Gadolinium Gd

spore: profile
id: gadolinium
spore_version: 0.2
family: rare-earth-metals
name: Gadolinium
abbreviation: Gd
role: neutron absorber, magnetocaloric material and scintillator host
category: metals
type: heavy-metals
summary: |
  Gadolinium is the element Gd (atomic number 64), a silvery, ductile rare-earth metal with a density of 7.895 g/cm3 at 25 °C and a melting point of 1313 °C. It is found only in oxidized form in minerals such as monazite and bastnasite, with an abundance of 6.2 mg/kg in the Earth's crust. Metal is made by calcium reduction of its oxide or salts at 1450 °C under argon. Its strongest neutron capture (259,000 barns for the isotope Gd-157) drives its use as a neutron absorber in reactor control and shielding. It is also the magnetocaloric reference material near room temperature, and its Curie transition at 293.4 K is sharp. The metal is flammable as fine chips or dust and releases hydrogen on contact with water, so it needs dry, inert handling.
best_for: Neutron absorption (259,000 barns for Gd-157) and room-temperature magnetocaloric research near its 293.4 K Curie transition (Wikipedia)
weakest_at: Fine chips and dust that ignite, and metal that releases hydrogen on contact with water (Apollo SDS, Lesker MSDS)
identity:
  formula: Gd (element, atomic number 64); unalloyed metal, sold as a 99 % (2N) disc by Goodfellow
  cas: 7440-54-2
  source: pubchem-gd
  where: Other Identifiers, CAS entry (PubChem CID 23982); EC number 231-162-2 is printed in the Apollo SDS, Section 1.1
tags:
  environments:
    - low-earth-orbit
  applications:
    - radiation-shielding
    - electronics-and-chips
    - thermal-control
properties:
  - benchmark: density
    label: Density, gadolinium disc (99 % purity, as rolled)
    value: 7.895
    unit: g/cm3
    scope: material
    conditions:
      temperature: 25 °C
      purity: 99% (2N)
      form: disc, as rolled
    method: Typical value printed in a supplier product datasheet
    status: ground
    source: goodfellow-gd
    where: Physical Properties table, row Density (7.895@25°C)
  - benchmark: density
    label: Density, gadolinium
    value: 7.899
    unit: g/cm3
    scope: material
    conditions:
      temperature: 20 °C
      unit_in_source: 7.899 g/cm3
    method: Value printed in the Wikipedia infobox, which cites a reference for it
    status: ground
    source: wikipedia-gd
    where: Infobox, row Density (at 20° C) 7.899 g/cm3
  - benchmark: melting_point
    label: Melting point, gadolinium disc (99 % purity)
    value: 1313
    unit: °C
    scope: material
    conditions:
      pressure: not stated
      purity: 99% (2N)
    method: Value printed in a supplier product datasheet
    status: ground
    note: The Lesker MSDS (1991) and the ESPI MSDS (2012) print 1313 °C too. Wikipedia gives 1312 °C.
    source: goodfellow-gd
    where: Thermal Properties table, row Melting point (1313)
  - benchmark: melting_point
    label: Melting point, gadolinium
    value: 1312
    unit: °C
    scope: material
    conditions:
      pressure: not stated
      unit_in_source: 1585 K (1312 °C, 2394 °F)
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-gd
    where: Infobox, row Melting point, 1585 K (1312 °C, 2394 °F)
  - benchmark: boiling_point
    label: Boiling point, gadolinium
    value: 3266
    unit: °C
    scope: material
    conditions:
      pressure: not stated
    method: Value printed in a supplier product datasheet
    status: ground
    note: The Wikipedia infobox gives 3273 °C, and PubChem gives the same 3273 °C. The sources differ by 7 °C, so both are kept.
    source: goodfellow-gd
    where: Physical Properties table, row Boiling point (3266)
  - benchmark: boiling_point
    label: Boiling point, gadolinium (Wikipedia)
    value: 3273
    unit: °C
    scope: material
    conditions:
      pressure: not stated
      unit_in_source: 3546 K (3273 °C, 5923 °F)
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-gd
    where: Infobox, row Boiling point, 3546 K (3273 °C, 5923 °F)
  - benchmark: specific_heat
    label: Specific heat capacity, gadolinium disc
    value: 230
    unit: J/(kg·K)
    scope: material
    conditions:
      temperature: 25 °C
      purity: 99% (2N)
    method: Typical value printed in a supplier product datasheet
    status: ground
    source: goodfellow-gd
    where: Thermal Properties table, row Specific heat (230@25°C)
  - benchmark: specific_heat
    label: Specific heat capacity, gadolinium (Wikipedia)
    value: 235.485
    unit: J/(kg·K)
    scope: material
    conditions:
      temperature: not stated in the infobox
    method: Value printed in the Wikipedia infobox
    status: ground
    note: The Wikipedia infobox gives this value with no temperature, and the supplier value is at 25 °C.
    source: wikipedia-gd
    where: Infobox, row Specific heat capacity 235.485 J/(kg·K)
  - benchmark: thermal_conductivity
    label: Thermal conductivity, gadolinium disc
    value: 10.5
    unit: W/(m·K)
    scope: material
    conditions:
      temperature: 0 to 100 °C
      purity: 99% (2N)
    method: Typical value printed in a supplier product datasheet
    status: ground
    source: goodfellow-gd
    where: Thermal Properties table, row Thermal conductivity (10.5@0-100°C)
  - benchmark: thermal_conductivity
    label: Thermal conductivity, gadolinium (Wikipedia)
    value: 10.6
    unit: W/(m·K)
    scope: material
    conditions:
      temperature: not stated in the infobox
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-gd
    where: Infobox, row Thermal conductivity 10.6 W/(m⋅K)
  - benchmark: cte
    label: Coefficient of thermal expansion, gadolinium disc
    value: 6.4
    unit: ppm/K
    scope: material
    conditions:
      temperature: 0 to 100 °C
      purity: 99% (2N)
      unit_in_source: 6.4 x10-6 K-1
    method: Typical value printed in a supplier product datasheet
    status: ground
    source: goodfellow-gd
    where: Thermal Properties table, row Coefficient of thermal expansion (6.4@0-100°C)
  - benchmark: cte
    label: Coefficient of thermal expansion, gadolinium crystal average at 100 °C
    value: 11.1
    unit: ppm/K
    scope: material
    conditions:
      temperature: 100 °C
      crystal_form: hexagonal close-packed single crystal, averaged over axes (alpha_average = alpha_V/3)
      unit_in_source: 11.1×10−6/K
    method: Value printed in the Wikipedia infobox and footnote a; the footnote gives the a-axis value as 6.6 and the c-axis value as 20.1 (x10-6/K) at 100 °C, so the average is strongly axis-dependent
    status: ground
    note: At 20 °C the Wikipedia infobox gives a crystal average of −21.4 x10-6/K, a negative value that comes from the strongly anisotropic c axis (−83.0 x10-6/K at 20 °C). It is not a polycrystal figure, so it is not entered.
    source: wikipedia-gd
    where: Infobox, row Thermal expansion, 11.1×10−6/K (at 100 °C); footnote a
  - benchmark: elastic_modulus
    label: Tensile modulus, gadolinium disc
    value: 56.2
    unit: GPa
    scope: material
    conditions:
      temperature: not stated in the table
      purity: 99% (2N)
      material_condition: polycrystalline, as rolled
    method: Typical value printed in a supplier product datasheet
    status: ground
    source: goodfellow-gd
    where: Mechanical Properties table, row Tensile modulus (56.2)
  - benchmark: elastic_modulus
    label: Young's modulus, gadolinium alpha form
    value: 54.8
    unit: GPa
    scope: material
    conditions:
      temperature: not stated in the infobox
      form: alpha (hexagonal close-packed) form
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-gd
    where: Infobox, row Young's modulus, alpha form 54.8 GPa
  - benchmark: elastic_modulus
    label: Young's modulus, gadolinium
    value: 55
    unit: GPa
    scope: material
    conditions:
      temperature: not stated
    method: Value printed on the WebElements physical-properties page
    status: ground
    source: webelements-gd
    where: Elastic properties, row Young's modulus 55 GPa
  - benchmark: shear_modulus
    label: Shear modulus (rigidity), gadolinium alpha form
    value: 21.8
    unit: GPa
    scope: material
    conditions:
      temperature: not stated in the infobox
      form: alpha (hexagonal close-packed) form
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-gd
    where: Infobox, row Shear modulus, alpha form 21.8 GPa
  - benchmark: shear_modulus
    label: Rigidity modulus, gadolinium
    value: 22
    unit: GPa
    scope: material
    conditions:
      temperature: not stated
    method: Value printed on the WebElements physical-properties page
    status: ground
    source: webelements-gd
    where: Elastic properties, row Rigidity modulus 22 GPa
  - benchmark: bulk_modulus
    label: Bulk modulus, gadolinium disc
    value: 39.1
    unit: GPa
    scope: material
    conditions:
      temperature: not stated in the table
      purity: 99% (2N)
    method: Typical value printed in a supplier product datasheet
    status: ground
    source: goodfellow-gd
    where: Mechanical Properties table, row Bulk modulus (39.1)
  - benchmark: bulk_modulus
    label: Bulk modulus, gadolinium alpha form
    value: 37.9
    unit: GPa
    scope: material
    conditions:
      temperature: not stated in the infobox
      form: alpha (hexagonal close-packed) form
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-gd
    where: Infobox, row Bulk modulus, alpha form 37.9 GPa
  - benchmark: poissons_ratio
    label: Poisson's ratio, gadolinium disc
    value: 0.26
    unit: '-'
    scope: material
    conditions:
      temperature: not stated in the table
      purity: 99% (2N)
    method: Typical value printed in a supplier product datasheet
    status: ground
    source: goodfellow-gd
    where: Mechanical Properties table, row Poisson's ratio (0.26)
  - benchmark: poissons_ratio
    label: Poisson's ratio, gadolinium alpha form
    value: 0.259
    unit: '-'
    scope: material
    conditions:
      temperature: not stated in the infobox
      form: alpha (hexagonal close-packed) form
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-gd
    where: Infobox, row Poisson ratio, alpha form 0.259
  - benchmark: vickers_hardness
    label: Vickers hardness, gadolinium
    value: 570
    unit: MPa
    scope: material
    conditions:
      temperature: not stated
    method: Value printed on the WebElements physical-properties page, given as MN m-2 (equal to MPa)
    status: ground
    note: No canonical name exists for hardness in the property file, so vickers_hardness is a new name and is listed in gaps.
    source: webelements-gd
    where: Hardnesses, row Vickers hardness 570 MN m-2
  - benchmark: vickers_hardness
    label: Vickers hardness range, gadolinium
    value: 510
    value_high: 950
    unit: MPa
    scope: material
    conditions:
      temperature: not stated in the infobox
      note_on_range: the infobox gives a range, not a single test value
    method: Range printed in the Wikipedia infobox
    status: ground
    note: No canonical name exists for hardness, so vickers_hardness is a new name and is listed in gaps. The range is given by Wikipedia without test conditions.
    source: wikipedia-gd
    where: Infobox, row Vickers hardness 510–950 MPa
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, gadolinium disc, as rolled
    value: 193
    unit: MPa
    scope: material
    conditions:
      temper: as rolled
      purity: 99% (2N)
      material_condition: polycrystalline
      temperature: not stated in the table
    method: Typical value printed in a supplier product datasheet
    status: ground
    source: goodfellow-gd
    where: Mechanical Properties table, row Tensile strength (193)
  - benchmark: yield_strength
    label: Yield strength, gadolinium disc, as rolled
    value: 179
    unit: MPa
    scope: material
    conditions:
      temper: as rolled
      purity: 99% (2N)
      material_condition: polycrystalline
      temperature: not stated in the table
    method: Typical value printed in a supplier product datasheet
    status: ground
    source: goodfellow-gd
    where: Mechanical Properties table, row Yield strength (179)
  - benchmark: electrical_resistivity
    label: Electrical resistivity, gadolinium disc
    value: 134
    unit: µOhm·cm
    scope: material
    conditions:
      temperature: 20 °C
      purity: 99% (2N)
    method: Typical value printed in a supplier product datasheet
    status: ground
    source: goodfellow-gd
    where: Electrical Properties table, row Electrical resistivity (134@20°C)
  - benchmark: electrical_resistivity
    label: Electrical resistivity, gadolinium alpha form
    value: 1.31
    unit: µΩ·m
    scope: material
    conditions:
      temperature: not stated in the infobox
      form: alpha polycrystalline form
    method: Value printed in the Wikipedia infobox
    status: ground
    note: 1.310 µΩ·m equals 131 µΩ·cm, which WebElements prints as 131 x10-8 Ω m, and it is about 2 % below the Goodfellow figure of 134 µOhm·cm at 20 °C.
    source: wikipedia-gd
    where: Infobox, row Electrical resistivity, alpha poly 1.310 µΩ⋅m
  - benchmark: curie_temperature
    label: Ferromagnetic to paramagnetic transition, gadolinium
    value: 293.4
    unit: K
    scope: material
    conditions:
      transition: ferromagnetic to paramagnetic
      pressure: not stated
    method: Value printed in the Wikipedia infobox, row Magnetic ordering
    status: ground
    note: The supplier datasheet gives a Curie temperature of about 292 K, and the Wikipedia text says about 20 °C. PubChem prints 292.7 °C, which is a units error, so it is not entered.
    source: wikipedia-gd
    where: Infobox, row Magnetic ordering, ferromagnetic–paramagnetic transition at 293.4 K
  - benchmark: thermal_neutron_cross_section
    label: Thermal neutron capture cross-section, gadolinium-157
    value: 259000
    unit: barn
    scope: material
    conditions:
      neutron: thermal
      isotope: Gd-157 (not natural gadolinium)
      unit_in_source: about 259,000 barns
    method: Value printed in the Wikipedia text for the isotope with the highest thermal-neutron capture cross-section among stable nuclides
    status: ground
    note: Wikipedia gives about 259,000 barns for Gd-157 only. Natural gadolinium is a mix of isotopes, so this figure is not the value for the metal as supplied. No canonical name exists for this property, so thermal_neutron_cross_section is a new name and is listed in gaps.
    source: wikipedia-gd
    where: Section Atomic properties / Isotopes, paragraph on the isotope gadolinium-157
corrosion:
  - environment: Dry air at room temperature
    headline: Metallic gadolinium is relatively stable in dry air, unlike most other rare-earth metals.
    effect: Wikipedia says that unlike the other rare-earth elements, metallic gadolinium is relatively stable in dry air. It forms a black oxide coating only slowly.
    rating: low
    conditions:
      temperature: room temperature
      atmosphere: dry air
    source: wikipedia-gd
    where: Chemical properties section, first paragraph on air and moisture
  - environment: Moist air
    headline: Gadolinium tarnishes quickly in moist air, and the loose oxide spalls off and exposes fresh metal.
    effect: Wikipedia says it tarnishes quickly in moist air to form a loosely adhering Gd2O3 layer, which spalls off and exposes more surface to oxidation. The Lesker MSDS and the PubChem record also say it tarnishes in moist air.
    rating: moderate
    conditions:
      atmosphere: moist air
      temperature: not stated
    source: wikipedia-gd
    where: Chemical properties section, paragraph on moist air and the oxide layer
  - environment: Cold and hot water
    headline: Gadolinium reacts slowly with cold water and quite quickly with hot water, forming gadolinium hydroxide.
    effect: Wikipedia says the metal is strongly electropositive and reacts slowly with cold water and quite quickly with hot water to form gadolinium(III) hydroxide. The Apollo SDS (2024) classes the chips as releasing flammable gas on contact with water (H260 and H261).
    rating: moderate
    conditions:
      temperature: cold and hot water
      form: metal, chips and fines
    source: wikipedia-gd
    where: Chemical properties section, paragraph on water
  - environment: Dilute acids
    headline: Gadolinium dissolves in dilute acid.
    effect: PubChem gives the solubility as soluble in dilute acid. The Lesker MSDS says the metal reacts slowly with water, and the Apollo SDS warns against segregation from water and alcohol.
    rating: moderate
    conditions:
      acid: dilute, not named
      temperature: not stated
    source: pubchem-gd
    where: Chemical and Physical Properties, Experimental Properties, Solubility
  - environment: Halogens and strong oxidizers
    headline: Gadolinium is incompatible with halogens and strong oxidizers, which can make it burn vigorously.
    effect: The Lesker MSDS lists strong oxidizers and halogens as incompatible materials and halogens as a condition contributing to instability. PubChem says that rare earth metals in general burn vigorously in halogen vapors above 392 °F, which is a group statement and not a test on gadolinium.
    rating: severe
    conditions:
      atmosphere: halogen vapour or strong oxidizer
      temperature: above 392 °F for the group statement
    source: lesker-gd-msds
    where: Section VII Reactivity Data, Incompatibility; PubChem group statement is in Safety and Hazards, Stability and Reactivity
risks:
  hazards:
    - text: 'PubChem GHS summary (ECHA C&L notifications, 63 company reports): H228 flammable solid in 15.9 % of the notified classifications and H261 in contact with water releases flammable gases in 66.7 %, with signal word Danger. 11 of 63 reports say the substance does not meet GHS criteria.'
      ghs:
        - H228
        - H261
      source: pubchem-gd
      where: Safety and Hazards, Hazards Identification, GHS Classification
    - text: 'Apollo Scientific SDS for gadolinium chips, 12 mm and below (issue 10/05/2024): classified under CLP as flammable solid (H228), substances which in contact with water emit flammable gases, Category 1 (H260, may ignite spontaneously) and Category 2 (H261). Signal word Danger, shipping name metallic substance, water-reactive, n.o.s.'
      ghs:
        - H228
        - H260
        - H261
      source: apollo-gd-sds
      where: Section 2.1 Classification and 2.2 Label elements; Section 1.1 Proper shipping name
    - text: Kurt J. Lesker Company MSDS (1991) lists the metal as a DOT flammable solid, UN 1325, and says it is flammable in the form of dust or fine powder.
      ghs: []
      source: lesker-gd-msds
      where: Section IV Fire and Explosion Hazard Data; Section IX Transportation Requirements
    - text: ESPI Metals MSDS (2012) gives an OSHA permissible exposure limit of 15 mg/m3 for dust and 5 mg/m3 for respirable particulates, and an ACGIH TLV of 10 mg/m3 total dust.
      ghs: []
      source: espi-gd-msds
      where: Section II Hazardous Ingredients, OSHA/PEL and ACGIH/TLV rows
    - text: Wikipedia says water-soluble gadolinium(III) salts are highly toxic to mammals, while chelated compounds are largely excreted by healthy kidneys. PubChem's toxicity summary says no human or animal exposure data were found for the element.
      ghs: []
      source: wikipedia-gd
      where: Health and toxicity paragraph; PubChem Toxicity Summary is cited through pubchem-gd
  failure_risks:
    - mode: Fire in chips, fines and dust
      trigger: Gadolinium chips, turnings, powder or dust exposed to air, or to heat and sparks
      consequence: The metal is a flammable solid (H228) and the ESPI sheet warns that a fine powder can cause a dust explosion. Apollo says it may heat spontaneously, so fines need the same controls as a reactive metal.
      severity: critical
      source: apollo-gd-sds
      where: Section 2.1 (H228), Section 10.1 Reactivity (may heat spontaneously); Lesker Section IV; ESPI Section IV Unusual Fire and Explosion Hazards
    - mode: Hydrogen release on contact with water
      trigger: Metal in contact with water or moisture, or with alcohols
      consequence: Water releases flammable gas that may ignite spontaneously (H260 in the Apollo SDS), and PubChem's notifications record H261 in 66.7 % of reports. Water also feeds a fire on the metal, so it must not be used on the burning metal.
      severity: critical
      source: apollo-gd-sds
      where: Section 2.2 hazard statements H260 and H261; Section 10.2 Chemical stability; Section 5.1
    - mode: Loss of surface by oxide spalling
      trigger: Exposure to moist air at room temperature
      consequence: The loose oxide layer spalls off, which exposes fresh metal to further oxidation and thins the part over time.
      severity: moderate
      source: wikipedia-gd
      where: Chemical properties section, paragraph on moist air
    - mode: Reaction with halogens or strong oxidizers
      trigger: Contact with halogens or strong oxidizers
      consequence: The Lesker MSDS lists these as incompatible materials and as conditions that contribute to instability. The group-level PubChem note says the rare earth metals burn vigorously in halogen vapors.
      severity: moderate
      source: lesker-gd-msds
      where: Section VII Reactivity Data
  side_effects:
    - text: Soluble gadolinium(III) ions are highly toxic to mammals, and gadolinium-based MRI contrast agents have been linked to nephrogenic systemic fibrosis in some patients (PubChem).
      affects: Patients given gadolinium-based MRI contrast agents, and anyone handling soluble Gd salts
      source: pubchem-gd
      where: Safety and Hazards, Hazards Summary; Wikipedia health paragraph
  handling:
    - text: Keep the metal dry and in a closed container. The Apollo SDS calls for storage in a dry place, in a closed container, under inert gas, with protection from moisture (P231+P232 and P402+P404).
      source: apollo-gd-sds
      where: Section 2.2 precautionary statements; Section 7.2 Conditions for safe storage
    - text: The Lesker MSDS says to handle the metal in a dry box to prevent contact with air or moisture, and to keep containers closed.
      source: lesker-gd-msds
      where: Section VIII Other Protective Equipment and Section IX Special Precautions
    - text: Do not use water on a gadolinium fire. ESPI says to use a dry powder or Class D extinguisher. Lesker says to use a metal-fire agent such as G-1 powder. The Apollo SDS recommends dry chemical, soda ash or lime for small fires, and dry sand for large fires.
      source: espi-gd-msds
      where: Section IV Extinguishing Media; Apollo SDS Section 5.1
    - text: If dust is being generated, wear a half-mask air-purifying respirator, and use local exhaust ventilation, as the Lesker MSDS advises.
      source: lesker-gd-msds
      where: Section VIII Respiratory Protection and Ventilation
  mitigations: []
uses:
  - application: radiation-shielding
    device: Neutron absorber in some nuclear reactors and neutron radiography shielding
    example: Wikipedia says that gadolinium as a metal or salt absorbs neutrons and is used for shielding in neutron radiography and in nuclear reactors. It is an emergency shut-down measure in some CANDU reactors and a burnable poison in nuclear marine propulsion. PubChem records its oxide in the control rods of some reactors.
    source: wikipedia-gd
    where: Uses, Neutron absorber section; PubChem Use and Manufacturing, Sources/Uses
  - application: electronics-and-chips
    device: Gamma-ray detector on the GRID CubeSat (GAGG:Ce scintillator, a gadolinium garnet)
    example: The GRID detector uses four GAGG:Ce scintillators, which are Gd2Al2Ga3O12 doped with cerium, coupled to silicon photomultiplier arrays. The second unit was launched into a Sun-synchronous orbit at 500 km on 6 November 2020 and has accumulated more than 300 h of on-orbit data. This is a gadolinium compound, not the metal.
    source: grid-gagg-arxiv
    where: Abstract (GRID mission and detector) and the paragraph on the second detector's launch and on-orbit observation
  - application: thermal-control
    device: Magnetic refrigerator using the magnetocaloric effect (research)
    example: Gadolinium is the standard reference material for magnetic refrigeration near room temperature, with a large magnetocaloric effect near its Curie temperature. Wikipedia says gadolinium-based materials such as Gd5(SixGe1-x)4 are currently the most promising magnetocaloric materials. The Goodfellow sheet also lists magnetic refrigeration among its applications. This is laboratory and industrial research, not a flown system.
    source: wikipedia-gd
    where: Section Magnetic refrigeration via magnetocalorics
supply:
  - subject: Rare earths (gadolinium is not reported separately by USGS)
    abundance: 6.2 mg/kg in the Earth's crust (Wikipedia, which cites a crust figure; PubChem gives 6.2 ppm)
    producers:
      - country: China
        share_percent: 69.2
        year: 2025
      - country: United States
        share_percent: 13.1
        year: 2025
      - country: Australia
        share_percent: 7.4
        year: 2025
      - country: Burma
        share_percent: 5.6
        year: 2025
    critical_lists: []
    recycling: 'USGS: limited quantities of rare earths were recovered from batteries, permanent magnets and fluorescent lamps.'
    substitutes:
      - 'USGS: substitutes are available for many rare-earth applications but generally are less effective.'
    source: usgs-ree-2026
    where: 'World Mine Production table, 2025 (world total 390,000 t, rounded; shares calculated by Space Mushroom from China 270,000, United States 51,000, Australia 29,000 and Burma 22,000). Reserves: China 44,000,000 t of more than 75,000,000 t world total. Recycling and Substitutes sections. Abundance: Wikipedia Occurrence section.'
  - subject: Rare-earth compounds and metals imported into the United States
    producers:
      - country: China
        share_percent: 71
        year: 2024
      - country: Malaysia
        share_percent: 13
        year: 2024
      - country: Japan
        share_percent: 5
        year: 2024
      - country: Estonia
        share_percent: 5
        year: 2024
    critical_lists: []
    recycling: ''
    substitutes: []
    source: usgs-ree-2026
    where: Import Sources (2021–24) paragraph, China 71%, Malaysia 13%, Japan 5%, Estonia 5%; the year column shows the end of the 2021 to 2024 range. Net import reliance for compounds and metals in 2025e is 67 %, from the Salient Statistics table.
  - subject: Gadolinium oxide price (99.99 % minimum) and export controls
    producers: []
    critical_lists: []
    recycling: ''
    substitutes: []
    source: usgs-ree-2026
    where: 'Salient Statistics, price row Gadolinium oxide, 99.99% minimum, 30 dollars per kg in 2025e (28 in 2024). Events, Trends and Issues: in April 2025 China tightened export controls to include alloys, compounds, metals and oxides of gadolinium.'
documents:
  - title: 'USGS Mineral Commodity Summaries 2026: Rare Earths'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-rare-earths.pdf
    year: 2026
  - title: 'Wikipedia: Gadolinium'
    type: database
    url: https://en.wikipedia.org/wiki/Gadolinium
    year: 2026
  - title: PubChem compound record for gadolinium (CID 23982), including ECHA C&L Inventory classification
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/23982
    year: 2026
  - title: Gadolinium Disc, 99 % (2N), as rolled (Goodfellow product datasheet)
    type: datasheet
    url: https://www.goodfellow.com/uk/gadolinium-disc-group
  - title: 'WebElements: Gadolinium, physical properties (University of Sheffield)'
    type: datasheet
    url: https://winter.group.shef.ac.uk/webelements/gadolinium/physics.html
  - title: 'Safety data sheet: Gadolinium, chips 12mm and down, Apollo Scientific IN1801 (issue 10/05/2024)'
    type: sds
    url: https://store.apolloscientific.co.uk/storage/msds/IN1801_msds.pdf
    year: 2024
  - title: 'Kurt J. Lesker Company material safety data sheet: Gadolinium metal (revised 1/28/91)'
    type: sds
    url: https://www.lesker.com/newweb/deposition_materials/pdf/msds_gd.pdf
    year: 1991
  - title: 'ESPI Metals material safety data sheet: Gadolinium (2012 print), copy hosted by Purdue PRIMELab'
    type: sds
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/Retired%20SDS%20and%20MSDS/2017%20removed%20safety%20sheets/MSDS%20updated%20to%20SDS/gadolinium%20%20-%20ESPI.pdf
    year: 2012
  - title: Gamma-Ray Integrated Detectors (GRID) CubeSat detector, arXiv 2104.14228
    type: paper
    url: https://arxiv.org/pdf/2104.14228
    year: 2021
gaps:
  - 'Gadolinium-specific production: USGS reports rare earths as one group, so the producer shares above are for all rare earths, not for gadolinium. World output of pure gadolinium (about 400 tonnes a year, Wikipedia) has no year or source in the page and is not entered.'
  - 'Critical-mineral listing: the USGS 2025 critical minerals list and the EU critical raw materials list were not opened for gadolinium, so critical_lists is empty. Heavy rare earths are a separate USGS chapter that was not read.'
  - 'Space flight of gadolinium metal: the only flight use found is GAGG:Ce, a gadolinium garnet, on the GRID nanosatellites. No flown gadolinium magnetic refrigerator was confirmed in the sources read. The magnetocaloric entry is ground research only.'
  - 'Natural-gadolinium thermal neutron cross-section: the sources read give only the Gd-157 isotope value (about 259,000 barns). The natural-mix value was not found in an opened source.'
  - Vickers hardness and thermal neutron cross-section are entered under new names (vickers_hardness, thermal_neutron_cross_section) because the property file has no canonical name for them. Hardness is printed in MPa by WebElements and as a range by Wikipedia; the Goodfellow value of 55 kgf/mm2 was not converted.
  - Electrical resistivity disagrees by about 2 % between Goodfellow (134 µOhm·cm at 20 °C) and Wikipedia (1.310 µΩ·m, no temperature), and both are entered with their conditions.
  - 'Boiling point: Wikipedia and PubChem give 3273 °C, while Goodfellow and ESPI give 3266 °C. Both are entered.'
  - 'Curie temperature: PubChem prints 292.7 °C, which is a units slip for about 292.7 K, and is not entered. The Wikipedia value of 293.4 K is used.'
  - Mechanical strength is for an as-rolled 99 % disc from one supplier. No annealed, cast or high-temperature strength data were found in an opened source.
  - Corrosion data are qualitative (Wikipedia, PubChem and the MSDS sheets). No measured weight-gain or corrosion-rate figure for gadolinium in air or water was found.
  - 'Hazard data: the classifications differ between the PubChem notifications (H228 and H261 on a fraction of reports), the Apollo SDS (H228, H260 and H261) and the older Lesker and ESPI sheets, which have no GHS statements. The form (chips, powder or foil) matters and was not separated in every source.'
  - 'Environment: the GRID detector is in low Earth orbit, but no source tested gadolinium metal itself in vacuum, radiation or thermal cycling. Environment tags are set only for the GRID use.'
  - Lesker and ESPI sheets are 1991 and 2012 prints, and the ESPI sheet is a copy hosted by Purdue. The American Elements page returned an access block and was not read.
  - The rare-earth ignition statement from PubChem (rare earth metals ignite in air at 302 to 356 °F) covers rare earth metals as a group and is not a test on gadolinium, so it is not entered as a value.
sources:
  usgs-ree-2026:
    title: 'Mineral Commodity Summaries 2026: Rare Earths (USGS)'
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-rare-earths.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  wikipedia-gd:
    title: Gadolinium (Wikipedia)
    url: https://en.wikipedia.org/wiki/Gadolinium
    year: 2026
    kind: web
    license: CC BY-SA 4.0 (cited, not reproduced)
  pubchem-gd:
    title: 'PubChem compound record: Gadolinium (CID 23982), including ECHA C&L Inventory classification'
    id: CAS 7440-54-2
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/23982/JSON
    kind: database
    license: PubChem (NCBI), public domain; sections attributed to ECHA, Sax and others
  goodfellow-gd:
    title: Gadolinium Disc, 99 % (2N), as rolled (Goodfellow product datasheet)
    url: https://www.goodfellow.com/uk/gadolinium-disc-group
    kind: datasheet
    license: supplier web page (cited, not reproduced)
  webelements-gd:
    title: 'WebElements: Gadolinium, physical properties (University of Sheffield)'
    url: https://winter.group.shef.ac.uk/webelements/gadolinium/physics.html
    kind: database
    license: WebElements, cited not reproduced
  apollo-gd-sds:
    title: 'Safety Data Sheet: Gadolinium, chips 12mm & down (Apollo Scientific IN1801, issue 10/05/2024)'
    id: IN1801
    url: https://store.apolloscientific.co.uk/storage/msds/IN1801_msds.pdf
    year: 2024
    kind: datasheet
    license: supplier safety data sheet, cited not reproduced
  lesker-gd-msds:
    title: 'Kurt J. Lesker Company material safety data sheet: Gadolinium metal (1/28/91)'
    url: https://www.lesker.com/newweb/deposition_materials/pdf/msds_gd.pdf
    year: 1991
    kind: datasheet
    license: supplier safety data sheet, cited not reproduced
  espi-gd-msds:
    title: 'ESPI Metals material safety data sheet: Gadolinium (2012 print), copy hosted by Purdue PRIMELab'
    id: CAS 7440-54-2
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/Retired%20SDS%20and%20MSDS/2017%20removed%20safety%20sheets/MSDS%20updated%20to%20SDS/gadolinium%20%20-%20ESPI.pdf
    year: 2012
    kind: datasheet
    license: supplier safety data sheet, cited not reproduced
  grid-gagg-arxiv:
    title: The Gamma-Ray Integrated Detectors (GRID) CubeSat detector (arXiv 2104.14228)
    url: https://arxiv.org/pdf/2104.14228
    year: 2021
    kind: paper
    license: arXiv preprint, cited not reproduced
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 29
  unreachable: 2
  caveats: 6
  note: 'Read by an AI assistant on 2026-10-26 from the pages and PDFs named in each entry. Unreachable: American Elements gadolinium page (access block), Stanford Advanced Materials gadolinium page (404). Caveats: most physical values come from one supplier (Goodfellow) and one encyclopedia (Wikipedia); the mechanical strengths are for an as-rolled disc; supply shares are for all rare earths, not gadolinium; the boiling point and resistivity differ between sources; the hazard classifications differ by form and by date.'
story:
  risk_groups:
    - title: For people
      lead: The hazard is in the metal's form. The sources read give little human toxicity data for solid gadolinium, but chips and fines are flammable, and soluble gadolinium salts are toxic.
      level: 1
      verdict: Form-dependent
      points:
        - label: Chips and dust
          line: The Apollo SDS classifies chips as a flammable solid (H228) and warns of spontaneous heating (H260). ESPI warns that the fine powder can cause a dust explosion.
        - label: Water
          line: Contact with water releases hydrogen, which can ignite spontaneously (H260), and PubChem records H261 in 66.7 % of its notifications.
        - label: Dust limits
          line: The OSHA permissible exposure limit is 15 mg/m3 for dust and 5 mg/m3 for respirable particulates, and the ACGIH TLV is 10 mg/m3 total dust (ESPI and Lesker sheets).
        - label: Soluble salts
          line: Wikipedia says water-soluble gadolinium(III) salts are highly toxic to mammals. The MRI agents use chelated forms that are largely excreted by healthy kidneys.
    - title: If it fails
      lead: 'The sources give four failure routes: a fire in chips or dust, hydrogen release on contact with water, oxide spalling in moist air, and reaction with halogens.'
      points:
        - label: Fire
          line: A fire in fines needs dry, Class D or dry-powder agents, and water is not to be used on the burning metal (ESPI, Lesker, Apollo).
        - label: Moist air
          line: Gadolinium tarnishes quickly in moist air, and the loose oxide layer spalls off and exposes fresh metal (Wikipedia).
        - label: Halogens
          line: The Lesker MSDS lists halogens and strong oxidizers as incompatible, and says the metal is a flammable solid in dust form.
    - title: Handling and storage
      points:
        - label: Keep it dry
          line: Store dry, in a closed container, under inert gas, and protect it from moisture (Apollo SDS). Handle in a dry box (Lesker MSDS).
        - label: Fire agents
          line: Use dry powder or a Class D extinguisher (ESPI), a metal-fire agent (Lesker) or dry sand for large fires (Apollo). Do not use water on the metal itself.
  why: Gadolinium is a rare-earth metal whose main property is its strong capture of thermal neutrons. Its isotope Gd-157 captures neutrons about 259,000 barns, and that drives its use in reactor control and neutron shielding. In the ferromagnetic range near room temperature it also shows a large magnetocaloric effect, which is why it is the standard reference material for magnetic refrigeration research. Its space record is limited to a gadolinium garnet scintillator on the GRID nanosatellites, not to the metal.
  uses:
    - where: Reactor and neutron shielding
      line: Wikipedia says gadolinium absorbs neutrons and is used for shielding in neutron radiography and in nuclear reactors, including as an emergency shut-down measure in some CANDU reactors.
    - where: Gamma-ray detection in orbit
      line: The GRID nanosatellites carry GAGG:Ce scintillators, a gadolinium garnet. The second unit has flown in a Sun-synchronous orbit at 500 km since 6 November 2020, and it has returned more than 300 h of data.
    - where: Magnetic refrigeration research
      line: Gadolinium is the standard reference for magnetic refrigeration near room temperature. Its Curie transition is at 293.4 K, and gadolinium alloys are studied for a tunable transition temperature.
  can_do:
    - label: Absorb neutrons
      value: 259000 barns
      line: Gd-157 has a thermal-neutron capture cross-section of about 259,000 barns, the highest among stable nuclides in the Wikipedia text.
    - label: Stay ferromagnetic near room temperature
      value: 293.4 K
      benchmark: curie_temperature
      line: The ferromagnetic to paramagnetic transition is at 293.4 K (Wikipedia), and the supplier sheet gives about 292 K.
    - label: Weight
      value: 7.895 g/cm3
      benchmark: density
      line: Density is 7.895 g/cm3 at 25 °C for a 99 % disc (Goodfellow), and 7.899 g/cm3 at 20 °C in the Wikipedia infobox.
    - label: Melting
      value: 1313 °C
      benchmark: melting_point
      line: Melting point is 1313 °C for a 99 % disc (Goodfellow). Wikipedia gives 1312 °C.
    - label: Stiffness
      value: 56.2 GPa
      benchmark: elastic_modulus
      line: The tensile modulus of an as-rolled 99 % disc is 56.2 GPa (Goodfellow). WebElements gives 55 GPa.
    - label: Heat conduction
      value: 10.5 W/(m·K)
      benchmark: thermal_conductivity
      line: Thermal conductivity is 10.5 W/(m·K) from 0 to 100 °C (Goodfellow), and 10.6 W/(m·K) in the Wikipedia infobox.
  compare: Gadolinium is a dense metal, at 7.895 g/cm3 for the Goodfellow disc, with a melting point of 1313 °C. Its thermal conductivity of 10.5 W/(m·K) is modest for a metal, and its tensile strength of 193 MPa as rolled is low for a structural metal. Its neutron capture is the property that matters most for its uses. It tarnishes in moist air and reacts with water, so it needs dry handling. No comparison profile is carried in this file, so the rows below list gadolinium values only.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Melting point
      benchmark: melting_point
    - label: Thermal conductivity
      benchmark: thermal_conductivity
  recipe:
    line: Gadolinium is a single-element metal (Gd). Wikipedia says the metal is made by heating its oxide or salts with calcium at 1450 °C in argon, or by reducing molten GdCl3 with another metal to give sponge. It occurs in minerals such as monazite and bastnasite, which are opened with acid and separated from the other rare earths.
    parts:
      - name: Gadolinium
        symbol: Gd
        atoms: 1
        atomic_weight: 157.249
        role: The whole material. The Goodfellow disc is 99 % (2N) pure, and Wikipedia says separated gadolinium usually carries impurities of other rare earths.
  handling:
    - Keep the metal dry and sealed under inert gas, and avoid moisture (Apollo SDS).
    - Use a dry box for handling and keep containers closed (Lesker MSDS).
    - Do not use water on a fire. Use dry powder or a Class D extinguisher (ESPI), or dry sand for large fires (Apollo).
    - Wear a half-mask respirator and use local exhaust when dust is generated (Lesker MSDS).
  good_for:
    - 'Neutron absorption: Gd-157 has a thermal-neutron capture cross-section of about 259,000 barns (Wikipedia).'
    - 'Magnetic refrigeration research: the Curie transition is at 293.4 K, close to room temperature (Wikipedia).'
    - 'Scintillator host: GAGG:Ce detectors have flown on the GRID nanosatellites (arXiv 2104.14228).'
  watch_out:
    - Chips and dust are flammable, and the fine powder can explode as dust (Apollo SDS, ESPI).
    - Water releases flammable hydrogen, and the metal tarnishes quickly in moist air (Apollo SDS, Wikipedia).
    - 'Supply is concentrated: China produced about 69 % of world rare-earth mine output in 2025, and China''s April 2025 export controls include gadolinium metal, alloys and oxides (USGS).'
    - Most figures come from one supplier and one encyclopedia, and the hazard classes differ between sources.
  verdict: Gadolinium is a neutron absorber and a room-temperature magnetocaloric reference, with a density of 7.895 g/cm3 and a melting point of 1313 °C. Its space record is a gadolinium garnet detector on the GRID nanosatellites, not the metal. The metal needs dry handling because its chips and dust burn and its contact with water releases hydrogen.