SIGRAFLEX® High-Purity Flexible Graphite Foil and Sheets

What is high-purity flexible graphite?

SGL Carbon’s standard quality high-purity flexible graphite foils und sheets contain less than 0.15 % ash. Such low ash contents are demanded by the challenging processes and systems in high-temperature applications applied especially in the semiconductor, solar or ceramic industries. Post purification of high-purity flexible graphite allows even for production of ultra-high purity grades with ash contents down to only 5 ppm.

SIGRAFLEX high-purity expanded graphite foil and sheets are smart solutions for heat treatment processes like hardening, carbonizing and brazing, hot press molding and sintering, for quartz glass and crystalline silicon production as well as for various other furnace applications.

SIGRAFLEX materials are predestined to be used in high-temperature technology due to their unique properties. Not only do they improve the performance of high-temperature systems and processes, but also allow for increasing their efficiency, minimizing energy consumption as well as increasing the lifetime of furnace parts.

Soft and flexible, lightweight
Highly impermeable
Superior thermally and electrically conductive
Resistant against most media and corrosion
No aging
No wetting by glass, ceramic, metal melts
No static charging

Due to its extraordinary properties – first and foremost the thermal stability and resistance – SIGRAFLEX high-purity flexible graphite can be used in ultra-high temperature applications ranging up to 3000 °C (5400 °F) in inert atmosphere or vacuum.

SIGRAFLEX high-purity materials are manufactured into various reliable high temperature resistant products like:

Heat shields
Release liners
Surface coating for insulation felts
Heating elements
Gas diffusion barriers in sandwich insulation
Protective liners and strips e. g. for welding, solding and sintering
External cladding
Linings for melting crucibles
Casting molds
Hot-press molds
Carrier materials for separating thin metal foils from the gaseous phase
Protective materials against laser beams

To produce SIGRAFLEX high-purity flexible graphite materials we use carefully selected highly pure natural graphite, which is first mixed with an intercalation agent and then thermally treated. The resulting product is expanded, voluminous graphite flakes. Those are either rolled into flexible foils or pressed into sheets or molds – without adding an adhesive or binder.

The high purity of SIGRAFLEX products is key to prevent product contamination resulting from outgassing of furnace parts and components. If requested, ultra-high purity foil and sheet materials with ash contents as low as 5 ppm are also available. SGL Carbon’s post-purification processes allow to specifically adjust the purity.

Properties		Units	Typical values
Sublimation temperature		°C	> 3000
Temperature resistance	in air inert gas / vacuum	°C	approx. 400 approx. 3000
Specific electrical resistivity (20 °C)	parallel to surface perpendicular to surface	μΩm	11 700
Thermal conductivity (20 °C)	parallel to surface perpendicular to surface	Wm⁻¹K⁻¹	220 5
Specific heat capacity (20 °C)		kJkg⁻¹K⁻¹	0.7
Thermal expansion coefficient (20-1000 °C)	parallel to surface perpendicular to surface	10⁻⁶K⁻¹	approx. 1 approx. 50
Shore hardness (D)			30
Elongation at break		%	≥ 1
Tensile strength		N/mm²	≥ 4
Permeability coefficient for air	perpendicular to surface	cm²/s	2 x 10⁻⁵
Coefficient of emission (1500 °C)			0.65
Ash content		%	approx. 0.1

SIGRAFLEX high-purity foil and sheets are easy to process. They can be cut or punched without special tooling and easily machined. To meet our customers’ requirements best, the material is available in various sizes, thicknesses and densities.

SGL Carbon offers the broadest carbon and graphite materials portfolio for high-temperature applications on the market. We manufacture and supply not only SIGRAFLEX^® high-purity flexible graphite but also SIGRAFINE^® fine-grain graphite, SIGRAFINE SiC coating, SIGRATHERM^® soft and rigid graphite felt and SIGRABOND^® carbon fiber-reinforced carbon – everything from just one source and with long-term experience. Get in contact with the one stop shop when looking for different materials or even multi-material systems.

Overview of our Materials

In high-temperature applications, SIGRAFLEX is often also used in combination with other materials from SGL Carbon:

SIGRATHERM soft and rigid felts
SIGRABOND carbon fiber-reinforced carbon
SIGRAFINE synthetic graphite

Those material combinations provide clear benefits for furnace insulation. SIGRAFLEX foil coated SIGRATHERM rigid felt products for example combine the excellent insulation properties of the felt with the reflective properties of the foil for optimal composite thermal insulation, best possible temperature distribution and optimum gas tightness.

Also, SIGRAFLEX can function as a gas-tight barrier when combined with SIGRATHERM rigid felt insulation ensuring a homogeneous insulation and avoiding unwanted convection. The materials are put together to form a sandwich insulation structure that reliable prevents the infiltration of the insulation layers from product outgassing. The outstanding insulation properties of rigid felt remain intact. In addition, SIGRATHERM/SIGRAFLEX sandwich structures also guarantee a high availability due to the long service life and energy-efficient operation.

Its extraordinary properties make SIGRAFLEX a suitable material for a wide range of parts and components in heat treatment furnaces, polycrystalline silicon, semiconductor, solar and other ceramic production equipment.