spore: profile
id: glassy-carbon
spore_version: 0.2
family: carbon-materials
name: Glassy carbon
abbreviation: GC
role: dense amorphous carbon for crucibles, electrodes and high-temperature labware
category: carbon
type: Graphite
summary: |
  Glassy carbon, also called vitreous carbon, is a dense, non-graphitising carbon made by carbonising a phenolic resin. It has no layered crystal structure, so it is hard, gas-tight and resistant to attack by acids, alkalis and melts. SPI Supplies sells it as SIGRADUR in a K grade rated to 1000 °C and a G grade rated to 3000 °C in vacuum or inert gas.
best_for: High-temperature crucibles and electrodes that must resist attack by acids, alkalis and melts
weakest_at: Hard and brittle, and it oxidises in air above about 500 to 600 °C
identity:
  formula: C
  cas: 7440-44-0
  source: pubchem-carbon
  where: 'PubChem Carbon record (CID 5462310): formula C, CAS 7440-44-0 in the synonym list. Glassy carbon has no separate CAS number in the sources read; the CAS is that of the element.'
tags:
  applications:
    - electronics-and-chips
properties:
  - benchmark: density
    value: 1.54
    unit: g/cm3
    scope: material
    conditions:
      grade: Sigradur K
      heat_treatment_temperature: 1100 °C
      temperature: not stated in the table
    method: Bulk density printed in the SPI Supplies grade table
    status: ground
    source: spi-sigradur-info
    where: Available Grades table, row Bulk Density, Sigradur K column
  - benchmark: density
    value: 1.42
    unit: g/cm3
    scope: material
    conditions:
      grade: Sigradur G
      heat_treatment_temperature: 2200 °C
      temperature: not stated in the table
    method: Bulk density printed in the SPI Supplies grade table
    status: ground
    source: spi-sigradur-info
    where: Available Grades table, row Bulk Density, Sigradur G column
  - benchmark: density
    value: 1.43
    value_high: 1.46
    bound: range
    unit: g/cm3
    scope: material
    conditions:
      grade: Tokai GC-30, heat-treated at 3000 °C (a different manufacturer's grade, used as a cross-check only)
      method_in_source: apparent density from sample weight and measured volume
    method: Range printed in a 1966 NASA JPL report on two Tokai glassy carbon grades
    status: ground
    source: nasa-tm-32-842
    where: Table I, Apparent density row, GC-30 column
  - benchmark: max_service_temp
    value: 1000
    unit: °C
    scope: material
    conditions:
      grade: Sigradur K
      atmosphere: not stated in the table
    method: Maximum service temperature printed in the SPI Supplies grade table
    status: ground
    source: spi-sigradur-info
    where: Available Grades table, row Maximum Service Temperature, Sigradur K column
  - benchmark: max_service_temp
    value: 3000
    unit: °C
    scope: material
    conditions:
      grade: Sigradur G
      atmosphere: not stated in the table
    method: Maximum service temperature printed in the SPI Supplies grade table
    status: ground
    source: spi-sigradur-info
    where: Available Grades table, row Maximum Service Temperature, Sigradur G column
  - benchmark: max_service_temp
    value: 500
    value_high: 600
    bound: range
    unit: °C
    scope: material
    conditions:
      grade: Goodfellow glassy carbon 3000C sheet
      atmosphere: air
    method: Maximum temperature in air printed on the Goodfellow product page
    status: ground
    source: goodfellow-gc-3000c
    where: Properties list, Max Temperature line (500 to 600 °C in air)
  - benchmark: vickers_hardness
    value: 340
    unit: HV1
    scope: material
    conditions:
      grade: Sigradur K
      test: Vickers, HV1 as printed in the table
    method: Vickers hardness printed in the SPI Supplies grade table
    status: ground
    source: spi-sigradur-info
    where: Available Grades table, row Vickers Hardness, Sigradur K column
  - benchmark: vickers_hardness
    value: 230
    unit: HV1
    scope: material
    conditions:
      grade: Sigradur G
      test: Vickers, HV1 as printed in the table
    method: Vickers hardness printed in the SPI Supplies grade table
    status: ground
    source: spi-sigradur-info
    where: Available Grades table, row Vickers Hardness, Sigradur G column
  - benchmark: mohs_hardness
    value: 7
    unit: Mohs
    scope: material
    conditions:
      form: standard glassy carbon (not the 2011 high-pressure form)
    method: Mohs hardness stated in the Physical properties section of the encyclopedia article
    status: ground
    source: wiki-glassy-carbon
    where: Physical properties section, Hardness
  - benchmark: flexural_strength
    value: 210
    unit: N/mm2
    scope: material
    conditions:
      grade: Sigradur K
      specimen: as footnoted in the SPI Supplies table (the footnotes give the test geometry)
    method: Flexural strength printed in the SPI Supplies grade table
    status: ground
    source: spi-sigradur-info
    where: Available Grades table, row Flexural Strength, Sigradur K column
  - benchmark: flexural_strength
    value: 260
    unit: N/mm2
    scope: material
    conditions:
      grade: Sigradur G
      specimen: as footnoted in the SPI Supplies table (the footnotes give the test geometry)
    method: Flexural strength printed in the SPI Supplies grade table
    status: ground
    source: spi-sigradur-info
    where: Available Grades table, row Flexural Strength, Sigradur G column
  - benchmark: elastic_modulus
    value: 35
    unit: kN/mm2
    scope: material
    conditions:
      grade: Sigradur K
      test: 4-point bending on a circular rod, 3 mm diameter and 60 mm long (table footnote 1)
    method: Young's modulus printed in the SPI Supplies grade table
    status: ground
    source: spi-sigradur-info
    where: Available Grades table, row Young's Modulus, Sigradur K column; footnote 1
  - benchmark: elastic_modulus
    value: 35
    unit: kN/mm2
    scope: material
    conditions:
      grade: Sigradur G
      test: 4-point bending on a circular rod, 3 mm diameter and 60 mm long (table footnote 1)
    method: Young's modulus printed in the SPI Supplies grade table
    status: ground
    source: spi-sigradur-info
    where: Available Grades table, row Young's Modulus, Sigradur G column; footnote 1
  - benchmark: cte
    value: 2.5
    unit: x10-6 K-1
    scope: material
    conditions:
      grade: Sigradur K
      temperature: 20 to 2000 °C
    method: Mean coefficient of thermal expansion printed in the SPI Supplies grade table
    status: ground
    source: spi-sigradur-info
    where: Available Grades table, row Coefficient of Thermal Expansion (20 to 2000 °C), Sigradur K column
  - benchmark: cte
    value: 2.6
    unit: x10-6 K-1
    scope: material
    conditions:
      grade: Sigradur G
      temperature: 20 to 2000 °C
    method: Mean coefficient of thermal expansion printed in the SPI Supplies grade table
    status: ground
    source: spi-sigradur-info
    where: Available Grades table, row Coefficient of Thermal Expansion (20 to 2000 °C), Sigradur G column
  - benchmark: thermal_conductivity
    value: 4.6
    unit: W/(K.m)
    scope: material
    conditions:
      grade: Sigradur K
      temperature: 30 °C
    method: Thermal conductivity printed in the SPI Supplies grade table
    status: ground
    source: spi-sigradur-info
    where: Available Grades table, row Thermal Conductivity (30 °C), Sigradur K column
  - benchmark: thermal_conductivity
    value: 6.3
    unit: W/(K.m)
    scope: material
    conditions:
      grade: Sigradur G
      temperature: 30 °C
    method: Thermal conductivity printed in the SPI Supplies grade table
    status: ground
    source: spi-sigradur-info
    where: Available Grades table, row Thermal Conductivity (30 °C), Sigradur G column
  - benchmark: electrical_resistivity
    value: 50
    unit: ohm µm
    scope: material
    conditions:
      grade: Sigradur K
      temperature: not stated in the table
    method: Specific electrical resistance printed in the SPI Supplies grade table
    status: ground
    source: spi-sigradur-info
    where: Available Grades table, row Specific electrical resistance, Sigradur K column
  - benchmark: electrical_resistivity
    value: 45
    unit: ohm µm
    scope: material
    conditions:
      grade: Sigradur G
      temperature: not stated in the table
    method: Specific electrical resistance printed in the SPI Supplies grade table
    status: ground
    source: spi-sigradur-info
    where: Available Grades table, row Specific electrical resistance, Sigradur G column
risks:
  hazards:
    - text: 'PubChem''s Carbon record (aggregated company reports): 40.2% of 2727 reports (1095) say the chemical does not meet GHS hazard criteria. Among reports that give hazard codes, H319 is notified in 55.1% and H335 in 51.1%. The record covers the element carbon, not glassy carbon specifically.'
      ghs: []
      source: pubchem-carbon
      where: Safety and Hazards, GHS Classification (Carbon, CID 5462310)
  failure_risks:
    - mode: Devitrification and growth of a graphite phase at high temperature
      trigger: Heating above about 2500 °C, depending on grade
      consequence: Some devitrification occurs, nucleating and growing a graphite phase. The higher the density, the higher the temperature at which this happens.
      severity: moderate
      source: spi-sigradur-info
      where: Thermal Properties section
    - mode: Oxidation in air at high temperature
      trigger: Heating in air above about 500 to 600 °C
      consequence: The material reacts with air and forms CO and CO2 unless heated under vacuum or inert gas.
      severity: moderate
      source: spi-sigradur-info
      where: Thermal Properties section, air paragraph
    - mode: Brittle fracture
      trigger: Mechanical shock or bending load on a hard part
      consequence: The material is described as hard and brittle, so it can fracture without much plastic deformation.
      severity: low
      source: nasa-tm-32-842
      where: Introduction (first pages), description of glassy carbon
  side_effects:
    - text: Above 600 °C, water or water vapour reacts with the material and gives off CO and H2.
      affects: The furnace atmosphere and any gas-handling equipment
      source: spi-sigradur-info
      where: Thermal Properties section, water vapour paragraph
  handling:
    - text: Heat above about 600 °C only under vacuum or argon. In air the Sigradur grades are safe only up to about 600 °C.
      source: spi-sigradur-info
    - text: Keep water vapour away from the part above 600 °C, because it gives off CO and H2.
      source: spi-sigradur-info
  mitigations:
    - text: Heat in vacuum or in an inert gas such as argon for temperatures above 600 °C; the SPI sheet says this avoids the reaction.
      source: spi-sigradur-info
corrosion:
  - environment: Air at high temperature
    headline: In air the material is stable only to about 500 to 600 °C.
    effect: Goodfellow rates its 3000C glassy carbon sheet at 500 to 600 °C in air, against 3000 °C in vacuum or inert gas. Oxidation in air is the limit on use.
    rating: moderate
    conditions:
      atmosphere: air
      temperature: 500 to 600 °C and above
    source: goodfellow-gc-3000c
    where: Properties list, Max Temperature line
  - environment: Water vapour above 600 °C
    headline: Above 600 °C, water vapour attacks the material and gives off CO and H2.
    effect: SPI Supplies says that above 600 °C, water or water vapour reacts with glassy carbon and gives off CO and H2, the same as dry air does with CO and CO2.
    rating: moderate
    conditions:
      atmosphere: water or water vapour
      temperature: above 600 °C
    source: spi-sigradur-info
    where: Thermal Properties section, water vapour paragraph
  - environment: Acids, alkalis and molten materials
    headline: Glassy carbon resists acids, alkalis and melts.
    effect: SPI Supplies says glassy carbon has high resistance to corrosion by acid and alkaline agents and melts. Its disordered structure prevents intercalation compounds from forming, and the high density limits attack. The source gives no acid concentrations or temperatures.
    rating: low
    conditions:
      exposure: acids, alkalis and melts; concentrations and temperatures not stated
    source: spi-sigradur-info
    where: Chemical Resistance section; Characteristic Properties list
  - environment: Very high temperature under vacuum or inert gas
    headline: Above about 2500 °C, the structure starts to change.
    effect: Depending on grade, the material is stable to about 2500 °C without significant devitrification. Above that, some devitrification occurs as a graphite phase grows.
    rating: moderate
    conditions:
      atmosphere: vacuum or inert gas
      temperature: about 2500 °C and above
    source: spi-sigradur-info
    where: Thermal Properties section
uses:
  - application: electronics-and-chips
    device: High-temperature crucible for zone refining of gallium arsenide
    example: The encyclopedia article lists high-temperature crucibles, including zone refining of gallium arsenide, because the material does not react with the melt.
    source: wiki-glassy-carbon
    where: Introduction and Applications
  - application: electronics-and-chips
    device: Electrode for electrochemistry and chemically modified sensors
    example: SPI Supplies recommends the Sigradur grade only for electrochemical work, because of its much greater corrosion resistance and better electrical conductivity.
    source: spi-sigradur-info
    where: Electrochemical Application section
supply:
  - subject: Natural graphite (mine feedstock; not the precursor of glassy carbon, shown for context only)
    abundance: The rest of the world's graphite resources exceed 800 million tons of recoverable graphite, according to USGS.
    producers:
      - country: China
        share_percent: 77.8
        year: 2025
      - country: Madagascar
        share_percent: 4.4
        year: 2025
      - country: Brazil
        share_percent: 3.6
        year: 2025
      - country: Mozambique
        share_percent: 3.3
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (graphite)
        listed: true
    recycling: 'USGS: the abundance of graphite in the world market inhibits recycling. Information on the quantity of recycled graphite was not available.'
    substitutes:
      - 'USGS: synthetic graphite powder and secondary synthetic graphite from machined shapes compete for battery applications.'
    source: usgs-mcs2026-graphite
    where: 'World Mine Production and Reserves table, 2025e (world total 1,800,000 t; shares calculated from the printed production: China 1,400,000 t, Madagascar 80,000 t, Brazil 65,000 t, Mozambique 60,000 t; the narrative says China produced an estimated 82%); Recycling; Substitutes'
media: []
documents:
  - title: 'SPI Supplies: Sigradur Glassy (Vitreous) Carbon Products information sheet (revised 04/25)'
    type: datasheet
    url: https://www.2spi.com/catalog/documents/Glassy-Vitreous-Carbon-Info.pdf
    year: 2025
  - title: 'Goodfellow: Glassy carbon 3000C sheet, product page'
    type: datasheet
    url: https://www.goodfellow.com/usa/glassy-carbon-3000c-glassy-carbon-rvc-sheet-group
    year: 2026
  - title: 'NASA JPL Technical Report 32-842: Tensile and Structural Properties of Glassy Carbon'
    type: report
    url: https://ntrs.nasa.gov/citations/19660004265
    year: 1966
  - title: 'USGS Mineral Commodity Summaries 2026: Graphite (natural)'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-graphite.pdf
    year: 2026
  - title: 'PubChem: Carbon (CID 5462310), GHS classification and properties'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/5462310
    year: 2026
gaps:
  - No safety data sheet for SIGRADUR was read. The OSHA chemical data page for graphite returned HTTP 403 in this run, so no dust limit is given. The hazard entries rest on the PubChem record for the element carbon.
  - No producer or production share was found for glassy carbon or for its phenolic resin precursor. SPI Supplies is a distributor, and the SGL Carbon encyclopedia page does not name SIGRADUR, so the maker is not stated.
  - 'No space data for glassy carbon was found: no atomic oxygen erosion yield, outgassing, radiation or thermal-cycling result.'
  - The 1966 NASA report (Tokai GC-20 and GC-30) is a different manufacturer's product line. Only its GC-30 density is used, as a labelled cross-check; its other values are not used because their units do not match the SIGRADUR table.
  - Compressive strength is printed in the SPI table as 580 and 480 kN/mm2. That unit gives values about a thousand times too large for this material, so the figures are left out as a probable unit error.
  - The SPI table prints an ash value (below 100 ppm), open porosity (0 %) and a permeability coefficient. The permeability exponents did not extract cleanly from the PDF, and no canonical property name fits ash or porosity, so these are left out.
  - Vickers hardness and Mohs hardness are not canonical names in property-canon.yaml. The names vickers_hardness and mohs_hardness are used.
  - Chemical resistance is qualitative in the source. No acid or alkali concentration, temperature or exposure time is given.
  - Thermal conductivity is given at 30 °C only. The encyclopedia article calls it high in one place and low thermal resistance in another, and carries a citation-needed tag, so no number from it is used.
  - Flexural strength footnote markers in the SPI table are hard to read in the PDF text. The test geometry is given as the footnote numbers, so the specimen condition is recorded only as footnoted.
sources:
  wiki-glassy-carbon:
    title: 'Wikipedia: Glassy carbon'
    id: en.wikipedia.org, Glassy_carbon
    url: https://en.wikipedia.org/wiki/Glassy_carbon
    year: 2026
    kind: web
    license: CC BY-SA 4.0 (cited)
  spi-sigradur-info:
    title: 'SPI Supplies: Sigradur Glassy (Vitreous) Carbon Products, information sheet with grade table'
    id: SPI Supplies, 206 Garfield Avenue, West Chester PA, revised 04/25
    url: https://www.2spi.com/catalog/documents/Glassy-Vitreous-Carbon-Info.pdf
    year: 2025
    kind: datasheet
    license: cited, not reproduced
  spi-plates-page:
    title: 'SPI Supplies: Glassy (Vitreous) Carbon Plates, category page'
    id: 2spi.com, glassy-carbon-plates category
    url: https://www.2spi.com/category/glassy-carbon-plates/
    year: 2026
    kind: web
    license: cited, not reproduced
  spi-rods-page:
    title: 'SPI Supplies: Sigradur K Glassy (Vitreous) Carbon Rods, 10 mm long, product page'
    id: 2spi.com, item z4177gc
    url: https://www.2spi.com/item/z4177gc/
    year: 2026
    kind: web
    license: cited, not reproduced
  goodfellow-gc-3000c:
    title: 'Goodfellow: Glassy carbon 3000C glassy carbon RVC sheet group, product page'
    id: Goodfellow, grade Glassy Carbon - 3000C
    url: https://www.goodfellow.com/usa/glassy-carbon-3000c-glassy-carbon-rvc-sheet-group
    year: 2026
    kind: datasheet
    license: cited, not reproduced
  nasa-tm-32-842:
    title: 'NASA JPL Technical Report 32-842: Tensile and Structural Properties of Glassy Carbon (Kotlensky and Fischbach)'
    id: NASA NTRS 19660004265, JPL TR 32-842
    url: https://ntrs.nasa.gov/citations/19660004265
    year: 1966
    kind: report
    license: NASA public domain (cited)
  pubchem-carbon:
    title: 'PubChem compound record: Carbon (CID 5462310)'
    id: CID 5462310; CAS 7440-44-0 (synonym list)
    url: https://pubchem.ncbi.nlm.nih.gov/compound/5462310
    year: 2026
    kind: database
    license: public domain (NCBI)
  usgs-mcs2026-graphite:
    title: 'Mineral Commodity Summaries 2026: Graphite (natural)'
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-graphite.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-critical-2025:
    title: 'USGS: Interior Department releases final 2025 List of Critical Minerals (science snippet)'
    id: USGS science snippet, 14 November 2025
    url: https://www.usgs.gov/news/science-snippet/interior-department-releases-final-2025-list-critical-minerals
    year: 2025
    kind: web
    license: public domain (USGS)
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 19
  note: Values read by an AI assistant from pages fetched in this run. The SIGRADUR grade values come from the SPI Supplies information sheet, a distributor document; no manufacturer datasheet was reached.
story:
  recipe:
    line: Glassy carbon is pure carbon made by heating a phenolic resin until it carbonises. The resin sets without a catalyst and can be shaped while uncured, and the carbon that remains is amorphous, with no layered crystal structure.
    parts:
      - name: Carbon
        symbol: C
        atoms: 1
        atomic_weight: 12.011
        role: The only element in the material. The carbon atoms are sp2-bonded in a disordered network, and X-ray diffraction shows only an amorphous halo.
  risk_groups:
    - title: For people
      level: 0
      verdict: Few hazard data; no SDS read
      lead: No safety data sheet for SIGRADUR was read in this run. The PubChem carbon record says most company reports do not meet GHS hazard criteria, but some notify eye and respiratory irritation codes.
      points:
        - label: Reports
          line: 'PubChem: 40.2% of 2727 reports (1095) say the chemical does not meet GHS hazard criteria. Among reports that give codes, H319 is notified in 55.1% and H335 in 51.1%.'
        - label: Gases
          line: Above 600 °C, heating in air gives off CO and CO2, and water vapour gives off CO and H2.
    - title: At high temperature
      lead: The temperature limit depends on the atmosphere, and the SPI sheet gives the limits.
      points:
        - label: In air
          line: In air the material is safe only to about 600 °C, and the Goodfellow sheet gives 500 to 600 °C.
        - label: In vacuum or argon
          line: The G grade is rated to 3000 °C in vacuum or inert gas, and the Goodfellow 3000C sheet gives the same limit.
        - label: Devitrification
          line: Above about 2500 °C, depending on grade, a graphite phase can grow inside the material.
    - title: Handling
      points:
        - label: Atmosphere
          line: Heat above 600 °C under vacuum or argon only, as the SPI sheet recommends.
  why: 'Glassy carbon is a dense, non-graphitising carbon with an amorphous structure. It combines the hardness and gas tightness of a ceramic with the conduction and high-temperature stability of graphite. SIGRADUR comes in two grades: K, with a maximum service temperature of 1000 °C and a bulk density of 1.54 g/cm3, and G, rated to 3000 °C with a bulk density of 1.42 g/cm3.'
  uses:
    - where: High-temperature crucibles
      line: The encyclopedia article lists crucibles among its uses, including zone refining of gallium arsenide, because the material does not react with the melt.
    - where: Electrochemistry
      line: SPI Supplies recommends the Sigradur grade only for electrochemical work, because of its greater corrosion resistance and better electrical conductivity.
  can_do:
    - label: Heat
      benchmark: max_service_temp
      value: Up to 3000 °C
      line: The G grade is rated to 3000 °C and the K grade to 1000 °C in the SPI table. In vacuum or inert gas, Goodfellow's 3000C sheet is rated to 3000 °C as well.
    - label: Density
      benchmark: density
      value: 1.54 g/cm3
      line: The K grade has a bulk density of 1.54 g/cm3 and the G grade 1.42 g/cm3. A 1966 NASA report on a different manufacturer's grade measured 1.43 to 1.46 g/cm3.
    - label: Hardness
      benchmark: vickers_hardness
      value: 340 HV1
      line: Vickers hardness is 340 HV1 for the K grade and 230 HV1 for the G grade. The encyclopedia article gives a Mohs hardness of 7.
    - label: Conduction
      benchmark: thermal_conductivity
      value: 4.6 W/(K.m)
      line: Thermal conductivity at 30 °C is 4.6 W/(K.m) for K and 6.3 W/(K.m) for G. Specific electrical resistance is 50 ohm µm for K and 45 ohm µm for G.
  compare: Glassy carbon is amorphous, unlike layered graphite, and it is non-porous, unlike most graphites. Its hardness is in the ceramic range, and its G grade is rated to 3000 °C in vacuum or inert gas. The table sets out its maximum temperature, density and thermal conductivity by grade.
  compare_rows:
    - label: Maximum service temperature
      benchmark: max_service_temp
    - label: Density
      benchmark: density
    - label: Thermal conductivity
      benchmark: thermal_conductivity
  handling:
    - Heat above 600 °C only under vacuum or argon, because in air the material reacts.
    - Keep water vapour away from the part above 600 °C, because it gives off CO and H2.
    - SPI Supplies makes plates only up to 6 mm thick, so plan the part size around that limit.
  good_for:
    - High-temperature crucibles and labware. The G grade is rated to 3000 °C in vacuum or inert gas.
    - Electrodes and chemically resistant parts, because the material resists attack by acids, alkalis and melts.
    - Parts that need a smooth, dense surface. SPI says the material can be polished to a mirror finish.
  watch_out:
    - Hard and brittle, according to the 1966 NASA report.
    - It oxidises in air above about 500 to 600 °C, and its structure starts to devitrify above about 2500 °C.
    - Plate thickness is limited to 6 mm by SPI Supplies' present process.
    - 'The grades differ: 1.54 against 1.42 g/cm3, and 4.6 against 6.3 W/(K.m) for conduction.'
  verdict: Glassy carbon suits crucibles and corrosion-resistant electrodes. The K grade is rated to 1000 °C; the G grade reaches 3000 °C in vacuum or inert gas but must be kept out of air above about 600 °C.