Carbon and Graphite
Graphite is crystalline carbon in layered sheets, which is why it conducts heat and electricity, lubricates itself and machines faster than any metal, yet does not melt — it sublimes near 3,650 °C and actually gets stronger up to about 2,500 °C. The synthetic grades differ by how the coke and pitch were formed: isostatic graphite has a fine (1–20 µm), isotropic grain and 40–80 MPa flexural strength, extruded graphite is coarse and cheap, molded sits between. Its limit is oxidation, which starts around 450 °C in air and runs away above 700 °C, so hot service means vacuum, inert gas or a protective coating.
Popular graphite grades
Compare in the explorer| Grade | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Weldability | Best for |
|---|---|---|---|---|---|---|
| Isostatic Graphite | — | 27 | 1.77 | Excellent | — | EDM electrodes, precision fixtures, semiconductor |
| Extruded Graphite | — | 9 | 1.7 | Excellent | — | Heating elements, electrodes, large blanks |
| Molded Graphite | — | 15 | 1.72 | Excellent | — | Medium-grain blocks and machined furnace parts |
| Pyrolytic Graphite | — | 100 | 2.2 | Good | — | Directional heat spreading and shielding |
| Flexible Graphite | — | 5 | 1 | Excellent | — | High-temperature gaskets and packing |
| C/C Composite | — | 200 | 1.7 | Fair | — | Strength at 2,000 °C: brakes, hot-press dies |
| CVD Diamond | — | 600 | 3.51 | Not recommended | — | Heat spreaders and windows above 1,000 W/m·K |
All 21 graphite grades
- Amorphous Graphite
- C/C Composite
- CVD Diamond
- EG Carbon Brush
- Extruded Graphite
- Flexible Graphite
- Glassy Carbon
- Graphite
- Graphite Felt
- HP Graphite Electrode
- Impervious Graphite
- Isostatic Graphite
- MG Carbon Brush
- Molded Graphite
- Natural Flake Graphite
- Nuclear Graphite
- Prebaked Carbon Anode
- Pyrolytic Graphite
- RP Graphite Electrode
- RVC
- UHP Graphite Electrode
Choose graphite for
EDM electrodes and hot-press or sintering tooling; crucibles, boats and trays for molten metal, glass, silicon and brazing; furnace heating elements, heat shields and fixtures in vacuum or inert atmosphere; seals, bearings, pump vanes and brushes that must run dry; and anodes, electrodes and current collectors in electrochemistry.
Look elsewhere when
The part runs above about 450 °C in air for long periods (Silicon Carbide, Alumina 99.5 or a SiC-coated graphite), it must insulate electrically (Boron Nitride machines the same way and insulates), the design carries bending or impact loads (graphite is 40–80 MPa in bending and chips at edges — use a metal or Silicon Nitride), the melt reacts with carbon (titanium, zirconium and some superalloys form carbides — use zirconia or yttria crucibles), or dust and porosity are unacceptable without impregnation.
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Graphite by application
- EDM electrodes
- Isostatic Graphite in a fine grade (under 10 µm grain) for detail, ribs and fine finish; a coarser isostatic or Molded Graphite grade for roughing electrodes where wear rate matters less than cost.
- Crucibles and molten metal
- Isostatic Graphite and Impervious Graphite (resin- or pitch-impregnated) for aluminum, copper, gold and silicon; Glassy Carbon where the melt must not pick up carbon dust; Natural Flake Graphite and clay-graphite for foundry crucibles.
- Furnace heating and fixtures
- Extruded Graphite and Molded Graphite heating elements, shields and trays in vacuum and inert furnaces to 2,500 °C; Graphite Felt and RVC for insulation and porous electrodes; C/C Composite where a fixture must carry load hot.
- Seals, brushes and electrodes
- Flexible Graphite for gaskets and valve packing; EG Carbon Brush and MG Carbon Brush (metal-graphite for high current) for motors and slip rings; UHP Graphite Electrode, HP Graphite Electrode and RP Graphite Electrode for arc furnaces in descending current density.
Working with graphite
- Forming & sintering
- Synthetic graphite is made by mixing calcined coke with pitch, forming it by isostatic pressing, extrusion or molding, baking at about 1,000 °C and graphitizing at 2,500–3,000 °C — a cycle of weeks, which is why blocks are bought and machined rather than formed to shape. Pyrolytic graphite and CVD diamond are deposited from gas; C/C composites are carbon fibre densified by repeated impregnation.
- Grinding & lapping
- Graphite is machined, not ground: dry, at high spindle speeds with carbide or diamond-coated tools and strong dust extraction, holding ±0.01 mm and Ra below 1 µm on isostatic grades. Thin ribs down to 0.3 mm and sharp corners are practical in fine-grain material; coarser grades chip. Flexible graphite is die-cut; CVD diamond is laser-cut and polished.
- Joining & sealing
- Graphite parts are threaded (coarse threads, 1.5 mm pitch or more), pinned or assembled with graphite cement cured at 200–1,000 °C. Brazing to metal uses active fillers or a metallized layer; it is rarely worth it. Pores are sealed by resin, pitch or pyrolytic-carbon impregnation, and an SiC or pyrolytic-graphite coating stops oxidation and dusting in air.
- Tolerances & design rules
- Design as for a stiff, brittle plastic: keep walls above 1 mm, radius corners and let graphite carry compression. Allow for grade anisotropy in extruded material (properties differ with and across the grain) and for oxidation loss in air above 450 °C — about 1 % mass per hour at 700 °C is a working rule of thumb.
Other ceramic series
Carbon and Graphite — frequently asked
What is graphite?
Graphite is crystalline carbon in layered sheets, which is why it conducts heat and electricity, lubricates itself and machines faster than any metal, yet does not melt — it sublimes near 3,650 °C and actually gets stronger up to about 2,500 °C. The synthetic grades differ by how the coke and pitch were formed: isostatic graphite has a fine (1–20 µm), isotropic grain and 40–80 MPa flexural strength, extruded graphite is coarse and cheap, molded sits between. Its limit is oxidation, which starts around 450 °C in air and runs away above 700 °C, so hot service means vacuum, inert gas or a protective coating.
Which grade of graphite should I use?
Isostatic Graphite for anything precise: EDM electrodes, semiconductor and crystal-growth parts, sintering and brazing fixtures, continuous-casting dies and hot-press molds — fine grain gives sharp detail and a fine finish. Extruded Graphite for heating elements, electrodes, large crucible blanks and anything where cost and length matter more than surface. Molded Graphite for medium-grain blocks, plates and machined furnace parts. Pyrolytic Graphite when heat must be steered — it conducts about 100 times better along the layers than across them. Flexible Graphite for gaskets and packing to 450 °C in air (far higher in inert gas). Glassy Carbon for impermeable crucibles and electrodes in analytical chemistry, C/C Composite for brake discs, hot-press dies and rocket parts that need strength at 2,000 °C, and CVD Diamond for heat spreaders and optical windows where conductivity above 1,000 W/m·K pays for itself.
Which grade of graphite is easiest to machine?
EG Carbon Brush (machinability excellent, 95/100), then Graphite Felt (95/100).
Isostatic, extruded or molded graphite — which for my part?
Grain size and isotropy decide it. Isostatic graphite (1–20 µm grain, same properties in every direction, 40–80 MPa flexural) is for EDM electrodes, semiconductor tooling and anything with fine detail or tight tolerance. Extruded graphite has a coarse grain, is anisotropic (stronger and more conductive along the extrusion axis) and costs least, so it goes into heating elements, electrodes and large crucibles. Molded graphite is medium-grain and moderately isotropic — furnace plates, trays and blocks that are machined but not detailed.
How hot can graphite really go?
In vacuum or argon, well past 2,500 °C — it sublimes near 3,650 °C and gains strength to about 2,500 °C, which is why it is the standard hot-zone material. In air the limit is oxidation, not melting: weight loss begins around 450 °C, becomes noticeable at 600 °C and rapid above 700 °C, so unprotected graphite in air is a consumable. SiC coating or pyrolytic-carbon sealing raises the working limit to roughly 1,500 °C in air, and C/C composites use the same coatings for brakes and re-entry parts.