Hafnium hydride (HfH2) HfH2

spore: profile
id: hafnium-hydride
spore_version: 0.2
family: hafnium
name: Hafnium hydride (HfH2)
abbreviation: HfH2
role: Hydrogen-loaded hafnium powder for powder metallurgy, metal foaming and nuclear shielding research
category: shielding
type: hydrogen-rich-polymers
summary: |
  Hafnium hydride (HfH2) is a grey to black powder of hafnium and hydrogen. Albemarle's technical data sheet gives its density as 11.4 g/cm3 at 20 °C. It is a highly flammable solid that releases flammable gas on contact with water, so the powder is handled under inert gas.
best_for: Powder metallurgy alloy additions and a hydrogen source for foaming metals, as Albemarle sells grade PS
weakest_at: 'Safe handling: a flammable solid with a dust explosion hazard that releases flammable gas on contact with water (Stanford SDS)'
identity:
  formula: HfH2 (hafnium dihydride; the Albemarle sheet prints the formula as H2-Hf)
  cas: 12770-26-2
  space_group: I 4/m
  source: cod-2310960
  where: Structure parameters, Hermann-Mauguin space group symbol on the COD card; CAS 12770-26-2 and formula HfH2 in the Stanford SDS sections 1 and 3; CAS and H2-Hf in the Albemarle sheet
tags:
  environments: []
  stresses: []
  applications:
    - structures
    - radiation-shielding
properties:
  - benchmark: density
    label: Density, grade PS powder
    value: 11.4
    unit: g/cm3
    scope: material
    conditions:
      temperature: 20 °C
      form: powder, grade PS (product 10002021)
    method: Value printed in a manufacturer technical data sheet (Albemarle, issued 2024/03/15)
    status: ground
    source: albemarle-ps
    where: Physical properties, row Density
  - benchmark: density
    label: Specific gravity, printed in gm/ml
    value: 11.5
    unit: gm/ml
    scope: material
    conditions:
      form: gray-black powder (SDS section 9)
      temperature: not stated
    method: Value printed as specific gravity in a supplier safety data sheet
    status: ground
    note: The safety data sheet conflicts with the 11.4 g/cm3 of the manufacturer sheet and the AZoM table.
    source: sama-sds
    where: Section 9, SPECIFIC GRAVITY
  - benchmark: density
    label: Density, AZoM key properties table
    value: 11.4
    unit: g/cm3
    scope: material
    conditions:
      form: grey to black powder
      temperature: not stated
    method: Value in the Key Properties table of an AZoM properties page; no temperature is printed
    status: ground
    source: azom-hfh2
    where: Key Properties table, row Density (g/cm3)
  - benchmark: density
    label: Density, supplier article
    value: 10.5
    unit: g/cm3
    scope: material
    conditions:
      form: hafnium hydride (HfH2) powder
      temperature: not stated
    method: Value printed in a supplier article on hafnium-based powders
    status: ground
    note: The same article prints 10.5 g/cm3 for hafnium boride as well, and the value conflicts with the 11.4 and 11.5 values above; treat it as doubtful.
    source: sama-powders-article
    where: Hafnium Hydride Powder, Physical Properties paragraph
  - benchmark: melting_point
    label: Melting point or range, grade PS
    value: 400
    bound: lower
    unit: °C
    scope: material
    conditions:
      grade: PS powder
      printed: '''>= 400 °C'' under ''Melting point/range'''
      basis: The sheet does not say whether this figure is melting or decomposition
    method: Lower bound printed in a manufacturer technical data sheet
    status: ground
    note: AZoM gives decomposition at 300 °C, and the Stanford SDS prints 'No data available' for melting point.
    source: albemarle-ps
    where: Physical properties, row Melting point/range
  - benchmark: decomposition_temperature
    label: Decomposition onset
    value: 300
    unit: °C
    scope: material
    conditions:
      form: grey to black powder
      atmosphere: not stated
    method: Printed in the Key Properties table (Melting Point row reads 'Decomposes at 300 °C') and in the Background paragraph
    status: ground
    source: azom-hfh2
    where: Key Properties table, row Melting Point (°C); Background paragraph
  - benchmark: autoignition_temperature
    label: Autoignition temperature
    value: 190
    unit: °C
    scope: material
    conditions:
      form: powder, as described in the SDS
      test: test method not stated on the sheet
    method: Value printed in section 5 (firefighting measures) of a supplier safety data sheet
    status: ground
    source: sama-sds
    where: Section 5, Autoignition line
  - benchmark: molecular_weight
    label: Molecular weight
    value: 180.5
    unit: g/mol
    scope: material
    conditions:
      grade: PS powder
    method: Value printed in a manufacturer technical data sheet
    status: ground
    source: albemarle-ps
    where: Physical properties, row Molecular weight
  - benchmark: hafnium_zirconium_content
    label: Hafnium plus zirconium, minimum
    value: 95
    bound: lower
    unit: '%'
    scope: material
    conditions:
      grade: PS powder
      basis: Hf plus Zr as printed; the sheet's method is gravimetric analysis of hafnium
    method: Minimum specification value printed in a manufacturer technical data sheet
    status: ground
    source: albemarle-ps
    where: Specification, row Hf + Zr
  - benchmark: hydrogen_content
    label: Hydrogen, minimum
    value: 1
    bound: lower
    unit: '%'
    scope: material
    conditions:
      grade: PS powder
      basis: H as printed; the sheet does not state whether this is a weight or atom basis
    method: Minimum specification value printed in a manufacturer technical data sheet
    status: ground
    source: albemarle-ps
    where: Specification, row H
  - benchmark: particle_size_d50
    label: Particle size D50, maximum
    value: 5
    bound: upper
    unit: µm
    scope: material
    conditions:
      grade: PS powder
      measure: D50 from the particle size distribution
    method: Maximum value printed in a manufacturer technical data sheet
    status: ground
    note: The same sheet's Grain Size row gives D50 = 6 µm, so the two statements conflict.
    source: albemarle-ps
    where: Additional Physical Properties, Particle size D50 (page 2)
  - benchmark: particle_size_d90
    label: Particle size D90, maximum
    value: 18
    bound: upper
    unit: µm
    scope: material
    conditions:
      grade: PS powder
      measure: D90 from the particle size distribution
    method: Maximum value printed in a manufacturer technical data sheet
    status: ground
    source: albemarle-ps
    where: Additional Physical Properties, Particle size D90
  - benchmark: lattice_parameter_a
    label: Cell edge a, hafnium dihydride card (1954)
    value: 3.461
    unit: Å
    scope: material
    conditions:
      composition: printed as H1.98Hf on the COD card
      temperature: not stated on the card
    method: Cell edge recorded in the COD card from Sidhu, Acta Crystallographica (1954); the experimental method is not stated on the card
    status: ground
    source: cod-2310960
    where: 'CIF data block, _cell_length_a (COD card: Structure parameters, a)'
  - benchmark: lattice_parameter_c
    label: Cell edge c, hafnium dihydride card (1954)
    value: 4.395
    unit: Å
    scope: material
    conditions:
      composition: printed as H1.98Hf on the COD card
      temperature: not stated on the card
    method: Cell edge recorded in the COD card from Sidhu, Acta Crystallographica (1954); the experimental method is not stated on the card
    status: ground
    source: cod-2310960
    where: 'CIF data block, _cell_length_c (COD card: Structure parameters, c)'
  - benchmark: cell_volume
    label: Cell volume, hafnium dihydride card (1954)
    value: 52.646
    unit: Å3
    scope: material
    conditions:
      composition: printed as H1.98Hf on the COD card
      temperature: not stated on the card
    method: Cell volume recorded in the COD card from Sidhu, Acta Crystallographica (1954)
    status: ground
    source: cod-2310960
    where: 'CIF data block, _cell_volume (COD card: Cell volume)'
corrosion:
  - environment: Humid air and contact with water
    headline: Contact with water releases a flammable gas, so humid air is a hazard for the powder.
    effect: The Stanford SDS gives the hazard statement 'In contact with water releases flammable gas' (H261), lists humidity as a condition to avoid, and says to protect the material from moisture. The sheet gives no corrosion rate or mass change, so none is recorded.
    rating: unknown
    conditions:
      exposure: water or humid air; duration and temperature not stated
    source: sama-sds
    where: Section 2 (H261), Section 7 and Section 10, conditions to avoid
  - environment: Air at room temperature
    headline: The powder burns slowly in air.
    effect: The Albemarle datasheet describes the powder as 'slowly burning in air' and says it yields hydrogen by a reversible reaction in vacuum. No oxide growth or mass gain in air is reported in the sources read.
    rating: unknown
    conditions:
      basis: statement in the handling section; exposure time and humidity not stated
    source: albemarle-ps
    where: Handling and storage, row Handling
  - environment: Heating above 300 °C
    headline: Above 300 °C the hydride gives off hydrogen.
    effect: AZoM says that at temperatures above 300 °C hafnium hydride decomposes, evolving hydrogen. The page gives no rate or time and does not describe the residue.
    rating: unknown
    conditions:
      basis: decomposition onset as printed; heating time and atmosphere not stated
    source: azom-hfh2
    where: Background paragraph
risks:
  hazards:
    - text: Stanford Advanced Materials SDS (revised 06/02/2023) gives the signal word Danger, with H228 flammable solid, H261 in contact with water releases flammable gas, H302+H312+H332 harmful if swallowed, in contact with skin or if inhaled, H315 causes skin irritation, H319 causes serious eye irritation and H335 may cause respiratory irritation.
      ghs:
        - H228
        - H261
        - H302
        - H312
        - H332
        - H315
        - H319
        - H335
      source: sama-sds
      where: Section 2, Signal Word and Hazard Statements
    - text: 'Albemarle datasheet: signal word Danger; highly flammable solid with a dust explosion hazard; labelling per EU GHS (EC) 1272/2008 as the sheet states; UN 3182, class 4.1, packing group II in its transport section.'
      ghs: []
      source: albemarle-ps
      where: Transport and packaging; Signal Word and Labelling
    - text: The Stanford SDS gives UN3132 (water-reactive solid, flammable, class 4.3 (4.1), packing group II), which differs from the UN 3182 in the Albemarle sheet, so the shipping paper must be checked.
      ghs: []
      source: sama-sds
      where: Section 14, Transport Information
    - text: The Stanford SDS states that the toxicological effects of this compound have not been fully investigated and that it contains no substances with occupational exposure limit values.
      ghs: []
      source: sama-sds
      where: Section 8 and Section 11
  failure_risks:
    - mode: Hydrogen release on heating
      trigger: Heating above 300 °C
      consequence: The powder decomposes and evolves hydrogen (AZoM).
      severity: moderate
      source: azom-hfh2
      where: Background paragraph
    - mode: Dust fire or explosion
      trigger: Fine powder with an ignition source or electrostatic discharge
      consequence: A highly flammable solid with a dust explosion hazard (Albemarle); the Stanford SDS gives an autoignition temperature of 190 °C.
      severity: high
      source: albemarle-ps
      where: Handling and storage
    - mode: Reaction with water
      trigger: Water or humid air in contact with the powder
      consequence: Releases flammable gas (H261 in the Stanford SDS).
      severity: high
      source: sama-sds
      where: Section 2, H261
  side_effects:
    - text: On decomposition the powder gives off hydrogen, hafnium oxides, nitrogen oxides and corrosive hafnium halide vapours, according to the Stanford SDS.
      affects: Nearby people and equipment during a fire or hot decomposition
      source: sama-sds
      where: Sections 5 and 10, decomposition products
  handling:
    - text: Handle under inert gas and store under nitrogen or argon, protected from moisture, acids and oxidisers, between 15 and 30 °C (SDS section 7).
      source: sama-sds
      where: Section 7, precautions for safe handling and conditions for safe storage
    - text: Keep away from flames and sparks, and use ground-connected metallic apparatus against electrostatic ignition; in a fire cover only with sand, limestone or a dry Class D powder, and do not use water (Albemarle).
      source: albemarle-ps
      where: Handling and storage
    - text: Avoid dust formation, use local exhaust ventilation and wear eye, face and skin protection, as the Stanford SDS directs.
      source: sama-sds
      where: Sections 6 and 8
  mitigations: []
uses:
  - application: structures
    device: Powder for powder metallurgy and metal foaming
    example: Albemarle sells grade PS as a binding component between grinding agents, carbides, ceramics and metal, as an alloying constituent in powder metallurgy, and as a hydrogen source for the foaming of metals.
    source: albemarle-ps
    where: Application section, first page
  - application: radiation-shielding
    device: Nuclear reactor control rods and shields (research)
    example: A 2026 Imperial College London preprint says hafnium hydride is a promising material for next-generation nuclear reactors, particularly as control rods for fast fission and shielding in fusion systems.
    source: wang2026-arxiv
    where: Abstract
supply:
  - subject: 'Hafnium metal (unwrought): import shares for 2021 to 2024, not production shares'
    abundance: Hafnium resources are associated with those of zircon and baddeleyite; the USGS gives no quantitative estimate of hafnium resources or of primary hafnium production.
    producers:
      - country: Germany
        share_percent: 54
      - country: China
        share_percent: 21
      - country: France
        share_percent: 12
      - country: United Kingdom
        share_percent: 8
    critical_lists: []
    recycling: 'USGS: hafnium metal recycling was minimal.'
    substitutes:
      - 'USGS: boron or cadmium-silver-indium alloys can substitute for hafnium metal in nuclear control rods.'
    source: usgs-mcs2026-zr-hf
    where: 'Zirconium and Hafnium chapter: World Mine Production and Reserves paragraph; Import Sources (2021-24); Recycling; Substitutes'
media: []
documents:
  - title: 'Albemarle technical data sheet: Hafnium Hydride, Grade PS (product 10002021, issued 2024/03/15)'
    type: datasheet
    url: https://www.albemarle.com/sites/default/files/documents/hafnium-hydride-grade-ps.PDF
    year: 2024
  - title: 'Stanford Advanced Materials safety data sheet: Hafnium Hydride, CAS 12770-26-2'
    type: sds
    url: https://samaterials.com/tds/1697119779-hafnium-hydride-sds.pdf
    year: 2023
  - title: 'AZoM: Hafnium Hydride (HfH2) - Properties'
    type: datasheet
    url: https://www.azom.com/article.aspx?ArticleID=2359
    year: 2004
  - title: 'Stanford Advanced Materials: Comparison of Properties and Applications of Different Hafnium-Based Powders'
    type: datasheet
    url: https://powder.samaterials.com/comparison-of-properties-and-applications-of-different-hafnium-based-powders.html
  - title: 'Crystallography Open Database entry 2310960: hafnium dihydride, Sidhu, Acta Crystallographica (1954)'
    type: database
    url: https://www.crystallography.net/cod/2310960.html
    year: 1954
  - title: Wang et al., Microstructural characteristics and growth mechanisms of deuterides in hafnium, arXiv:2603.15420 (Imperial College London)
    type: paper
    url: https://arxiv.org/abs/2603.15420
    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: NIST Atomic Weights and Isotopic Compositions for All Elements (hafnium row)
    type: database
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Hf&all=all
gaps:
  - No flight, vacuum, radiation or thermal-cycling test of hafnium hydride was found in the sources read, so the profile has no space-environment result.
  - 'Density conflicts across sources: 11.4 g/cm3 (Albemarle and AZoM), 11.5 gm/ml (Stanford SDS) and 10.5 g/cm3 (Stanford article, which prints the same figure for hafnium boride). Each value is recorded with its source; none is chosen.'
  - 'Melting behaviour is not settled: Albemarle gives 400 °C or more as melting point or range, AZoM gives decomposition at 300 °C, and the Stanford SDS gives no data. No measured melting point was found.'
  - 'Transport numbers differ: UN 3182 class 4.1 (Albemarle) against UN3132 class 4.3 (4.1) (Stanford SDS). The shipping classification was not resolved.'
  - AZoM also gives HfH1.86 forming above 700 °C. That is a different hydrogen-to-hafnium ratio, so it is not recorded as a property of HfH2.
  - Thermal conductivity, electrical conductivity, elastic modulus, hardness, hydrogen storage capacity and neutron absorption cross-section for HfH2 were not found as values in the sources read. The arXiv preprint describes neutron behaviour and brittleness only in words.
  - The arXiv preprint and the 2015 first-principles paper (PMC4476111) give the HfH2 ground state as tetragonal, and the preprint says c/a is below 1. Their figures are pressure-dependent or calculated, so none is recorded as an ambient value.
  - The 1954 cell card reads H1.98Hf, not exact HfH2, and does not state its temperature or method. The space group is recorded as printed on the card.
  - 'Hydrogen atomic weight was not recorded: the NIST page prints it as an interval, so no single value is entered.'
  - Corrosion rate in humid air and in water was not measured in the sources read; ratings are set to unknown.
  - Manufacturing process for the powder is not described in the sources read.
  - The USGS 2025 critical-minerals status and the EU critical raw materials status for hafnium were not checked.
  - PubChem was not reachable from this run, so no PubChem GHS summary is cited; the hazard data rest on the Stanford SDS and the Albemarle datasheet.
  - No type in the shielding list fits a metal hydride; hydrogen-rich-polymers is used as the closest match, as for lithium hydride.
sources:
  albemarle-ps:
    title: 'Technical data sheet: Hafnium Hydride, Grade PS (Albemarle Corporation, product 10002021)'
    id: CAS 12770-26-2; EC 235-812-6; product 10002021
    url: https://www.albemarle.com/sites/default/files/documents/hafnium-hydride-grade-ps.PDF
    year: 2024
    kind: datasheet
    license: Manufacturer technical data sheet (cited, not reproduced)
  sama-sds:
    title: 'Safety data sheet: Hafnium Hydride (Stanford Advanced Materials), revised 06/02/2023'
    id: CAS 12770-26-2; formula HfH2
    url: https://samaterials.com/tds/1697119779-hafnium-hydride-sds.pdf
    year: 2023
    kind: datasheet
    license: Supplier safety data sheet (cited, not reproduced)
  azom-hfh2:
    title: 'AZoM: Hafnium Hydride (HfH2) - Properties'
    url: https://www.azom.com/article.aspx?ArticleID=2359
    year: 2004
    kind: web
    license: Supplier property summary (cited, not reproduced)
  sama-powders-article:
    title: Comparison of Properties and Applications of Different Hafnium-Based Powders (Stanford Advanced Materials article)
    url: https://powder.samaterials.com/comparison-of-properties-and-applications-of-different-hafnium-based-powders.html
    kind: web
    license: Supplier article (cited, not reproduced)
  cod-2310960:
    title: 'Crystallography Open Database entry 2310960: hafnium dihydride (H1.98Hf), Sidhu, Acta Crystallographica 7 (1954)'
    id: COD 2310960
    url: http://www.crystallography.net/cod/2310960.cif
    year: 1954
    kind: database
    license: CC0 (Crystallography Open Database)
  wang2026-arxiv:
    title: Microstructural characteristics, atomic-scale features, and growth mechanisms of deuterides (hydrides) in hafnium (Wang, McGilvery, Douglas, Wang; Imperial College London)
    id: arXiv:2603.15420
    url: https://arxiv.org/abs/2603.15420
    year: 2026
    kind: paper
    license: arXiv preprint (cited, not reproduced)
  usgs-mcs2026-zr-hf:
    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)
  nist-atomic-weights:
    title: NIST Atomic Weights and Isotopic Compositions for All Elements (hafnium row, standard atomic weight)
    id: NIST Physical Measurement Laboratory
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Hf&all=all
    kind: database
    license: NIST public web page
license: CC-BY-4.0
updated: '2026-11-01'
review:
  status: draft
  method: assistant
  checked_values: 15
  unreachable: 1
  caveats: 4
  note: 'Values read by an AI assistant on 2026-11-01 from the pages and PDFs named in each entry. Unreachable: PubChem (blocked to this run). Caveats: the density values conflict across three sources; the melting figure is a lower bound of unstated meaning; the lattice values are from a 1954 card with no stated method; the particle size D50 conflicts with the sheet''s own grain-size row.'
story:
  recipe:
    line: Hafnium hydride is hafnium combined with hydrogen at one hafnium atom to two hydrogen atoms (HfH2). Albemarle's grade PS powder contains at least 95 % hafnium plus zirconium and at least 1 % hydrogen. The sources read do not describe how the powder is made.
    parts:
      - name: Hafnium
        symbol: Hf
        atoms: 1
        atomic_weight: 178.49
        role: The metal framework. Hafnium atoms form the crystal lattice that holds the hydrogen.
        source: nist-atomic-weights
        where: Hafnium row, standard atomic weight 178.49(2)
      - name: Hydrogen
        symbol: H
        role: Held in the metal lattice. It is released as hydrogen on heating above 300 °C (AZoM) and as a flammable gas on contact with water (Stanford SDS).
  risk_groups:
    - title: For people
      lead: The powder is a flammable solid. The sources agree on the fire hazard but disagree on how hazardous it is to breathe or swallow.
      level: 2
      verdict: Flammable solid, reacts with water
      points:
        - label: Fire and dust
          line: The Albemarle datasheet calls the powder a highly flammable solid with a dust explosion hazard. Its sheet advises a dry Class D extinguishing powder, not water.
        - label: Water
          line: The Stanford safety data sheet says contact with water releases flammable gas. Its hazard statements include H228, flammable solid.
        - label: Health
          line: The Stanford sheet classes the powder as harmful if swallowed, in contact with skin or if inhaled, and as irritating to skin, eyes and airways. It also says its toxicological effects have not been fully investigated.
    - title: If it is heated
      lead: These are decomposition figures from a supplier web page and two datasheets, not tests of a finished part.
      level: 2
      verdict: Hydrogen release above 300 °C
      points:
        - label: Decomposition
          line: AZoM reports that above 300 °C hafnium hydride decomposes and gives off hydrogen. Albemarle gives a melting point or range of 400 °C or more. The sheets do not say whether they describe the same process.
        - label: Ignition
          line: The Stanford sheet gives an autoignition temperature of 190 °C.
    - title: Handling and storage
      points:
        - label: Atmosphere
          line: Handle under inert gas and store under nitrogen or argon, away from moisture, acids and oxidisers.
        - label: Dust
          line: Avoid dust. Use ground-connected metal equipment and keep the powder away from flames and sparks.
  why: 'Hafnium hydride (HfH2) is a grey to black powder. Albemarle''s technical data sheet gives its density as 11.4 g/cm3 at 20 °C. Its hydrogen is what makes it useful in nuclear work: hydrogen slows fast neutrons, and hafnium absorbs them. A 2026 Imperial College London preprint describes it as a promising material for next-generation reactor control rods and for shielding in fusion systems. Commercially it is sold as a powder for powder metallurgy and for foaming metals.'
  uses:
    - where: Powder metallurgy and metal foaming
      line: Albemarle sells grade PS as an alloying constituent in powder metallurgy and as a hydrogen source for the foaming of metals.
    - where: Nuclear research
      line: A 2026 preprint from Imperial College London calls hafnium hydride a promising material for next-generation reactor control rods and for shielding in fusion systems.
  can_do:
    - label: Density
      line: Albemarle gives 11.4 g/cm3 at 20 °C for grade PS powder. AZoM prints 11.4 with no temperature, and the Stanford sheet prints 11.5 gm/ml.
    - label: Melting
      line: Albemarle lists a melting point or range of 400 °C or more. AZoM says it decomposes at 300 °C, and the Stanford sheet has no melting data.
    - label: Crystal cell
      line: A 1954 crystal-structure card for hafnium dihydride, as recorded in the Crystallography Open Database, gives cell edges of 3.461 Å and 4.395 Å and a cell volume of 52.646 Å3.
    - label: Powder size
      line: Grade PS has a D50 of at most 5 µm and a D90 of at most 18 µm, according to Albemarle.
  compare: Hafnium hydride is the hydrogen-loaded form of hafnium. Hafnium metal absorbs neutrons and is used for control rods, while the hydride adds hydrogen, which slows fast neutrons. The Imperial College preprint says bulk hafnium hydride is intrinsically brittle, so it is often used as a composite with hafnium metal. The USGS names boron and cadmium-silver-indium alloys as substitutes for hafnium metal in nuclear control rods. The table below compares density, melting behaviour and hydrogen content.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Melting or decomposition
      benchmark: melting_point
    - label: Hydrogen content
      benchmark: hydrogen_content
  handling:
    - Handle under inert gas and keep the powder dry. The Stanford sheet says to store it under nitrogen or argon.
    - Keep away from flames, sparks and heat, and use ground-connected metal equipment (Albemarle).
    - Do not use water on a fire. The Albemarle sheet calls for a dry Class D powder, sand or limestone.
  good_for:
    - 'Powder metallurgy: Albemarle sells grade PS as an alloying constituent and as a hydrogen source for foaming metals.'
    - 'Shielding research: the 2026 preprint points to control rods and fusion shielding, but gives no shielding values.'
  watch_out:
    - 'Density disagrees across sources: 11.4 g/cm3 (Albemarle and AZoM), 11.5 gm/ml (Stanford SDS) and 10.5 g/cm3 (Stanford article, which prints the same figure for hafnium boride).'
    - 'Melting is not settled: Albemarle gives 400 °C or more as melting point or range, AZoM gives decomposition at 300 °C, and the Stanford SDS gives no data.'
    - 'The powder is highly flammable, with a dust explosion hazard and water reactivity. The transport numbers differ between sheets: UN 3182 in one and UN3132 in the other.'
    - No space-flight, vacuum or radiation test of the powder was found in the sources read.
  verdict: Hafnium hydride is a hydrogen-loaded hafnium powder with a density of 11.4 g/cm3 according to Albemarle. It is sold for powder metallurgy and studied for nuclear shielding. It is a flammable solid that releases flammable gas on contact with water, and the sources disagree on its density and melting behaviour.