spore: profile
id: zirconium-hydride
spore_version: 0.2
family: zirconium-hydride
name: Zirconium hydride (ZrH2)
abbreviation: ZrH2
role: neutron moderator, getter and hydrogen source
category: metals
type: refractory-metals
summary: |
  Zirconium hydride (ZrH2) is a grey-black powder of zirconium and hydrogen, with two hydrogen atoms for each zirconium atom in the formula. Albemarle's Grade G sets a minimum zirconium-plus-hafnium content of 97.6 % and a minimum hydrogen content of 1.9 %, with a density of 5.6 g/cm3 at 25 °C. The datasheet gives a decomposition temperature above 400 °C and says the material decomposes before it melts. It is a flammable solid with a dust explosion hazard, and PubChem records that it releases flammable gas on contact with water.
best_for: 'Compact hydrogen storage in a powder: 1.9 % minimum hydrogen content (Albemarle Grade G) with decomposition only above 400 °C'
weakest_at: 'Fire and water safety: a flammable solid with a dust explosion hazard that can give off flammable gas on contact with water (datasheet and PubChem)'
identity:
  formula: ZrH2
  cas: 7704-99-6
  source: albemarle-zrh-g
  where: Title block of the Albemarle datasheet (CAS-No. 7704-99-6, Molecular formula ZrH2). PubChem CID 4137802 prints the same CAS number.
  designations:
    - system: Trade name
      code: Zirconium Hydride, Grade G
      source: albemarle-zrh-g
      where: Title of the technical data sheet
tags:
  applications:
    - structures
    - propulsion-and-tanks
    - electronics-and-chips
properties:
  - benchmark: density
    label: Density, Grade G at 25 °C
    value: 5.6
    unit: g/cm3
    scope: material
    conditions:
      temperature: 25 °C
      grade: Zirconium Hydride, Grade G (product numbers 10000387, 10001973, 10001974)
    method: Value printed in the manufacturer's technical data sheet, which says the value is taken from reference works and the literature rather than a supplier measurement
    status: ground
    note: A reseller page for the same compound prints a density of 5,80 g/cm3 with no conditions. It conflicts with this value and is not recorded as a second property (see gaps).
    source: albemarle-zrh-g
    where: Physical properties table, Density row
  - benchmark: decomposition_temperature
    label: Decomposition temperature (decomposes before melting)
    value: 400
    bound: lower
    unit: °C
    scope: material
    conditions:
      grade: Grade G powder
      note_in_source: Decomposes before melting
    method: Printed in the datasheet as > 400 °C; the datasheet gives no melting point
    status: ground
    source: albemarle-zrh-g
    where: Physical properties table, Decomposition temperature row
  - benchmark: molecular_weight
    label: Molecular weight
    value: 93.24
    unit: g/mol
    scope: material
    conditions:
      formula: ZrH2
    method: Value printed in the manufacturer's technical data sheet
    status: ground
    source: albemarle-zrh-g
    where: Physical properties table, Molecular weight row
  - benchmark: zirconium_hafnium_content
    label: Zirconium plus hafnium content (minimum)
    value: 97.6
    bound: lower
    unit: '%'
    scope: material
    conditions:
      grade: Grade G
      tolerance: +/- 0.5 % as printed
      basis: Zr + Hf, the datasheet's wording
    method: Specification minimum printed in the manufacturer's datasheet
    status: ground
    source: albemarle-zrh-g
    where: Specification table, row Zr + Hf
  - benchmark: hafnium_content
    label: Hafnium content (natural)
    value: 2
    unit: '%'
    scope: material
    conditions:
      basis: natural hafnium content, printed as approx. 2 %
    method: Value printed in the manufacturer's datasheet
    status: ground
    source: albemarle-zrh-g
    where: Specification table, row Hf
  - benchmark: hydrogen_content
    label: Hydrogen content (minimum)
    value: 1.9
    bound: lower
    unit: '%'
    scope: material
    conditions:
      basis: minimum hydrogen content as printed in the specification
    method: Specification minimum printed in the manufacturer's datasheet
    status: ground
    source: albemarle-zrh-g
    where: Specification table, row H
  - benchmark: iron_content
    label: Iron impurity (maximum)
    value: 0.08
    bound: upper
    unit: '%'
    scope: material
    conditions:
      basis: maximum impurity as printed
    method: Specification maximum printed in the manufacturer's datasheet
    status: ground
    source: albemarle-zrh-g
    where: Specification table, row Fe
  - benchmark: silicon_content
    label: Silicon impurity (maximum)
    value: 0.5
    bound: upper
    unit: '%'
    scope: material
    conditions:
      basis: maximum impurity as printed
    method: Specification maximum printed in the manufacturer's datasheet
    status: ground
    source: albemarle-zrh-g
    where: Specification table, row Si
  - benchmark: ignition_temperature
    label: Ignition point of the powder
    value: 200
    value_high: 310
    bound: range
    unit: °C
    scope: material
    conditions:
      form: powder, Grade G
    method: Range printed in the manufacturer's datasheet under Additional Physical Properties
    status: ground
    source: albemarle-zrh-g
    where: Physical properties table, Additional Physical Properties row (Ignition Point)
  - benchmark: bulk_density
    label: Bulk density of the powder
    value: 1000
    value_high: 2000
    bound: range
    unit: kg/m3
    scope: material
    conditions:
      form: powder, as printed
    method: Range printed in the manufacturer's datasheet
    status: ground
    source: albemarle-zrh-g
    where: Physical properties table, Bulk density row
  - benchmark: water_solubility
    label: Water solubility
    value: 0.00008
    bound: upper
    unit: g/l
    scope: material
    conditions:
      temperature: 23 °C
      test: OECD Test Guideline 29, as printed
    method: Printed in the datasheet as < 0.00008 g/l at 23 °C
    status: ground
    source: albemarle-zrh-g
    where: Physical properties table, Water solubility row
  - benchmark: average_particle_size
    label: Average particle size (Blaine)
    value: 5.5
    unit: µm
    scope: material
    conditions:
      method_printed: Blaine
      tolerance: +/- 1 µm as printed
    method: Printed in the datasheet as average particle size acc. to Blaine
    status: ground
    source: albemarle-zrh-g
    where: Physical properties table, Grain Size row
  - benchmark: particle_size_under_45um
    label: Share of powder finer than 45 µm (minimum)
    value: 99.9
    bound: lower
    unit: '%'
    scope: material
    conditions:
      size_limit: below 45 µm
    method: Printed in the datasheet as min. 99.9 % < 45 µm
    status: ground
    source: albemarle-zrh-g
    where: Physical properties table, Grain Size row
  - benchmark: gain_on_ignition
    label: Weight gain on combustion
    value: 31.8
    unit: '%'
    scope: material
    conditions:
      basis: weight increase by combustion, as the datasheet defines it
      tolerance: +/- 0.7 % as printed
    method: Printed in the datasheet under Additional Physical Properties
    status: ground
    source: albemarle-zrh-g
    where: Physical properties table, Additional Physical Properties row (Gain on Ignition)
  - benchmark: relative_density
    label: Relative density of cold-pressed disks
    value: 73
    unit: '% of theoretical density'
    scope: material
    conditions:
      form: cold-pressed disk of zirconium hydride (ZrHx) powder, commercial 99 % purity, 50 mesh
      pressure: 400 MPa
    method: Density calculated by the authors from the weight and dimensions of the pressed disk
    status: ground
    note: A pressed compact from a research study, not a bulk value for this grade. The same report gives thermal conductivity only as a figure, so no thermal value is recorded.
    source: nifs-zrhx-pressed
    where: Text, paragraph beginning 'Sample with 73 % of theoretical density'
  - benchmark: purity
    label: Stated purity of a micron powder
    value: 99.5
    bound: lower
    unit: '%'
    scope: material
    conditions:
      grade: micron powder, size printed as 1-10 µm on the reseller page
      definition: not defined on the page
    method: Stated in the product title and specification table of a reseller's product page
    status: ground
    note: The reseller does not define its purity figure. The datasheet's Zr + Hf minimum of 97.6 % is defined differently, so the two are not directly comparable.
    source: nanografi-zrh
    where: 'Product title (''Purity: 99.5+%'') and specification table, Purity row'
checked_values: 16
corrosion:
  - environment: Water, or humid air
    headline: Sources disagree on whether zirconium hydride reacts with water. Both say that any gas released is flammable.
    effect: PubChem's record description says the powder does not react with water under normal conditions. Its hazards summary says the powder reacts slowly with water to form zirconium hydroxide and hydrogen gas, which is flammable, and another entry says it releases flammable gases on contact with water.
    rating: moderate
    conditions:
      water: temperature and exposure time not stated
      form: powder
    source: pubchem-zrh
    where: Chemical and Physical Properties, Physical Description; Safety and Hazards, Hazards Summary; Stability and Reactivity, Air and Water Reactions
  - environment: Heating in air
    headline: Heated in air, the powder incandesces and can give mild explosions.
    effect: PubChem cites Bretherick (1979) for heating in air causing incandescence and mild explosions. The datasheet gives an ignition point of 200 to 310 °C and a gain of 31.8 % in weight on combustion.
    rating: moderate
    conditions:
      basis: heating in air, no exposure time stated
    source: pubchem-zrh
    where: Stability and Reactivity, Air and Water Reactions
  - environment: Dry, sealed storage
    headline: The datasheet gives an unlimited shelf life for dry, sealed storage.
    effect: Albemarle states an unlimited shelf life and packs the powder dry in tin cans. It gives no ageing data, such as change in hydrogen content over time.
    rating: none
    conditions:
      packaging: dry, in sealed tin cans
      condition: dry storage
    source: albemarle-zrh-g
    where: Handling and Storage; Transport and Packaging
risks:
  hazards:
    - text: 'PubChem''s GHS summary: signal word Danger. Hazard statements H228 (flammable solid), H260 (in contact with water releases flammable gases which may ignite spontaneously), H315 (causes skin irritation) and H319 (causes serious eye irritation). Percentages are shares of ECHA notifications, not of tests.'
      ghs:
        - H228
        - H260
        - H315
        - H319
      source: pubchem-zrh
      where: Safety and Hazards, GHS Classification (CID 4137802)
    - text: 'Albemarle datasheet: signal word Danger and EU-GHS labelling. Transport: UN 1437, Class 4.1 flammable solid, Packing Group II for road, rail and sea, and Packing Group II for air.'
      ghs: []
      source: albemarle-zrh-g
      where: Transport and Packaging; Labelling
    - text: Exposure limits in PubChem (5.0 mg/m3 as Zr, the PEL and TLV, and 10.0 mg/m3 as Zr for the STEL) are for zirconium compounds in general, not for zirconium hydride alone.
      ghs: []
      source: pubchem-zrh
      where: Exposure Control and Personal Protection, PEL and TLV entries
  failure_risks:
    - mode: Dust ignition
      trigger: Powder dust formed during handling or transfer, or an open flame or spark nearby
      consequence: The datasheet calls the powder a highly flammable solid with a dust explosion hazard. It gives an ignition point of 200 to 310 °C and says the powder is less ignitable than other grades because of its coarse particle size.
      severity: high
      source: albemarle-zrh-g
      where: Handling and Storage; Physical properties table, Ignition Point
    - mode: Reaction with water
      trigger: Contact with water, including water sprayed on a fire
      consequence: Flammable hydrogen gas is released. PubChem's GHS statement H260 says contact with water releases flammable gases which may ignite spontaneously, and the ERG notes say the product may re-ignite after a fire is put out.
      severity: high
      source: pubchem-zrh
      where: GHS Classification (H260); Fire Hazards, ERG 2024 Guide 138
    - mode: Hydrogen loss on heating
      trigger: Heating above the decomposition temperature
      consequence: The datasheet reports decomposition above 400 °C, not melting. It does not state how much hydrogen is released or how the lost hydrogen affects the material's behaviour.
      severity: moderate
      source: albemarle-zrh-g
      where: Physical properties table, Decomposition temperature row
  side_effects:
    - text: Fire produces irritating, corrosive and/or toxic gases (ERG 2024, Guide 138).
      affects: Responders and nearby people
      source: pubchem-zrh
      where: Safety and Hazards, Health Hazards (ERG 2024 Guide 138)
    - text: Runoff from fire control or dilution water may cause environmental contamination (ERG 2024, Guide 138).
      affects: Waterways near the site
      source: pubchem-zrh
      where: Safety and Hazards, Health Hazards (ERG 2024 Guide 138)
  handling:
    - text: 'Datasheet: highly flammable solid with a dust explosion hazard. Keep away from open flame and use ground-connected metal apparatus to avoid sudden ignition by electrostatic discharge.'
      source: albemarle-zrh-g
      where: Handling and Storage
    - text: 'Datasheet: store dry in tightly closed tin cans. The datasheet says the product has an unlimited shelf life.'
      source: albemarle-zrh-g
      where: Handling and Storage; Packaging
    - text: 'PubChem''s ERG 2024 Guide 138 notes: eliminate ignition sources and cover powder spills with plastic sheet to keep the powder dry; do not clean up powder except under specialist supervision.'
      source: pubchem-zrh
      where: Accidental Release Measures; Nonfire Spill Response
  mitigations:
    - text: Fight fires with dry sand or dry powder only, and never with water. PubChem's ERG notes say do not use water or foam.
      source: pubchem-zrh
      where: Fire Fighting; Emergency Response Planning Guidelines (ERG 2024 Guide 138)
    - text: Use ground-connected metallic equipment to prevent sudden ignition by electrostatic discharge.
      source: albemarle-zrh-g
      where: Handling and Storage
uses:
  - application: structures
    device: Hydrogen source for foaming metals
    example: The datasheet names zirconium hydride as a hydrogen source for the foaming of metals. PubChem also lists its use as a metal foaming agent.
    source: albemarle-zrh-g
    where: Application paragraph; PubChem Uses, Sources/Uses entry
  - application: propulsion-and-tanks
    device: Moderator block in a nuclear thermal propulsion reactor (conceptual reference design, not flown)
    example: A 2021 NETS paper on NASA's space nuclear propulsion fuel and moderator plan says the Heat Transfer Reactor Experiment used solid zirconium-hydride moderator blocks, and it recommends a ZrH moderator block for the reference core it describes.
    source: nets-snp-fmdp
    where: Section I, paragraph on moderator material selection (HTRE reference)
  - application: electronics-and-chips
    device: Getter material (the device is not named in the datasheet)
    example: The datasheet says the grade is for the production of highly effective getters, which are activated by dehydrogenation.
    source: albemarle-zrh-g
    where: Application paragraph
supply:
  - subject: Zirconium (from zircon and zirconium mineral concentrates)
    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: []
    recycling: 'USGS: companies in Oregon and Utah recycled zirconium from new scrap and post-commercial old scrap.'
    substitutes:
      - 'USGS: niobium, stainless steel and tantalum provide some substitution in nuclear applications. The chapter covers zirconium and hafnium together.'
    source: usgs-mcs2026-zirconium-hafnium
    where: 'World Mine Production and Reserves table, zirconium mineral concentrates, 2025 (thousand metric tons gross weight: Australia 400, South Africa 270, Mozambique 160, China 100, against a world total of 1,200). Shares are calculated by Space Mushroom against that rounded total, so they are approximate. Recycling and Substitutes sections.'
documents:
  - title: 'Zirconium Hydride, Grade G: technical data sheet (Albemarle, date of issue 2021/07/22)'
    type: datasheet
    url: https://www.albemarle.com/sites/default/files/documents/zirconium-hydride-grade-g.PDF
    year: 2021
  - title: 'PubChem: Zirconium hydride (CID 4137802), GHS classification and safety summaries'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/4137802
    year: 2026
  - title: 'Mineral Commodity Summaries 2026: Zirconium and Hafnium (USGS, February 2026)'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-zirconium-hafnium.pdf
    year: 2026
  - title: Applicability Study of Hydride Materials, NIFS Annual Report 2013, section 41, p. 360
    type: report
    url: https://www.nifs.ac.jp/report/annrep13/pdf/360.pdf
    year: 2013
  - title: High-Temperature Thermodynamic Functions for Zirconium and Unsaturated Zirconium Hydrides (J. Res. NBS 67A, 1963)
    type: paper
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC5319804/
    year: 1963
  - title: 'Space Nuclear Propulsion Fuel and Moderator Development Plan: Conceptual Testing Reference Design (NETS 2021)'
    type: report
    url: https://ntrs.nasa.gov/api/citations/20220000493/downloads/SNP%20FMDP%20Conceptual%20Testing%20Reference%20Design_NETS.pdf
    year: 2021
  - title: TRIGA Type U-ZrH Cladding Steady State Mechanical Limitations (Sandia National Laboratories slides, SAND2009-7374C)
    type: report
    url: https://www.trtr.org/wp-content/uploads/2024/12/TRIGA-Type-U-ZrH-Cladding-Steady-State-Mechanical-Limitations.pdf
    year: 2009
  - title: Zirconium Hydride (ZrH2) Micron Powder, Purity 99.5+% (Nanografi product page)
    type: datasheet
    url: https://shop.nanografi.com/microparticles/zirconium-hydride-zrh2-micron-powder-purity-99-5-size-1-10-m/
    year: 2026
  - title: Atomic Weights and Isotopic Compositions for All Elements (NIST), entry for Zr
    type: database
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Zr&all=all
    year: 2026
gaps:
  - 'No melting point for this grade: the datasheet says the material decomposes before melting and gives no melting temperature. A reseller page prints a melting point of 800 °C with no conditions, which conflicts with the datasheet, so it is not recorded.'
  - The reseller page also prints a density of 5,80 g/cm3 with no conditions. It conflicts with the datasheet's 5.6 g/cm3 at 25 °C, so only the datasheet value is recorded.
  - No thermal conductivity, thermal expansion, elastic modulus or hydrogen equilibrium pressure for pure ZrH2 was read in a fetched source. The NIFS thermal conductivity is shown only as a figure, and the 1963 Douglas paper's thermodynamic tables were not extracted.
  - The NIFS report's bulk-sample comparison (about 80 W/(m·K)) is a literature figure for a bulk sample, not for this grade, so it is not recorded.
  - The datasheet gives the decomposition temperature only. It does not state how much hydrogen is released on decomposition.
  - No flight, vacuum, radiation or space-environment test result for zirconium hydride was found. The NETS paper is a conceptual reference design, not a test result.
  - The Sandia slide values (density, elastic modulus, thermal expansion) are for uranium-zirconium hydride (U-ZrH) TRIGA fuel, not pure ZrH2, so they are not recorded as properties.
  - The manufacturing route for the powder was not found in the sources read.
  - The atomic weight of hydrogen is printed by NIST as an interval rather than a single standard value, so none is recorded in the recipe.
  - No UNS, EN, ASTM, AMS or other standard designation was found for this grade. Only the trade name Zirconium Hydride, Grade G is listed.
  - The USGS 2025 critical-minerals list and the EU critical raw materials list were not checked for zirconium, so the supply section names no critical-list entry.
  - The PubChem exposure limits (5.0 mg/m3 as Zr) apply to zirconium compounds in general and are not limits set for ZrH2 itself.
  - The fire, water and corrosion hazards rest on PubChem's summaries and the Albemarle datasheet. No supplier safety data sheet for ZrH2 was read.
sources:
  albemarle-zrh-g:
    title: 'Zirconium Hydride, Grade G: technical data sheet'
    id: Albemarle, product numbers 10000387, 10001973, 10001974; date of issue 2021/07/22; CAS 7704-99-6; EC 231-727-3
    url: https://www.albemarle.com/sites/default/files/documents/zirconium-hydride-grade-g.PDF
    year: 2021
    kind: datasheet
    license: manufacturer document, linked not reproduced
  pubchem-zrh:
    title: PubChem compound record, Zirconium hydride (CID 4137802)
    id: CID 4137802; CAS 7704-99-6; UN 1437
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/4137802/JSON
    year: 2026
    kind: database
    license: public domain (NCBI)
  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)
  nifs-zrhx-pressed:
    title: Applicability Study of Hydride Materials (section 41), NIFS Annual Report 2013
    id: NIFS annual report 2013, p. 360
    url: https://www.nifs.ac.jp/report/annrep13/pdf/360.pdf
    year: 2013
    kind: report
    license: NIFS report, cited not reproduced
  douglas1963:
    title: High-Temperature Thermodynamic Functions for Zirconium and Unsaturated Zirconium Hydrides
    id: J. Res. Natl. Bur. Stand. A 67A(5), 403-426 (1963); doi:10.6028/jres.067A.043; PMC5319804
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC5319804/
    year: 1963
    kind: paper
    license: public domain (NBS/NIST publication, as hosted by PMC)
  nets-snp-fmdp:
    title: 'Space Nuclear Propulsion Fuel and Moderator Development Plan: Conceptual Testing Reference Design'
    id: NETS 2021 (ORNL, April 2021), NTRS 20220000493
    url: https://ntrs.nasa.gov/api/citations/20220000493/downloads/SNP%20FMDP%20Conceptual%20Testing%20Reference%20Design_NETS.pdf
    year: 2021
    kind: report
    license: public domain (NASA)
  sandia-trga-uzrh:
    title: TRIGA Type U-ZrH Cladding Steady State Mechanical Limitations (slides)
    id: Sandia National Laboratories, SAND2009-7374C
    url: https://www.trtr.org/wp-content/uploads/2024/12/TRIGA-Type-U-ZrH-Cladding-Steady-State-Mechanical-Limitations.pdf
    year: 2009
    kind: report
    license: slides, cited not reproduced
  nanografi-zrh:
    title: Zirconium Hydride (ZrH2) Micron Powder, Purity 99.5+% (reseller product page)
    id: Nanografi SKU NG04CO2801
    url: https://shop.nanografi.com/microparticles/zirconium-hydride-zrh2-micron-powder-purity-99-5-size-1-10-m/
    year: 2026
    kind: web
    license: reseller page, cited not reproduced
  nist-atomic-weights:
    title: Atomic Weights and Isotopic Compositions for All Elements
    id: NIST Physical Measurement Laboratory, entry for Zr (standard atomic weight 91.224)
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Zr&all=all
    year: 2026
    kind: database
    license: public domain (NIST)
license: CC-BY-4.0
updated: '2026-11-01'
review:
  status: draft
  method: assistant
  checked_values: 16
  unreachable: 0
  caveats: 3
  note: Written by an AI assistant on 2026-11-01 from pages fetched in that run. Values are as printed in the cited sources. The reseller density and melting point conflict with the datasheet and are left out (see gaps).
story:
  recipe:
    line: 'Zirconium hydride is the compound ZrH2, zirconium dihydride: one zirconium atom bonded to two hydrogen atoms. The Albemarle datasheet''s Grade G is a commercial powder with a minimum zirconium-plus-hafnium content of 97.6 % and a minimum hydrogen content of 1.9 %.'
    parts:
      - name: Zirconium
        symbol: Zr
        atoms: 1
        atomic_weight: 91.224
        role: The metal framework. NIST prints a standard atomic weight of 91.224 for zirconium.
      - name: Hydrogen
        symbol: H
        role: Stored inside the metal lattice. It is the part that gives the material its moderating, getter and foaming uses, and it is lost when the material decomposes above 400 °C.
  risk_groups:
    - title: For people
      verdict: Flammable solid; irritant; reacts with water
      lead: The powder is a flammable solid under GHS, and it is an irritant. The hazard data come from a chemical database and from the manufacturer's datasheet.
      points:
        - label: The powder
          line: PubChem's GHS summary gives H228 (flammable solid), H315 (skin irritation) and H319 (serious eye irritation), with the signal word Danger.
        - label: Dust
          line: The datasheet warns of a dust explosion hazard. It gives an ignition point of 200 to 310 °C for the powder.
        - label: Water
          line: PubChem reports that the compound reacts slowly with water to form zirconium hydroxide and hydrogen gas, which is flammable. Another PubChem entry says it does not react with water under normal conditions. The two statements disagree.
    - title: In a fire
      verdict: 'Fire fighting: dry sand or powder only, never water'
      lead: The fire guidance comes from the ERG 2024 entry for this compound, which PubChem reproduces.
      points:
        - label: What to use
          line: Use dry sand, dry chemical, soda ash or lime. PubChem's ERG notes say do not use water or foam.
        - label: Fire products
          line: Fire gives off irritating, corrosive and/or toxic gases, and runoff can contaminate the environment.
    - title: Handling and storage
      verdict: Keep dry and sealed; ground all equipment
      points:
        - label: Storage
          line: The datasheet says to store the powder dry in tightly closed containers. It gives the product an unlimited shelf life under those conditions.
        - label: Static
          line: Use ground-connected metal equipment. The datasheet warns of sudden ignition from electrostatic discharge.
        - label: Transport
          line: Shipped as UN 1437, Class 4.1, flammable solid, Packing Group II.
  why: 'Zirconium hydride (ZrH2) is a grey-black zirconium powder with a high hydrogen content, sold for three jobs: as a hydrogen source for foaming metals, as a getter that is activated by dehydrogenation, and for illumination effects in pyrotechnics. Its hydrogen makes it a useful neutron moderator. In a 1963 review of the zirconium-hydrogen system, Douglas described zirconium hydrides as potentially valuable thermal neutron moderators that can reach high temperatures without excessive pressure. The datasheet does not name a space application, so the space use here comes from a NASA-sponsored reference design study.'
  uses:
    - where: Metal foaming
      line: The datasheet names zirconium hydride as a hydrogen source for the foaming of metals. PubChem also lists its use as a metal foaming agent.
    - where: Space nuclear propulsion
      line: A 2021 NETS paper on NASA's space nuclear propulsion fuel and moderator plan says the Heat Transfer Reactor Experiment used solid zirconium-hydride moderator blocks. The paper recommends a ZrH moderator block for the reference core it describes. This is a conceptual reference design, not a flown system.
    - where: Getters and pyrotechnics
      line: Albemarle makes this grade for highly effective getters, which are activated by dehydrogenation, and for illumination effects in pyrotechnics.
    - where: Research reactor fuel (a different material)
      line: TRIGA research-reactor fuel uses a uranium-zirconium hydride (U-ZrH) matrix that combines fuel and moderator. A Sandia slide set describes it. That matrix is a different material from pure ZrH2, so its figures are not used in this profile.
  can_do:
    - label: Hydrogen foaming
      line: Supplies hydrogen for foaming metals, the datasheet's stated application.
    - label: Getter
      line: Works as a getter material once it is activated by dehydrogenation, as the datasheet describes.
    - label: Moderation
      line: Moderates neutrons in a reactor core. Douglas (1963) calls zirconium hydrides potentially valuable thermal neutron moderators, and the 2021 NETS paper recommends a ZrH moderator block for a space nuclear propulsion core.
  compare: Two zirconium dihydride powders are on sale from the sources we read. Albemarle's Grade G gives a minimum zirconium-plus-hafnium content of 97.6 % and a minimum hydrogen content of 1.9 %, and it decomposes above 400 °C before melting. Nanografi's micron powder is stated as 99.5+% purity, but its page does not define that figure, so it cannot be set against the Albemarle minimum. Nanografi also prints a melting point with no conditions, which conflicts with the datasheet, and that figure is not used here.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Decomposition temperature
      benchmark: decomposition_temperature
    - label: Ignition point
      benchmark: ignition_temperature
  handling:
    - Keep the powder dry and tightly closed. The datasheet says it has an unlimited shelf life under those conditions.
    - Keep it away from open flame and sparks. Use ground-connected metal equipment because of the risk of ignition by static discharge.
    - Put out fires with dry sand or dry powder only, never water. PubChem's ERG notes say do not use water or foam.
    - Cover powder spills with plastic sheet to keep them dry, and leave cleanup to specialists.
  good_for:
    - 'Hydrogen delivery in a powder: the datasheet sets a minimum hydrogen content of 1.9 %, which is released only above the decomposition temperature of 400 °C.'
    - Hydrogen-rich moderation in reactor designs, as Douglas (1963) noted and as the 2021 NETS reference design uses it.
  watch_out:
    - A flammable solid with a dust explosion hazard. The datasheet gives an ignition point of 200 to 310 °C.
    - Water releases flammable gas. PubChem's GHS statement H260 says contact with water releases flammable gases which may ignite spontaneously.
    - No melting point, thermal conductivity or elastic modulus for this grade was found in any source we read. The NIFS pressed-disk density of 73 % of theoretical is a research compact, not a bulk value.
  verdict: Zirconium hydride is a fire-risk powder that stores hydrogen. It suits foaming, getter and reactor-moderator uses only with fire and water controls in place, and the thermal data a designer would need are not in the sources we hold.