spore: profile
id: titanium-hydride
spore_version: 0.2
family: refractory-metals
name: Titanium hydride
abbreviation: TiH2
role: hydrogen reservoir, foaming agent and neutron moderator (titanium, zirconium and hafnium hydrides)
category: metals
type: refractory-metals
summary: |
  This profile covers three metal dihydrides that share one powder form and one behaviour: titanium hydride (TiH2), zirconium hydride (ZrH2) and hafnium hydride (HfH2). Albemarle grade N gives TiH2 a density of 3.91 g/cm3 at 20 °C, and its data sheet describes it as a reservoir for pure hydrogen and as a hydrogen source for foaming metals. Hydrogen comes out of the powder on heating: a KTU paper gives 763 K as the release temperature for untreated TiH2. ZrH2 was used as a moderator in the SNAP reactor program, and an INL and Los Alamos review gives a dissociation pressure of 30 atm at 800 °C for the epsilon phase of ZrH1.85. HfH2 powder releases hydrogen in three steps near 350, 415 and 700 °C (Bangor University).
best_for: Hydrogen reservoirs and foaming agents for metal powder processing (Albemarle grade N and the KTU aluminium foam paper), and zirconium hydride as a moderator with a high moderating ratio (ORNL Table 1)
weakest_at: 'Hydrogen loss on heating: TiH2 releases hydrogen from about 763 K, ZrH2 evolves hydrogen above 300 °C (ATI), and all three powders are flammable with a dust-explosion risk'
identity:
  formula: TiH2 (titanium dihydride), ZrH2 (zirconium dihydride) and HfH2 (hafnium dihydride). Albemarle lists the molecular formula TiH2 for grade N and ZrH2 for grade PS. The Bangor paper writes the hafnium phase as HfH2-x, and the INL review writes zirconium hydride phases as ZrH1.6 and ZrH1.85
  cas: 7704-98-5
  source: albemarle-tih2-n
  where: Title block, CAS-No. row (TiH2, grade N). CAS 7704-99-6 for ZrH2 (grade PS, Albemarle) and 12770-26-2 for HfH2 (Albemarle product page, metadata)
tags:
  environments: []
  stresses:
    - extreme-heat
  applications:
    - propulsion-and-tanks
    - radiation-shielding
    - structures
properties:
  - benchmark: density
    label: Density, TiH2 powder, 20 °C
    value: 3.91
    unit: g/cm3
    scope: material
    conditions:
      temperature: 20 °C
      form: powder, grade N
    method: Density printed in the Albemarle grade N technical data sheet, method OPPTS 830.7300
    status: ground
    source: albemarle-tih2-n
    where: Physical and chemical properties table, Density row
  - benchmark: density
    label: Density, TiH2, 25 °C (supplier SDS)
    value: 3.91
    unit: g/cm3
    scope: material
    conditions:
      temperature: 25 °C (77 °F)
    method: Relative density printed in the Sigma-Aldrich SDS, physical and chemical properties section
    status: ground
    source: sigma-tih2
    where: Physical and chemical properties, item m, Relative density
  - benchmark: density
    label: Hydride density, TiH2, ORNL Table 1
    value: 3.78
    unit: g/cm3
    scope: material
    conditions:
      basis: hydride density as tabulated by ORNL, which cites a reference for the table
    method: Printed in the ORNL Table 1 column Hydride density (g/cm3). It differs from the 3.91 g/cm3 manufacturer values and is kept as printed
    status: ground
    source: ornl-zrh-2020
    where: Table 1, TiH2 row, Hydride density column
  - benchmark: molar_mass
    label: Molar mass, TiH2
    value: 49.88
    unit: g/mol
    scope: material
    conditions:
      basis: molecular weight printed in the supplier SDS, formula H2Ti
    method: Molecular weight printed in the Sigma-Aldrich SDS
    status: ground
    source: sigma-tih2
    where: Composition or ingredients section, Molecular Weight row
  - benchmark: hydrogen_content
    label: Hydrogen content, TiH2 grade N, minimum
    value: 3.8
    unit: '%'
    scope: material
    conditions:
      grade: 'N'
      bound: minimum
    method: Specification minimum printed in the Albemarle grade N data sheet
    status: ground
    source: albemarle-tih2-n
    where: Specification table, Hydrogen row
  - benchmark: melting_point
    label: Melting point range, TiH2 (decomposes before melting)
    value: 400
    bound: lower
    unit: °C
    scope: material
    conditions:
      basis: decomposes before melting
    method: Printed as greater than 400 °C with the note decomposes before melting
    status: ground
    source: albemarle-tih2-n
    where: Physical and chemical properties table, Melting point/range row
  - benchmark: auto_ignition_temperature
    label: Auto-ignition temperature, TiH2 powder
    value: 400
    bound: lower
    unit: °C
    scope: material
    conditions:
      form: powder, grade N, min. 99.9 % below 63 µm
    method: Printed as greater than 400 °C in the Albemarle grade N specification. The Sigma-Aldrich SDS gives no auto-ignition data
    status: ground
    source: albemarle-tih2-n
    where: Specification table, Auto Ignition Temperature row
  - benchmark: hydrogen_release_temperature
    label: Hydrogen release onset, untreated TiH2
    value: 763
    unit: K
    scope: material
    conditions:
      basis: approximately 763 K for untreated TiH2, as cited by the paper from Kennedy et al.
    method: Secondhand figure quoted in the KTU paper introduction. Kept in kelvin as printed
    status: ground
    source: ktu-tih2-foam
    where: Introduction, first paragraph
  - benchmark: volume_change
    label: Volume expansion on hydriding, TiH2
    value: 19
    unit: '%'
    scope: material
    conditions:
      basis: metal to hydride transformation, as printed for TiH2
    method: Printed in the ORNL introduction (e.g., 19% in the case of TiH2)
    status: ground
    source: ornl-zrh-2020
    where: Section 1 Introduction, paragraph on volume expansion during hydriding
  - benchmark: hydrogen_density
    label: Hydrogen density, TiH2
    value: 0.152
    unit: g H/cm3
    scope: material
    conditions:
      basis: mass of hydrogen per volume of hydride, as tabulated
    method: Printed in ORNL Table 1, TiH2 row
    status: ground
    source: ornl-zrh-2020
    where: Table 1, TiH2 row, g H/cm3 column
  - benchmark: moderating_ratio
    label: Moderating ratio, TiH2
    value: 6.3
    unit: '-'
    scope: material
    conditions:
      basis: ratio of macroscopic slowing-down power to macroscopic neutron absorption cross section, as defined in the report
    method: Printed in ORNL Table 1, TiH2 row
    status: ground
    source: ornl-zrh-2020
    where: Table 1, TiH2 row, Moderating ratio column
  - benchmark: density
    label: Density, ZrH2 powder, 25 °C
    value: 5.6
    unit: g/cm3
    scope: material
    conditions:
      temperature: 25 °C
      form: powder, grade PS
    method: Density printed in the Albemarle grade PS technical data sheet, with the note information taken from reference works and the literature
    status: ground
    source: albemarle-zrh-ps
    where: Physical and chemical properties table, Density row
  - benchmark: density
    label: Hydride density, ZrH2, ORNL Table 1
    value: 5.56
    unit: g/cm3
    scope: material
    conditions:
      basis: hydride density as tabulated by ORNL
    method: Printed in ORNL Table 1, ZrH2 row, Hydride density column
    status: ground
    source: ornl-zrh-2020
    where: Table 1, ZrH2 row, Hydride density column
  - benchmark: hydrogen_density
    label: Hydrogen density, ZrH2
    value: 0.122
    unit: g H/cm3
    scope: material
    conditions:
      basis: mass of hydrogen per volume of hydride, as tabulated
    method: Printed in ORNL Table 1, ZrH2 row
    status: ground
    source: ornl-zrh-2020
    where: Table 1, ZrH2 row, g H/cm3 column
  - benchmark: moderating_ratio
    label: Moderating ratio, ZrH2
    value: 55
    unit: '-'
    scope: material
    conditions:
      basis: ratio of macroscopic slowing-down power to macroscopic neutron absorption cross section, as defined in the report
    method: Printed in ORNL Table 1, ZrH2 row. ORNL calls ZrHx the most promising moderator on this ratio
    status: ground
    source: ornl-zrh-2020
    where: Table 1, ZrH2 row, Moderating ratio column
  - benchmark: slowing_down_power
    label: Slowing-down power, ZrH2
    value: 1.45
    unit: '-'
    scope: material
    conditions:
      basis: as tabulated by ORNL, dimensionless
    method: Printed in ORNL Table 1, ZrH2 row
    status: ground
    source: ornl-zrh-2020
    where: Table 1, ZrH2 row, Slowing down power column
  - benchmark: volume_change
    label: Volume expansion on hydriding, ZrH2
    value: 14.3
    unit: '%'
    scope: material
    conditions:
      basis: metal to ZrH2 transformation, as printed
    method: Printed in the ORNL introduction (14.3% in the case of ZrH2)
    status: ground
    source: ornl-zrh-2020
    where: Section 1 Introduction, paragraph on volume expansion during hydriding
  - benchmark: hydrogen_content
    label: Hydrogen content, ZrH2 grade PS, minimum
    value: 1.5
    unit: '%'
    scope: material
    conditions:
      grade: PS
      bound: minimum
    method: Specification minimum printed in the Albemarle grade PS data sheet
    status: ground
    source: albemarle-zrh-ps
    where: Specification table, H row
  - benchmark: hydrogen_content
    label: Hydrogen content, ZrH2 grade G, minimum
    value: 1.9
    unit: '%'
    scope: material
    conditions:
      grade: G
      bound: minimum
    method: Specification minimum printed in the Albemarle grade G data sheet
    status: ground
    source: albemarle-zrh-g
    where: Specification table, H row
  - benchmark: dissociation_pressure
    label: Dissociation pressure, epsilon ZrH1.85 at 800 °C
    value: 30
    unit: atm
    scope: material
    conditions:
      phase: epsilon, ZrH1.85
      temperature: 800 °C
    method: Phase stability entry printed in the INL and Los Alamos overview. The slide gives no further detail
    status: ground
    source: inl-gain-2026
    where: Phase stability slide, epsilon ZrH1.85 entry
  - benchmark: dissociation_pressure
    label: Dissociation pressure, delta ZrH1.6 at 800 °C
    value: 1
    unit: atm
    scope: material
    conditions:
      phase: delta, ZrH1.6
      temperature: 800 °C
    method: Phase stability entry printed in the INL and Los Alamos overview
    status: ground
    source: inl-gain-2026
    where: Phase stability slide, delta ZrH1.6 entry
  - benchmark: hydrogen_evolution_onset
    label: Hydrogen evolution onset, ZrH2
    value: 300
    bound: lower
    unit: °C
    scope: material
    conditions:
      basis: printed as evolves hydrogen above 300 °C
    method: Printed in the ATI safety data sheet, melting point and freezing point row
    status: ground
    source: ati-zrh-sds
    where: Physical and chemical properties table, Melting point/freezing point row
  - benchmark: density
    label: Density, HfH2 powder, 20 °C
    value: 11.4
    unit: g/cm3
    scope: material
    conditions:
      temperature: 20 °C
      form: powder, grade PS (technical grade)
    method: Commercial powder specification printed on the Albemarle product page. It is not a measured value for pure stoichiometric HfH2
    status: ground
    source: albemarle-hfh-ps
    where: Physical and chemical properties table, Density row
  - benchmark: hydrogen_content
    label: Hydrogen content, HfH2 grade PS, minimum
    value: 1
    unit: '%'
    scope: material
    conditions:
      grade: PS
      bound: minimum
    method: Typical specification printed on the Albemarle product page
    status: ground
    source: albemarle-hfh-ps
    where: Specifications list, H min row
  - benchmark: molar_mass
    label: Molar mass, HfH2 grade PS
    value: 180.5
    unit: g/mol
    scope: material
    conditions:
      basis: molecular weight printed on the Albemarle product page
    method: Printed as 180.50 g/mol in the Albemarle physical and chemical properties table
    status: ground
    source: albemarle-hfh-ps
    where: Physical and chemical properties table, Molecular Weight row
  - benchmark: hydrogen_desorption_temperature
    label: Hydrogen desorption step near 350 °C, HfH2-x
    value: 350
    unit: °C
    scope: material
    conditions:
      phase: epsilon, HfH2-x
      method: isochronal heating by thermogravimetry from 25 to 1000 °C
    method: Approximate step temperature printed in the Bangor abstract
    status: ground
    source: bangor-hfh
    where: Abstract, first desorption region
  - benchmark: hydrogen_desorption_temperature
    label: Hydrogen desorption step near 415 °C, HfH2-x
    value: 415
    unit: °C
    scope: material
    conditions:
      phase: delta, HfH1.6-x
      method: isochronal heating by thermogravimetry from 25 to 1000 °C
    method: Approximate step temperature printed in the Bangor abstract
    status: ground
    source: bangor-hfh
    where: Abstract, second desorption region
  - benchmark: hydrogen_desorption_temperature
    label: Hydrogen desorption step near 700 °C, HfH2-x
    value: 700
    unit: °C
    scope: material
    conditions:
      phase: alpha, Hf
      method: isochronal heating by thermogravimetry from 25 to 1000 °C
    method: Approximate step temperature printed in the Bangor abstract
    status: ground
    source: bangor-hfh
    where: Abstract, third desorption region
  - benchmark: activation_energy
    label: Kissinger activation energy, first desorption step, HfH2-x
    value: 150
    unit: kJ/mol
    scope: material
    conditions:
      phase: epsilon, HfH2-x
    method: Approximate Kissinger value printed in the Bangor abstract
    status: ground
    source: bangor-hfh
    where: Abstract, Kissinger analysis sentence
  - benchmark: activation_energy
    label: Kissinger activation energy, second desorption step, HfH2-x
    value: 170
    unit: kJ/mol
    scope: material
    conditions:
      phase: delta, HfH1.6-x
    method: Approximate Kissinger value printed in the Bangor abstract
    status: ground
    source: bangor-hfh
    where: Abstract, Kissinger analysis sentence
  - benchmark: activation_energy
    label: Kissinger activation energy, third desorption step, HfH2-x
    value: 90
    unit: kJ/mol
    scope: material
    conditions:
      phase: alpha, Hf
    method: Approximate Kissinger value printed in the Bangor abstract
    status: ground
    source: bangor-hfh
    where: Abstract, Kissinger analysis sentence
corrosion:
  - environment: Oxidizing agents, acids and cold hydrofluoric acid
    headline: TiH2 resists most reagents but oxidizing agents, acids and cold hydrofluoric acid attack it
    effect: Albemarle says that like titanium metal, TiH2 resists most chemical reagents, but is attacked at elevated temperature by oxidizing agents and acids, and is attacked by cold hydrofluoric acid solutions. The rating moderate is the assistant's judgement from this statement. The sheet gives no test numbers.
    rating: moderate
    conditions:
      basis: statement in the handling section of the grade N data sheet
    source: albemarle-tih2-n
    where: Handling and storage section
  - environment: Elevated temperature at low pressure
    headline: TiH2 gives off hydrogen on heating, so hydrogen loss must be planned for
    effect: Albemarle says that at elevated temperatures and low pressures the generation of hydrogen must be considered. The KTU paper gives 763 K as the release temperature for untreated TiH2 and reports that pre-treatment at 753 K for 30 min was best for aluminium foam. The rating moderate is the assistant's judgement; neither source rates it.
    rating: moderate
    conditions:
      basis: heating in the foaming process, and at low pressure per the data sheet
    source: ktu-tih2-foam
    where: Introduction and Section 3.1 Structural features
  - environment: Air, fine powder at room temperature
    headline: Fine ZrH2 powder burns slowly in air and must be kept from flames and sparks
    effect: 'Albemarle grade PS calls the powder a highly flammable solid with a dust explosion hazard that burns slowly in air. The sheet gives the handling rules: keep away from flames, sparks and heat sources, and use ground-connected apparatus to avoid ignition by electrostatic discharge. The rating moderate is the assistant''s judgement.'
    rating: moderate
    conditions:
      basis: handling statement in the grade PS data sheet, no test data
    source: albemarle-zrh-ps
    where: Handling row
  - environment: Heating above 300 °C, and reversible hydrogen loss in vacuum
    headline: ZrH2 evolves hydrogen above 300 °C and its reaction runs back and forth in vacuum
    effect: The ATI sheet says ZrH2 evolves hydrogen above 300 °C. Albemarle grade PS says it yields hydrogen by a reversible reaction in vacuum. The INL overview says the hydrogen pressure in the cladding gives a higher burst risk for ZrH than for YH, and that no thermal testing data exist for ZrH in cladding. The rating moderate is the assistant's judgement.
    rating: moderate
    conditions:
      basis: heating and vacuum statements from two suppliers, and the INL overview of reactor moderators
    source: ati-zrh-sds
    where: Physical and chemical properties table, Melting point/freezing point row
  - environment: Air, fine powder at room temperature
    headline: Fine HfH2 powder burns slowly in air and must not be fought with water
    effect: Albemarle grade PS for hafnium hydride calls it a highly flammable solid with a dust explosion hazard that burns slowly in air. Its fire guidance is to cover only with sand, limestone or a dry class D powder, and the sheet says do not use water. The rating moderate is the assistant's judgement.
    rating: moderate
    conditions:
      basis: handling instructions on the product page, no test data
    source: albemarle-hfh-ps
    where: Handling Instructions
  - environment: Heating from 25 to 1000 °C
    headline: HfH2 gives off hydrogen in three steps near 350, 415 and 700 °C
    effect: The Bangor study heats epsilon HfH2-x powder and finds three hydrogen release regions, one for each phase (epsilon HfH2-x, delta HfH1.6-x and alpha Hf). The study says hydrogen release degrades the moderating function, so the phase change matters for a moderator in service. The rating moderate is the assistant's judgement.
    rating: moderate
    conditions:
      basis: isochronal heating by thermogravimetry and X-ray diffraction; atmosphere not stated in the abstract
    source: bangor-hfh
    where: Abstract, desorption regions and degradation sentence
risks:
  hazards:
    - text: 'Sigma-Aldrich SDS: flammable solid, Category 1, hazard statement H228 (flammable solid), with the signal word Danger, and precautionary statement P241 (use explosion-proof electrical, ventilating and lighting equipment)'
      ghs:
        - H228
      source: sigma-tih2
      where: Section 2 Hazards identification; Section 2 Precautionary statements
    - text: 'Albemarle grade N: highly flammable solid, dust explosion hazard. In case of fire, cover with dry sand or dry chemical, never with water, carbon dioxide or halocarbon'
      ghs: []
      source: albemarle-tih2-n
      where: Handling and storage section
    - text: 'ATI safety data sheet for zirconium hydride: flammable solids, Category 1, signal word Danger'
      ghs: []
      source: ati-zrh-sds
      where: Section 2 Hazards identification, Label elements
    - text: 'Albemarle hafnium hydride: highly flammable solid, dust explosion hazard. Do not use water on a fire'
      ghs: []
      source: albemarle-hfh-ps
      where: Handling Instructions
  failure_risks:
    - mode: Dust cloud or powder ignition
      trigger: Powder dispersed in air near a flame, spark or electrostatic discharge
      consequence: Albemarle warns of a dust explosion hazard and of sudden ignition by electrostatic discharge for the ZrH2 powder, and gives the same warning for TiH2 and HfH2
      severity: high
      source: albemarle-zrh-ps
      where: Handling row
    - mode: Hydrogen release on heating, TiH2
      trigger: Heating above about 763 K in a melt or at low pressure
      consequence: The hydrogen released forms bubbles that become pores in aluminium foam. Early release before the aluminium melts causes crack-like pores and loss of foaming control
      severity: moderate
      source: ktu-tih2-foam
      where: Introduction and Section 3 Results and discussion
    - mode: Cladding burst, ZrH moderator
      trigger: High-temperature operation of a ZrH moderator in cladding
      consequence: The INL overview says ZrH has a higher plenum pressure and a higher burst risk than YH, and that no thermal testing data for ZrH in cladding are known
      severity: high
      source: inl-gain-2026
      where: Main operational differences between YH and ZrH slide
    - mode: Loss of moderating function, HfH2
      trigger: Heating to about 350 °C and above
      consequence: The Bangor abstract says hydrogen release leads to degradation of the moderating function of hafnium hydride
      severity: moderate
      source: bangor-hfh
      where: Abstract, first paragraph
  side_effects:
    - text: At high temperature the hydrides release hydrogen, which is flammable. Albemarle and ATI both say that water on a fire can cause an explosion
      affects: Equipment and people near a fire of hydride powder
      source: ati-zrh-sds
      where: Section 5 Extinguishing media
  handling:
    - text: Keep away from flames, sparks and heat sources. Use ground-connected metallic apparatus to avoid sudden ignition by electrostatic discharge. Wear gloves, a face shield or goggles (ZrH2 grade PS, HfH2 product page)
      source: albemarle-zrh-ps
      where: Handling row
    - text: Use explosion-proof electrical, ventilating and lighting equipment (P241), and provide exhaust ventilation where dust is formed
      source: sigma-tih2
      where: Section 7 Handling and storage
    - text: Packed dry under argon in tins of at most 5 kg (ZrH2 grade PS)
      source: albemarle-zrh-ps
      where: Packaging row
  mitigations:
    - text: Cover fires only with dry sand, limestone or a class D dry powder. Do not use water, carbon dioxide or halocarbon (TiH2 grade N, HfH2 product page)
      source: albemarle-tih2-n
      where: Handling and storage section
uses:
  - application: propulsion-and-tanks
    device: Titanium hydride as a reservoir for pure hydrogen
    example: Albemarle lists TiH2 as a reservoir for pure hydrogen and says it yields hydrogen at elevated temperatures in a reversible reaction. The ORNL report says metal hydrides have been seen as an efficient, low-risk option for dense hydrogen storage since the late 1970s.
    source: albemarle-tih2-n
    where: Application section; Handling row
  - application: radiation-shielding
    device: Zirconium hydride moderator in SNAP and TRIGA reactors
    example: The ORNL report names the SNAP program and TRIGA research reactors as users of ZrHx as a high-performance moderator. It ranks zirconium hydride as the most promising moderator of the hydrides it tabulates, on the moderating ratio.
    source: ornl-zrh-2020
    where: Section 1 Introduction, paragraph on moderator examples
  - application: radiation-shielding
    device: Hafnium hydride neutron moderator and attenuator for compact reactors
    example: The Bangor University abstract calls hafnium hydride a candidate neutron moderator and attenuator for compact nuclear reactors, where hydrogen release would reduce its moderating performance.
    source: bangor-hfh
    where: Abstract, first sentence
  - application: structures
    device: Titanium hydride as a foaming agent for closed-cell aluminium foam
    example: The KTU paper adds 1.5 wt% TiH2 to melted commercially pure aluminium and stirs it to make closed-cell foam with a porosity of about 80 %. The best pre-treatment was 753 K for 30 min.
    source: ktu-tih2-foam
    where: Section 2 Experimental, and Section 3.1 Structural features
  - application: structures
    device: Hafnium and zirconium hydride grades as hydrogen sources for foaming metals and as alloying additions in powder metallurgy
    example: Albemarle lists the hafnium hydride grade PS and the zirconium hydride grade PS as hydrogen sources for foaming metals and as alloying constituents in powder metallurgy.
    source: albemarle-hfh-ps
    where: Applications paragraph
supply:
  - subject: Titanium (feedstock for TiH2)
    producers:
      - country: China
        share_percent: 70.3
        year: 2025
      - country: Japan
        share_percent: 14.3
        year: 2025
      - country: Russia
        share_percent: 6.8
        year: 2025
      - country: Kazakhstan
        share_percent: 4.3
        year: 2025
      - country: Saudi Arabia
        share_percent: 3.2
        year: 2025
    critical_lists:
      - list: EU critical raw materials list (titanium metal, as shown on the European Commission page)
        listed: true
    recycling: 'USGS 2026: consumption data for titanium scrap metal for the titanium metal industry were withheld, because survey responses were limited.'
    substitutes: []
    source: usgs-mcs2026-titanium
    where: 'World Sponge Metal Production table, 2025 column (world total 370,000 t); shares calculated by Space Mushroom from the printed tonnages. Recycling paragraph. Lists: EU page (see sources)'
  - subject: Zirconium (feedstock for ZrH2)
    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
      - country: Senegal
        share_percent: 5.8
        year: 2025
    critical_lists:
      - list: EU critical raw materials list (zirconium is not in the list printed on the European Commission page)
        listed: false
    recycling: 'USGS 2026: companies in Oregon and Utah recycled zirconium from new scrap generated during metal production. Refractories are often recycled but could not be quantified.'
    substitutes: []
    source: usgs-mcs2026-zirconium-hafnium
    where: World Mine Production and Reserves table, zirconium mineral concentrates, 2025 column (world total 1,200 thousand t, gross weight); shares calculated by Space Mushroom from the printed tonnages. These are mine shares of concentrate, not sponge metal
  - subject: Hafnium (feedstock for HfH2)
    producers: []
    critical_lists:
      - list: EU critical raw materials list (hafnium, as shown on the European Commission page)
        listed: true
    recycling: 'USGS 2026: hafnium metal recycling was minimal.'
    substitutes:
      - 'USGS 2026: boron or cadmium-silver-indium alloys can substitute for hafnium metal in nuclear control rods, and zirconium can be used interchangeably with hafnium in certain superalloys.'
    source: usgs-mcs2026-zirconium-hafnium
    where: Hafnium paragraph of the USGS 2026 summary. The table gives no world primary hafnium production (the USGS text says the data were not available)
media: []
documents:
  - title: Sigma-Aldrich safety data sheet, titanium hydride (archived copy hosted by Purdue University)
    type: sds
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/SDS/titanium%20hydride%20%20-%20Aldrich.pdf
  - title: Albemarle technical data sheet, Titanium Hydride, Grade N (issue 2021-07-22)
    type: datasheet
    url: https://www.albemarle.com/sites/default/files/2025-10/titanium-hydride-grade-n.PDF
    year: 2021
  - title: Albemarle technical data sheet, Titanium Hydride, Grade G
    type: datasheet
    url: https://www.albemarle.com/sites/default/files/documents/titanium-hydride-grade-g.PDF
  - title: Albemarle technical data sheet, Zirconium Hydride, Grade PS
    type: datasheet
    url: https://www.albemarle.com/sites/default/files/documents/zirconium-hydride-grade-ps.PDF
  - title: Albemarle technical data sheet, Zirconium Hydride, Grade G
    type: datasheet
    url: https://www.albemarle.com/sites/default/files/documents/zirconium-hydride-grade-g.PDF
  - title: Albemarle product page, Hafnium Hydride, Grade PS
    type: datasheet
    url: https://www.albemarle.com/au/en/product/hafnium-hydride-grade-ps
  - title: ATI safety data sheet, SAC050 Zirconium Hydride (EU, Rev 2)
    type: sds
    url: https://www.atimaterials.com/safety-data-sheets/Documents/EuropeanUnion/EU-EN/SAC/SAC050%20Zirconium%20Hydride%20EU-EN%20Rev2.pdf
  - title: ORNL/SPR-2020/1672, Fabrication of Zirconium Hydride with Controlled Hydrogen Loading (Table 1, metal hydride properties)
    type: report
    url: https://info.ornl.gov/sites/publications/Files/Pub146553.pdf
  - title: INL GAIN, High Temperature Moderator Overview (2026 MRP Review), Los Alamos slides
    type: report
    url: https://gain.inl.gov/content/uploads/4/2026/03/16-Kohnert_HighTemperatureModeratorOverview_2026-MRP-Review.pdf
    year: 2026
  - title: Pollard et al., Hydrogen desorption kinetics of hafnium hydride powders (Bangor University research output)
    type: paper
    url: https://research.bangor.ac.uk/en/publications/hydrogen-desorption-kinetics-of-hafnium-hydride-powders/
  - title: Zhang et al., The Influence of Titanium Hydride Pretreatment on the Compressive Properties of Aluminum Foam, Materials Science (Medziagotyra) 20(4), 2014
    type: paper
    url: https://matsc.ktu.lt/index.php/MatSc/article/view/6082/4359
    year: 2014
  - title: NIST atomic weights and isotopic compositions, Titanium
    type: database
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Ti&ascii=html&isotype=some
  - title: PubChem compound record, titanium hydride (CID 197094), molecular formula and weight
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/197094
  - title: USGS Mineral Commodity Summaries 2026, Titanium and Titanium Dioxide
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-titanium.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
gaps:
  - Hardness, thermal conductivity, thermal expansion and elastic constants of TiH2, ZrH2 and HfH2 were not found in any page read in this run. They are left out.
  - 'Melting point of ZrH2 and HfH2: no fetched source. The Albemarle sheets give decomposition, not melting.'
  - Crystal structure and space group were not read for TiH2 or ZrH2 in a fetched page, so the identity block has no crystal_system. The HfH2 structure is only in a first-principles paper, which is not used.
  - Theoretical density of stoichiometric HfH2 and ZrH2 were not found. The HfH2 value of 11.4 g/cm3 is a commercial powder specification.
  - 'Density conflict: TiH2 values are 3.91 g/cm3 (Albemarle, Sigma) and 3.78 g/cm3 (ORNL Table 1). Both are kept, each with its source.'
  - Crustal abundance of titanium, zirconium and hafnium was not read in a fetched page in this run, so supply has no abundance entry.
  - 'USGS 2025 List of Critical Minerals: the USGS page could not be read in this run. Only the EU list is recorded for titanium, zirconium and hafnium.'
  - 'World primary hafnium production: the USGS 2026 summary says the data were not available, so no producer shares are given for hafnium.'
  - 'Production route of TiH2, ZrH2 and HfH2 (hydriding of the metal with hydrogen): the ORNL report gives the general method only, so the recipe names the metal and hydrogen without a process temperature.'
  - 'Atomic weight of hydrogen: NIST gives the standard atomic weight as the interval [1.00784, 1.00811]. The recipe uses 1.008, which lies inside the interval.'
  - 'Ageing under radiation, long-term vacuum storage, and space flight: no source read in this run. The SNAP reactor history is taken from the ORNL introduction only, not from a flight record.'
  - 'Hazard statements (H codes) for ZrH2 and HfH2: only the ATI sheet (flammable solids, Category 1, Danger) and the Albemarle handling text were read. American Elements'' H315, H319 and H335 were seen in a search snippet only and are not used.'
  - 'Designations (UNS, EN, ASTM and others): no fetched page printed one for these hydrides, so none are listed. The CAS numbers are in identity.cas and in the properties source notes.'
  - Hydrogen release curves for TiH2 (the 450 to 560 C and 500 to 670 C pre-treatment figures) were seen in search snippets only and are not used. The 763 K figure is from the KTU paper, which cites Kennedy et al.
  - Patent statements on ZrH dissociation pressure at 600 to 800 C in SNAP reactors were seen in search snippets only and are not used.
  - 'Property names not in property-canon.yaml: hydrogen_content, hydrogen_density, hydrogen_release_temperature, hydrogen_evolution_onset, hydrogen_desorption_temperature, auto_ignition_temperature, slowing_down_power, moderating_ratio, dissociation_pressure, activation_energy, volume_change and molar_mass. Canonical units are used where the source printed them.'
  - 'Environments: no source read supports a space environment tag, so tags.environments is empty.'
sources:
  sigma-tih2:
    title: Sigma-Aldrich, Safety data sheet for titanium hydride (archived copy hosted by Purdue University)
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/SDS/titanium%20hydride%20%20-%20Aldrich.pdf
    kind: datasheet
    license: supplier safety data sheet, cited not reproduced
  albemarle-tih2-n:
    title: Albemarle, Titanium Hydride, Grade N, technical data sheet (issue 2021-07-22)
    url: https://www.albemarle.com/sites/default/files/2025-10/titanium-hydride-grade-n.PDF
    kind: datasheet
    year: 2021
    license: supplier technical data sheet, cited not reproduced
  albemarle-tih2-g:
    title: Albemarle, Titanium Hydride, Grade G, technical data sheet
    url: https://www.albemarle.com/sites/default/files/documents/titanium-hydride-grade-g.PDF
    kind: datasheet
    license: supplier technical data sheet, cited not reproduced
  albemarle-zrh-ps:
    title: Albemarle, Zirconium Hydride, Grade PS, technical data sheet
    url: https://www.albemarle.com/sites/default/files/documents/zirconium-hydride-grade-ps.PDF
    kind: datasheet
    license: supplier technical data sheet, cited not reproduced
  albemarle-zrh-g:
    title: Albemarle, Zirconium Hydride, Grade G, technical data sheet
    url: https://www.albemarle.com/sites/default/files/documents/zirconium-hydride-grade-g.PDF
    kind: datasheet
    license: supplier technical data sheet, cited not reproduced
  albemarle-hfh-ps:
    title: Albemarle, Hafnium Hydride, Grade PS, product page with specifications and handling instructions
    url: https://www.albemarle.com/au/en/product/hafnium-hydride-grade-ps
    kind: datasheet
    license: supplier product page, cited not reproduced
  ati-zrh-sds:
    title: ATI, SAC050 Zirconium Hydride, safety data sheet (EU, Rev 2)
    url: https://www.atimaterials.com/safety-data-sheets/Documents/EuropeanUnion/EU-EN/SAC/SAC050%20Zirconium%20Hydride%20EU-EN%20Rev2.pdf
    kind: datasheet
    license: supplier safety data sheet, cited not reproduced
  ornl-zrh-2020:
    title: Hu et al., ORNL/SPR-2020/1672, Fabrication of Zirconium Hydride with Controlled Hydrogen Loading (Oak Ridge National Laboratory)
    url: https://info.ornl.gov/sites/publications/Files/Pub146553.pdf
    kind: report
    license: US Department of Energy report
  inl-gain-2026:
    title: Kohnert, High Temperature Moderator Overview, 2026 MRP Review (INL GAIN, Los Alamos slides)
    url: https://gain.inl.gov/content/uploads/4/2026/03/16-Kohnert_HighTemperatureModeratorOverview_2026-MRP-Review.pdf
    kind: report
    year: 2026
    license: DOE GAIN presentation, cited not reproduced
  bangor-hfh:
    title: Pollard et al., Hydrogen desorption kinetics of hafnium hydride powders (Bangor University research output)
    url: https://research.bangor.ac.uk/en/publications/hydrogen-desorption-kinetics-of-hafnium-hydride-powders/
    kind: paper
    license: journal article, abstract cited not reproduced
  ktu-tih2-foam:
    title: Zhang et al., The Influence of Titanium Hydride Pretreatment on the Compressive Properties of Aluminum Foam, Materials Science (Medziagotyra) 20(4), 2014, doi 10.5755/j01.ms.20.4.6082
    url: https://matsc.ktu.lt/index.php/MatSc/article/view/6082/4359
    kind: paper
    year: 2014
    license: open-access journal article, cited not reproduced
  usgs-mcs2026-titanium:
    title: USGS Mineral Commodity Summaries 2026, Titanium and Titanium Dioxide
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-titanium.pdf
    kind: report
    license: public domain (USGS)
  usgs-mcs2026-zirconium-hafnium:
    title: USGS Mineral Commodity Summaries 2026, Zirconium and Hafnium
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-zirconium-hafnium.pdf
    kind: report
    license: public domain (USGS)
  ec-crm:
    title: European Commission, Critical raw materials (list of critical raw materials, including titanium metal and hafnium)
    url: https://single-market-economy.ec.europa.eu/sectors/raw-materials/areas-specific-interest/critical-raw-materials_en
    kind: web
    license: European Commission web page
  nist-atomic-weights:
    title: NIST, Atomic weights and isotopic compositions for hydrogen, titanium, zirconium and hafnium
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Ti&ascii=html&isotype=some
    kind: database
    license: NIST public data
  pubchem-tih2:
    title: PubChem compound record, titanium hydride (CID 197094)
    url: https://pubchem.ncbi.nlm.nih.gov/compound/197094
    kind: database
    license: public domain (NCBI)
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 31
  unreachable: 3
  caveats: 9
  note: 'Written in this run from pages read in this run: the Sigma-Aldrich TiH2 SDS, Albemarle TiH2 grades N and G, Albemarle ZrH grades PS and G, Albemarle HfH2 product page, the ATI ZrH2 SDS, the ORNL ZrH report (Table 1), the INL GAIN moderator slides, the Bangor HfH2 abstract, the KTU TiH2 foaming paper, the USGS 2026 titanium and zirconium-hafnium summaries, the EC critical raw materials page, NIST atomic weights and PubChem CID 197094. Unreachable: USGS 2025 critical minerals page (no readable text), and the NASA NTRS record for the 2021 moderator paper (download failed). Hafnium production and ZrH2 melting point not found.'
story:
  recipe:
    line: TiH2, ZrH2 and HfH2 each have one metal atom and two hydrogen atoms per formula unit. The metal is bonded to hydrogen in a hydride lattice that expands on hydriding (ORNL). The common preparation is direct reaction of the metal with hydrogen gas, guided by the phase diagram (ORNL); no process temperature for these grades was sourced.
    parts:
      - name: Titanium
        symbol: Ti
        atoms: 1
        atomic_weight: 47.867
        role: Metal in TiH2. NIST gives 47.867 (1).
      - name: Zirconium
        symbol: Zr
        atoms: 1
        atomic_weight: 91.224
        role: Metal in ZrH2. NIST gives 91.224 (2).
      - name: Hafnium
        symbol: Hf
        atoms: 1
        atomic_weight: 178.49
        role: Metal in HfH2. NIST gives 178.49 (2).
      - name: Hydrogen
        symbol: H
        atoms: 2
        atomic_weight: 1.008
        role: Stored in the lattice and released on heating. NIST gives [1.00784, 1.00811] as the standard atomic weight, so 1.008 is used.
  risk_groups:
    - title: For people
      level: 0
      verdict: Flammable powder with a dust-explosion risk
      lead: The three powders are sold as highly flammable solids with a dust-explosion hazard. The supplier sheets give the handling rules and the fire guidance.
      points:
        - label: Ignition
          line: The Sigma-Aldrich SDS classifies TiH2 as a flammable solid with H228. Keep it away from flames, sparks and heat sources.
        - label: Dust
          line: Albemarle warns of a dust explosion hazard for TiH2, ZrH2 and HfH2. Avoid dust and provide exhaust ventilation where dust is formed.
        - label: Fire
          line: Cover a fire only with dry sand, limestone or a class D powder. Do not use water, carbon dioxide or halocarbon.
    - title: If a powder or part heats up
      lead: These results come from the sources listed, not from incidents.
      points:
        - label: TiH2
          line: The KTU paper gives 763 K as the release temperature for untreated TiH2, and says that pre-treatment at 753 K for 30 min is the most suitable for aluminium foam.
        - label: ZrH2
          line: ATI says ZrH2 evolves hydrogen above 300 °C. The INL overview gives a 30 atm dissociation pressure for the epsilon phase at 800 °C.
        - label: HfH2
          line: The Bangor study finds hydrogen release near 350, 415 and 700 °C in three steps.
    - title: Handling and storage
      points:
        - label: Storage
          line: Store dry and closed. ZrH2 grade PS is packed dry under argon in tins of at most 5 kg.
        - label: Electrostatic discharge
          line: Use ground-connected metallic apparatus to avoid sudden ignition by electrostatic discharge (Albemarle).
  why: Titanium hydride and its zirconium and hafnium relatives store a large amount of hydrogen in a dense solid. Albemarle sells TiH2 as a reservoir for pure hydrogen, a hydrogen source for foaming metals and an alloying aid in powder metallurgy. ZrH2 has long been the moderator of choice for compact reactors, because it combines a high moderating ratio (55 in ORNL Table 1) with hydrogen density. HfH2 is studied as a moderator and attenuator for compact reactors. The trade is that all three release hydrogen when heated, so their use depends on keeping the hydrogen in place.
  uses:
    - where: Hydrogen reservoir
      line: Albemarle says TiH2 is used as a reservoir for pure hydrogen and yields hydrogen at elevated temperatures in a reversible reaction. The ORNL report describes metal hydrides as a low-risk option for dense hydrogen storage.
    - where: Reactor moderators
      line: ORNL names the SNAP program and TRIGA reactors as users of zirconium hydride as a moderator. The Bangor abstract calls hafnium hydride a candidate moderator and attenuator for compact reactors.
    - where: Foaming and powder metallurgy
      line: The KTU paper foams commercially pure aluminium with 1.5 wt% TiH2 to a porosity of about 80 %. Albemarle lists the ZrH2 and HfH2 grades as hydrogen sources for foaming metals and as alloying additions in powder metallurgy.
  can_do:
    - label: Hydrogen density
      benchmark: hydrogen_density
      value: '0.152'
      line: TiH2 holds 0.152 g of hydrogen per cm3 of hydride, and ZrH2 holds 0.122 g per cm3, both from ORNL Table 1.
    - label: Moderation
      benchmark: moderating_ratio
      value: '55'
      line: In ORNL Table 1, ZrH2 has a moderating ratio of 55 against 6.3 for TiH2. The ratio measures slowing-down power against neutron absorption.
    - label: Density
      benchmark: density
      value: '3.91'
      line: TiH2 has a density of 3.91 g/cm3 at 20 °C (Albemarle). ZrH2 is 5.6 g/cm3 at 25 °C and HfH2 is 11.4 g/cm3 at 20 °C (Albemarle grades).
  compare: The three hydrides are light and dense in hydrogen content, but they differ in density by a factor of about three. TiH2 is the least dense, which suits powder metallurgy. ZrH2 has the highest moderating ratio of the three tabulated in ORNL and it is the moderator in SNAP-type reactors. HfH2 is the densest and releases hydrogen in steps near 350, 415 and 700 °C. The three are compared on density, hydrogen content and hydrogen density because those are the values that all sources give.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Hydrogen content
      benchmark: hydrogen_content
    - label: Hydrogen density
      benchmark: hydrogen_density
  handling:
    - Keep the powder away from flames, sparks and heat. Use ground-connected equipment against electrostatic ignition (Albemarle).
    - Avoid dust and use explosion-proof electrical equipment and exhaust ventilation where dust forms (Sigma-Aldrich P241).
    - Fight a fire with dry sand, limestone or a class D powder. Do not use water (Albemarle, ATI).
  good_for:
    - Hydrogen reservoirs and foaming agents, where a dense, stable powder that gives off hydrogen on heating is wanted (Albemarle, KTU).
    - Compact-reactor moderators, where ZrH2 has a high moderating ratio (ORNL Table 1) and HfH2 is studied as a moderator and attenuator (Bangor).
  watch_out:
    - 'Hydrogen loss on heating: TiH2 near 763 K, ZrH2 above 300 °C, and HfH2 in steps near 350, 415 and 700 °C.'
    - Dust explosion and flammability. All three are flammable solids and the powder is dangerous in a dust cloud.
    - 'The density of TiH2 differs by source: 3.91 g/cm3 from Albemarle and Sigma, and 3.78 g/cm3 in ORNL Table 1.'
  verdict: Metal hydride powders are a good hydrogen store and foaming agent, and ZrH2 is a proven reactor moderator. They give off hydrogen on heating and burn as dust, so each use needs the hydrogen kept in place and the powder kept from ignition. Melting, hardness, thermal conductivity and flight data are not sourced here.