Graphite is a type of crystalline carbon that comes in three natural forms: 1) amorphous; 2) flake; and 3) vein. The three forms of graphite are distinguished by differences in grade/carbon content, particle size, and purity.
Amorphous graphite is the most abundant form, but occurs at the lowest in grades. It is formed by the metamorphism of previously existing anthracite coal seams. The term “amorphous” refers to its very small crystal size of particles, which are not visible unless viewed under magnification. Amorphous is used for lower value graphite products, such as pencils, brake pads, and rubber additives, and is the lowest priced graphite. The grade of amorphous graphite ranges from 20-40% in Cg (graphite content), and the purity varies between 70-85% carbon after refining. Large amorphous graphite deposits are found in China, Mexico, and United States.
Flake graphite is a less common form of natural graphite, and is of higher quality than amorphous graphite. It is formed in metamorphic rocks or calcareous sedimentary rocks. The grade of flake graphite ranges from 10-12% Cg, and the purity varies from 85-95% carbon after refining. The primary use of flake graphite includes brake linings, batteries, and fuel cells. Flake graphite can be sold for four times the price of amorphous graphite. China, Brazil, Canada are the largest producers of flake graphite.
Vein graphite is the rarest, most valuable, and highest quality form of natural graphite. It is formed from the direct deposition of solid, graphitic carbon from subterranean, high temperature fluids. The grade of vein graphite is typically above 90% Cg, with a purity of 95-99% carbon without refining. Vein graphite has higher thermal and electrical conductivity, and it also has the highest degree of cohesive integrity of all natural graphite. Vein graphite is easy to mold and can be formed into solid shapes without the aid of a binder addition, which leads to considerable cost savings over lower grade feedstock. Sri Lanka is the only jurisdiction that currently produces vein graphite.
What makes a good graphite deposit?
- Large flake size – a higher purity of concentrate
- High grade – determines project cash costs
- High purity – requires less processing to upgrade the graphite for high-value applications
Attributes of graphite
- A layered material made of hexagonal carbon rings
- Highest natural strength and stiffness
- Corrosion and heat resistant
- High natural lubricity
- High thermal resistance, up to 4,500 F
- Thermally and electrically conductive
- Chemically stable
- Flame retardant
- Low friction
- High compressive strength
Use of Graphite Refractory
- Steel industry historically has been a primary driver for high quality, large , graphite
- High-temperature alumina bricks as linings in steel ladles, furnaces and oxygen converters
– Account for 35% of the market
- Requires graphite with a size of 100 mesh and a purity of 95% to 99%
Lithium-ion battery- electric vehicles –will fuel future
- Smaller, lighter, and more powerful than traditional batteries
- Fastest growing area for graphite, 25% of the market
- Use 20-30x more of graphite than lithium in weight
- 1Kwh Li-ion battery contains 1.2-1.6kg graphite
- ~40kg graphite required in an electric car with a 24Kw battery pack
- Requires high purity graphite (93%C+) and medium to large flake
Nuclear Reactors—a growing use of graphite in existing and new reactors
- Used as high-temperature, gas-cooled, pebble bed reactor
- 3,000 tonnes graphite need to build a 1000 MW reactor