Terbium Tb

spore: profile
id: terbium
spore_version: 0.2
family: rare-earth-metals
name: Terbium
abbreviation: Tb
role: green phosphor activator, magnetostrictive alloy component (Terfenol-D) and Faraday rotator garnet
category: metals
type: heavy-metals
summary: |
  Terbium is the element Tb (atomic number 65), a silvery-white rare-earth metal that is malleable, ductile and soft enough to be cut with a knife. It has a density of 8.229 g/cm3 at 20 °C and a melting point of 1356 °C (Wikipedia). It is not found as a mineral of its own: it occurs with other rare earths in monazite and xenotime, with a crust abundance of 1.2 mg/kg (Wikipedia). The metal is made by reducing the anhydrous chloride or fluoride with calcium metal (Wikipedia). Most of the world's terbium goes into green phosphors, and the alloy Terfenol-D, which expands or contracts in a magnetic field, is used in actuators and sonar (Wikipedia). The metal tarnishes in air, reacts with hot water and dilute acid, and is flammable as dust, so it needs dry, inert handling (Ames SDS, WebElements).
best_for: Green phosphors for lighting and displays, and magnetostrictive Terfenol-D actuators (Wikipedia; NASA 1991 report)
weakest_at: Dust and fines that ignite, and metal that releases hydrogen on contact with water or dilute acid (Ames SDS, WebElements)
identity:
  formula: Tb (element, atomic number 65); unalloyed metal sold as pieces, ingot, rod, foil, sheet and target by the Ames Laboratory
  cas: 7440-27-9
  source: pubchem-tb
  where: Other Identifiers, CAS entry (PubChem CID 23958); EC number 231-137-6 is printed in the Ames SDS, section 3
tags:
  environments: []
  applications:
    - mechanisms
    - optics-and-cameras
    - electronics-and-chips
properties:
  - benchmark: density
    label: Density, terbium (Wikipedia infobox)
    value: 8.229
    unit: g/cm3
    scope: material
    conditions:
      temperature: 20 °C
      unit_in_source: 8.229 g/cm3
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-tb
    where: Infobox, row Density (at 20° C) 8.229 g/cm3
  - benchmark: density
    label: Relative density, terbium
    value: 8.23
    unit: g/cm3
    scope: material
    conditions:
      temperature: not stated
      unit_in_source: 8.230 g/cc
    method: Value printed in the Ames Laboratory safety data sheet, section 9
    status: ground
    source: ames-tb-sds
    where: Section 9 Physical and Chemical Properties, row Relative Density (Specific Gravity) 8.230 g/cc
  - benchmark: melting_point
    label: Melting point, terbium (Wikipedia infobox)
    value: 1356
    unit: °C
    scope: material
    conditions:
      pressure: not stated
      unit_in_source: 1629 K (1356 °C, 2473 °F)
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-tb
    where: Infobox, row Melting point, 1629 K (1356 °C, 2473 °F)
  - benchmark: melting_point
    label: Melting point, terbium (Ames SDS)
    value: 1356
    unit: °C
    scope: material
    conditions:
      pressure: not stated
      unit_in_source: 1356 oC
    method: Value printed in the Ames Laboratory safety data sheet, section 9
    status: ground
    source: ames-tb-sds
    where: Section 9, row Melting Point 1356 oC
  - benchmark: boiling_point
    label: Boiling point, terbium (Wikipedia infobox)
    value: 3123
    unit: °C
    scope: material
    conditions:
      pressure: not stated
      unit_in_source: 3396 K (3123 °C, 5653 °F)
    method: Value printed in the Wikipedia infobox
    status: ground
    note: The Ames SDS and PubChem give 3230 °C, about 107 °C higher. Both values are kept.
    source: wikipedia-tb
    where: Infobox, row Boiling point, 3396 K (3123 °C, 5653 °F)
  - benchmark: boiling_point
    label: Boiling point, terbium (PubChem)
    value: 3230
    unit: °C
    scope: material
    conditions:
      pressure: 760 mmHg
    method: Value printed in the PubChem experimental properties section
    status: ground
    source: pubchem-tb
    where: Chemical and Physical Properties, Experimental Properties, Boiling Point 3230 °C @760 mm Hg
  - benchmark: boiling_point
    label: Boiling point, terbium (Ames SDS)
    value: 3230
    unit: °C
    scope: material
    conditions:
      pressure: not stated
      unit_in_source: 3230 oC
    method: Value printed in the Ames Laboratory safety data sheet, section 9
    status: ground
    source: ames-tb-sds
    where: Section 9, row Boiling Point 3230 oC
  - benchmark: specific_heat
    label: Specific heat capacity, terbium (Wikipedia infobox)
    value: 181.904
    unit: J/(kg·K)
    scope: material
    conditions:
      temperature: not stated in the infobox
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-tb
    where: Infobox, row Specific heat capacity 181.904 J/(kg·K)
  - benchmark: thermal_conductivity
    label: Thermal conductivity, terbium (Wikipedia infobox)
    value: 11.1
    unit: W/(m·K)
    scope: material
    conditions:
      temperature: not stated in the infobox
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-tb
    where: Infobox, row Thermal conductivity 11.1 W/(m⋅K)
  - benchmark: thermal_conductivity
    label: Thermal conductivity, terbium (WebElements)
    value: 11
    unit: W/(m·K)
    scope: material
    conditions:
      temperature: not stated
      unit_in_source: 11 W m-1 K-1
    method: Value printed on the WebElements physical-properties page
    status: ground
    source: webelements-tb
    where: Heat and conduction, row Thermal conductivity 11 W m-1 K-1
  - benchmark: cte
    label: Coefficient of thermal expansion, terbium (Wikipedia infobox)
    value: 10.3
    unit: µm/(m·K)
    scope: material
    conditions:
      temperature: room temperature
      form: polycrystalline
      unit_in_source: 10.3 µm/(m⋅K)
    method: Value printed in the Wikipedia infobox, row Thermal expansion at r.t. poly
    status: ground
    source: wikipedia-tb
    where: Infobox, row Thermal expansion, at r.t. poly 10.3 µm/(m⋅K)
  - benchmark: cte
    label: Coefficient of linear thermal expansion, terbium (WebElements)
    value: 10.3
    unit: ppm/K
    scope: material
    conditions:
      temperature: not stated
      unit_in_source: 10.3 × 10-6 K-1
    method: Value printed on the WebElements physical-properties page
    status: ground
    source: webelements-tb
    where: Heat and conduction, row Coefficient of linear thermal expansion 10.3 × 10-6 K-1
  - benchmark: elastic_modulus
    label: Young's modulus, terbium (Wikipedia infobox)
    value: 55.7
    unit: GPa
    scope: material
    conditions:
      temperature: not stated in the infobox
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-tb
    where: Infobox, row Young's modulus 55.7 GPa
  - benchmark: elastic_modulus
    label: Young's modulus, terbium (WebElements)
    value: 56
    unit: GPa
    scope: material
    conditions:
      temperature: not stated
    method: Value printed on the WebElements physical-properties page
    status: ground
    source: webelements-tb
    where: Elastic properties, row Young's modulus 56 GPa
  - benchmark: shear_modulus
    label: Shear modulus, terbium (Wikipedia infobox)
    value: 22.1
    unit: GPa
    scope: material
    conditions:
      temperature: not stated in the infobox
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-tb
    where: Infobox, row Shear modulus 22.1 GPa
  - benchmark: shear_modulus
    label: Rigidity modulus, terbium (WebElements)
    value: 22
    unit: GPa
    scope: material
    conditions:
      temperature: not stated
    method: Value printed on the WebElements physical-properties page; WebElements calls the shear modulus the rigidity modulus
    status: ground
    source: webelements-tb
    where: Elastic properties, row Rigidity modulus 22 GPa
  - benchmark: bulk_modulus
    label: Bulk modulus, terbium (Wikipedia infobox)
    value: 38.7
    unit: GPa
    scope: material
    conditions:
      temperature: not stated in the infobox
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-tb
    where: Infobox, row Bulk modulus 38.7 GPa
  - benchmark: bulk_modulus
    label: Bulk modulus, terbium (WebElements)
    value: 38.7
    unit: GPa
    scope: material
    conditions:
      temperature: not stated
    method: Value printed on the WebElements physical-properties page
    status: ground
    source: webelements-tb
    where: Elastic properties, row Bulk modulus 38.7 GPa
  - benchmark: poissons_ratio
    label: Poisson's ratio, terbium (Wikipedia infobox)
    value: 0.261
    unit: '-'
    scope: material
    conditions:
      temperature: not stated in the infobox
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-tb
    where: Infobox, row Poisson ratio 0.261
  - benchmark: poissons_ratio
    label: Poisson's ratio, terbium (WebElements)
    value: 0.26
    unit: '-'
    scope: material
    conditions:
      temperature: not stated
    method: Value printed on the WebElements physical-properties page
    status: ground
    source: webelements-tb
    where: Elastic properties, row Poisson's ratio 0.26 (no units)
  - benchmark: vickers_hardness
    label: Vickers hardness, terbium (WebElements)
    value: 863
    unit: MPa
    scope: material
    conditions:
      temperature: not stated
      unit_in_source: 863 MN m-2
    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-tb
    where: Hardnesses, row Vickers hardness 863 MN m-2
  - benchmark: vickers_hardness
    label: Vickers hardness range, terbium (Wikipedia infobox)
    value: 450
    value_high: 865
    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: The Wikipedia range is 450–865 MPa with no test conditions. vickers_hardness is a new name and is listed in gaps.
    source: wikipedia-tb
    where: Infobox, row Vickers hardness 450–865 MPa
  - benchmark: electrical_resistivity
    label: Electrical resistivity, terbium alpha polycrystalline form (Wikipedia infobox)
    value: 1.15
    unit: µΩ·m
    scope: material
    conditions:
      temperature: room temperature
      form: alpha, polycrystalline
      unit_in_source: 1.150 µΩ⋅m
    method: Value printed in the Wikipedia infobox, row Electrical resistivity alpha poly 1.150 µΩ⋅m (at r.t.)
    status: ground
    source: wikipedia-tb
    where: Infobox, row Electrical resistivity, α poly 1.150 µΩ⋅m (at r.t.)
  - benchmark: magnetic_transition_temperature
    label: Ferromagnetic to helical antiferromagnetic transition, terbium
    value: 219
    unit: K
    scope: material
    conditions:
      transition: ferromagnetic ordering below this temperature, helical antiferromagnetic above it
      pressure: not stated
    method: Value printed in the Wikipedia Physical properties section, magnetic ordering paragraph
    status: ground
    note: The Wikipedia infobox gives the magnetic ordering as paramagnetic at 300 K and does not print a Curie temperature. magnetic_transition_temperature is a new name and is listed in gaps.
    source: wikipedia-tb
    where: Physical properties, paragraph on magnetic ordering, transition at 219 K
  - benchmark: paramagnetic_transition_temperature
    label: Helical antiferromagnetic to paramagnetic transition, terbium
    value: 230
    unit: K
    scope: material
    conditions:
      transition: helical antiferromagnetic to disordered paramagnetic
      pressure: not stated
    method: Value printed in the Wikipedia Physical properties section, magnetic ordering paragraph
    status: ground
    note: paramagnetic_transition_temperature is a new name and is listed in gaps.
    source: wikipedia-tb
    where: Physical properties, paragraph on magnetic ordering, paramagnetic state at 230 K
corrosion:
  - environment: Air at room temperature
    headline: Terbium tarnishes slowly in air and burns readily to form a terbium oxide.
    effect: WebElements says terbium metal tarnishes slowly in air and burns readily to form a terbium oxide of approximate formula Tb4O7. Wikipedia says the metal is relatively stable in air compared with the more reactive lanthanides, but also that it oxidizes readily in air to a mixed terbium(III,IV) oxide. The two statements disagree in emphasis and are both kept.
    rating: moderate
    conditions:
      temperature: room temperature
      atmosphere: air
    source: webelements-tb-chem
    where: Reaction of terbium with air, paragraph on tarnishing and Tb4O7
  - environment: Cold and hot water
    headline: Terbium reacts slowly with cold water and quite quickly with hot water, releasing hydrogen.
    effect: WebElements says the metal is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form terbium hydroxide, Tb(OH)3, and hydrogen gas. The Ames SDS says the metal may react with water under fire conditions to liberate flammable hydrogen gas.
    rating: severe
    conditions:
      temperature: cold and hot water
      form: metal
    source: webelements-tb-chem
    where: Reaction of terbium with water, paragraph on cold and hot water
  - environment: Dilute acids
    headline: Terbium dissolves readily in dilute sulphuric acid, releasing hydrogen.
    effect: WebElements says terbium metal dissolves readily in dilute sulphuric acid to form Tb(III) ions and hydrogen gas. The Ames SDS says contact with acids may evolve hydrogen gas.
    rating: severe
    conditions:
      acid: dilute sulphuric acid, and acids in general
      temperature: not stated
    source: webelements-tb-chem
    where: Reaction of terbium with acids, first paragraph
  - environment: Halogens
    headline: Terbium reacts with all the halogens to form terbium(III) halides.
    effect: WebElements says terbium reacts with all the halogens, fluorine, chlorine, bromine and iodine, to form terbium(III) halides. The Ames SDS lists halogens as incompatible materials.
    rating: severe
    conditions:
      atmosphere: halogen gas
      temperature: not stated
    source: webelements-tb-chem
    where: Reaction of terbium with the halogens, first paragraph; Ames SDS section 10, Incompatible Materials
risks:
  hazards:
    - text: 'PubChem GHS summary (ECHA C&L notifications, 62 company reports): H228 flammable solid in 79 % of notifications, with signal word Danger. 13 of 62 reports say the substance does not meet GHS hazard criteria.'
      ghs:
        - H228
      source: pubchem-tb
      where: Safety and Hazards, Hazards Identification, GHS Classification
    - text: 'Ames Laboratory safety data sheet for terbium (revised January 26, 2016): GHS classification under 29 CFR 1910.1200 is Not classified as hazardous, with no signal word or hazard statements.'
      ghs: []
      source: ames-tb-sds
      where: Section 2 Hazards Identification, GHS Classification
    - text: 'Ames SDS: flammable in the form of dust when exposed to heat, sparks or flame. May react with water under fire conditions to liberate flammable hydrogen gas. May emit fumes of terbium oxide under fire conditions.'
      ghs: []
      source: ames-tb-sds
      where: Section 5 Firefighting Measures, Specific Hazards Arising from the Material
    - text: 'PubChem hazards summary: little is known about its toxicity. Wikipedia says terbium is poorly studied in toxicology and that few health-based guidance values for safe exposure are available.'
      ghs: []
      source: pubchem-tb
      where: Safety and Hazards, Hazards Summary; Wikipedia Health and environmental impacts paragraph
    - text: Wikipedia says no values are established by OSHA or ACGIH at which terbium exposure becomes hazardous. The Ames SDS lists OSHA/PEL and ACGIH/TLV as No exposure limit established.
      ghs: []
      source: wikipedia-tb
      where: Health and environmental impacts paragraph; Ames SDS section 8, Exposure Limits
  failure_risks:
    - mode: Fire in dust, fines and turnings
      trigger: Terbium dust, fume or fine pieces exposed to heat, sparks or flame, as in grinding, melting or welding
      consequence: The Ames SDS says the metal is flammable in the form of dust when exposed to heat, sparks or flame, and PubChem records H228 (flammable solid) in 79 % of notifications.
      severity: high
      source: ames-tb-sds
      where: Section 5 Specific Hazards; Section 4 General Measures (grinding, melting or welding create dusts or fumes); PubChem GHS Classification
    - mode: Hydrogen release on contact with water or acid
      trigger: Metal in contact with cold or hot water, or with dilute acid, including water applied to a fire
      consequence: WebElements says the metal reacts quite quickly with hot water and dissolves readily in dilute sulphuric acid, both releasing hydrogen gas. The Ames SDS says water can liberate flammable hydrogen under fire conditions.
      severity: high
      source: webelements-tb-chem
      where: Reaction of terbium with water; Reaction of terbium with acids; Ames SDS section 5
    - mode: Surface oxidation in air and moisture
      trigger: Exposure to air or moisture during storage or handling
      consequence: The metal tarnishes slowly in air and forms a terbium oxide of approximate formula Tb4O7, and the Ames SDS calls it air and moisture sensitive.
      severity: moderate
      source: webelements-tb-chem
      where: Reaction of terbium with air; Ames SDS section 7, Precautions for Safe Handling
    - mode: Reaction with halogens
      trigger: Contact with halogen gas or with halogen-containing materials
      consequence: The metal reacts with all the halogens to form terbium(III) halides, and the Ames SDS lists halogens as incompatible.
      severity: moderate
      source: webelements-tb-chem
      where: Reaction of terbium with the halogens; Ames SDS section 10, Incompatible Materials
  side_effects:
    - text: PubChem lists the adverse effect of terbium as fibrogenic, meaning it induces tissue injury and fibrosis (scarring). No dose or exposure data are given on the record.
      affects: Workers exposed to terbium dust or fume, for example during grinding, melting or welding
      source: pubchem-tb
      where: Toxicity, Toxicological Information, Adverse Effects
  handling:
    - text: Store in tightly-closed containers under argon or mineral oil, in a cool, dry area, and protect from moisture (Ames SDS).
      source: ames-tb-sds
      where: Section 7 Conditions for Safe Storage
    - text: Handle in an enclosed, controlled process under dry protective gas such as argon when possible, because the metal is air and moisture sensitive (Ames SDS).
      source: ames-tb-sds
      where: Section 7 Precautions for Safe Handling
    - text: Do not use water on a fire. Use Class D dry powder extinguishing agent (Ames SDS).
      source: ames-tb-sds
      where: Section 5 Extinguishing Media and Unsuitable Extinguishing Media
    - text: Use local exhaust or other engineering controls for dust and fume, wear impermeable gloves and safety glasses, and use a NIOSH approved dust respirator if permissible levels are exceeded (Ames SDS).
      source: ames-tb-sds
      where: Section 8 Engineering Controls and Personal Protection
  mitigations: []
uses:
  - application: mechanisms
    device: Terfenol-D magnetostrictive actuator and direct-drive rotary stepper motor (research concept)
    example: NASA's 1991 report says Tb.3Dy.7Fe2, commercially known as TERFENOL-D, has been used in high power actuators and linear motors, and that NASA researchers were investigating it as the basis of a direct micro-stepping rotary motor. This is a research study, not a flown system.
    source: nasa-ntrs-1991
    where: Abstract of the 1991 Magnetostrictive direct drive motor report (Naik and Dehoff, NTRS 19910013248)
  - application: optics-and-cameras
    device: Terbium gallium garnet (TGG) crystal in Faraday rotators and optical isolators
    example: The 2023 arXiv preprint uses TGG for its broadband isolator study because it is one of the most common crystals for Faraday rotators. TGG is a terbium garnet compound, not the metal. Wikipedia also says terbium-doped garnets are used in optical isolators.
    source: arxiv-tgg-2023
    where: Section on the broadband isolator design (Fig. 1 text, paragraph on TGG); Wikipedia Applications section for the garnet isolator statement
  - application: electronics-and-chips
    device: Terbium-activated green phosphor in fluorescent lamps, colour TV tubes and flat-screen monitors
    example: Wikipedia says most of the world's terbium supply is used in green phosphors. Terbium oxides are used in green phosphors in fluorescent lamps, colour TV tubes and flat screen monitors, and terbium green phosphors are combined with europium phosphors for trichromatic lighting.
    source: wikipedia-tb
    where: Applications section, paragraphs on green phosphors
supply:
  - subject: Rare earths (terbium is not reported separately by USGS)
    abundance: 1.2 mg/kg crust abundance (Wikipedia, Occurrence section)
    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 applications but generally are less effective.'
    source: usgs-ree-2026
    where: 'World Mine Production and Reserves table, 2025 column: China 270,000 t, United States 51,000 t, Australia 29,000 t, Burma 22,000 t, world total 390,000 t (rounded). Shares are calculated from those printed figures. Reserves: China 44,000,000 t of more than 75,000,000 t world total.'
  - 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: rare-earth compounds and metals, China 71%, Malaysia 13%, Japan 5%, Estonia 5%. The year column shows the end of the 2021 to 2024 range.'
  - subject: Export controls on terbium
    producers: []
    critical_lists: []
    recycling: ''
    substitutes: []
    source: usgs-ree-2026
    where: 'Events, Trends, and Issues: In April 2025, China tightened its export controls on rare-earth elements, adding specific controls on alloys, compounds, metals, and oxides of samarium, gadolinium, terbium, dysprosium, lutetium, scandium, and yttrium. The April controls remained in effect, and China began to issue general export licenses to selected exporters.'
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: Terbium'
    type: database
    url: https://en.wikipedia.org/wiki/Terbium
    year: 2026
  - title: PubChem compound record for terbium (CID 23958), including ECHA C&L Inventory classification
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/23958
    year: 2026
  - title: Terbium Safety Data Sheet, Ames Laboratory Materials Preparation Center (revised January 26, 2016)
    type: sds
    url: https://www.ameslab.gov/sites/default/files/inline-files/65_Terbium_SDS.pdf
    year: 2016
  - title: 'WebElements: Terbium, physical properties (University of Sheffield)'
    type: database
    url: https://www.webelements.com/terbium/physics.html
  - title: 'WebElements: Terbium, chemical reactions (University of Sheffield)'
    type: database
    url: https://www.webelements.com/terbium/chemistry.html
  - title: Magnetostrictive direct drive motor, NASA NTRS 19910013248 (Naik and Dehoff, 1991)
    type: report
    url: https://ntrs.nasa.gov/citations/19910013248
    year: 1991
  - title: Broadband composite nonreciprocal polarization wave plates and optical isolators, arXiv 2305.06431 (Gevorgyan, Rangelov and Vitanov)
    type: paper
    url: https://arxiv.org/pdf/2305.06431
    year: 2023
gaps:
  - 'Terbium-specific production: USGS 2026 reports rare earths as one group, so the producer shares above are for all rare earths, not terbium. World output of terbium alone was not found in an opened source.'
  - 'Critical-mineral listing: the USGS 2025 critical minerals list and the EU critical raw materials list were not opened for terbium, so critical_lists is empty.'
  - 'Space flight of terbium: no flown terbium metal or flown terbium part was found in the sources read. The NASA item is a 1991 research study of a motor concept. The TGG item is a 2023 simulation preprint and a garnet, not the metal. Environment tags are left empty because no source ties terbium metal to a space environment.'
  - Terfenol-D magnetostriction (about 2000 ppm, NASA 1991) is for the alloy Tb.3Dy.7Fe2, not terbium metal, so it is not entered as a terbium property.
  - The TGG Verdet constant is for a garnet crystal, and the text layer of the arXiv paper is garbled at that point, so no Verdet value is entered.
  - 'Density: WebElements prints 8219 kg m-3 with no temperature, and PubChem prints 8.234 at 25 °C with no unit. Neither is entered. Wikipedia (8.229 at 20 °C) and the Ames SDS (8.230 g/cc) are entered.'
  - 'Boiling point: Wikipedia gives 3123 °C and the Ames SDS and PubChem give 3230 °C. Both are entered with their sources.'
  - 'Hardness: vickers_hardness is a new name because the property file has no canonical name for it. Wikipedia gives a range of 450–865 MPa and WebElements gives 863 MN m-2.'
  - 'Magnetic transitions: 219 K and 230 K are entered under the new names magnetic_transition_temperature and paramagnetic_transition_temperature, because the property file has no canonical name for them and the Curie temperature is not printed for terbium.'
  - 'Electrical resistivity: WebElements prints 115 × 10-8 Ω m, which is the same as the Wikipedia value of 1.150 µΩ·m, and it is not entered separately.'
  - 'Mechanical strength: no tensile or yield strength for terbium metal was found in an opened source, and WebElements gives no tensile figures.'
  - Corrosion data are qualitative (WebElements, Wikipedia, Ames SDS). No measured corrosion rate or weight-gain figure for terbium in air or water was found. Wikipedia says terbium is relatively stable in air and also that it oxidizes readily in air, and both are kept.
  - 'Hazard data conflict: PubChem records H228 in 79 % of notifications, while the Ames SDS says not classified as hazardous. Both are entered and the form of the metal (dust or solid) is not separated in every source.'
  - 'Specific heat: the Wikipedia infobox gives 181.904 J/(kg·K) with no temperature, and no temperature was found in another source.'
  - 'Goodfellow terbium datasheet: the product page returned HTTP 404 and was not read. The PubChem compound web page was blocked by a browser check, so the PubChem REST JSON record was read instead.'
  - 'Optics Express 2010 (Sun and Jiang, doi 10.1364/OE.18.012191) on terbium-doped fibre Verdet constant: the abstract page returned only a loading page and was not read.'
sources:
  wikipedia-tb:
    title: Terbium (Wikipedia)
    url: https://en.wikipedia.org/wiki/Terbium
    year: 2026
    kind: web
    license: CC BY-SA 4.0 (cited, not reproduced)
  pubchem-tb:
    title: 'PubChem compound record: Terbium (CID 23958), including ECHA C&L Inventory classification'
    id: CAS 7440-27-9
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/23958/JSON
    kind: database
    license: PubChem (NCBI), public domain; sections attributed to ECHA and others
  ames-tb-sds:
    title: Terbium Safety Data Sheet, Ames Laboratory Materials Preparation Center (revised January 26, 2016)
    url: https://www.ameslab.gov/sites/default/files/inline-files/65_Terbium_SDS.pdf
    year: 2016
    kind: datasheet
    license: supplier safety data sheet, cited not reproduced
  webelements-tb:
    title: 'WebElements: Terbium, physical properties (University of Sheffield)'
    url: https://www.webelements.com/terbium/physics.html
    kind: database
    license: WebElements, cited not reproduced
  webelements-tb-chem:
    title: 'WebElements: Terbium, chemical reactions (University of Sheffield)'
    url: https://www.webelements.com/terbium/chemistry.html
    kind: database
    license: WebElements, cited not reproduced
  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)
  nasa-ntrs-1991:
    title: Magnetostrictive direct drive motor (NASA NTRS 19910013248, Naik and Dehoff, 1991)
    url: https://ntrs.nasa.gov/citations/19910013248
    year: 1991
    kind: report
    license: NASA public document, cited not reproduced
  arxiv-tgg-2023:
    title: Broadband composite nonreciprocal polarization wave plates and optical isolators (arXiv 2305.06431)
    url: https://arxiv.org/pdf/2305.06431
    year: 2023
    kind: paper
    license: arXiv preprint, cited not reproduced
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 25
  unreachable: 3
  caveats: 6
  note: 'Read by an AI assistant on 2026-10-26 from the pages and PDFs named in each entry. Unreachable: Goodfellow terbium product page (HTTP 404), Optics Express abstract page (loading page only), DTIC magnetostrictive shape-control PDF (not a PDF). Caveats: the physical values come from Wikipedia, WebElements and the Ames SDS; the boiling point and density differ between sources; the hazard classes differ between PubChem and the Ames SDS; supply shares are for all rare earths, not terbium; the magnetic transitions use new property names; the Verdet value for TGG was not entered.'
story:
  risk_groups:
    - title: For people
      lead: The sources read say little about human toxicity. The hazard is mainly in the form of the metal, because dust and fumes from grinding, melting or welding can be inhaled.
      level: 1
      verdict: Form-dependent
      points:
        - label: Dust and fumes
          line: Grinding, melting or welding may create dusts or fumes that can be inhaled or contact skin or eyes (Ames SDS, section 4).
        - label: Classification
          line: PubChem records H228 (flammable solid) in 79 % of 62 notifications, while the Ames SDS says the metal is not classified as hazardous.
        - label: Toxicity data
          line: Wikipedia says terbium is poorly studied in toxicology, and no OSHA or ACGIH exposure limit is established.
    - title: If it fails
      lead: 'The sources give four failure routes: a dust fire, hydrogen release with water or acid, tarnishing in air, and reaction with halogens.'
      points:
        - label: Fire
          line: The metal is flammable as dust when exposed to heat, sparks or flame, and water can liberate hydrogen under fire conditions (Ames SDS).
        - label: Water and acid
          line: The metal reacts quite quickly with hot water and dissolves readily in dilute sulphuric acid, releasing hydrogen (WebElements).
        - label: Air
          line: Terbium tarnishes slowly in air and burns readily to form a terbium oxide of approximate formula Tb4O7 (WebElements).
    - title: Handling and storage
      points:
        - label: Keep it dry
          line: Store in tightly-closed containers under argon or mineral oil, in a cool, dry area, and protect it from moisture (Ames SDS).
        - label: Fire agents
          line: Use a Class D dry powder extinguishing agent. Do not use water (Ames SDS).
  why: 'Terbium is a rare-earth metal whose best-known roles are light and magnetism. Its strong green emission is the reason most of the world''s terbium goes into green phosphors. Its magnetostriction, as part of the alloy Terfenol-D, drives actuators and sonar. The pure metal is a research material: it is reactive, it is sold in small pieces, and its space-relevant use is through alloys and garnet crystals rather than the metal itself.'
  uses:
    - where: Magnetostrictive actuators and motors
      line: NASA's 1991 report says Terfenol-D, a terbium alloy, has been used in high power actuators and linear motors, and NASA studied it for a direct-drive rotary stepper motor. This is a research concept, not a flown system.
    - where: Phosphors in lighting and displays
      line: Terbium oxides are used in green phosphors in fluorescent lamps, colour TV tubes and flat-screen monitors (Wikipedia).
    - where: Garnet crystals in optical isolators
      line: Terbium gallium garnet (TGG) is one of the most common crystals for Faraday rotators, according to a 2023 arXiv preprint. TGG is a compound, not the metal.
  can_do:
    - label: Melt
      value: 1356 °C
      benchmark: melting_point
      line: The melting point is 1356 °C (Wikipedia), and the Ames SDS prints the same 1356 °C.
    - label: Weight
      value: 8.229 g/cm3
      benchmark: density
      line: The density is 8.229 g/cm3 at 20 °C (Wikipedia), and the Ames SDS prints 8.230 g/cc.
    - label: Heat conduction
      value: 11.1 W/(m·K)
      benchmark: thermal_conductivity
      line: Thermal conductivity is 11.1 W/(m·K) in the Wikipedia infobox, and WebElements prints 11 W/(m·K).
    - label: Stiffness
      value: 55.7 GPa
      benchmark: elastic_modulus
      line: Young's modulus is 55.7 GPa (Wikipedia), and WebElements prints 56 GPa.
    - label: Magnetic transition
      value: 219 K
      benchmark: magnetic_transition_temperature
      line: The ferromagnetic ordering lies below 219 K, and the state becomes paramagnetic at 230 K (Wikipedia).
  compare: Terbium is a dense rare-earth metal at 8.229 g/cm3 (Wikipedia), with a melting point of 1356 °C. Its thermal conductivity of 11.1 W/(m·K) is modest for a metal. It is relatively stable in air compared with the more reactive lanthanides (Wikipedia), but it reacts with hot water and dilute acid. No comparison profile is carried in this file, so the rows below list terbium values only.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Melting point
      benchmark: melting_point
    - label: Thermal conductivity
      benchmark: thermal_conductivity
  recipe:
    line: Terbium is a single-element metal (Tb). Wikipedia says the metal is produced by reducing the anhydrous chloride or fluoride with calcium metal, after ion-exchange separation from the other rare earths. Calcium and tantalum impurities can be removed by vacuum remelting, distillation, amalgam formation or zone melting.
    parts:
      - name: Terbium
        symbol: Tb
        atoms: 1
        atomic_weight: 158.92535
        role: The whole material. The Ames SDS lists terbium as the only ingredient of the product.
  handling:
    - Store in tightly-closed containers under argon or mineral oil, in a cool, dry area (Ames SDS).
    - Handle in an enclosed, controlled process under dry gas such as argon when possible (Ames SDS).
    - Do not use water on a fire. Use a Class D dry powder extinguishing agent (Ames SDS).
    - If permissible exposure levels are exceeded, use a NIOSH approved dust respirator (Ames SDS).
  good_for:
    - 'Green phosphors: most of the world''s terbium supply goes into green phosphors (Wikipedia).'
    - 'Magnetostrictive actuators: Terfenol-D, a terbium alloy, expands or contracts in a magnetic field (Wikipedia; NASA 1991).'
    - 'Research: the Ames Laboratory sells terbium for scientific research (Ames SDS).'
  watch_out:
    - Dust and fines are flammable, and the Ames SDS says the metal is flammable as dust when exposed to heat, sparks or flame.
    - Water and dilute acid release hydrogen, and the metal reacts quite quickly with hot water (WebElements).
    - China's April 2025 export controls cover terbium alloys, compounds, metals and oxides (USGS).
    - 'Hazard classes differ: PubChem records H228 for most notifications, while the Ames SDS says not classified (PubChem, Ames SDS).'
  verdict: Terbium is a rare-earth metal whose value lies in its green luminescence and in Terfenol-D, its magnetostrictive alloy. The metal is dense at 8.229 g/cm3 and melts at 1356 °C, and it is flammable as dust and reactive with water and acid, so it needs dry, inert handling. The space evidence is a 1991 NASA study of a Terfenol-D motor concept, not a flown terbium part.