Graphite is an allotrope of carbon, which is a gray-black opaque solid with stable chemical properties, corrosion resistance and difficult to react with chemicals such as acid and alkali. Carbon dioxide produced by combustion in oxygen can be oxidized by strong oxidants such as concentrated nitric acid and potassium permanganate. It can be used as antiwear agent and lubricant, high purity graphite can be used as neutron moderator in atomic reactors, and can also be used to manufacture crucibles, electrodes, brushes, dry batteries, graphite fibers, heat exchangers, coolers, electric arc furnaces, arc lamps, pencil refills, etc.

Graphite is a transition crystal among atomic crystal, metal crystal and molecular crystal. In the crystal, valence bonds are formed between carbon atoms in the same layer by sp2 hybridization, each carbon atom is connected with three other carbon atoms, and six carbon atoms form a regular hexagonal ring on the same plane, which is stretched to form a layered structure. The carbon atoms in the same plane each have a P orbit, which overlap each other to form delocalized π bonds. Electrons can move freely in the lattice and can be excited, so graphite has metallic luster and can conduct electricity and heat. Because the distance between layers is large, the binding force (van der Waals force) is small, and each layer can slide, so the density of graphite is smaller than that of diamond, which is soft and has a sense of satiny.

trait

Due to its special structure, graphite has the following special properties:

(1) High temperature resistance

The melting point of graphite is 3850 50℃. Even after ultra-high temperature arc combustion, the weight loss and thermal expansion coefficient are very small. The strength of graphite increases with the increase of temperature. At 2000℃, the strength of graphite doubles.

(2) Electrical conductivity and thermal conductivity

The conductivity of graphite is one hundred times higher than that of general nonmetallic minerals. Thermal conductivity exceeds that of steel, iron, lead and other metal materials. The thermal conductivity decreases with the increase of temperature, and even at extremely high temperature, graphite becomes an insulator. Graphite can conduct electricity because each carbon atom in graphite only forms trivalent bonds with other carbon atoms, and each carbon atom still retains 1 free electrons to transfer charges.

(3) lubricity

The lubricity of graphite depends on the size of graphite flake. The larger the scale, the smaller the friction coefficient and the better the lubrication performance.

(4) chemical stability

Graphite has good chemical stability at room temperature and can resist the corrosion of acid, alkali and organic solvents.

(5) Plasticity

Graphite has good toughness and can be ground into very thin slices.

(6) Thermal shock resistance

When graphite is used at room temperature, it can withstand drastic changes in temperature without damage. When the temperature changes suddenly, the volume of graphite changes little and cracks will not occur.

other

Graphite can be divided into natural graphite and artificial graphite. Natural graphite comes from graphite deposits, and it can also be divided into flake graphite, soil graphite and massive graphite. The graphite obtained by natural mining contains a lot of impurities, and it needs mineral processing to reduce its impurity content before it can be used. The main uses of natural graphite are to produce refractories, brushes, flexible graphite products, lubricants, anode materials for lithium ion batteries, etc. Sometimes a certain amount of natural graphite is added to some carbon products.