What Is Graphite? Properties And Functions Of Graphite
What is graphite? Main properties of graphite
1, high temperature resistance: the melting point of graphite is 3850±50℃, the boiling point is 4250℃, even if the ultra-high temperature arc burning, the weight loss is very small, the coefficient of thermal expansion is also very small. The strength of graphite is strengthened with the increase of temperature, and the strength of graphite is doubled at 2000℃.
2, electrical and thermal conductivity: the electrical conductivity of graphite is one hundred times higher than that of general non-metallic ores. Thermal conductivity than steel, iron, lead and other metal materials. The thermal conductivity decreases with increasing temperature, and even at extremely high temperatures, graphite becomes an adiabatic. Graphite can conduct electricity because each carbon atom in graphite forms only three covalent bonds with other carbon atoms, and each carbon atom still retains one free electron to transfer charge.
3, lubricity: the lubrication performance of graphite depends on the size of the graphite flake, the larger the flake, the smaller the friction coefficient, the better the lubrication performance.
4, chemical stability: graphite has good chemical stability at room temperature, can resist acid, alkali and organic solvent corrosion.
5, plasticity: graphite toughness is good, can be rolled into a very thin sheet.
6, thermal shock resistance: graphite can withstand drastic changes in temperature when used at room temperature without damage, when the temperature changes, the volume of graphite does not change much, will not produce cracks.
Advantages of graphite
(1) Faster processing speed: under normal circumstances, the mechanical processing speed of graphite can be 2-5 times faster than that of copper; The discharge processing speed is 2-3 times faster than that of copper, and the material is not easy to deform: it has obvious advantages in the processing of thin rib electrodes; The softening point of copper is about 1000 degrees, which is easy to be deformed by heat; The sublimation temperature of graphite is 3650 degrees; The coefficient of thermal expansion is only 1/30 of copper.
(2) Lighter weight: the density of graphite is only 1/5 of copper, and the burden of the machine tool (EDM) can be effectively reduced when the large electrode is discharged. It is more suitable for the application of large molds.
(3) Less discharge consumption; Because the spark oil also contains C atoms, during the discharge processing, the high temperature causes the C atoms in the spark oil to be decomposed, and the protective film is formed on the surface of the graphite electrode, which compensates for the loss of the graphite electrode.
(4) No burrs; After the copper electrode is processed, it needs to be manually trimmed to remove burrs, while the graphite is processed without burrs, saving a lot of costs and making it easier to automate production.
(5) Graphite is easier to grind and polish; Because the cutting resistance of graphite is only 1/5 of that of copper, it is easier to grind and polish by hand.
(6) Lower material costs and more stable prices; Due to the rise in copper prices in recent years, the price of isotropic graphite is now lower than that of copper, under the same volume, the price of carbon's universal graphite products is 30% to 60% lower than that of copper, and the price is more stable, and the short-term price fluctuation is very small. It is this unparalleled advantage that graphite has gradually replaced copper as the material of choice for EDM electrodes.
The main role of graphite
1, as refractory material: graphite and its products have high temperature resistance, high strength properties, in the metallurgical industry is mainly used to make graphite crucible, in steelmaking commonly used graphite as a protective agent of ingot, metallurgical furnace lining.
Graphite crucible
2, as conductive material: used in the electrical industry to manufacture electrodes, brushes, carbon rods, carbon tubes, mercury positives, graphite washers, telephone parts, TV picture tube coating.
Graphite washer
3, for wear-resistant lubrication materials: graphite is often used as a lubricant in the machinery industry. Lubricating oil often can not be used under high-speed, high temperature, high pressure conditions, and graphite wear-resistant materials can be used at 200-2000 ℃ at a very high sliding speed, without lubricating oil. Many corrosive media conveying equipment, widely used graphite materials made of piston cups, seals and bearings, they do not need to add lubricating oil when running. Graphite milk is also a good lubricant for many metal processing (wire drawing, tube drawing).
Graphite piston cup, sealing ring, etc
4, graphite has good chemical stability. After special processing of graphite, with corrosion resistance, good thermal conductivity, low permeability, it is widely used in the production of heat exchangers, reaction tanks, condensers, combustion towers, absorption towers, coolers, heaters, filters, pump equipment. Widely used in petrochemical, hydrometallurgy, acid and alkali production, synthetic fiber, paper and other industrial sectors, can save a lot of metal materials.
Graphite material for the reaction tank
5, for casting, sanding, pressing and high-temperature metallurgical materials: due to the small coefficient of thermal expansion of graphite, and the ability to change cold and heat, can be used as a glass casting mold, the use of graphite after the black metal casting size is accurate, the surface smooth yield is high, can be used without processing or slightly processed, thus saving a lot of metal. The production of tungsten carbide and other powder metallurgy processes, usually made of graphite materials for pressing and sintering of porcelain boats. The processing of monocrystalline silicon crystal growth crucible, regional refining container, bracket fixture, induction heater and so on are inseparable from high purity graphite. In addition, graphite can also be used as vacuum smelting graphite insulation plate and base, high temperature resistance furnace furnace tube, rod, plate, grid and other components.
6, used in the atomic energy industry and defense industry: graphite has a good neutron moderator used in atomic reactors, uranium graphite reactor is a more widely used atomic reactor. As a power for atomic energy reactor deceleration material should have a high melting point, stability, corrosion resistance, graphite can fully meet the above requirements. The purity of graphite used in atomic reactors is very high, and the impurity content should not exceed dozens of PPM. In particular, the boron content should be less than 0.5PPM. In the defense industry, graphite is also used to make nozzles for solid fuel rockets, nose cones for missiles, parts for space navigation equipment, thermal insulation and radiation protection materials.
7, graphite can also prevent boiler scaling, the relevant unit tests show that adding a certain amount of graphite powder in water (about 4-5 grams per ton of water) can prevent scale on the boiler surface. In addition, graphite applied to metal chimneys, roofs, Bridges, pipelines can be anti-corrosion and anti-rust.
8, graphite can be used as pencil lead, pigment, polishing agent. After special processing of graphite, various special materials can be made for relevant industrial sectors.
9, electrode, graphite can replace copper as electrode. In the 1960s, copper was widely used as an electrode material, with a usage rate of about 90%, and graphite was only about 10%; In the 21st century, more and more users began to choose graphite as the electrode material, in Europe, more than 90% of the electrode material is graphite. Copper, once the dominant electrode material, has almost lost its advantage over graphite. What caused this dramatic change? Of course, many advantages of graphite electrodes.
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