Carbon

CARBON / GRAPHITE

GENERAL PROPERTIES

MATERIAL OVERVIEW

Characteristics: Relatively soft greasy feel; steel gray to black color with a metallic sheen.  High electrical and thermal conductivity. Resistant to oxidation and thermal shock.  Graphite has characteristics representative of both metals and nonmetals and thus is generally classified as a metalloid. It is the thermodynamically stable modification of carbon at high temperatures and, once formed, no phase transitions occur on cooling to room temperature.  Graphite has thermal and electrical characteristics usually associated with metals. Also, these are the properties most affected by the anisotropy of graphite.

Graphite is highly refractory material. In comparison to other elemental substances, its vapor pressure is quite low. Sublimation (-3350 °C) precedes melting (-3700 °C) at normal pressure.  Compared to metals and ceramics, the elastic modulus of graphite is quite low and is affected by the directionality of the atom layers. Measured values for polycrystalline commercial graphite can differ by a factor of two or more because of this directional effect. The modulus of graphite increases with temperature. Graphite is a soft material even though the hardness within the atom layers approaches that of diamond. The softness is a result of the weak bonding between atom layers which provide little resistance to interlayer movement.

The specific heat of graphite at room temperature is low, significantly less than the classical figure of 6 Cal/g atom/deg. (it increases with temperature). Polycrystalline commercial graphite has approximately 1/3 the thermal conductivity of copper. The conductivity parallel to the atom layers is generally somewhat greater than that in the perpendicular direction. In pyrolytic graphite, the conductivity in the direction of the atom layers is very high; in fact, values exceeding that of copper have been reported. The conductivity in the perpendicular direction is lower by a factor of 100 or so. The thermal conductivity of graphite decreases with temperature.  The thermal expansion of graphite is low in comparison to metals, being about 1/4 that of iron.  In the direction perpendicular to the atom layers the thermal expansion is approximately onethird

higher than that in the parallel direction. The rate of expansion increases with temperature.  Graphite has excellent thermal shock resistance for a brittle material due to its high thermal conductivity, low thermal expansion and low elastic modulus.  Although graphite is considered an electrical conductor, the electrical resistivity of polycrystalline commercial Graphite is several hundred-fold higher than that of copper. At low and moderate temperatures, the temperature effect is negative, but becomes positive at high

temperatures. The anisotropy of graphite is revealed most strikingly by electrical resistivity measurements. For pyrolytic graphite, the resistivity in the direction parallel to the atom layers is lower by a factor of 1000 in comparison to that in the perpendicular direction. The ratio is appreciably less, approximately 100, for single crystal graphite.  Graphite is highly inert to chemical attack at normal temperatures. It is sufficiently oxidation resistant for practical utilization at moderate temperatures but deteriorates rapidly at high

temperatures. The chemical activity of graphite is increased in the presence of very strong oxidizing agents. Several ionic lamellar-type compounds have been prepared but their isolation is difficult due to instability. A deep blue coloration is a common characteristic of these substances. Oxygen or fluorine can enter the Graphite structure in a layered pattern.  However, covalent rather than ionic bonds are formed, and in consequence, the metallic characteristics of the graphite are lost.  Because of the high temperatures required during synthesis, Graphite is reasonably free of elemental impurities. Further purification can be achieved through use of a halogen-containing atmosphere during graphitization or in a post-synthesis treatment.  Hazards: (powder, natural) Fire risk. Tolerance, 15 million particles/ft3. Low toxicity.  We can supply thin masks of our high-purity graphite. They are available in varying sizes and would be made in accordance with customer’s specifications.

Our various grades are listed as follows:

Lectromet Grade Graphite: Typically used as cups for growing silicon crystals and other similar applications.

Electro Grade: For use in metal alloying unitized boats. Electro chemical, precious metal plating, excellent corrosion resistance as well as wetting resistance.

Aeromet Grade: For use in aerospace applications such as missile components, rocket nozzles, etc.

ESPI Super-Conductive Grade: For use in the electronic field when high purity is required;

nuclear applications for neutron absorption epitaxial heaters, etc.

These various grades and types are available in rod and plate stock and can be supplied in

varying sizes and shapes in accordance with customer’s requirements.

  TYPICAL ANALYSES

Impurities in ppm

ROD

Additional diameters can be manufactured in 5-7 days.
Rod is cut to order and sold by the inch or foot.

FOIL

Foil is cut to order and sold by the square inch.

SHEET

Sheet thicknesses are available in increments of .001”.
Sheet is cut to order and sold by the square inch.