What is graphite?

History

Graphite is one of the most interesting elements found on the earth. It is found naturally in its mineral form as well as produced in synthetic processes. The earliest use of graphite dates back to primitive man, who used it to draw on cave walls. It was also used by Egyptians to decorate pottery. During the Middle Ages, graphite was used as a refractory to line molds for the purpose of making smoother cannon balls, which could be fired farther. Almost all of us have had it in our hands at some time or another, mostly in the form of a pencil: Graphite. The term “graphite” is derived from the Greek “graphein” which means “to write”. But the material graphite has many more exciting and unique properties, which we will explore in detail below. Furthermore, we will have a closer look at the manifold areas of application of the various types of graphite.

CHEMISTRY

Graphite and Diamond: it all starts with Carbon… Natural Graphite is one of only two naturally occurring forms of pure carbon, the other being diamonds. Graphite occurs in a two dimensional, planar molecular structure whereas diamonds have a three dimensional crystal structure. They are identical chemically – both are composed of carbon (C), but physically, they are very different. Graphite generally occurs as flakes, which are multiple layers of graphene held together by weak bonds. Natural graphite is the most stable form of carbon under standard conditions. Therefore, it is used in thermochemi-stry as the standard state for defining the heat of formation of carbon compounds. Graphite has a layer structure. In each layer each carbon atom is bound to three others. This results in a two-dimensional network of hexagons. Within each layer there are strong bonds, but between the different layers the bonds are very weak. Thus, the layers can easily be shifted against each other and even separated. This structure is the reason graphite is very soft and is even used as a lubricant. But graphite has other special properties as well.

Graphite Properties

Graphite is a non-metal but has many properties of metals. It is an excellent conductor of heat nd electricity and has the highest natural strength and stiffness of any material. It maintains its strength and tability to temperatures in excess of 3,600°C and is very esistant to chemical attack. At the same time it is one of the ightest of all reinforcing agents and has high natural lubricity.

Types of graphite

Graphite is formed naturally through the metamorphism of carbon rich materials in rock which leads to the formation of either crystalline flake graphite, fine grained amorphous graphite, or crystalline vein or lump graphite.

Amorphous Graphite

Crystalline Flake Graphite

Crystalline Vein Graphite

Synthetic Graphite

Occurrence & production of graphite

Graphite is a non-metal but has many properties of metals. It is an excellent conductor of heat and electricity and has the highest natural strength and stiffness of any material. It maintains its
strength and stability to temperatures in excess of 3,600°C and is very resistant to chemical attack. At the same time it is one of the highest of all reinforcing agents and has high natural lubricity.

Manufacturing process of synthetic graphite

The manufacturing processes or synthetic graphite are comparable to those for ceramic materials. The solid raw materials coke and graphite are ground and mixed in mixing units with carbonaceous pitcheses 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 exclusion of oxygen at about 1000 °C. During this process solid particles are formed. 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.