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HTW Hochtemperatur-
Werkstoffe GmbH

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Glassy carbon

Glassy carbon, also called vitreous carbon, is an advanced material of pure carbon combining glassy and ceramic properties with these of graphite. Unlike graphite, glassy carbon has a fullerene-related microstructure. This leads to a great variety of unique material properties.

Glassy carbon SIGRADUR® is characterized by the following properties:

High temperature resistance in inert gas or vacuum up to 3000C

Glassy carbon SIGRADUR® is high temperature resistant in inert gas or vacuum up to 3000C. Unlike all other ceramic and metallic high temperature materials, glassy carbon increase in strength with a rise in temperature up to 2700 K. Glassy carbon shows at 2700 K compared to room temperature the double strength. Compared to ceramic and metallic materials, glassy carbon shows even at high temperatures no embrittlement.

High purity

Glassy carbon SIGRADUR® consists of pure carbon. Already the used raw materials show an extreme low content of foreign elements.
SIGRADUR® G is heated over 2000C. At these high temperatures the most foreign elements vaporize and only pure carbon remains. Due to the high purity glassy carbon is suitable for applications in the chemical analysis, semiconductor technology and ultra pure materials technology. Glassy carbon shows no memory effects which is advantageous in the ultratrace analysis.

Extreme corrosion resistance

Glassy carbon SIGRADUR® has an extreme corrosion resistance. Due to the closed microstructure glassy carbon doesn't form intercalation compounds. This gives extremely high resistance to corrosion by acid and alkaline agents and melts. Strong oxidizing substances like oxygen over 600C and hot melts and acids with a powerful oxidizing action are the only substances to attack glassy carbon. But even here tests showed that glassy carbon is the most oxidation resistant carbon material.
Due to the high purity the catalytic action of foreign elements (reaction centres) concerning oxidation and corrosion is limited to a minimum. SIGRADUR® G shows a higher corrosion resistance to oxidizing substances like nitric acid, perchloric acid or oxygen. The oxidation speed of SIGRADUR® G in boiling 65% nitric acid is 24 fold lower than this of SIGRADUR® K.

Impermeability to gas and liquids, no open porosity

Glassy carbon is an impermeable material comparable with silica glass. The helium permeability as determined by the vacuum drop method is only 10-11 cm2 s-1. Thus glassy carbon is an ideal material for the vacuum technology.

No wetting by melts

Glassy carbon SIGRADUR® shows no wetting by many saline, metallic and ceramic melts. This is advantageous in the metallurgy, ultra pure materials technology and glass industry.

High hardness and strength

The mechanical properties of glassy carbon SIGRADUR®, like hardness and strength, are comparable with these of high-performance ceramics. Unlike all other ceramic and metallic high temperature materials, glassy carbon increase in strength with a rise in temperature up to 2700 K. Glassy carbon shows at 2700 K compared to room temperature the double strength.

Low density

Glassy carbon SIGRADUR® has despite the high strength a very low density. E.g. charging equipment made of glassy carbon has due to the low mass a very low thermal absorption which enables short heating and cooling times. Also for light weight constructions and high dynamic stressed units glassy carbon is used due to its low density.

High surface quality, no particle generation

Glassy carbon SIGRADUR® has a very high surface quality and can be polished. Due to the hard and smooth surface glassy carbon doesn't show any particle generation like other carbon materials. Therefore it is very suitable for the semiconductor and glass industry.

Low thermal expansion

Glassy carbon SIGRADUR® has a very low and isotropic thermal expansion comparable with silica glass. Therefore it retains its shape under heat which is very advantageous for all high temperature applications.

Extreme resistance to thermal shock

In comparison to the most ceramic and metallic materials glassy carbon SIGRADUR® has an extremely high resistance to thermal shock. Therefore short heating and cooling times are possible without any problems.

Isotropy of physical and chemical properties

Glassy carbon SIGRADUR® is an isotropic material. Due to its fullerene-related microstructure glassy carbon has no directional material properties.

Good electrical conductivity

Glassy carbon SIGRADUR® is electrical conductive and thus suitable for e.g. the electrochemistry and sensor technology. Melting crucibles can be heated inductively.


Glassy carbon SIGRADUR® is resistant against biological systems and shows an excellent compatibility with blood and tissue. Good mechanical properties at low density, high purity and biocompatibility make glassy carbon SIGRADUR® to an interesting material for medical technology and biotechnology.