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Expandable Graphite

Expandable Graphite, Graphite Foil and Packs

In recent years, a large variety of expandable graphites has been developed which are suitable for the production of graphite foils, sheets, strips, gaskets, sleeves, bearings, moulded parts, etc.

Expandable graphite has penetrated a wide and promising range of applications. One focus today is on flame retardancy. In this case, three of its various properties are essentially utilised:

Firstly, when exposed to heat, it expands up to 600 times on certain grades and thus forms a very large surface, which enables rapid oxidation of the carbon. This removes oxygen from the ambient air and the air becomes inert. The air then acts as an extinguishing agent against the fire and suffocates it.

Secondly, graphite does not form flames and extinguishes when no more heat is supplied. Therefore, the graphite cannot cause a fire.

Thirdly, in some cases the enormous volume increase of the expandable graphite is used, so that with clever application plugs can be formed which prevent the fire from spreading.

Other fields of application include metallurgy, the electrical industry, the chemical industry and the lubricant industry.


Scanning electron microscope "SEM" images:

Expandable Graphite - Properties and Applications

There are many traditional and new applications for expandable graphite. The expansion process causes the destruction of the crystal structure of graphite. This result is an enormous increase of volume, a very large surface, and a perfect plasticity of the expanded graphite.

In former times the expandable graphite was mainly utilized for covering of molten metals to protect from oxidation and quick cooling down. During previous years expandable graphite types were developed to produce graphite foil, sheets, tapes, seals, gaskets, bearings, formed piece parts, etc...

Today expandable graphite is discovered for many promising applications

The utilization of expandable graphite as a flame retardant is of greatest importance.
The special combination of four of its properties is utilized for effective firefighting:

  • First
    The expandable graphite expands under the impact of heat up to 600 times of its original volume and creates a very large surface area. It allows a quick oxidation of the carbon. The oxygen is taken out of the air by oxidation and makes the air almost inert. This inert air distinguishes the fire.
  • Second
    Graphite does not create flames while oxidation and will distinguish if no more heat will be applied to the glowing graphite. Therefore, no source of fire will be generated by the oxidizing graphite.
  • Third
    Graphite needs heat from outside for oxidation. It does not create additional heat during oxidation but reduces the heat of the surroundings.
  • Fourth
    In some cases the enormous increase of volume is utilised when expandable graphite is used as a flame retardant. It will form a plug and prevent further supply of air and spreading of fire, e. g. around windows, doors, etc. and in ventilation systems.

We noted further applications of expandable graphite in the electrical industry, in the chemical industry, and in the lubricating industry.

There are hundreds of different grades of expandable graphite for general use and for very special applications. The expansion volume of the expanded graphite is the larger, the larger the size of the graphite flakes is. The finer the particles of the expandable graphite are, the smaller is the expansion volume of the expanded graphite.

The same refers to the expansion pressure. Larger flakes have higher expansion pressure, but fine powders have almost no expansion pressure.

Representatively some expandable graphite grades

NGS fine expandable graphite powder - grade Ex -200 95 40 (neutral pH)
particle size approx. 85 % finer than 200 mesh = 75 µm
pH value of the flake surface 6 - 8
activation temperature approx. 200 °C
expansion volume at 1000 °C  40 cm³/g min. (typical: 46 cm³/g)

NGS coarse expandable graphite powder - grade Ex EF -80 (neutral pH)
particle size 85 % min. finer than 80 mesh = 180 µm
pH value of the flake surface 6 - 8
activation temperature 185 °C
expansion volume at 1000 °C 100 cm³/g min. (typical: 145 cm³/g)

NGS expandable graphite made of coarse flakes – grade Ex 180 (neutral pH)

particle size 90 % min. coarser than 80 mesh = 180 µm
pH value of the flake surface 7 - 9 or 9 - 11, according to customers' requirements
activation temperature 180 °C
expansion volume at 1000 °C approx. 320 cm³/g

NGS very strong expandable graphite made of very coarse flakes - grade Ex 250 (neutral pH)
particle size 80 % min. coarser than 50 mesh = 300 µm
pH value of the flake surface 7 - 9
activation temperature 180 °C
expansion volume at 1000 °C approx. 360 cm³/g

NGS expandable graphite made of extremely large flakes - grade Ex 99 32 480 (neutral pH)
particle size 80 % min. coarser than 30 mesh = 500 µm
pH value of the flake surface 4 - 9
activation temperature 180 °C
expansion volume at 1000 °C approx. 480 cm³/g