Graphite: Definition, Structure, Types, and Uses

What is Graphite?

Graphite, also called plumbago or black lead is a naturally occurring form of crystalline carbon. Graphite has a layered structure that consists of rings of six carbon atoms arranged in a widely spaced horizontal sheet. Graphite crystallizes in the hexagonal structure, Under high pressures and temperatures, it converts to octahedral or tetrahedral structures as diamond.

It is formed by the metamorphosis of sediments containing carbonaceous material. By the reaction of carbon compounds with hydrothermal solutions or magmatic fluids, or possibly by crystallization of magmatic carbon.

It is extremely soft, Cleaves with very light pressure, and has a very low specific gravity. In contrast, it is extremely heat-resistant and almost inert when in contact with almost any other material. These extreme properties give it a wide range of uses in metallurgy and manufacturing. Later on in this article, we will discuss in detail the various uses of graphite.

Who synthesized the first Graphite?

Graphite was first synthesized accidentally by Edward G. Acheson while he was doing high-temperature experiments on Carborundum. They found that about 4,150°C (7,500°F) silicon is vaporizing in the carborundum, leaving carbon behind in graphical form.

Acheson was granted a patent for graphite manufacturing in 1896, and commercial production began in 1897. Since 1918, petroleum coke, the small and incomplete graphite surrounded by organic compounds, has been a major raw material in the production of 99 to 99.5 percent pure graphite.

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Graphite

color of graphite

Graphite is a medium gray color. As a color name, it is used interchangeably with “charcoal”. It

Graphite, a hue of gray, is a color of basically no emotion. Detached, neutral, and indecisive, it is a transition between white and black. Gray may be seen as mature and responsible; it is often associated with gray hair and old age.

Gray has a stabilizing effect on other colors with which it comes in contact. It downplays stronger and brighter colors and enlightens softer colors. Light gray is relaxing and soothing and can help in difficult life situations.

Dark gray on the other hand is serious and is associated with self-denial and self-discipline. A few effects the color gray may have on someone are emphasizing the will to obey, creates expectations, reduces energy from other colors, and provides a sense of isolation.

Graphite ranges in color from gray to black and is both opaque and metallic in appearance. It is composed of carbon atoms and can be considered coal in its highest grade, though it is not typically used as a fuel. Graphite has a hardness of 1 to 2 on the Mohs scale and has a streak color of black.

what color is graphite

The swatches shown here are drawn from the following sources

  • Top Row: the Color Harmony Manual for the Ostwald System; RAL Classic; Pantone Fashion, Home + Interiors; Australian Standards;
  • Bottom Row: Kona Fabrics, Moda Bella Fabrics, the British Color Council; the Textile Color Card Association; the Dictionary of Color by Maerz & Paul, and a second color (note the different name) from Pantone Fashion, Home + Interiors.

Note that all of these are neutral or slightly cool, with the exception of the BCC sample, which is lighter than the others and ever-so-slightly warm. The numbers in the swatch captions are approximate hex codes.

Structure of Graphite

Graphite has a layered structure that consists of rings of six carbon atoms arranged in widely spaced horizontal sheets. Graphite thus crystallizes in the hexagonal system, in contrast to the same element crystallizing in the octahedral or tetrahedral system as diamond.

Graphite has a giant layered structure in which: each carbon atom is joined to three other carbon atoms by covalent bonds. The carbon atoms form layers with a hexagonal arrangement of atoms. That layers have weak forces between them. Each carbon atom has one non-bonded outer electron, which becomes delocalized.

Graphite has a layered structure that is difficult to draw convincingly in three dimensions. The following diagram shows the arrangement of the atoms in each layer and the spacing between the layers.

Graphite has a giant layered structure in which: each carbon atom is joined to three other carbon atoms by covalent bonds. The carbon atoms form layers with a hexagonal arrangement of atoms. That layers have weak forces between them.
The Structure of Graphite

Note that you can’t actually draw the side view of the layer at the same scale as the atoms in the layer without one or the other part of the diagram being either very spread out or severely squeezed. In this case, it is important to give an idea of the distances.

The distance between the layers is about 2.5 times the distance between the atoms within each layer. The layers, of course, span a large number of atoms – not just some of the ones shown above.

“ You might argue that carbon has to form 4 bonds because of its 4 unpaired electrons, whereas in this diagram it only seems to be forming 3 bonds to the neighboring carbons. This diagram is something of a simplification, and shows the arrangement of atoms rather than the bonding.”

Properties of Graphite

Graphite is an allotrope of carbon that is used for making moderator rods in nuclear power plants. Its properties are as follows:

  • A greyish black, opaque substance.
  • Lighter than diamond, smooth and slippery to touch.
  • A good conductor of electricity (Due to the presence of free electrons) and good conductor of heat.
  • A crystalline solid
  • Very soapy to touch.
  • Non-inflammable.
  • Soft due to weak Vander wall forces.
  • The conductor of electricity.

physical properties of graphite

Graphite has a high melting point, similar to that of a diamond. To melt graphite, it is not enough to loosen one sheet from another. You have to break the covalent bond throughout the structure.

It is soft and slippery to the touch and is used in pencils and as a dry lubricant for things like locks. You can think of graphite more like a pack of cards – each card is strong, but the cards slide on top of each other or even fall off the pack altogether. When you use a pencil, the sheets will rub off and stick to the paper.

Also, it has a lower density than diamond. This is due to the relatively large amount of space that is “wasted” between the sheets.

It is insoluble in water and organic solvents – for the same reason that diamond is insoluble. The force of attraction between solvent molecules and carbon atoms will never be strong enough to overcome the strong covalent bonds in graphite.

Graphite conducts electricity. The delocalized electrons can move freely through the sheets. When a piece of graphite is tied into a circuit, electrons can fall off one end of the sheet and be replaced with new ones at the other end.

Chemical properties of Graphite

Color

Iron-black to steel-gray; deep blue in transmitted light

Chemical Classification

Native element

Streak

Black

Luster

Metallic, sometimes earthy

Diaphaneity

Opaque

Cleavage

Perfect in one direction

Mohs Hardness

1 to 2

Specific Gravity

2.1 to 2.3

Diagnostic Properties

Color, streak, slippery feel, specific gravity

Chemical Composition

C

Crystal System

Hexagonal

Types of Graphite

The Different types of graphite:  

  1. Natural Graphite
    1. High Crystalline graphite
    2. Amorphous graphite
    3. Flake graphite
  2. Synthetic Graphite.

1. Natural Graphite

Natural graphite is a mineral form of graphitic carbon. It varies considerably in crystallinity. Most of the commercial graphite is mine and usually contains other minerals. After graphite is mine, it usually requires a considerable amount of mineral processing like froth flotation to concentrate the graphite.

Natural graphite is an excellent conductor of heat and electricity that is stable over a wide temperature range and is a high-strength material with a high melting point of 3650 ° C. It is mostly used for refractories, batteries, steelmaking, expanded graphite, brake linings, foundry facings, and lubricants.

Natural graphite is available in three forms, all of which are processed from naturally sourced graphite material. The three forms each have unique properties that make them well-suited for certain applications.

1.1 Crystalline Graphite

It is said that crystalline vein or lump graphite is considered to be the rarest, most valuable, and highest quality form of natural graphite. It is formed by direct deposition of solid graphitic carbon from underground high-temperature fluids such as crude oil and has been converted to graphite by time, temperature and pressure.

Sri Lanka is the only jurisdiction currently producing crystalline vein graphite. Crystalline venous graphite is easy to shape and can be formed into solid shapes without the aid of a binder additive, resulting in significant cost savings over lower-quality raw materials.

Crystalline vine graphite cracks typically have a thickness between 1 cm and 1 m and usually have a purity of more than 90% Cg. It has a purity of 95-99% carbon without refining. It is suitable for many uses as flake graphite and provides a distinct competitive advantage in terms of market prices and product applications such as lubricants, batteries, grinding wheel, and powder metallurgy.

1.2 Amorphous Graphite

Amorphous graphite is commonly formed by contact metamorphosis between an anthracite coal seam and a metamorphic agent. The result is microcrystalline graphite, commonly known as amorphous graphite. Amorphous graphite is the most limited graphite among natural graphite. The graphite content varies between 25% and 85% depending on the geological environment.

It was found as extremely small, crystal-like particles in beds of mesomorphic rocks such as coal, slate, and slate. The comparatively low carbon purity varies between 70 and 85% carbon after refining. It is not visible unless viewed under magnification.

It is used for low-quality graphite products such as pencils, lubricants, refractories, paint making, metallurgy, coatings, brake pads, and rubber additives. It’s the cheapest form of graphite. Large deposits of amorphous graphite are found in China, Mexico, and the United States.

1.3 Flake Graphite

Natural flake graphite is formed when carbon material is exposed to high pressure and temperature. The carbon source material can be either organic or inorganic, although most commercially available flake graphite is derived from organic deposits. The pressure required is usually greater than 1 gigapascal and the temperature required is usually greater than 750 degrees Celsius.

Flake graphite can be found in metamorphic rocks that are evenly distributed throughout the ore body or in concentrated lens-shaped pockets. The range of carbon concentrations varies between 5% and 40%. Flake graphite can be found as a lamellar or flaky shape in certain metamorphic rocks such as limestone, gneiss, and schists.

Foam flotation is used to extract flake graphite. “Floating” graphite has a graphite content of 80% -90%. More than 98% of the layer was made using graphite chemical preparation processes. Flake graphite can be found in many places around the world.

2. Synthetic Graphite

Synthetic graphite can be generated from coke and pitch. Although this graphite is not as crystalline as natural graphite. It is possible to have highly ordered pyrolytic graphite or highly oriented pyrolytic graphite(HOPG) refers to graphite with an angular spread between the graphite sheets of less than 1°.

There are basically two types of synthetic graphite. One is electro graphite, pure carbon produced from coal tar pitch, and calcined petroleum coke in an electric furnace.

The second is synthetic graphite, created by heating calcined petroleum pitch to 2800 °C.

Basically, synthetic graphite has higher electrical resistance and porosity, and lower density. Its enhanced porosity makes it unsuitable for refractory applications.

Synthetic graphite contains mainly graphitic carbon that has been attained by graphitization, heat treatment of non-graphitic carbon, or chemical vapor deposition from hydrocarbons at temperatures over 2100 K.

Application of synthetic graphite aerospace applications, carbon brushes, graphite electrodes, batteries, and moderator rods in nuclear power plants

The high level of porosity of synthetic graphite makes it unsuitable in refractory applications.

Uses of Graphite

Graphite has been used since ancient times. It has a wide range of applications in the modern world too.

Let’s look at some common uses of graphite below:

  • Writing Materials
  • Lubricants
  • Refractory
  • Nuclear Reactors
  • Batteries
  • Graphene Sheets

1. Writing Materials

The word graphite is from the Greek language which translates as ‘to write’. So the most common use of graphite is in making the lead in pencils. This lead is a mixture of clay and graphite which is in an amorphous form.

2. Lubricants/Repellents

Graphite is one of the main ingredients in lubricants like grease, etc. This mineral reacts with atmospheric water vapor and creates a thin film or layer over the surface applied and thus reduces friction. Graphite is also used in car brakes and clutches.

The powdered form of lump graphite is also used in paints. Why? Well, graphite by nature is water-repellent. So it offers a protective coating on wood and other surfaces.

3. Refractories

Due to its high tolerance to heat and unchangeability, Graphite is a widely used refractory material. It finds its use in the manufacturing industry and it helps in the production of glass and steel as well as the processing of iron.

4. Nuclear Reactors

Graphite can absorb fast-moving neutrons. As a result, it is used in reactors to stabilize nuclear reactions.

5. Electrical Industry

Crystalline flake graphite is used in the manufacturing of carbon electrodes, brushes, and plates needed in dry cell batteries and the electrical industry. Interestingly, natural graphite is also processed into synthetic graphite. This type of graphite is useful in lithium-ion batteries.

6. Graphene Sheets

Graphite can be used to make graphene sheets. These sheets are said to be 100 times stronger and 10 times lighter than steel. This derivative of graphite is further used in making lightweight and strong sports equipment. Many are considering future applications in the field of the medical and aerospace industry.

FAQs.

What is Graphite?

Graphite, also called plumbago or black lead is a naturally occurring form of crystalline carbon. Graphite has a layered structure that consists of rings of six carbon atoms arranged in a widely spaced horizontal sheet. Graphite crystallizes in the hexagonal structure, Under high pressures and temperatures, it converts to octahedral or tetrahedral structures as diamond.

What are the types of Graphite?

The Different types of graphite:  
1. Natural Graphite
1.1. High Crystalline graphite
1.2. Amorphous graphite
1.3. Flake graphite
2. Synthetic Graphite.

What is The structure of Graphite?

Graphite has a giant covalent structure in which: each carbon atom is joined to three other carbon atoms by covalent bonds. the carbon atoms form layers with a hexagonal arrangement of atoms. the layers have weak forces between them.

What are the properties of Graphite?

Properties of graphite:
1. A greyish black, opaque substance.
2. Lighter than diamond, smooth and slippery to touch.
3. A good conductor of electricity (Due to the presence of free electrons) and a good conductor of heat.
4. A crystalline solid
5. Very soapy to touch.
6. Non-inflammable.
7. Soft due to weak Vander wall forces.
8. The conductor of electricity.

What is graphite used for?

Graphite is used in pencils and lubricants. It is a good conductor of heat and electricity. Its high conductivity makes it useful in electronic products such as electrodes, batteries, and solar panels. Due to its high tolerance to heat and unchangeability, Graphite is widely used in refractory materials.

What color is graphite?

Gray
Graphite, a hue of gray, is a color of basically no emotion. Detached, neutral, and indecisive, it is a transition between white and black. Gray may be seen as mature and responsible, it is often associated with gray hair and old age.

Reference:

Graphite materials: usgs.gov