graphite

Graphite is carbon crystal and nonmetal material with the natures of silver gray, soft texture, metal luster, Mohs hardness 1~2, specific gravity 2.2~2.3 and volumetric weight 1.5~1.8 in general.

Graphite features very high melting point. It starts to melt at 3000°C in vacuum and evaporates at 3600°C. Strength of most materials decreases under high temperature but, on the contrary, the strength of graphite will increase in double when it is heated to 2000°C. However, graphite’s oxidation resistance property is poor and temperature rise may quicken the Oxidation process of graphite.

Graphite is noted for excellent thermal and electrical conductivity, which is 4 times that of stainless steel, 2 times that of carbon steel and 100 times that of most nonmetal materials. Of graphite, thermal conductivity is better than that of metals, including steel, iron and lead, but decreases when temperature rises. Unlike metals, when temperature is extremely high, graphite will be of thermal insulation. So, the property of graphite in heat insulation under high temperature is accountable.

Graphite features excellent lubrication and plasticity. Friction coefficient of graphite is less than 0.1. Graphite can be extended into poromeric and transparent thin flakes. Due to high strength, graphite is unlikely processed even with a diamond cutter.

Graphite has stable chemical properties and resists corrosions of acid, alkali and organic solvent. Currently, graphite has been widely used in modern industries.

1. Fireproof material: graphite and graphite products have the properties of high temperature resistance and high strength and are used for production of graphite crucible, protection of iron ingot and inner lining in metallic furnace.

2. Electric conducting material: in electrical industry, graphite is used for production of electrode, brush, carbon rod, carbon tube, positive pole of mercury rectifier, washer, telephone component and coating of television tube.

3. Antifriction material: graphite is often used as lubricant in machinery production. Common lubricating oil cannot be used under high rotation speed, high temperature and high pressure. The equipment made of graphite antifriction materials can be operated at high rotation speed under 200~2000°C without any lubricating oil. Graphite is also used in piston ring, sealing ring and bearing of the equipment of corrosive medium delivery and does not require any lubricant. Graphite emulsion can be used as lubricant in metal wire and tube drawing.

4. Graphite with stable chemical property: specially treated graphite features excellent corrosion resistance and thermal conductivity and low penetration rate and, as a result, can be used in heat exchanger, reaction tank, condensator, combustion tower, absorbing tower, cooling and heating systems, as well as filter and pump in industries of petrochemical, hydrometallurgy, acid/alkali, synthetic fiber and paper making as a substitution of metal materials.

5. Used in foundry, molding, pressing die and high temp metallurgy: due to minor coefficient of thermal dilation and property of thermal shock resistance, graphite is used in glass ware molding to ensure precise dimensions of cast ferrous metal and excellent surface smoothness, resulting in significant reduction of metal consumption. In production of metal powder, such as hard metal alloy, graphite is used in pressing die and sintering crucible. Highly purified graphite is used in single crystal silicon growth crucible, regional refinery vessel, support clamp and induction heating apparatus. In addition, graphite can also used in heat insulation, base support, high temperature furnace tube, rod, panel and grate in process of vacuum metallurgy.

6. Used in A-energy and national defense industry: as a neutron moderator, graphite is used in atomic reactor, ie. uranium-graphite reactor, the most popular one in the world at present. Graphite meets the requirements of atomic reactor due to its properties of high melting point, stability and corrosion resistance when used as a moderator. When used in atomic reactor, impurity in graphite must not be in excess of some dozens of PPM. Especially the content of boron should be less than 0.5PPM. In national defense industry, graphite is used for production of nozzles of solid fuel for rockets, nose cone of missiles, and parts, insulation and ray-proof components of spacecrafts.

7. Graphite has the function to prevent scale from buildup in boilers. Experiment result shows that scale does not form on boiler surfaces if a certain quantity of graphite is added into water, usually 4~5g per ton. In addition, graphite can prevent rusts on metal chimney, building roof, bridge and pipeline.

8. Graphite can be used as pencil core, pigment and polishing agent. After special treatment, graphite is used in some industries as impervious graphite, highly oriented graphite and graphite fabrics.