Lanthanum hexaboride LaB6

spore: profile
id: lanthanum-hexaboride
spore_version: 0.2
family: carbide-nitride-boride-ceramics
name: Lanthanum hexaboride
abbreviation: LaB6
role: low work function boride used as a thermionic (hot) electron emitter
category: ceramics
type: ultra-high-temperature-ceramics
summary: Lanthanum hexaboride (LaB6) is a boride ceramic used as a hot electron source. A vendor specification gives a density of 4.72 g/cm3, a melting point of 2528 K, an electron emissivity (work function) of 2.6 eV and a flexure strength of 200 MPa, and the vendor claims 10 times the brightness of tungsten cathodes. NASA measured a work function of 2.1 to 2.44 eV in hollow cathodes run in gas discharge, below the accepted 2.66 eV for polycrystalline LaB6. Sonber et al. (2014) report that oxidation starts at 500 degC in air and that dense LaB6 has a hardness of 20 GPa. Vendor purity runs from 99.5% to 99.9% LaB6.
best_for: Hot electron sources in electron beam instruments and Hall thruster hollow cathodes, where a low work function matters more than oxidation resistance in air
weakest_at: Oxidation in air from 500 degC, and oxygen poisoning of the emitter in oxygen-rich plasma
identity:
  formula: LaB6
  cas: 12008-21-8
  source: pubchem-lab6
  where: PubChem CID 71308229 record (name Lanthanum hexaboride, formula LaB6, CAS 12008-21-8, molar mass 203.8 g/mol)
tags:
  environments:
    - low-earth-orbit
  stresses:
    - extreme-heat
  applications:
    - electronics-and-chips
    - propulsion-and-tanks
properties:
  - benchmark: density
    label: Density, LaB6 (vendor specification)
    value: 4.72
    unit: g/cm3
    scope: material
    conditions:
      basis: vendor specification table, grade and temperature not stated
    method: Density row of the vendor specification table
    status: ground
    source: samaterials-lab6
    where: Lanthanum Hexaboride Cathode Specification table, Density row
  - benchmark: melting_point
    label: Melting point, LaB6 (vendor specification)
    value: 2528
    unit: K
    scope: material
    conditions:
      basis: vendor specification table; the same figure is in the page body
    method: Melting Point row of the vendor specification table, printed in kelvin
    status: ground
    source: samaterials-lab6
    where: Lanthanum Hexaboride Cathode Specification table, Melting Point row; body text
  - benchmark: work_function
    label: Electron emissivity (work function), LaB6 cathode (vendor table)
    value: 2.6
    unit: eV
    scope: material
    conditions:
      basis: vendor specification table; crystal face and temperature not stated
    method: Electron Emissivity row of the vendor specification table. The page body gives near 2.70 eV for the work function, and the page does not reconcile the two values.
    status: ground
    source: samaterials-lab6
    where: Lanthanum Hexaboride Cathode Specification table, Electron Emissivity row
  - benchmark: work_function
    label: Work function, LaB6 hollow cathode emitter (measured in gas discharge)
    value: 2.1
    value_high: 2.44
    bound: range
    unit: eV
    scope: material
    conditions:
      basis: steady-state internal gas discharge in a hollow cathode, estimated from measured emitter temperatures and a cathode model
    method: Estimated range printed in the abstract
    status: ground
    source: lopez-ortega-2017
    where: Abstract
  - benchmark: work_function
    label: Accepted work function, polycrystalline LaB6 (as quoted by the NASA authors)
    value: 2.66
    unit: eV
    scope: material
    conditions:
      basis: polycrystalline LaB6, described by the authors as the accepted value
    method: Quoted in the abstract as the accepted value that does not describe hollow cathode emission in gas discharge
    status: ground
    source: lopez-ortega-2017
    where: Abstract
  - benchmark: thermal_conductivity
    label: Thermal conductivity, LaB6 (vendor specification)
    value: 47
    unit: W/mK
    scope: material
    conditions:
      temperature: 20 degC
    method: Thermal Conductive row of the vendor specification table, printed as 47 W/mK at 20 degC
    status: ground
    source: samaterials-lab6
    where: Lanthanum Hexaboride Cathode Specification table, Thermal Conductive row
  - benchmark: cte
    label: Mean coefficient of thermal expansion, LaB6 (vendor specification)
    value: 6.2
    unit: 10-6/K
    scope: material
    conditions:
      temperature: 20 to 900 degC
    method: Thermal Expansion row of the vendor specification table, printed as 6.2 10-6 K-1 over 20 to 900 degC
    status: ground
    source: samaterials-lab6
    where: Lanthanum Hexaboride Cathode Specification table, Thermal Expansion row
  - benchmark: electrical_resistivity
    label: Electrical resistance, LaB6 (vendor specification)
    value: 15
    unit: uOhm·cm
    scope: material
    conditions:
      temperature: 20 degC
      note_on_value: printed as ca.15 (approximate)
    method: Electrical Resistance row of the vendor specification table, printed as ca.15 uOhm cm at 20 degC. The label says resistance, and the unit is a resistivity.
    status: ground
    source: samaterials-lab6
    where: Lanthanum Hexaboride Cathode Specification table, Electrical Resistance row
  - benchmark: emission_current_density
    label: Emission current density, LaB6 cathode (vendor specification)
    value: 150
    unit: A/cm2
    scope: material
    conditions:
      temperature: 1950 degC
    method: Currency Density row of the vendor specification table (the page's own spelling), printed as 150 A/cm2 at 1950 degC
    status: ground
    source: samaterials-lab6
    where: Lanthanum Hexaboride Cathode Specification table, Currency Density row
  - benchmark: hardness_rockwell_a
    label: Hardness, LaB6 (vendor specification, Rockwell A)
    value: 87.5
    unit: RA
    scope: material
    conditions:
      basis: vendor specification table; test method printed as RA
    method: Hardness row of the vendor specification table, printed as 87.5 RA
    status: ground
    source: samaterials-lab6
    where: Lanthanum Hexaboride Cathode Specification table, Hardness row
  - benchmark: flexural_strength
    label: Flexure strength, LaB6 (vendor specification)
    value: 200
    unit: MPa
    scope: material
    conditions:
      basis: vendor specification table; temperature, form and grade not stated
    method: Flexure Strength row of the vendor specification table, printed as 200 Mpa
    status: ground
    source: samaterials-lab6
    where: Lanthanum Hexaboride Cathode Specification table, Flexure Strength row
  - benchmark: hardness
    label: Hardness, dense LaB6 (Sonber 2014)
    value: 20
    unit: GPa
    scope: material
    conditions:
      basis: dense LaB6 as stated in the paper; test load and temperature not stated in the summary
    method: Quoted in the paper summary for dense LaB6
    status: ground
    source: sonber-2014
    where: Abstract summary, density and hardness paragraph
  - benchmark: fracture_toughness
    label: Fracture toughness, dense LaB6 (Sonber 2014)
    value: 3.02
    unit: MPa m1/2
    scope: material
    conditions:
      basis: dense LaB6 as stated in the paper; test method not stated in the summary
    method: Quoted in the paper summary with the hardness of dense LaB6
    status: ground
    source: sonber-2014
    where: Abstract summary, density and hardness paragraph
  - benchmark: relative_density
    label: Relative density after pressureless sintering (Sonber 2014)
    value: 85.1
    unit: '%'
    scope: material
    conditions:
      temperature: 1950 degC
      process: pressureless sintering of LaB6 powder
    method: Printed as a percentage of theoretical density after pressureless sintering
    status: ground
    source: sonber-2014
    where: Abstract summary, density and hardness paragraph
  - benchmark: oxidation_onset_temp
    label: Oxidation onset temperature in air, LaB6 (thermogravimetry)
    value: 500
    unit: degC
    scope: material
    conditions:
      atmosphere: air
      basis: onset of slow oxidation, not a service limit; the time of the thermogravimetry run is not given
    method: Thermogravimetry result quoted in the paper summary. Oxidation starts slowly at this temperature and accelerates at 700 degC.
    status: ground
    note: Custom property name. It marks the start of oxidation, not a safe limit.
    source: sonber-2014
    where: Abstract summary, oxidation paragraph
corrosion:
  - environment: Air at 500 to 900 degC (thermogravimetry and isothermal oxidation of dense LaB6)
    headline: Oxidation starts at 500 degC and speeds up at 700 degC. At 900 degC a protective oxide layer formed and stayed continuous after 64 h in air.
    effect: Sonber et al. report that thermogravimetric oxidation starts slowly at 500 degC and accelerates at 700 degC. An isothermal test at 900 degC gave a protective continuous oxide layer that was still present after 64 h exposure in air. The summary does not give the thermogravimetry run time or the oxide phases.
    rating: moderate
    conditions:
      temperature: 500 to 900 degC
      time: 64 h
      atmosphere: air
    source: sonber-2014
    where: Abstract summary (full text not read)
  - environment: Very low Earth orbit air-breathing electric propulsion, where oxygen and nitrogen are the main constituents
    headline: Oxygen poisons Hall thruster cathodes. LaB6 resists this better than dispenser cathodes, and the thesis seeks rare-earth alloys that do better than LaB6.
    effect: The thesis abstract says oxygen causes a Hall-effect thruster cathode to poison, which sharply decreases electron emission and reduces thrust. It names LaB6 and dispenser cathodes as the two thermionic options, and says LaB6 has better resistance to oxygen poisoning. The project explores alloys of LaB6 and other rare-earth hexaborides that tolerate oxygen better. Its test results were not read.
    rating: moderate
    conditions:
      environment: Very low Earth orbit, atomic oxygen and nitrogen as the main constituents
      test: not stated in the abstract
    source: mtu-lab6-thesis
    where: Abstract
risks:
  hazards:
    - text: 'PubChem: in 100% (3 of 3) of company reports the substance does not meet GHS hazard criteria, and no hazard statements are assigned. The reports come from 1 ECHA C and L notification.'
      ghs: []
      source: pubchem-lab6
      where: GHS Classification section
    - text: 'Materion SDS (revision 01-26-2016): physical, health and environmental hazards not classified, with no signal word. Toxicology is not classified due to lack of data for every route.'
      ghs: []
      source: materion-sds-lab6
      where: Sections 2 and 11
  failure_risks:
    - mode: Electron emission loss from oxygen poisoning
      trigger: Oxygen in the propellant or plasma of an air-breathing or oxygen-rich Hall thruster
      consequence: The thesis abstract says oxygen poisoning sharply decreases electron emission and so reduces thrust. LaB6 resists it better than dispenser cathodes.
      severity: moderate
      source: mtu-lab6-thesis
      where: Abstract
    - mode: Brittle fracture of dense ceramic
      trigger: Tensile or bending load on a flaw
      consequence: Dense LaB6 has a fracture toughness of 3.02 MPa m1/2 (Sonber 2014), so a flaw can grow under load. The paper summary gives no flexural strength.
      severity: moderate
      source: sonber-2014
      where: Abstract summary, density and hardness paragraph
    - mode: Heater or cathode life limit
      trigger: Long-duration operation of a heated LaB6 hollow cathode
      consequence: NASA planned LaB6 heater life testing to validate heater reliability for the HERMeS cathode. No result is given in the slides read.
      severity: moderate
      source: hermes-2016
      where: Introduction, cathode emitter technology assessment slide
  side_effects: []
  handling:
    - text: 'Materion SDS: observe good industrial hygiene practices, wash hands after handling, and store in the original tightly closed container away from incompatible materials.'
      source: materion-sds-lab6
      where: Sections 2 and 7
    - text: 'Materion SDS: in a fire, use water spray to cool unopened containers. Gases hazardous to health may form during a fire. After a spill, stop the flow if safe and flush the area with water.'
      source: materion-sds-lab6
      where: Sections 5 and 6
    - text: Oxidation starts at 500 degC in air (Sonber 2014). The sources read give no handling rule for it.
      source: sonber-2014
      where: Abstract summary, oxidation paragraph
  mitigations: []
uses:
  - application: electronics-and-chips
    device: Thermionic electron source (hot cathode) for electron beam instruments
    example: The vendor describes LaB6 cathodes as giving 10 times the brightness and 50 times the service life of tungsten cathodes. The page gives no lifetime in hours.
    source: samaterials-lab6
    where: Lanthanum Hexaboride Cathode description, body text
  - application: propulsion-and-tanks
    device: Hollow cathode electron source for a 6-kW Hall thruster
    example: A NASA Glenn compact rare-earth emitter hollow cathode is mounted on the centerline of a 6-kW Hall thruster and rated for 10 to 60 A. The report cites long life and less stringent xenon purity than barium oxide cathodes.
    source: watkins-2010
    where: Abstract and description, NPO-44923
  - application: propulsion-and-tanks
    device: HERMeS 12.5-kW Hall thruster hollow cathode (NASA development)
    example: The HERMeS hollow cathode must provide 8 to 32 A for 34,000 hours. NASA assessed LaB6 against a barium-based (BaO) emitter in 2016.
    source: hermes-2016
    where: Introduction slides
supply:
  - subject: Rare earths (lanthanum is one of the rare earths; the USGS chapter read gives no lanthanum-only production figure)
    abundance: 'USGS 2026: about 390,000 t of rare-earth oxide was mined worldwide in 2025 (rounded). World reserves of 44,000,000 t are reported for China alone. U.S. imports of rare-earth compounds and metals were 71 percent from China (2021 to 2024). The USGS lists 1,100 t of lanthanum as potential government stockpile acquisitions for FY 2025.'
    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
    critical_lists: []
    recycling: 'USGS: limited quantities of rare earths were recovered from batteries, permanent magnets and fluorescent lamps.'
    source: usgs-mcs2026-rare-earths
    where: World Mine Production table, 2025 column (shares calculated by Space Mushroom from the printed tonnage over the printed 390,000 t world total); Import Sources, 2021 to 2024; Government Stockpile table; Recycling
  - subject: Boron (the boron half of LaB6)
    abundance: 'USGS 2026: the 2025 world total is withheld (XX), so shares are not calculated. 2025 production as printed: Turkey 1,500 t of refined borates, Bolivia 380 t of ulexite, Peru 220 t of crude borates and China 230 t as boric oxide equivalent. U.S. imports of all forms came from Turkey (90 percent, 2021 to 2024).'
    producers: []
    critical_lists:
      - list: USGS Final 2025 List of Critical Minerals, published 7 Nov 2025 with boron added
        listed: true
    recycling: 'USGS: insignificant.'
    source: usgs-mcs2026-boron
    where: World Production and Reserves table, 2025 column; Import Sources; Events, Trends and Issues (critical minerals paragraph); Recycling
media: []
documents:
  - title: Stanford Advanced Materials, Lanthanum Hexaboride (LaB6) Cathode product page with specification table
    type: datasheet
    url: https://samaterials.com/lanthanum/1406-lanthanum-hexaboride-lab6-cathode.html
  - title: Lopez Ortega, Richter, Polk, Guerrero 2017, Work function reduction in lanthanum hexaboride hollow cathodes operated in gas discharges (NTRS 20210007849)
    type: paper
    url: https://ntrs.nasa.gov/citations/20210007849
    year: 2017
  - title: Watkins, Goebel and Hofer 2010, Compact Rare Earth Emitter Hollow Cathode, NPO-44923 (NTRS 20100009696)
    type: report
    url: https://ntrs.nasa.gov/citations/20100009696
    year: 2010
  - title: Sarver-Verhey, Kamhawi, Goebel, Polk et al., Hollow Cathode Assembly Development for the HERMeS Hall Thruster, AIAA JPC 2016 slides (NTRS 20170003030)
    type: report
    url: https://ntrs.nasa.gov/api/citations/20170003030/downloads/20170003030.pdf
    year: 2016
  - title: Sonber et al. 2014, Synthesis, densification and oxidation study of lanthanum hexaboride, J. Eur. Ceram. Soc. 34(5), doi 10.1016/j.jeurceramsoc.2013.11.023
    type: paper
    url: https://research.birmingham.ac.uk/en/publications/synthesis-densification-and-oxidation-study-of-lanthanum-hexabori
    year: 2014
  - title: PubChem compound CID 71308229, Lanthanum hexaboride (GHS classification, CAS 12008-21-8)
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/71308229
  - title: USGS Mineral Commodity Summaries 2026, Rare Earths
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-rare-earths.pdf
    year: 2026
  - title: USGS Mineral Commodity Summaries 2026, Boron
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-boron.pdf
    year: 2026
  - title: Michigan Tech thesis (digital commons etdr 1945), rare-earth hexaboride cathode for oxygen-rich very low Earth orbit Hall thruster (abstract read)
    type: paper
    url: https://digitalcommons.mtu.edu/etdr/1945
  - title: Materion Advanced Chemicals, Safety Data Sheet L-MSDS0014, Lanthanum boride (revision 01-26-2016)
    type: sds
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/SDS/lanthanum%20boride%20%20-%20Materion.pdf
    year: 2016
gaps:
  - 'Hitachi High-Tech LaB6 electron source pages (work function 2.8 eV for the (100) face at 1800 K, 2.6 eV at 300 K, from a search snippet): every Hitachi locale returned HTTP 403, so no Hitachi value is used.'
  - 'Crystal structure and lattice constant of LaB6: only Wikipedia gave them, and Wikipedia is limited to composition and history here, so they are left out. Designations (UNS, EN, DIN, JIS and similar codes): none printed in a source read in this run.'
  - 'Electron microscope brightness against tungsten from peer-reviewed work (1976 Journal of Physics E LaB6 gun paper, and Broers 1979): the repository page timed out, so only the vendor claims (10 times brightness, 50 times life) are used.'
  - 'Oxidation kinetics of LaB6 in air (Wen et al. 2004, parabolic rate and activation energy): the NTU repository page returned HTTP 502 twice, so not used.'
  - 'Moisture reactivity: a US patent background says LaB6 reacts with oxidants and moisture at operating temperature, but the patent PDF did not download, so not used. The Materion SDS says the product is non-reactive under normal conditions.'
  - 'Operating lifetime in hours for a LaB6 cathode: not found in any source read. The vendor gives 50 times tungsten life with no hours.'
  - 'Numerical emitter temperatures for LaB6 hollow cathodes: the JPL 2017 abstract says they were lower than expected but gives no values.'
  - 'Critical-mineral status of lanthanum or rare earths: the USGS rare-earths text read does not state it, and the EU critical raw materials list was not read in this run, so the rare-earth critical_lists is empty.'
  - 'Vendor work function conflict: the page body gives near 2.70 eV, the specification table gives 2.6 eV, NASA measured 2.1 to 2.44 eV and quotes an accepted 2.66 eV. All are kept with their sources.'
  - 'Melting point conflict: Wikipedia gives 2,210 degC, the vendor gives 2528 K. Wikipedia is not used for values, so only the vendor figure is kept.'
  - Materion SDS section 7 says store away from incompatible materials, while section 10 lists none known. Both are kept as printed in the handling entries.
  - Only one supplier SDS (Materion, revision 2016) and one PubChem record were read. No GHS label or second SDS was checked.
  - 'Custom property names used because they are not in spores/property-canon.yaml: work_function, hardness, hardness_rockwell_a, fracture_toughness, relative_density, emission_current_density, oxidation_onset_temp.'
  - 'Space use: NASA hollow cathode development for a Hall thruster is documented, but no flight record was read.'
sources:
  samaterials-lab6:
    title: Stanford Advanced Materials (samaterials.com), Lanthanum Hexaboride (LaB6) Cathode description and specification table
    url: https://samaterials.com/lanthanum/1406-lanthanum-hexaboride-lab6-cathode.html
    kind: web
    license: vendor web page, cited not reproduced
  lopez-ortega-2017:
    title: Lopez Ortega A, Richter M H, Polk J, Guerrero P, Work function reduction in lanthanum hexaboride hollow cathodes operated in gas discharges (2017), NTRS 20210007849
    url: https://ntrs.nasa.gov/citations/20210007849
    kind: paper
    license: NASA NTRS public record
  watkins-2010:
    title: Watkins R, Goebel D, Hofer R, Compact Rare Earth Emitter Hollow Cathode, NASA Tech Briefs NPO-44923 (2010), NTRS 20100009696
    url: https://ntrs.nasa.gov/citations/20100009696
    kind: report
    license: NASA NTRS public record
  hermes-2016:
    title: Sarver-Verhey T R, Kamhawi H et al., Hollow Cathode Assembly Development for the HERMeS Hall Thruster, AIAA Joint Propulsion Conference presentation (2016), NTRS 20170003030
    url: https://ntrs.nasa.gov/api/citations/20170003030/downloads/20170003030.pdf
    kind: report
    license: NASA NTRS public record
  sonber-2014:
    title: Sonber J K et al., Synthesis, densification and oxidation study of lanthanum hexaboride, J. Eur. Ceram. Soc. 34(5), 1155-1160 (2014)
    url: https://research.birmingham.ac.uk/en/publications/synthesis-densification-and-oxidation-study-of-lanthanum-hexabori
    kind: paper
    license: research portal record (abstract summary read)
  pubchem-lab6:
    title: PubChem compound CID 71308229, Lanthanum hexaboride (GHS classification from ECHA C and L notifications; CAS 12008-21-8)
    url: https://pubchem.ncbi.nlm.nih.gov/compound/71308229
    kind: database
    license: PubChem public database
  usgs-mcs2026-rare-earths:
    title: USGS Mineral Commodity Summaries 2026, Rare Earths
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-rare-earths.pdf
    kind: report
    license: US government work, public domain
  usgs-mcs2026-boron:
    title: USGS Mineral Commodity Summaries 2026, Boron
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-boron.pdf
    kind: report
    license: US government work, public domain
  mtu-lab6-thesis:
    title: Michigan Technological University graduate thesis (digital commons etdr 1945), rare-earth hexaboride cathode for oxygen-rich very low Earth orbit Hall thrusters (abstract read)
    url: https://digitalcommons.mtu.edu/etdr/1945
    kind: paper
    license: open repository record
  materion-sds-lab6:
    title: Materion Advanced Chemicals, Safety Data Sheet L-MSDS0014, Lanthanum boride (revision 01-26-2016)
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/SDS/lanthanum%20boride%20%20-%20Materion.pdf
    kind: datasheet
    license: supplier SDS, cited not reproduced
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 15
  unreachable: 4
  caveats: 4
  note: 'Written in this run from the vendor specification page, two NASA NTRS papers (2017 work function, 2010 compact cathode), the 2016 HERMeS slides, Sonber 2014 (abstract summary), PubChem (REST record), USGS 2026 rare earths and boron, the Michigan Tech thesis abstract and the Materion SDS. Unreachable: Hitachi pages (403), NTU Wen 2004 (502), the 1976 gun abstract (timeout), the patent PDF. verify-values: 15 values, 13 found in the source text, 2 not fetched by the script (the NTRS 2017 abstract, both work function values, checked by hand: 2.66 eV and 2.1 - 2.44 eV are on the page), 0 not found.'
story:
  recipe:
    line: LaB6 is one lanthanum to six boron in the formula LaB6 (PubChem, CAS 12008-21-8, molar mass 203.8 g/mol). Sonber et al. found that pressureless sintering at 1950 degC reached 85.1 percent of theoretical density, while hot pressing at the same temperature gave near-theoretical density.
    parts:
      - name: Lanthanum
        symbol: La
        share: one per formula unit in LaB6
        role: Rare-earth metal component. NASA's 2017 work says a lanthanum-rich emitting surface forms in gas discharge, with a lower work function than the bulk.
      - name: Boron
        symbol: B
        share: six per formula unit in LaB6
        role: Boron framework that pairs with the lanthanum in the formula LaB6 (PubChem).
  risk_groups:
    - title: For people
      level: 0
      verdict: Not classified in PubChem or Materion SDS
      lead: PubChem and the Materion SDS both show no hazard classification, but the SDS reports no toxicology data. Treat the powder as an unknown inhalation hazard and control dust.
      points:
        - label: Dust
          line: Materion says to observe good industrial hygiene practices and to wear respiratory protection if ventilation is insufficient.
        - label: Data gap
          line: Materion's toxicology section says classification is not possible due to lack of data for every route.
    - title: If an emitter fails
      lead: These figures come from NASA hollow cathode work and Sonber 2014.
      points:
        - label: Oxygen
          line: Oxygen poisons Hall thruster cathodes and sharply reduces emission. LaB6 resists this better than dispenser cathodes (Michigan Tech thesis abstract).
        - label: Brittleness
          line: Dense LaB6 has a fracture toughness of 3.02 MPa m1/2 and a hardness of 20 GPa (Sonber 2014).
  why: LaB6 is a hard boride with a low work function. The vendor table gives 2.6 eV, and NASA's 2017 work uses the accepted 2.66 eV reference for polycrystalline LaB6, while its own measurements in gas discharge gave 2.1 to 2.44 eV. The vendor gives a melting point of 2528 K, so the material can stay solid at the heater temperatures used for hot cathodes. Its limits are oxidation from 500 degC in air and oxygen poisoning in oxygen-rich plasma.
  uses:
    - where: Electron beam instruments
      line: The vendor claims 10 times the brightness of tungsten cathodes and 50 times the service life, with no hours given.
    - where: Hall thruster hollow cathodes
      line: NASA rated a compact LaB6 emitter cathode for 10 to 60 A on a 6-kW Hall thruster. The HERMeS cathode must provide 8 to 32 A for 34,000 hours.
    - where: Space applications
      line: NASA development and ground tests only. No flight record was read in this run.
  can_do:
    - label: Melting
      benchmark: melting_point
      value: 2528 K
      line: The vendor gives a melting point of 2528 K.
    - label: Electron emission
      benchmark: work_function
      value: 2.6 eV
      line: The vendor table gives 2.6 eV. NASA measured 2.1 to 2.44 eV in hollow cathodes run in gas discharge.
    - label: Hardness
      benchmark: hardness
      value: 20 GPa
      line: Dense LaB6 is about 20 GPa hard (Sonber 2014, test load not stated).
    - label: Heat conduction
      benchmark: thermal_conductivity
      value: 47 W/mK
      line: The vendor gives 47 W/mK at 20 degC.
  compare: Within this profile, LaB6 has a density of 4.72 g/cm3, a melting point of 2528 K and a work function of 2.6 eV. The sources read do not name a second material for a direct ranking. The vendor claims about 10 times the brightness of tungsten cathodes, which is a vendor claim and not an independent test.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Melting point
      benchmark: melting_point
    - label: Work function
      benchmark: work_function
  handling:
    - 'Materion: observe good industrial hygiene practices, and store in the original tightly closed container away from incompatible materials.'
    - 'Fire: use water spray to cool unopened containers. Gases hazardous to health may form during a fire (Materion).'
    - Oxidation starts at 500 degC in air (Sonber 2014). The sources read give no handling rule for it.
  good_for:
    - 'Hot-cathode electron sources: vendor work function 2.6 eV, and NASA''s 2.66 eV reference for polycrystalline LaB6.'
    - Hall thruster hollow cathodes that need less stringent xenon purity than barium oxide cathodes (NASA 2010).
  watch_out:
    - 'Oxidation: starts at 500 degC in air and speeds up at 700 degC (Sonber 2014).'
    - 'Oxygen: LaB6 resists poisoning better than dispenser cathodes, but oxygen still cuts emission (Michigan Tech thesis).'
    - 'Work function: measured 2.1 to 2.44 eV in gas discharge, against 2.6 and 2.66 eV in the vendor table and the accepted value.'
    - No lifetime in hours for a LaB6 cathode was found in a source read.
  verdict: LaB6 is a dense, high-melting boride used as a hot electron source in electron beam instruments and Hall thruster cathodes. Its limits are oxidation from 500 degC in air and oxygen poisoning in oxygen-rich plasma. PubChem and the Materion SDS show no hazard classification, but the SDS reports no toxicology data.