{
  "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",
    "designations": [],
    "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,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "melting_point",
      "label": "Melting point, LaB6 (vendor specification)",
      "value": 2528,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "work_function",
      "label": "Electron emissivity (work function), LaB6 cathode (vendor table)",
      "value": 2.6,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "work_function",
      "label": "Accepted work function, polycrystalline LaB6 (as quoted by the NASA authors)",
      "value": 2.66,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "thermal_conductivity",
      "label": "Thermal conductivity, LaB6 (vendor specification)",
      "value": 47,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "cte",
      "label": "Mean coefficient of thermal expansion, LaB6 (vendor specification)",
      "value": 6.2,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "electrical_resistivity",
      "label": "Electrical resistance, LaB6 (vendor specification)",
      "value": 15,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "emission_current_density",
      "label": "Emission current density, LaB6 cathode (vendor specification)",
      "value": 150,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "hardness_rockwell_a",
      "label": "Hardness, LaB6 (vendor specification, Rockwell A)",
      "value": 87.5,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "flexural_strength",
      "label": "Flexure strength, LaB6 (vendor specification)",
      "value": 200,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "hardness",
      "label": "Hardness, dense LaB6 (Sonber 2014)",
      "value": 20,
      "bound": "exact",
      "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",
      "source_detail": {
        "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)"
      }
    },
    {
      "benchmark": "fracture_toughness",
      "label": "Fracture toughness, dense LaB6 (Sonber 2014)",
      "value": 3.02,
      "bound": "exact",
      "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",
      "source_detail": {
        "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)"
      }
    },
    {
      "benchmark": "relative_density",
      "label": "Relative density after pressureless sintering (Sonber 2014)",
      "value": 85.1,
      "bound": "exact",
      "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",
      "source_detail": {
        "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)"
      }
    },
    {
      "benchmark": "oxidation_onset_temp",
      "label": "Oxidation onset temperature in air, LaB6 (thermogravimetry)",
      "value": 500,
      "bound": "exact",
      "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",
      "source_detail": {
        "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)"
      }
    }
  ],
  "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.",
      "substitutes": [],
      "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.",
      "substitutes": [],
      "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."
  ],
  "story": {
    "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",
        "line": "The vendor gives a melting point of 2528 K.",
        "benchmark": "melting_point",
        "scope": "material",
        "value": "2528 K"
      },
      {
        "label": "Electron emission",
        "line": "The vendor table gives 2.6 eV. NASA measured 2.1 to 2.44 eV in hollow cathodes run in gas discharge.",
        "benchmark": "work_function",
        "scope": "material",
        "value": "2.6 eV"
      },
      {
        "label": "Hardness",
        "line": "Dense LaB6 is about 20 GPa hard (Sonber 2014, test load not stated).",
        "benchmark": "hardness",
        "scope": "material",
        "value": "20 GPa"
      },
      {
        "label": "Heat conduction",
        "line": "The vendor gives 47 W/mK at 20 degC.",
        "benchmark": "thermal_conductivity",
        "scope": "material",
        "value": "47 W/mK"
      }
    ],
    "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",
        "scope": "material"
      },
      {
        "label": "Melting point",
        "benchmark": "melting_point",
        "scope": "material"
      },
      {
        "label": "Work function",
        "benchmark": "work_function",
        "scope": "material"
      }
    ],
    "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.",
    "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",
          "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",
          "role": "Boron framework that pairs with the lanthanum in the formula LaB6 (PubChem)."
        }
      ]
    },
    "risk_groups": [
      {
        "title": "For people",
        "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."
          }
        ],
        "level": 0,
        "verdict": "Not classified in PubChem or Materion SDS"
      },
      {
        "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)."
          }
        ]
      }
    ]
  },
  "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."
  },
  "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",
  "url": "https://spacemushroom.com/profiles/lanthanum-hexaboride/"
}