The Most Promising Materials And Applications in The 21st Century

Introduction:

Graphite is an allotrope of elemental carbon. The periphery of each carbon atom is connected with three other carbon atoms (multiple hexagons arranged in a honeycomb) covalently bonded to form a covalent molecule. Since each carbon atom emits an electron, those electrons can move freely, so graphite is an electrical conductor. Graphite is one of the softest minerals, and its uses include the manufacture of pencil leads and lubricants. Carbon is a non-metallic element, located in the IVA group of the second period of the periodic table.

Characteristic

The chemical properties of elemental carbon are relatively stable at room temperature, and it is insoluble in water, dilute acid, dilute alkali and organic solvents; it reacts and burns with oxygen at different high temperatures to generate carbon dioxide or carbon monoxide; among halogens, only fluorine can directly react with elemental carbon; Under high temperature, elemental carbon is easier to be oxidized by acid; at high temperature, carbon can also react with many metals to form metal carbides. Carbon is reductive and can smelt metals at high temperatures. Graphite is a crystalline mineral of carbon elements, and its crystal lattice is a hexagonal layered structure. The distance between each mesh layer is 340pm, and the distance between carbon atoms in the same mesh layer is 142pm;. It belongs to the hexagonal crystal system with complete layered cleavage. The cleavage surface is dominated by molecular bonds, which has weaker attraction to molecules, so its natural floatability is very good. Graphite, diamond, carbon 60, carbon nanotubes, etc. are all simple substances of carbon, and they are allotropes. The special properties of graphite, high temperature resistance: the melting point of graphite is 3850±50°C, and the boiling point is 4250°C. Even after ultra-high temperature arc burning, the weight loss is very small, and the thermal expansion coefficient is also very small. The strength of graphite increases with increasing temperature. At 2000°C, the strength of graphite doubles.

Refractory

In the iron and steel industry, graphite refractories are used for refractory linings of arc blast furnaces and oxygen converters, ladle refractory linings, etc.; graphite refractories are mainly integral casting materials, magnesia carbon bricks and aluminum graphite refractories. Graphite is also used as a film-forming material for powder metallurgy and metal casting. Graphite powder is added to molten steel to increase the carbon content of steel, so that high-carbon steel has many excellent properties.

Conductive material

In the electrical industry, it is used to make electrodes, brushes, carbon rods, carbon tubes, positive electrodes of mercury positive current devices, graphite washers, telephone parts, coatings for television picture tubes, etc.

Wear-resistant lubricating material

Graphite is often used as a lubricant in the machinery industry. Lubricating oil can not be used under high-speed, high-temperature, and high-pressure conditions, while graphite wear-resistant materials can work at high sliding speeds at a temperature of -200 to 2000°C without lubricating oil. Many equipment that transports corrosive media widely use graphite materials to make piston cups, seals and bearings. They do not need to add lubricating oil when they are running. Graphite emulsion is also a good lubricant for many metal processing (wire drawing, pipe drawing).

Corrosion-resistant materials

Specially processed graphite, which has the characteristics of corrosion resistance, good thermal conductivity, and low permeability, is widely used in the production of heat exchangers, reaction tanks, condensers, combustion towers, absorption towers, coolers, heaters, and filters , Pump equipment. It is widely used in petrochemical industry, hydrometallurgy, acid-base production, synthetic fiber, papermaking and other industrial sectors, which can save a lot of metal materials

High temperature metallurgical materials

Because graphite has a small thermal expansion coefficient and can withstand rapid cold and rapid heat changes, it can be used as a glass mold. After graphite is used, ferrous metals can obtain castings with precise dimensions and a high surface finish rate. It can be used without processing or a little processing. Save a lot of metal. The production of cemented carbide and other powder metallurgy processes usually use graphite materials to make porcelain boats for compression molds and sintering. Single crystal silicon crystal growth crucibles, regional refining vessels, support fixtures, induction heaters, etc. are all made of high-purity graphite. In addition, graphite can also be used for vacuum smelting graphite insulation boards and bases, high-temperature resistance furnace tubes and other components.

Atomic Energy and Defense Industry

Graphite has a good neutron moderator used in atomic reactors. Uranium-graphite reactors are currently the most widely used atomic reactors. The deceleration material in the nuclear reactor used as power should have a high melting point, stability, and 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 tens of ppm. In particular, the boron content should be less than 0.5 ppm. In the national defense industry, graphite is also used to make solid fuel rocket nozzles, missile nose cones, parts of aerospace equipment, heat insulation materials and radiation protection materials.