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Carbon - one element, many variants

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Graphite

Alongside diamond, graphite is one of the natural modifications of the chemical element carbon (C) and is characterised by its typical hexagonal crystal structure. In addition to natural graphite, there are synthetic variants that are produced using special manufacturing processes and used in numerous industrial applications.

Synthetic graphite is produced by coking and then graphitising carbons (e.g. coke). Coarse-grained coke is ground and mixed with binders (e.g. pitch). The material is moulded using processes such as extrusion, vibration compaction or isostatic pressing. The material has the characteristic hexagonal crystal structure.

The shaping processes determine the properties of different types of graphite:

Extruded graphite
Is produced in round or rectangular shapes using the extrusion process. The maximum grain size is 0.8 mm, and the material properties are direction-dependent (anisotropic).

Vibration molded graphite
Round or rectangular shapes are produced by vibration and uniaxial pressure. The grain size is 0.3-0.5 mm and the properties are mostly direction-independent (isotropic).

Isostatic graphite (iso-graphite)
Is densified in a cold isostatic press (CIP) from particularly fine-grained powder (15-30 µm). This method produces an isotropic property profile with high flexural strength (approx. 50 MPa) and a high level of purity.

All variants of synthetic graphite share common properties:

  • High thermal and electrical conductivity
  • Excellent thermal and chemical resistance
  • High thermal shock resistance
  • Medium flexural strength for extruded and vibration molded graphite (~20 MPa)
  • Higher flexural strength with iso-graphite (~50 MPa)

The varied properties of synthetic graphite make it ideal for numerous industrial applications, particularly in furnace construction, metallurgy and the manufacture of glass, ceramics and semiconductors.

Furnace construction

  • Resistance heaters
  • Support beams
  • Connecting bridges
  • Power connections

Metallurgy

  • Crucibles for melting processes
  • Continuous casting molds

Glass and ceramics industry

  • Molds for glass production
  • Charging plates and recipients

Semiconductor and LED production

  • High-purity components for sensitive processes
Graphite Materials Materialien Graphit
Graphite Materials Materialien CFC Befestigungselemente

CFC

Carbon fibre reinforced carbon (CFC) is a high-strength composite material consisting of carbon fibres embedded in a carbon or graphite matrix. This material is characterized by exceptional mechanical properties, high temperature resistance and low thermal expansion.

The variety of CFC materials results from different carbon fibre types, the processing into fabrics or meshes, and the choice of matrix.

The production of CFC requires several steps:

  1. Fibre production: Carbon fibres are made from organic precursors such as polyacrylonitrile (PAN) by pyrolysis
  2. Embedding in the matrix: The fabric is impregnated with selected resins (prepreg) and cured
  3. High-temperature treatment: After curing, the material is exposed to high temperatures to achieve the final carbon structure

The shape is created by processes such as hand laminating, hot pressing or winding for sheets and tubes. Precise molded parts can be produced by CNC machining or other mechanical processes.

  • High strength and stiffness: Excellent strength- and stiffness-to-weight ratio, ideal for lightweight and stable components
  • Thermal shock resistance: Resistant to extreme temperature changes, e.g. during heat treatment of steels
  • Low thermal expansion: Retains its shape and dimensions even with significant temperature changes

The property profile makes CFC particularly suitable for high-temperature processes such as:

  • Production of semiconductor materials (e.g. silicon, silicon carbide)
  • Heat treatment of steels (hardening, tempering)
  • Brazing of ceramic-metal compounds
  • Sintering of hard metals and technical ceramics

CFC is used in industries such as automotive, electronics, energy, chemicals, aerospace, furnace and plant construction, as well as toolmaking.

Typical applications include charging systems, structural components, and heating systems.

Soft felts

Carbon and graphite soft felts are made of carbon fibres and are characterized by exceptional thermal, electrical and chemical properties.

They are varied and particularly suitable for high-temperature and special applications.

The production of soft felts requires several steps:

  1. Fibre preparation: starting materials such as polyacrylonitrile (PAN), rayon or pitch are processed into fibres and formed into webs of variable width, thickness and length in a felting process
  2. Pre-oxidation: The felts are heated in order to thermally stabilize them.
  3. Carbonization: At 800-1,600 °C in an oxygen-free atmosphere, non-carbon components are removed, resulting in carbon felt
  4. Graphitization: For graphite felt, the carbon felt is heated to over 2,000 °C, creating a graphite-like structure
  5. Shaping: The felt is adapted to the desired dimensions by cutting, needling or impregnation
  • Thermal stability: Carbon felt is stable up to 1,400 °C; graphite felt withstands temperatures up to 3,000 °C in protective atmospheres
  • Low thermal conductivity: Both materials minimize heat loss and are easy to evacuate due to their low density
  • High purity: A low ash and sulphur content makes them ideal for high-purity applications
  • Chemical resistance: Resistant to aggressive media and corrosive substances
  • Flexibility and moldability: Easy to cut and adapt to specific requirements
  • Electrical conductivity: Graphite felt offers good electrical conductivity

The unique properties enable use in numerous areas:

  • Thermal insulation: In high-temperature furnaces, crucibles and reactors under vacuum or oxygen-free atmosphere
  • Energy storage: As electrode layers in redox flow batteries and fuel cells
  • Semiconductor industry: Insulation material for the production of silicon and silicon carbide single crystals
  • Chemical industry: Filter material for high-purity chemical reagents or corrosive liquids
Graphite Materials Materialien Weichfilz
Graphite Materials Materialien Hartfilz

Hard felts

Rigid felts are dimensionally stable insulation materials made of carbon fibres that are characterized by low thermal conductivity and high temperature resistance.

They are particularly suitable for applications in oxygen-free atmospheres and vacuum environments at temperatures above 800 °C.

The production of rigid felts requires several steps:

  1. Material mixing: Fibre batches are mixed with binders such as phenolic resins
  2. Pressing: The mixture is pressed into the desired shape
  3. High-temperature treatment: After pressing, the molded body is thermally treated at temperatures of up to 2,200 °C, which creates the final structure

The binder ensures that the fibres are reliably fixed in the material. Rigid felts are usually produced as boards, billets or cylinders, but can be shaped into other geometries by mechanical processing.

To improve surface resistance, graphite coatings, CFC fabrics or graphite foil can be applied to protect the felt from mechanical damage or chemical attack.

Rigid felts share many properties with soft felts, but have additional advantages:

  • Thermal stability: Suitable for high-temperature applications up to 3,000 °C
  • Dimensional stability: Retains its shape even under thermal and mechanical loads
  • Machinability: Easily adaptable through mechanical processing
  • Composite structure: Combination with CFC fabric and graphite foil enables optimized insulation solutions

Rigid felts are mainly used in high-temperature processes, especially in:

  • Semiconductor industry: Thermal insulation in vacuum furnaces for the production of silicon carbide (SiC) single crystals
  • Powder metallurgy: Pressure sintering of hard metals
  • Industrial heat treatment: Hardening, tempering, sintering and brazing of metals
  • Furnace technology: Resistively or inductively heated vacuum and inert gas furnaces

Graphite foil

Graphite foil is a material made from natural graphite. After intensive cleaning, the flake-like raw material is thermally treated and then rolled into foils or sheets.

This compression process creates an anisotropic structure with direction-dependent properties.

Graphite foil is flexible, compressible and can be easily cut, punched or embossed. It can also be combined with other materials by rolling or gluing to create composite materials with improved properties.

  • High thermal conductivity: Efficient heat dissipation, ideal for electronics applications
  • High electrical conductivity: Suitable for electrical and electronic applications
  • Flexibility: Thin and conformable, easy to integrate into various designs, ideal for seals due to compressibility and elastic recovery
  • Chemical resistance: Withstands high temperatures and aggressive chemicals
  • High radiation resistance: Reflects heat radiation, making it ideal for thermal insulation at high temperatures
Graphite Materials Materialien Graphit Folie