Glassy Carbon Material Properties

Glassy carbon, also known as vitreous carbon or glass-like carbon, is a non-graphitizing form of pure carbon that exhibits a unique combination of ceramic and graphite-like properties. While the exact microstructure of glassy carbon is still a topic of ongoing research it is commonly agreed upon that its basic building blocks consist of irregularly stacked and curved sheets of graphene. This mixture of ordered and amorphous microstructures leads to a variety of unique material properties.

SIGRADUR® Glassy Carbon is an ultrapure form of glassy carbon heat treated up to 2200°C and is characterized by the following properties:

High Temperature Resistance of up to 3000°C

SIGRADUR® Glassy Carbon exhibits exceptional high temperature resistance and can withstand temperatures of up to 3000 °C in inert gas or vacuum. Unlike all other ceramic and metallic high-temperature materials, glassy carbon increases in strength with a rise in temperature up to 2400 °C and shows no signs of embrittlement.

High Purity

SIGRADUR® Glassy Carbon consists of pure carbon and is virtually free of any contaminations by foreign elements. Our specifically sourced raw material for fabrication of SIGRADUR® Glassy Carbon already exhibits an extremely high degree of purity with any residual impurities being eliminated in a 2200 °C hot high-temperature treatment.

Extreme Corrosion Resistance

SIGRADUR® Glassy Carbon exhibits a closed microstructure which does not form intercalation compounds. Also, due to its high purity, SIGRADUR® Glassy Carbon does not offer any reaction centres for catalytic action. This results in an extreme corrosion resistance to acidic and alkaline agents as well as corrosive melts. While free oxygen above temperatures of 600 °C and some potent superacids can corrode glassy carbon it is still by far the most oxidation resistant carbon material on the market.

Impermeability and Non-Porosity

SIGRADUR® Glassy Carbon is an impermeable material comparable with silica glass and therefore ideally suited for vacuum applications (Helium permeability 10-11 cm2s-1 as determined by the vacuum drop method).

Good Electrical Conductivity

Due to its microstructure of disordered graphene sheets SIGRADUR® Glassy Carbon exhibits very good electrical conductivity.

High Hardness and Strength

SIGRADUR® Glassy Carbon exhibits high hardness and strength comparable to high-performance ceramics and retains its strength even at high temperatures.

High Surface Quality and No Particle Generation

SIGRADUR® Glassy Carbon exhibits a very high surface quality and can be easily polished for high end surface finish. Due to the hard and smooth surface glassy carbon does not generate particles like other carbon materials.

No wetting by melts

SIGRADUR® Glassy Carbon shows no wetting by saline, metallic and ceramic melts.

Extreme Resistance to Thermal Shock and Low Thermal Expansion

SIGRADUR® Glassy Carbon demonstrates an extreme resistance to thermal shock, allowing for rapid heating and cooling cycles without any material damage even over long periods of time. It retains its shape under heat and thermal expansion is low and isotropic similar to silica glass.

Isotropy of Physical and Chemical Properties

SIGRADUR® Glassy Carbon is an isotropic material, meaning it exhibits consistent physical and chemical properties in all directions. Its microstructure imparts no directional material properties, providing uniformity in all its material characteristics.

Biocompatibility

SIGRADUR® Glassy Carbon exhibits excellent compatibility with blood and tissue.

Low Density

Despite its high strength, SIGRADUR® Glassy Carbon has a low density, making it suitable for lightweight constructions and high-dynamic-stress units.

SIGRADUR® Material Grades

SIGRADUR® Glassy Carbon can be supplied in two grades, namely SIGRADUR® G and SIGRADUR® K:


SIGRADUR® G

SIGRADUR® G (G as in graphitising temperatures) is heated up to 2200°C and fulfils highest standards in terms of material purity, inertness as well as hardness and strength.


SIGRADUR® K

SIGRADUR® K (K as in coking temperatures) has a production temperature of 1100°C and is used in applications where increased reactivity is desirable, as e.g. in electrochemical or analytical applications.

TEM images of (a) SIGRADUR® K glassy carbon and (b) SIGRADUR® G Glassy Carbon. SIGRADUR® G has a more ordered graphene structure with less open-ended reaction centres, which imparts superior temperature resistance and intertness to the material. (Images adapted from P J F Harris, Phil Mag 84, 3159 (2004).

Physical Properties

Data Sheet
SIGRADUR® K SIGRADUR® G
Bulk density g/cm³ 1.54 1.42
Ash values acc. to DIN 51903 ppm < 100 < 100
Maximum service temperature (vacuum or inert gas) °C 1000 3000
Electrical resistance Ω·cm 50 x 10⁻⁴ 45 x 10⁻⁴
Open porosity % 0 0
Permeability coefficient cm²/s 10⁻¹¹ 10⁻⁹
Vickers hardness HV1 340 230
Flexural strength¹ N/mm² 210 260
Compressive strength² N/mm² 580 480
Young’s modulus¹ kN/mm² 35 35
Coefficient of thermal expansion (20-200°C) 1/K 3.5 x 10⁻⁶ 2.6 x 10⁻⁶
Thermal conductivity W/(K x m) 4.6 6.3

1) = 4-point bending test; geometry of specimen: circular rod, diameter: 3 mm, length: 60 mm
2) = geometry of specimen: circular rod, diameter: 7 mm, length: 10 mm

Electrical Resistance

Figure 1: Specific electrical resistance of SIGRADUR® K and SIGRADUR® G Glassy Carbon

Thermal Conductivity

Figure 2: Thermal conductivity of SIGRADUR® K and SIGRADUR® G Glassy Carbon

Thermal Expansion

Figure 3: Coefficient of thermal expansion of SIGRADUR® K and SIGRADUR® G Glassy Carbon

Flexural Strength

Figure 4: Flexural strength of SIGRADUR® K and SIGRADUR® G Glassy Carbon as a function of corrosion time in 65% nitric acid at 120°C; 4-point bending test; geometry of test specimen: circular rod, diameter: 5 mm, length: 60 mm 

Loss of Mass

Figure 5: Loss of mass of SIGRADUR® K and SIGRADUR® G Glassy Carbon as a function of corrosion time in 65% nitric acid at 120°C