Graphite

Graphite is a crystalline form of carbon. It is an allotrope of the element carbon, and the periphery of each carbon atom is connected with three other carbon atoms (multiple hexagons arranged in a honeycomb pattern) to form a covalent molecule. Graphite is an electrical conductor because each carbon atom emits an electron and those electrons are free to move. Graphite is one of the softest minerals, and its uses include making pencil leads and lubricants. Carbon is a non-metallic element located in group IVA of the second period of the periodic table. Hexagonal crystal system, iron ink color to dark gray. The density is 2.25 g/cm3, the hardness is 1.5, the melting point is 3652°C, and the boiling point is 4827°C. Soft, creamy, and conductive. Chemical properties are inactive, corrosion-resistant, and not easy to react with acids and alkalis. Intensified heat in air or oxygen can burn and generate carbon dioxide. Strong oxidizing agents will oxidize it to organic acids. Used as anti-friction agent and lubricating material, making crucibles, electrodes, dry batteries, pencil leads. High-purity graphite can be used as a neutron moderator in nuclear reactors. Often called charcoal or black lead because it was previously mistaken for lead.

Carbon is a very common element that exists in various forms in the atmosphere and the earth's crust. Simple carbon has been known and utilized very early, and a series of compounds of carbon—organic matter is the foundation of life. Carbon is a constituent of pig iron, wrought iron and steel. Carbon is capable of chemically self-combining to form a multitude of compounds that are biologically and commercially important molecules. Most molecules in living organisms contain carbon.

Carbon exists in various forms, including crystalline simple carbon such as diamond and graphite; amorphous carbon such as coal; complex organic compounds such as animals and plants; carbonates such as marble. The physical and chemical properties of elemental carbon depend on its crystal structure. High-hardness diamond and soft and slippery graphite have different crystal structures, and each has its own appearance, density, melting point, etc.

Purification of graphite

1.Chemical purification is to use the properties of graphite to resist acid, alkali and corrosion, treat graphite concentrate with acid and alkali to dissolve impurities, and then wash them away to improve the grade of concentrate. Chemical purification can obtain high-carbon graphite with a grade of 99%. There are many methods of chemical purification, and the most widely used method in China is the high-temperature melting method of sodium hydroxide.

The basic principle is to make the impurities in graphite (mainly silicate minerals) react with caustic soda, that is, NaOH, under high temperature conditions above 500°C to generate water-soluble reactants, which can be eliminated by leaching the reactants with water. Impurities, another part of impurities, such as iron oxides, are neutralized with HCl after alkali fusion to form ferric chloride with soluble subwater, which can be removed by washing with water.
In the above process, the concentration of NaOH is about 50%, and it is mixed with graphite at a ratio of 1:0.8, that is, about 0.4 tons of NaOH are consumed to produce 1 ton of high-carbon graphite. The amount of HCl added is about 30% of that of graphite. The coal used as fuel is about 0.6-0.7t. The equipment used in the alkali fusion method mainly includes anchor mixers, melting furnaces, propeller mixers, V-shaped washing tanks, etc. The recovery rate is 85-90%. Although this process is more advanced, it also has the disadvantages of large water consumption, high graphite loss, low productivity, large alkali consumption, and environmental pollution by the discharged waste liquid.
In order to solve or improve the above-mentioned deficiencies, the Rock and Mineral Testing Center of the Henan Provincial Department of Geology and Mineral Resources has developed a new process for purifying high-carbon graphite, replacing the V-shaped washing tank with centrifugal washing, and recycling the waste liquid after treatment. Adopting this new technology can reduce the cost of materials by about 50%, save water by about 50%, increase the yield by about 10%, and reduce the pollution of waste liquid to the environment. The fixed carbon content of graphite is greater than 99%, and the recovery rate reaches 92.8%.

2.Physical purification is high-temperature purification. Using the high-temperature resistance of graphite, place it in an electric furnace and heat it to 2500°C without air to volatilize the ash (ie impurities), thereby improving the grade of the concentrate. High-temperature purification can obtain high-purity graphite with a grade of 99.9%.

Graphene is a new material with a single-layer sheet structure composed of carbon atoms. It is a planar film composed of carbon atoms with sp2 hybrid orbitals forming a hexagonal honeycomb lattice, and a two-dimensional material with a thickness of only one carbon atom. Graphene has always been considered as a hypothetical structure and cannot exist stably alone. Until 2004, physicists Andre Geim and Konstantin Novoselov of the University of Manchester in the United Kingdom succeeded in experimenting from graphite Graphene was isolated from the experiment, and it was confirmed that it can exist alone. The two also won the 2010 Nobel Prize in Physics for their "pioneering experiments on two-dimensional graphene materials".

Graphene is the thinnest but also the hardest nanomaterial in the world. It is almost completely transparent and only absorbs 2.3% of light. Electron mobility* exceeds 15000 cm²/V·s, which is higher than carbon nanotubes or silicon crystal*, while resistivity is only about 10-6 Ω·cm, lower than copper or silver, which is the material with the smallest resistivity in the world. Because of its extremely low resistivity and extremely fast electron migration, it is expected to be used to develop a new generation of electronic components or transistors that are thinner and conduct electricity faster. Since graphene is essentially a transparent and good conductor , is also suitable for making transparent touch screens, light panels, and even solar cells.

Another characteristic of graphene is the ability to observe the quantum Hall effect at room temperature.

The arrangement of carbon atoms in graphene is similar to that of graphite in a single atomic layer, and it is a single-layer two-dimensional crystal in which carbon atoms are arranged in a honeycomb crystal lattice with sp2 mixed orbitals. Graphene can be imagined as an atomically sized network of carbon atoms and their covalent bonds. The name of graphene comes from the English graphite (graphite) + -ene (ene end). Graphene is considered to be a planar crystal of polycyclic aromatic hydrocarbon atoms.

The structure of graphene is very stable, the carbon-carbon bond (carbon-carbon bond) is only 1.42 Å. The connection between carbon atoms inside graphene is very flexible. When an external force is applied to graphene, the surface of the carbon atoms will bend and deform, so that the carbon atoms do not need to be rearranged to adapt to the external force, thereby maintaining the stability of the structure. This stable lattice structure makes graphene have excellent thermal conductivity.

Graphene is the building block that makes up the following carbon allotropes: graphite, charcoal, carbon nanotubes, and fullerenes. Perfect graphene is two-dimensional, which only includes hexagons (equal-angled hexagons); if there are pentagons and heptagons, they will constitute the defects of graphene. Twelve pentagonal graphenes will form fullerenes together.

Graphene rolled into a cylindrical shape can be used as carbon nanotubes; in addition, graphene is also made into a ballistic transistor (ballistic transistor) and has attracted the interest of a large number of scientists. In March 2006, researchers at the Georgia Institute of Technology announced that they had successfully fabricated a graphene planar field effect transistor, observed the quantum interference effect, and based on this result, developed a circuit based on graphene.

The advent of graphene has caused a research boom all over the world. It is the thinnest known material, the material is very strong and hard, and at room temperature, it can transfer electrons faster than known conductors. The atomic-scale structure of graphene is so special that it can only be described by quantum field theory.

Graphene is a two-dimensional crystal. The common graphite is formed by stacking layers of planar carbon atoms arranged in a honeycomb order. The interlayer force of graphite is weak, and it is easy to peel off each other to form a thin layer. graphite flakes. When the graphite sheet is peeled off into a single layer, this single layer with a thickness of only one carbon atom is graphene. Features:
First: Graphene is the strongest material in the world. According to calculations, if graphene is used to make a film with a thickness equivalent to the thickness of an ordinary food plastic packaging bag (thickness is about 100 nanometers), then it will be able to bear about two tons of heavy objects. pressure without breaking;
Second: Graphene is the most conductive material in the world.

Graphene has a wide range of applications. According to the ultra-thin and super-strength characteristics of graphene, graphene can be widely used in various fields, such as ultra-light body armor, ultra-thin and ultra-light aircraft materials, etc. According to its excellent conductivity, it also has great application potential in the field of microelectronics. Graphene may become a substitute for silicon, making ultra-miniature transistors, used to produce future supercomputers, and the higher electron mobility of carbon can enable future computers to achieve higher speeds. In addition, graphene material is also an excellent modifier. In new energy fields such as supercapacitors and lithium-ion batteries, it can be used as an electrode material additive due to its high conductivity and high specific surface area.

There is still a lot of room for graphite to be studied...

                   Graphite and its products have the properties of high temperature resistance and high strength. They are mainly used to manufacture graphite crucibles in the metallurgical industry. In steelmaking, graphite is often used as a protective agent for steel ingots and as a lining for metallurgical furnaces.

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