Glassy carbon GC
C · CAS 7440-44-0
Glassy carbon, also called vitreous carbon, is a dense, non-graphitising carbon made by carbonising a phenolic resin.
Evidence level
2 of 5
Lab-measured
- 0Predicted only. No one has made it, or no measurement exists.
- 1Calculated. Only calculated or predicted values from sources.
- 2Lab-measured. Measured properties with their conditions stated.
- 3Space-relevant tests. Measured in conditions relevant to space, such as vacuum or atomic oxygen.
- 4Ground-qualified. Qualified for an application on the ground.
- 5Flown or field-proven. Flight or field results exist.
Heat
Up to 3000 °C
Density
1.54 g/cm3
Hardness
340 HV1
Conduction
4.6 W/(K.m)
Recipe, share of the weight
- C 100.0%Carbon
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
Risk at a glance
- People None found. Few hazard data; no SDS read
- If it fails Moderate. Devitrification and growth of a graphite phase at high temperature
- Corrosion Moderate. In air the material is stable only to about 500 to 600 °C.
Quick facts: GC
| Property | Value | Basis |
|---|---|---|
| Density | 1.42 to 1.54 g/cm³ | 3 sourced values across conditions |
| Young's modulus | 35 GPa | 2 sourced values across conditions |
| Thermal conductivity | 4.6 to 6.3 W/(K.m) | 2 sourced values across conditions |
| Thermal expansion (CTE) | 2.5 to 2.6 ppm/K | 2 sourced values across conditions |
| Electrical resistivity | 45 to 50 ohm µm | 2 sourced values across conditions |
| Maximum service temperature | 500 to 3,000 °C | 3 sourced values across conditions |
What is the density of Glassy carbon (GC)?
Glassy carbon (GC) has a density of 1.42 to 1.54 g/cm³. The range covers 3 sourced values across the tempers, forms and test conditions the sources report; room-temperature values are used where a source states a temperature.
What is the thermal conductivity of Glassy carbon (GC)?
Glassy carbon (GC) has a thermal conductivity of 4.6 to 6.3 W/(K.m). The range covers 2 sourced values across the tempers, forms and test conditions the sources report; room-temperature values are used where a source states a temperature.
What is the coefficient of thermal expansion of Glassy carbon (GC)?
Glassy carbon (GC) has a coefficient of thermal expansion of 2.5 to 2.6 ppm/K. The range covers 2 sourced values across the tempers, forms and test conditions the sources report; room-temperature values are used where a source states a temperature.
What is the Young's modulus of Glassy carbon (GC)?
Glassy carbon (GC) has a Young's modulus of 35 GPa. The range covers 2 sourced values across the tempers, forms and test conditions the sources report; room-temperature values are used where a source states a temperature.
What is the maximum service temperature of Glassy carbon (GC)?
Glassy carbon (GC) has a maximum service temperature of 500 to 3,000 °C. The range covers 3 sourced values across the tempers, forms and test conditions the sources report; room-temperature values are used where a source states a temperature.
What is Glassy carbon (GC) used for?
Uses recorded in the sources include High-temperature crucible for zone refining of gallium arsenide; Electrode for electrochemistry and chemically modified sensors.
Why it exists
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.
Where it's used
High-temperature crucibles
The encyclopedia article lists crucibles among its uses, including zone refining of gallium arsenide, because the material does not react with the melt.
Electrochemistry
SPI Supplies recommends the Sigradur grade only for electrochemical work, because of its greater corrosion resistance and better electrical conductivity.
Recipe
C
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.
| Ingredient | Atoms per unit | Share of the weight | What it does |
|---|---|---|---|
| Carbon C | 1 | 100.0% | 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. |
Weight shares are calculated from standard atomic weights.
What it can do
Heat
Up to 3000 °C
measured
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.
Density
1.54 g/cm3
measured
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.
Hardness
340 HV1
measured
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.
Conduction
4.6 W/(K.m)
measured
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.
How it compares
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.
The same measurements for each material, so you can compare them. Each row names the key condition under the value; the full conditions and methods are in the numbered notes under Technical details. Other materials are shown beside it; each was measured under its own conditions, so open its page before comparing closely. Compare every grade in the family.
| Measurement | GC | Gr-S | PG |
|---|---|---|---|
| Thermal behavior and safety | |||
| Thermal conductivity | 4.6 W/(K.m)16 | 105 W m-1 K-1 | 80 W m-1 K-1 |
| Thermal conductivity | 6.3 W/(K.m)17 | 105 W m-1 K-1 | 80 W m-1 K-1 |
| Physical and electrical | |||
| Density | 1.54 g/cm³1 | 1.72 g/cm³ | 2.25 g cm-3 |
| Density | 1.42 g/cm³2 | 1.72 g/cm³ | 2.25 g cm-3 |
| Density | 1.43 to 1.46 g/cm³3 | 1.72 g/cm³ | 2.25 g cm-3 |
| vickers hardness | 340 HV17 | no data | no data |
| vickers hardness | 230 HV18 | no data | no data |
| mohs hardness | 7 Mohs9 | no data | no data |
| electrical resistivity | 50 ohm µm18 | 12 µΩm | 1375 µOhm cm |
| electrical resistivity | 45 ohm µm19 | 12 µΩm | 1375 µOhm cm |
| Other measurements | |||
| Maximum service temperature | 1000 °C4 | 3000 °C | no data |
| Maximum service temperature | 3000 °C5 | 3000 °C | no data |
| Maximum service temperature | 500 to 600 °C6 | 3000 °C | no data |
| flexural strength | 210 N/mm210 | 45 MPa | no data |
| flexural strength | 260 N/mm211 | 45 MPa | no data |
| elastic modulus | 35 kN/mm212 | 14 GPa | 4.8 GPa |
| elastic modulus | 35 kN/mm213 | 14 GPa | 4.8 GPa |
| Thermal expansion (CTE) | 2.5 x10-6 K-114 | 3.2 x10-6 K-1 | 0.6 x10-6 K-1 |
| Thermal expansion (CTE) | 2.6 x10-6 K-115 | 3.2 x10-6 K-1 | 0.6 x10-6 K-1 |
Why choose it, and why not
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 for
- 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.
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.
Technical details
For scientists and researchers. Everything above comes from the record below: every number with its method, its conditions and its source.
Notes
The method, full conditions and any caveat for the numbered rows above.
| # | Measurement | Method | Conditions | Caveat |
|---|---|---|---|---|
| 1 | Density | Bulk density printed in the SPI Supplies grade table | grade Sigradur Kheat treatment temperature 1100 °Ctemperature not stated in the table | — |
| 2 | Density | Bulk density printed in the SPI Supplies grade table | grade Sigradur Gheat treatment temperature 2200 °Ctemperature not stated in the table | — |
| 3 | Density | Range printed in a 1966 NASA JPL report on two Tokai glassy carbon grades | 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 | — |
| 4 | Maximum service temperature | Maximum service temperature printed in the SPI Supplies grade table | grade Sigradur Katmosphere not stated in the table | — |
| 5 | Maximum service temperature | Maximum service temperature printed in the SPI Supplies grade table | grade Sigradur Gatmosphere not stated in the table | — |
| 6 | Maximum service temperature | Maximum temperature in air printed on the Goodfellow product page | grade Goodfellow glassy carbon 3000C sheetatmosphere air | — |
| 7 | vickers hardness | Vickers hardness printed in the SPI Supplies grade table | grade Sigradur Ktest Vickers, HV1 as printed in the table | — |
| 8 | vickers hardness | Vickers hardness printed in the SPI Supplies grade table | grade Sigradur Gtest Vickers, HV1 as printed in the table | — |
| 9 | mohs hardness | Mohs hardness stated in the Physical properties section of the encyclopedia article | form standard glassy carbon (not the 2011 high-pressure form) | — |
| 10 | flexural strength | Flexural strength printed in the SPI Supplies grade table | grade Sigradur Kspecimen as footnoted in the SPI Supplies table (the footnotes give the test geometry) | — |
| 11 | flexural strength | Flexural strength printed in the SPI Supplies grade table | grade Sigradur Gspecimen as footnoted in the SPI Supplies table (the footnotes give the test geometry) | — |
| 12 | elastic modulus | Young's modulus printed in the SPI Supplies grade table | grade Sigradur Ktest 4-point bending on a circular rod, 3 mm diameter and 60 mm long (table footnote 1) | — |
| 13 | elastic modulus | Young's modulus printed in the SPI Supplies grade table | grade Sigradur Gtest 4-point bending on a circular rod, 3 mm diameter and 60 mm long (table footnote 1) | — |
| 14 | Thermal expansion (CTE) | Mean coefficient of thermal expansion printed in the SPI Supplies grade table | grade Sigradur Ktemperature 20 to 2000 °C | — |
| 15 | Thermal expansion (CTE) | Mean coefficient of thermal expansion printed in the SPI Supplies grade table | grade Sigradur Gtemperature 20 to 2000 °C | — |
| 16 | Thermal conductivity | Thermal conductivity printed in the SPI Supplies grade table | grade Sigradur Ktemperature 30 °C | — |
| 17 | Thermal conductivity | Thermal conductivity printed in the SPI Supplies grade table | grade Sigradur Gtemperature 30 °C | — |
| 18 | electrical resistivity | Specific electrical resistance printed in the SPI Supplies grade table | grade Sigradur Ktemperature not stated in the table | — |
| 19 | electrical resistivity | Specific electrical resistance printed in the SPI Supplies grade table | grade Sigradur Gtemperature not stated in the table | — |
Corrosion and compatibility
What happens when it meets other materials and environments.
| Environment | Concern | What happens |
|---|---|---|
| Air at high temperature | moderate | In air the material is stable only to about 500 to 600 °C.1 |
| Water vapour above 600 °C | moderate | Above 600 °C, water vapour attacks the material and gives off CO and H2.2 |
| Acids, alkalis and molten materials | low | Glassy carbon resists acids, alkalis and melts.3 |
| Very high temperature under vacuum or inert gas | moderate | Above about 2500 °C, the structure starts to change.4 |
| # | Environment | Details | Test conditions |
|---|---|---|---|
| 1 | Air at high temperature | 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. | atmosphere airtemperature 500 to 600 °C and above |
| 2 | Water vapour above 600 °C | 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. | atmosphere water or water vapourtemperature above 600 °C |
| 3 | Acids, alkalis and molten materials | 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. | exposure acids, alkalis and melts; concentrations and temperatures not stated |
| 4 | Very high temperature under vacuum or inert gas | Depending on grade, the material is stable to about 2500 °C without significant devitrification. Above that, some devitrification occurs as a graphite phase grows. | atmosphere vacuum or inert gastemperature about 2500 °C and above |
Risks and side effects
Hazards to people, what happens when a cell overheats, and how the material is handled and stored.
For people
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.
- Reports
- 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%.
- Gases
- Above 600 °C, heating in air gives off CO and CO2, and water vapour gives off CO and H2.
At high temperature
The temperature limit depends on the atmosphere, and the SPI sheet gives the limits.
- In air
- In air the material is safe only to about 600 °C, and the Goodfellow sheet gives 500 to 600 °C.
- In vacuum or argon
- The G grade is rated to 3000 °C in vacuum or inert gas, and the Goodfellow 3000C sheet gives the same limit.
- Devitrification
- Above about 2500 °C, depending on grade, a graphite phase can grow inside the material.
Handling
- Atmosphere
- Heat above 600 °C under vacuum or argon only, as the SPI sheet recommends.
Test details
The original wording and numbers from the sources, for readers who want them.
Failure risks
| Failure | Trigger and consequence |
|---|---|
| Devitrification and growth of a graphite phase at high temperaturemoderate severity | Heating above about 2500 °C, depending on gradeSome devitrification occurs, nucleating and growing a graphite phase. The higher the density, the higher the temperature at which this happens. |
| Oxidation in air at high temperaturemoderate severity | Heating in air above about 500 to 600 °CThe material reacts with air and forms CO and CO2 unless heated under vacuum or inert gas. |
| Brittle fracturelow severity | Mechanical shock or bending load on a hard partThe material is described as hard and brittle, so it can fracture without much plastic deformation. |
Side effects on surrounding parts
| Affects | Effect |
|---|---|
| The furnace atmosphere and any gas-handling equipment | Above 600 °C, water or water vapour reacts with the material and gives off CO and H2. |
Handling and storage
- Heat above about 600 °C only under vacuum or argon. In air the Sigradur grades are safe only up to about 600 °C.
- Keep water vapour away from the part above 600 °C, because it gives off CO and H2.
Mitigations
- Heat in vacuum or in an inert gas such as argon for temperatures above 600 °C; the SPI sheet says this avoids the reaction.
Supply and geography
How common the raw materials are and where they come from.
Natural graphite (mine feedstock; not the precursor of glassy carbon, shown for context only)
The rest of the world's graphite resources exceed 800 million tons of recoverable graphite, according to USGS.
- Top producers (2025)
- China 77.8%, Madagascar 4.4%, Brazil 3.6%, Mozambique 3.3%
- Critical mineral lists
- US: listed
- 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.
Documents
Datasheets, safety data sheets, papers and standards you can open.
Full record
The complete spore, as stored. Free to reuse under CC-BY-4.0. Images keep the licence shown with each one.
Show the full YAML
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.
References
Every number above carries a reference number. Click one to see the source and where in it the value comes from.
| # | Source | Type | Year | Used for |
|---|---|---|---|---|
| Wikipedia: Glassy carbon | web | 2026 | 2 values | |
| SPI Supplies: Sigradur Glassy (Vitreous) Carbon Products, information sheet with grade table | datasheet | 2025 | 26 values | |
| SPI Supplies: Glassy (Vitreous) Carbon Plates, category page | web | 2026 | 0 values | |
| SPI Supplies: Sigradur K Glassy (Vitreous) Carbon Rods, 10 mm long, product page | web | 2026 | 0 values | |
| Goodfellow: Glassy carbon 3000C glassy carbon RVC sheet group, product page | datasheet | 2026 | 2 values | |
| NASA JPL Technical Report 32-842: Tensile and Structural Properties of Glassy Carbon (Kotlensky and Fischbach) | report | 1966 | 2 values | |
| PubChem compound record: Carbon (CID 5462310) | database | 2026 | 2 values | |
| Mineral Commodity Summaries 2026: Graphite (natural) | report | 2026 | 1 value | |
| USGS: Interior Department releases final 2025 List of Critical Minerals (science snippet) | web | 2025 | 0 values |