Graphite is an allotrope of elemental carbon, each atom connects other three atoms. (the arrangement of them like honeycomb, it is consisted of hexagon) They are bonded covalently to form covalent molecules. Graphite is conductor due to the free electrons which was emitted by the carbon atom. The graphite is one of the softest mineral, so it can be used to product the manufacture of pencil lead and lubricant. Carbon is a nonmetallic element, it located in second cycle of the periodic table Group IVA.
Graphite is soft, black and gray. It can contaminate the paper because it is greasy. The hardness of graphite is about 1-2, and it can grows to 3-5 owe to the increase of impurities in the vertical direction. Its specific gravity is 1.9 to 2.3 and specific surface area is about 1-20m2/g. the graphite is one of the most heat-resistant minerals, and its melting point is more than 3000 ℃ in condition of without oxygen. It is electricity and thermal conductive.
Graphite have a very wide industrial applications, will be used in almost every industry. The industry always use artificial graphite which is also be called the specialty graphite. It can be divided into the following by the way they were molded.
1. Isostatic graphite. A lot of people called it three high graphite but not all three high graphite is isostatic graphite.
2. Molded Graphite.
3. Extruded graphite, it was always used as the electrode material.
Graphite due to its special structure has the following special properties:
1). High temperature resistance: the melting point of graphite is 3850±50 ℃, and boiling point is 4250℃, it have the weight loss is small, the thermal expansion coefficient is small, even after burned under high temperature arc. The intensity of graphite will increase with the rise of temperature, and the intensity will be double at 2000℃.
2). The electrical and thermal conductivity: the electrical conductivity was higher than the average non-metallic minerals a hundred times, and its thermal conductivity was higher than steel, iron, lead, metal materials. Thermal conductivity will decreases with the increasing of temperature, even at very high temperatures, graphite will be the insulator. Graphite graphite can conduct electricity because each carbon atom other carbon atoms with only three covalent bonds are formed, each carbon atom still retains a charge transport free electrons.
3). Lubrication: the lubrication performance of the graphite depends on the size of graphite flake, the greater the scale, the smaller the coefficient of friction, the better the lubrication performance.
4). Chemical stability: graphite performs good chemical stability at room temperature, and has good resistance to acid, alkali and organic solvents corrosion.
5). Plasticity: graphite has good toughness, and can be crushed into thin flakes.
6). Thermal shock resistance: graphite can be used withstand dramatic changes in temperature without damage to live at room temperature, the volume of graphite changes little when sudden changes in temperature, and it will not cause cracks.