Flake graphite is a naturally occurring form of graphite that is typically found as discrete flakes ranging in size from 50-800 micrometers in diameter and 1-150 micrometers thick. This form of graphite has a high degree of crystallinity, which equates to near theoretical true density, high thermal and electric conductivity, and low springback (excellent molding characteristics).
Flake graphite is used in many applications including but not limited to powder metallurgy, fuel cell bi-polar plates, coatings, thermal materials, friction moderators, electrically conductive materials, refractories, general lubricant applications, pencils, gaskets, rubber compounds, and other advanced polymer systems. Commercial grades are available in purities ranging from 80-99.9% carbon, and sizes from 2-800 microns.
Amorphous graphite is a naturally occurring seam mineral that forms from the geologic metamorphism of anthracite coal. Contrary to the name, ‘amorphous’ graphite is not truly amorphous, but is a microcrystalline form of natural graphite. The morphology of amorphous graphite is typically granular except in extremely fine grinds, which have a flakey structure.
The term “amorphous” is applied to this form of natural graphite because the extremely small “crystallite” particles that make this material do not form crystal faces that are visible to the naked eye (anhedral opposed to euhedral). “As mined” material is available in sizes ranging from mixed 1 cm and smaller particles to 10 cm lumps
Vein graphite, also known as crystalline vein graphite, Sri Lankan graphite, or Celyon graphite, is a naturally occurring form of pyrolitic carbon (solid carbon deposited from a fluid phase). Vein graphite has a morphology that ranges from flake-like for fine particles, needle or acicular for medium sized particles, and grains or lumps for very coarse particles. As the name implies, this form of graphite occurs as a vein material. Vein fillings range in size from 1-150 cm. “As mined” material is available in sizes ranging from fine powder to 10 cm lumps.
Vein graphite has the highest “degree of crystalline” perfection of all conventional graphite materials. As a result of its high degree of crystallinity, vein graphite is utilized extensively in “formed” graphite products that are used in electrical applications. Many of the highest quality electrical motor brushes and other current-carrying carbons are based on formulations using vein graphite.
In friction applications, vein graphite is used in advanced brake and clutch applications. Other applications include most of those that can utilize flake graphite. Commercial grades are available in purities ranging from 80-99% carbon, and sizes from 3-micrometer powder to 8-10 cm lumps.
Synthetic graphite is a manufactured product made by high-temperature treatment of amorphous carbon materials. In the United States, the primary feedstock used for making synthetic graphite is calcined petroleum coke and coal tar pitch, both of which are composed of highly graphitizable forms of carbon.
The manufacturing process consists of various mixing, molding, and baking operations followed by heat-treating to temperatures between 2500 C and 3000 C. The ultra high heat treatment temperature is required to drive the solid/solid, amorphous carbon-to-graphite phase transformation. The morphology of most synthetic graphite varies from flakey in fine powders to irregular grains and needles in coarser products. Synthetic graphite is processed at ultra high temperatures, and impurities contained in the precursor carbons are significantly reduced in concentration during processing. This occurs as a result of the high temperature vaporization of volatile impurities, which at the process temperatures utilized includes most metal oxides, sulfur, nitrogen, hydrogen, and all organic components that were part of the original petroleum or coal tar pitch.
As a result of this thermal treatment, virtually all synthetic graphite products are high purity. Synthetic graphite is available in particle sizes from 2-micrometer powders to 2 cm pieces. Purities are typically 99+% carbon. Synthetic graphite is used in many applications including but not limited to friction, foundry, electrical carbons, fuel cell bi-polar plates, coatings, electrolytic processes, corrosion products, conductive fillers, rubber and plastic compounds, and drilling applications.
Asbury’s Graphco is a unique “flash” graphitized material manufactured using a proprietary thermal process. Graphco is made from only the highest quality petroleum coke, thermally engineered to provide a consistent, high quality product.
Graphco has the benefits of conventional synthetic graphite such as low ash, high electrical and thermal conductivity, and low sulfur. The method of production results in a “semi-graphite” with high compressibility. This property may prove effective in products and processes that require a powder or granular product with “springback.”
Expandable Graphite (Intumescent Flake Graphite)
Also known as “intumescent flake graphite,” expandable graphite is a synthesized intercalation compound of graphite that expands or exfoliates when heated. This material is manufactured by treating flake graphite with various intercalation reagents that migrate between the graphene layers in a graphite crystal and remain as stable species.
If exposed to a rapid increase in temperature, these intercalation compounds decompose into gaseous products, which results in high inter-graphene layer pressure. This pressure develops enough force to push apart graphite basal planes in the “c” axis direction. The result is an increase in the volume of the graphite of up to 300 times, a lowering of bulk density, and approximately a 10-fold increase in surface area.
Asbury’s expandable graphite is used as a fire suppressant intuminescent additive, as a raw material to manufacture graphite gasket products, as an electrically conductive filler, as a foundry additive, and in a wide variety of other industrial applications.