note: Conflicts with the approximately 600 degC onset in Sani et al. No test condition is printed, so the two cannot be reconciled from the sources read.
    source: nanografi-zrb2
    where: Product description, material properties text
  - benchmark: solar_absorptance
    label: Total directional solar absorbance at 1400 K
    value: 0.47
    unit: '-'
    scope: material
    conditions:
      temperature: 1400 K
      basis: dense monophasic ZrB2 sample of the paper, derived from measured optical spectra
    method: Calculated by the paper's authors from measured spectra
    status: calculated
    source: sani2016
    where: Optical properties section, paragraph giving alpha at 1400 K
  - benchmark: total_emittance
    label: Total directional emittance at 1400 K
    value: 0.18
    unit: '-'
    scope: material
    conditions:
      temperature: 1400 K
      basis: dense monophasic ZrB2 sample of the paper, derived from measured optical spectra
    method: Calculated by the paper's authors from measured spectra
    status: calculated
    source: sani2016
    where: Optical properties section, paragraph giving epsilon at 1400 K
corrosion:
  - environment: Air above about 600 degC (oxidative environment)
    headline: Monolithic ZrB2 starts to oxidize at about 600 °C in air and degrades quickly unless additives are present.
    effect: Sani et al. state that tantalum and zirconium diborides start to oxidize above approximately 600 °C, which produces rapid material degradation unless suitable additives are introduced. They cite oxidation tests on ZrB2 solar coatings whose maximum air operating temperature was about 600 °C.
    rating: severe
    conditions:
      atmosphere: air
      form: monolithic ZrB2 without additives
      exposure_time: not stated
    source: sani2016
    where: Conclusions, final paragraph (refs. 38 and 39 as cited there)
  - environment: Air at 1200 to 1400 degC (supplier claim)
    headline: A supplier claims oxidation resistance up to 1200 to 1400 °C, which conflicts with the 600 °C onset above.
    effect: The Nanografi product page for a ZrB2 nanopowder gives an oxidation-resistance range of 1200 to 1400 °C. No test atmosphere, time or sample state is printed, so the claim cannot be checked against the approximately 600 °C figure in Sani et al.
    rating: unknown
    conditions:
      basis: supplier product page; no test conditions printed
    source: nanografi-zrb2
    where: Product description, material properties text
risks:
  hazards:
    - text: PubChem prints the GHS statements H302 (85.2%), H312 (85.2%) and H332 (85.2%) from 54 company reports for zirconium diboride, in the acute toxicity category 4 (harmful if swallowed, in contact with skin or if inhaled).
      ghs:
        - H302
        - H312
        - H332
      source: pubchem-zrb2
      where: Safety and Hazards, GHS Classification and Hazard Classes and Categories
    - text: PubChem also notes that the chemical does not meet GHS hazard criteria in 7.4% of reports (4 of 54).
      ghs: []
      source: pubchem-zrb2
      where: Safety and Hazards, GHS Classification, Note line
    - text: The Nanografi product page for ZrB2 nanopowder prints no hazard statements (H-codes) and no safety data sheet link was read in this run.
      ghs: []
      source: nanografi-zrb2
      where: Product description; hazard statements not printed
  failure_risks:
    - mode: Oxidation of monolithic ZrB2 in air
      trigger: Air exposure above about 600 degC
      consequence: Rapid material degradation, according to Sani et al., unless suitable additives are introduced.
      severity: high
      source: sani2016
      where: Conclusions, final paragraph
    - mode: Incomplete densification in conventional pressure-assisted sintering
      trigger: Consolidating ZrB2 powder by conventional pressure-assisted sintering
      consequence: Residual porosity and coarse microstructure, according to Sani et al. Their introduction says the refractory character of zirconium and tantalum borides makes powder consolidation very difficult.
      severity: moderate
      source: sani2016
      where: Introduction, third paragraph
  handling:
    - text: Keep uncoated ZrB2 parts below about 600 °C in air, the approximate oxidation onset in Sani et al.
      source: sani2016
      where: Conclusions, final paragraph
    - text: Avoid breathing the powder, because PubChem reports the harmful-if-inhaled statement H332 for most company reports.
      source: pubchem-zrb2
      where: Safety and Hazards, GHS Classification
  mitigations:
    - text: Add silicon-containing additives, such as SiC, to improve oxidation resistance for more severe thermal conditions, as Sani et al. recommend.
      source: sani2016
      where: Conclusions, final paragraph
    - text: Use a powder made by self-propagating high-temperature synthesis before spark plasma sintering; Sani et al. report that this route gives higher density samples.
      source: sani2016
      where: Introduction, fourth paragraph
uses:
  - application: heat-shields
    device: Thermal protection on hypersonic vehicles and atmospheric entry probes (historical UHTC use, not ZrB2 alone)
    example: Sani et al. describe ultra-high-temperature ceramics as ideal for thermal protection systems and say they have mainly served hypersonic vehicles, rocket motor nozzles and atmospheric entry probes.
    source: sani2016
    where: Introduction, first and second paragraphs
  - application: propulsion-and-tanks
    device: Rocket motor nozzles (historical UHTC use)
    example: Sani et al. list rocket motor nozzles among the aerospace uses of ultra-high-temperature ceramics in general.
    source: sani2016
    where: Introduction, second paragraph
  - application: thermal-control
    device: Solar absorber receivers for concentrating solar thermal plants (proposed)
    example: Sani et al. propose transition-metal borides, including ZrB2, as solar absorbers for very high temperature operation, and measure the spectral optical properties of dense ZrB2.
    source: sani2016
    where: Introduction, second paragraph and optical properties section
supply:
  - subject: Zirconium (zirconium mineral concentrates as feedstock)
    producers:
      - country: Australia
        share_percent: 33.3
        year: 2025
      - country: South Africa
        share_percent: 22.5
        year: 2025
      - country: Mozambique
        share_percent: 13.3
        year: 2025
      - country: China
        share_percent: 8.3
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (zirconium listed on the USGS page)
        listed: true
    recycling: 'USGS: companies in Oregon and Utah recycled zirconium from new scrap generated during metal production.'
    substitutes: []
    source: usgs-mcs2026-zirconium-hafnium
    where: World mine production table, zirconium mineral concentrates, 2025 (world total rounded 1,200 thousand metric tons; shares calculated by Space Mushroom from the country values 400, 270, 160 and 100); Recycling; Events, Trends, and Issues. Critical-list status from the USGS 2025 critical minerals page (usgs-crit2025); the zirconium chapter itself does not mention it.
  - subject: Boron (feedstock for the diboride)
    abundance: 'USGS boron production 2025 (thousand metric tons as printed): Turkey 1,500 refined borates; Bolivia 380 ulexite; Chile 300 ulexite; China 230 boric oxide equivalent; Peru 220 crude borates; Argentina 170 crude ore; Russia 80 datolite ore; Germany 40 compounds.'
    producers:
      - country: Turkey
        year: 2025
      - country: Bolivia
        year: 2025
      - country: Chile
        year: 2025
      - country: China
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (boron added in the final 2025 list)
        listed: true
    recycling: 'USGS: boron recycling is ''Insignificant.'''
    substitutes:
      - 'USGS: substitution for boron is possible in detergents, enamels, insulation and soaps; the chapter does not discuss boride or ceramic uses.'
    source: usgs-mcs2026-boron
    where: World Production and Reserves table, 2025 column (no shares calculated because the world total is printed as XX); Recycling; Substitutes; Events, Trends, and Issues (boron added to the 2025 critical list).
media: []
documents:
  - title: Optical properties of dense zirconium and tantalum diborides for solar thermal absorbers (Renewable Energy 91, 340-346; arXiv copy)
    type: paper
    url: https://arxiv.org/pdf/1803.06528
    year: 2016
  - title: 'PubChem: Zirconium diboride (CID 9812765), GHS classification and experimental properties'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/9812765/JSON
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Boron'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-boron.pdf
    year: 2026
  - 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: 'Nanografi product page: Zirconium Diboride (ZrB2) nanopowder NG04CO2502'
    type: datasheet
    url: https://shop.nanografi.com/nanoparticles/compounds-nanoparticles/zirconium-diboride-zrb2-nanoparticles/
    year: 2026
  - title: 'Stanford Advanced Materials product page: NN0233 Nano Zirconium Diboride (ZrB2) powder'
    type: datasheet
    url: https://www.samaterials.com/micro-nano-materials/233-nano-zirconium-diboride.html
    year: 2026
gaps:
  - No flight, vacuum, radiation or space-environment result for ZrB2 was found in the sources read for this profile.
  - Thermal expansion coefficient (5.9 x 10-6 K-1 in Table 1 of Sani et al.) and electrical conductivity (1.0 x 10^7 S/m in Table 1) are printed in exponent form and are left out, as the brief requires.
  - Free energy of formation (-318.2 kJ, Table 1 of Sani et al.) is left out because its unit is printed incompletely in the table.
  - 'The Silvestroni 2018 and Scientific Reports 2017 strength data at 1500 degC were not read in this run: the CNR repository returned an access block and the Nature article redirected to a sign-in page. No high-temperature strength value is recorded.'
  - No fracture toughness, grain size or measured hardness test method was found in a fetched source.
  - No UNS, EN, DIN or other standard designation for ZrB2 was printed in a source read in this run, so identity.designations is empty.
  - Atomic weights for zirconium and boron were not printed in a fetched source, so the recipe lists atom counts only.
  - Boron producer shares are not calculated because the USGS boron table prints the world total as XX.
  - No zirconium-diboride safety data sheet was read in this run. The hazard entries rest on PubChem's GHS summary and a product page that prints no hazard statements.
  - Side effects of ZrB2 (for example oxidation products) were not found in a fetched source, so risks.side_effects is empty.
  - Nanografi and Stanford Advanced Materials are reseller product pages. They are used only for stated supplier ranges and for the disagreement shown; they are not treated as measured grade data.
  - The EU critical raw materials list was checked, but the fetched page did not confirm boron or zirconium by name, so no EU critical-list entry is recorded.
  - PubChem's experimental record quotes "3000 °C" for the melting point, which differs from the 3245 °C in Sani et al. It is not recorded as a property because the verifier could not match it in the fetched PubChem text, where the Melting Point section was cut off.
sources:
  sani2016:
    title: Optical properties of dense zirconium and tantalum diborides for solar thermal absorbers
    id: doi:10.1016/j.renene.2016.01.068 (Renewable Energy 91, 340-346; arXiv:1803.06528 copy)
    url: https://arxiv.org/pdf/1803.06528
    year: 2016
    kind: paper
    license: arXiv copy; cited, not reproduced
  pubchem-zrb2:
    title: PubChem compound record, Zirconium diboride (CID 9812765)
    id: CID 9812765; CAS 12045-64-6
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/9812765/JSON
    year: 2026
    kind: database
    license: public domain (NCBI)
  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)
  usgs-mcs2026-zirconium-hafnium:
    title: Mineral Commodity Summaries 2026, Zirconium and Hafnium
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-zirconium-hafnium.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-crit2025:
    title: About the 2025 List of Critical Minerals (USGS)
    id: USGS 2025 List of Critical Minerals
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
    kind: web
    license: public domain (USGS)
  nanografi-zrb2:
    title: Nanografi, Zirconium Diboride (ZrB2) Nanoparticles, product NG04CO2502
    id: Product page, 99.5% purity, about 45 nm
    url: https://shop.nanografi.com/nanoparticles/compounds-nanoparticles/zirconium-diboride-zrb2-nanoparticles/
    year: 2026
    kind: web
    license: supplier product page, cited not reproduced
  samaterials-zrb2:
    title: Stanford Advanced Materials, NN0233 Nano Zirconium Diboride (ZrB2) powder
    id: Product NN0233, CAS 12045-64-6, 99.9% purity
    url: https://www.samaterials.com/micro-nano-materials/233-nano-zirconium-diboride.html
    year: 2026
    kind: web
    license: supplier product page, cited not reproduced
  wiki-zrb2:
    title: Wikipedia, Zirconium diboride (composition and structure summary only)
    id: Wikipedia article, accessed 2026-11-01
    url: https://en.wikipedia.org/wiki/Zirconium_diboride
    year: 2026
    kind: web
    license: CC BY-SA 4.0 (text summarised, not reproduced)
license: CC-BY-4.0
updated: '2026-11-01'
review:
  status: draft
  method: assistant
  checked_values: 15
  unreachable: 2
  caveats: 4
  note: Written by an AI assistant on 2026-11-01 from pages fetched in that run. Sani et al. (2016) supplies the bulk property values; PubChem, Nanografi and Stanford Advanced Materials give conflicting or supplier-only figures, shown side by side.
story:
  recipe:
    line: ZrB2 is a zirconium diboride with one zirconium atom and two boron atoms per formula unit, in an AlB2-type hexagonal structure. Sani et al. make dense samples by spark plasma sintering, either from the elemental powders or from ZrB2 powder first made by self-propagating high-temperature synthesis.
    parts:
      - name: Zirconium
        symbol: Zr
        role: The metal atom in the hexagonal lattice. The reaction in Sani et al. is written as a metal plus boron forming the metal diboride, with zirconium as the metal.
      - name: Boron
        symbol: B
        role: Forms the flat boron layers of the AlB2-type structure with the zirconium between them.
  risk_groups:
    - title: For people
      level: 0
      verdict: Harmful if swallowed or inhaled; check the SDS
      lead: The hazard data for ZrB2 rest on PubChem's GHS summary, which lists acute toxicity statements. No safety data sheet for ZrB2 was read in this run.
      points:
        - label: The powder
          line: PubChem prints the statements H302, H312 and H332 (harmful if swallowed, in contact with skin or if inhaled) for most company reports, from 54 reports in total.
        - label: Reports that disagree
          line: PubChem also notes that the chemical does not meet GHS hazard criteria in 7.4% of reports (4 of 54).
        - label: Supplier page
          line: The Nanografi product page prints no hazard statements at all.
    - title: In air at high temperature
      verdict: Oxidizes above about 600 °C in air
      lead: The oxidation onset is the limit that matters most for ZrB2 parts, and the sources disagree on it.
      points:
        - label: Monolithic ZrB2
          line: Sani et al. write that tantalum and zirconium diborides start to oxidize above approximately 600 °C, with rapid material degradation unless additives are used.
        - label: Supplier claim
          line: A nanopowder supplier claims oxidation resistance up to 1200 to 1400 °C. No test condition is printed, so this cannot be reconciled with the 600 °C figure.
    - title: Handling and storage
      points:
        - label: Dust
          line: Avoid breathing the powder, given the harmful-if-inhaled statement that PubChem prints for most company reports.
        - label: Parts in service
          line: Keep uncoated parts below about 600 °C in air, or use silicon-containing additives as Sani et al. recommend.
  why: Zirconium diboride (ZrB2) is a hard, high-melting boride ceramic in the AlB2 structure. Sani et al. (2016) tabulate a melting temperature of 3245 °C and a density of 6.119 g/cm3 for dense ZrB2. The material is studied for hypersonic thermal protection and for solar absorbers, but its weak point in air is oxidation above about 600 °C for monolithic material.
  uses:
    - where: Thermal protection on hypersonic vehicles and entry probes
      line: Sani et al. describe ultra-high-temperature ceramics as ideal for thermal protection systems. They say these ceramics have mainly served hypersonic vehicles, rocket motor nozzles and atmospheric entry probes.
    - where: Solar absorbers (proposed)
      line: Sani et al. propose transition-metal borides, including ZrB2, as solar absorbers for very high temperature operation. They measure the optical properties of dense ZrB2 and give an absorbance of 0.47 and an emittance of 0.18 at 1400 K, calculated from the measured spectra.
    - where: Industry references
      line: PubChem's summary of uses lists ZrB2 as a refractory material for aircraft and rockets, a high-temperature electrical conductor, and a cutting-tool coating, citing Hawley.
  can_do:
    - label: Melting point
      benchmark: melting_point
      value: 3245 °C
      line: The literature melting temperature of dense ZrB2 is 3245 °C in Sani et al. PubChem's experimental record quotes "3000 °C" without a test method. The two figures differ, so both are reported.
    - label: Density
      benchmark: density
      value: 6.119 g/cm3
      line: The literature density of dense ZrB2 is 6.119 g/cm3 in Table 1 of Sani et al. The value is cited there to an earlier source and is not the paper's own measurement.
    - label: Stiffness and hardness
      benchmark: elastic_modulus
      value: 489 GPa
      line: The literature Young's modulus is 489 GPa and the hardness is 23 GPa in the same table. The supplier range for a nanopowder is 340 to 500 GPa, a second-hand figure.
    - label: Thermal conductivity
      benchmark: thermal_conductivity
      value: 60 W/(m·K)
      line: The literature thermal conductivity of dense ZrB2 is 60 W/(m·K) in Sani et al. Temperature is not stated in the table.
    - label: Oxidation in air
      benchmark: oxidation_onset_temperature
      value: 600 °C
      line: Monolithic ZrB2 starts to oxidize at approximately 600 °C in air, according to Sani et al. A supplier claims 1200 to 1400 °C for a nanopowder, with no test conditions printed.
  compare: 'ZrB2 is a dense, high-melting boride ceramic. Its literature melting temperature is 3245 °C and its hardness is 23 GPa, both from Sani et al. Its limit in air is the main drawback: monolithic material starts to oxidize at about 600 °C, and the authors say additives are needed for more severe conditions. A supplier''s claim of 1200 to 1400 °C oxidation resistance is not supported by a test condition in the sources read, so the table reports the lower, sourced onset.'
  compare_rows:
    - label: Melting temperature
      benchmark: melting_point
    - label: Density
      benchmark: density
    - label: Oxidation onset in air
      benchmark: oxidation_onset_temperature
  handling:
    - Keep uncoated parts below about 600 °C in air, or add silicon-containing oxidation-resistance additives.
    - Avoid breathing the powder; PubChem prints the harmful-if-inhaled statement H332 for most company reports.
    - Check the supplier's safety data sheet for the grade you buy; no ZrB2 SDS was read in this run.
  good_for:
    - 'High melting point: 3245 °C is the literature value in Sani et al. (2016).'
    - 'Stiffness and hardness: a Young''s modulus of 489 GPa and hardness of 23 GPa in the same table.'
  watch_out:
    - Oxidation in air above about 600 °C for monolithic material, unless additives are present.
    - 'Conflicting figures: PubChem quotes "3000 °C" as the melting point, and a supplier claims oxidation resistance to 1200 to 1400 °C.'
  verdict: A very high-melting boride that needs protection or additives once it sees air above about 600 °C.