What is graphite?

Graphite is an allotrope of carbon, grayish black, opaque solid with a density of 2.25 grams per cubic centimeter, a melting point of 3652 ° C, and a boiling point of 4827 ° C. It is chemically stable, corrosion-resistant, and resistant to reactions with acids and bases. Combustion in oxygen produces carbon dioxide at 687 °C. It can be oxidized by a strong oxidizing agent such as concentrated nitric acid, potassium permanganate or the like. It can be used as anti-wear agent and lubricant. High-purity graphite is used as a neutron moderator in atomic reactors. It can also be used in the manufacture of tantalum, electrodes, brushes, dry batteries, graphite fibers, heat exchangers, coolers, electric arc furnaces, Arc lamp, pencil refill, etc.

Structure and composition

Graphite is a transitional crystal between atomic crystals, metal crystals, and molecular crystals. In the crystal, the same layer of carbon atoms is sp2 hybridized to form a covalent bond, each carbon atom is associated with three other carbon atoms, and six carbon atoms form a regular hexagonal ring on the same plane, stretching to form a sheet structure. . The carbon atoms in the same plane also have one p orbital left, which overlap each other, and the delocalized π-bond electrons can move freely in the crystal lattice and can be excited. Therefore, graphite has metallic luster and can conduct electricity and heat. Since the distance between the layers is large, the bonding force (van der Waals force) is small, and the layers can slide, so the density of graphite is smaller than that of diamond, soft and smooth.

The distance between each layer of graphite is 3.40 Å, which is combined by van der Waals force, that is, the layer belongs to the molecular crystal, and the spacing of carbon atoms in the same network layer is 1.42 Å, due to the carbon atoms on the same plane layer. The combination is very strong and extremely difficult to destroy, so the melting point of graphite is also high and the chemical properties are also stable. Due to its special bonding method, it cannot be considered as a single crystal or a polycrystal. It is now generally considered that graphite is a mixed crystal.

Graphite is a hexagonal system with complete layered cleavage. The cleavage surface is mainly composed of molecular bonds, and its molecular attraction is weak, so its natural floatability is very good.