Graphite is a naturally occurring modification of the element carbon (C). Its atoms arrange themselves in the hexagonal pattern typical for carbon and thus form a hexagonal layered lattice. As a result, graphite gets its typical gray color from its opaque gray to black crystals.
Natural graphite is mainly used for refractories, batteries, steelmaking, brake linings, foundry facings, lubricants in pinewood derby, and headphones. Graphene, a one-atom-thick layer of graphite, is used to make the 40mm acoustic drivers that deliver sound to the ear in your headphones.
Graphite is also in pencils. In pencils, graphite particles are packed together inside a core made from wax or plastic. It’s most suitable for making pencils because graphite is soft and slippery. This makes it easy to rub off, leaving a mark on your paper. A soft pencil is about 90% graphite, while a harder one is around 20% graphite. To harden graphite, you need to mix graphite and clay with water and leave it out for about three days to dry and harden completely. Graphite of various hardness or softness results in different qualities and tones when used as an artistic medium.
Natural Graphite
Graphite occurs naturally on earth but can also be produced synthetically. Natural graphite is mainly mined underground and above ground in Brazil, China, India, Mexico, and Ukraine. The production process of synthetic graphite, on the other hand, is highly complex – but simultaneously offers the possibility of modifying the properties of graphite as desired.
Flexible graphite (expanded or exfoliated graphite) is produced from natural graphite flakes. The flakes are mixed with a highly oxidizing acid in the manufacturing process to produce graphite intercalation compounds. A sudden application of high temperature expands these. The resulting product, called expanded graphite, is mechanically compressed to shaped products, mainly graphite foil. Although still showing the unique properties of natural graphite, e.g., its excellent conductivity, expanded graphite foil is also flexible, soft, and easy to process in contrast to the raw material.
There are three types of natural graphite:
- High crystalline
- Amorphous
- Flake
Synthetic Graphite
The manufacturing processes for synthetic graphite are comparable to those for ceramic materials. First, the solid raw materials coke and graphite are ground and mixed in mixing units with carbonaceous binders such as pitches to form a homogeneous mass. This is followed by shaping. Various processes are available for this purpose: isostatic pressing, extrusion, vibration molding, or die molding. The pressed “green” bodies are then heated under the exclusion of oxygen at about 1000 °C. During this process, binder bridges are formed between the solid particles. Graphitization – the second thermal processing step – converts the amorphous carbon into three-dimensionally ordered graphite at about 3000 °C. The graphitized molded parts are then mechanically processed into complex components. Optionally, these can be further refined by additional cleaning processes and coating steps, such as silicon carbide (SiC) coating. The grain size of the graphite powder and the pressing method plays an important role.
The synthetic production of graphite has been technically possible since the end of the 19th century. In December 1895, a patent for the graphitization of carbon was registered in the USA. The electrographite obtained in this manufacturing process was then used as a current-transmitting element in the form of electrodes and graphite, thus becoming increasingly important for a wide range of industries.
Synthetic graphite is formed by two raw materials: a carbon carrier that is as pure as possible, usually coal from crude oil, and pitch as a binder. The two raw materials are mixed to form a homogeneous mass and then processed and refined in complex high-temperature processes. The processes vary depending on the desired properties and type of synthetic graphite. This way, a process can be reproduced in the shortest possible time, for which nature takes several million years.
Advantages
- Heat resistant
- Super lightweight
- Increased strength at higher temperatures
- Low thermal expansion (3 times lower than copper), which guarantees the stability of electrode geometry during electro-discharge machining
- Density is 5 times lower than that of copper, which results in lighter electrodes
- Provides a higher metal removal rate than copper, with less wear
- Good thermal conductivity
- Good electrical conductivity
- Self-lubricating
- Easy to machine
- Very resistant to thermal shock
- Available in large blocks
