Graphite can be divided into natural graphite and artificial graphite. The two structures are similar, and their physical and chemical properties are similar, but their uses are quite different. In many studies, some researchers did not notice the difference between the two and generally referred to as graphite. This result of confusing the two has caused a lot of misleading, even the mistakes of decision-making, resulting in great waste of resources and economic losses. In this paper, from the perspective of the composition and performance of natural graphite and artificial graphite, we will talk about the characteristics and differences of the two, as well as the important links and application progress.
1 graphite classification and characteristics
1.1 Natural graphite
Natural graphite is formed by the transformation of carbon-rich organic matter under the long-term action of high temperature and high pressure geological environment, and is the crystallization of nature. The process characteristics of natural graphite depend mainly on its crystalline form. Minerals with different crystal forms have different industrial values and uses. There are many types of natural graphite. According to different crystal forms, natural graphite is classified into three types: dense crystalline graphite, flake graphite, and cryptocrystalline graphite. China mainly has two types of scale graphite and cryptocrystalline graphite.
Natural flake graphite has good resistance to high temperature, electrical conductivity, thermal conductivity, lubrication, plasticity and acid and alkali resistance. According to the fixed carbon content, four categories are classified: high purity graphite (FC: 99.9%-99.99%), high carbon graphite (FC: 97-99.8%), medium carbon graphite (FC: 90-96%), low carbon graphite (FC) :70-90%).
Natural flake graphite has a melting point above 3000 °C and is one of the most temperature-resistant minerals. It has stable chemical properties at normal temperature, and has the characteristics of high temperature resistance, acid and alkali corrosion resistance and high electrical conductivity. It can be used as refractory materials, conductive materials and wear-resistant lubricating materials. Shandong Shuangyu Carbon Co., Ltd. specializes in the production and sales of natural flake graphite, natural graphite, expanded graphite and spherical graphite.
1.2 Artificial graphite
Artificial graphite is similar to polycrystals in crystallography. There are many kinds of artificial graphite, and the production process varies widely. Broadly speaking, all graphite materials obtained by carbonization of organic matter and high temperature treatment by graphitization can be collectively referred to as artificial graphite, such as carbon (graphite) fiber, pyrolytic carbon (graphite), foamed graphite and the like. In the narrow sense, artificial graphite generally refers to carbonaceous raw materials (petroleum coke, pitch coke, etc.) with low impurity content as binder, coal tar pitch and the like as binders, after compounding, kneading, molding and carbonization (industrially called A bulk solid material obtained by a process such as calcination and graphitization, such as a graphite electrode or a hot isostatic graphite.
(Synthetic) Graphite powder, also called artificial graphite, is usually distinguished from natural graphite powder, which is produced when processing graphite electrodes, and is a by-product thereof. In addition, petroleum coke powder can be obtained by calcination and graphitization. The artificial graphite powder has high purity (carbon content 98%-99.9%), excellent lubricating performance and strong electrical conductivity. Therefore, in most cases, graphite powder is used as a recarburizer to improve the carbon content of the product, such as: For steel, reducer, casting, the same graphite powder is also widely used in the fire protection industry. Sometimes graphite powder is also used as battery or brake lining.
2 The difference and connection between natural graphite and artificial graphite
In view of the above-mentioned natural graphite prepared from raw materials, which are usually narrowly defined artificial graphite, only the difference and connection between natural graphite and narrow artificial graphite are analyzed and discussed.
2.1 Crystal structure
Natural graphite: crystal development is relatively complete, the degree of graphitization of flake graphite is more than 98%, and the degree of graphitization of natural microcrystalline graphite is usually below 93%.
Artificial graphite: The degree of crystal development depends on the raw materials and heat treatment temperature. In general, the higher the heat treatment temperature, the higher the degree of graphitization. The artificial graphite produced in the industry currently has a degree of graphitization of usually less than 90%.
2.2 Organizational structure
Natural flake graphite: It is a single crystal with a simple structure and only crystallographic defects (such as point defects, dislocations, stacking faults, etc.), and macroscopically exhibits anisotropic characteristics. The crystallites of natural microcrystalline graphite are small, the crystal grains are arranged in disorder, and the pores after the impurities are removed are macroscopically isotropic.
Artificial graphite: can be regarded as a multi-phase material, including graphite phase transformed by carbon particles such as petroleum coke or pitch coke, graphite phase transformed by coal tar binder coated around particles, particle accumulation or coal tar pitch A pore formed by heat treatment of the junction.
2.3 Physical form
Natural graphite: usually in the form of powder, can be used alone, but usually used in combination with other materials.
Artificial graphite: It has many forms, both powdery, fibrous, and massive. In the narrow sense, artificial graphite is usually in the form of a block, which needs to be processed into a certain shape when used.
2.4 Physical and chemical properties
In terms of physical and chemical properties, natural graphite and artificial graphite have both commonalities and performance differences. For example, natural graphite and artificial graphite are good conductors of heat and electricity, but for graphite powder of the same purity and particle size, natural flake graphite has the best heat transfer performance and electrical conductivity, followed by natural microcrystalline graphite, artificial graphite. lowest. Graphite has good lubricity and certain plasticity. The crystal development of natural flake graphite is perfect, the friction coefficient is small, the lubricity is the best, the plasticity is the highest, and the dense crystalline graphite and cryptocrystalline graphite are the second, artificial graphite. Poor.
3 Application fields of natural graphite and artificial graphite
Graphite has many excellent properties and is widely used in industrial sectors such as metallurgy, machinery, electrical, chemical, textile, and defense. The application fields of natural graphite and artificial graphite have overlapping parts and different places.
3.1 Metallurgical Industry
In the metallurgical industry, natural flake graphite can be used to produce refractory materials such as magnesia carbon bricks and aluminum carbon bricks because of its good oxidation resistance. Artificial graphite can be used as a steelmaking electrode, and an electrode made of natural graphite is difficult to use in a more demanding steelmaking electric furnace.
3.2 Machinery Industry
In the mechanical industry, graphite materials are commonly used as wear and lubrication materials. Natural flake graphite has good lubricity and is often used as an additive for lubricating oils. For the equipment that transports corrosive media, piston rings, seals and bearings made of artificial graphite are widely used, and no lubricating oil is needed for work. Natural graphite and polymer resin composites can also be used in the above fields, but the abrasion resistance is not as good as that of artificial graphite.
3.3 Chemical Industry
Artificial graphite has the characteristics of corrosion resistance, good thermal conductivity and low permeability. It is widely used in the chemical industry to make heat exchangers, reaction tanks, absorption towers, filters and other equipment. Natural graphite and polymer resin composites can also be used in the above fields, but thermal conductivity and corrosion resistance are inferior to artificial graphite.
With the continuous development of research technology, the application prospect of artificial graphite is immeasurable. At present, the development of artificial graphite products using natural graphite as a raw material is one of the important ways to expand the application of natural graphite. Natural graphite has been used as an auxiliary raw material for some artificial graphite production, but the development of artificial graphite products with natural graphite as the main raw material is not enough research. It is the best way to achieve this goal by fully understanding and utilizing the structure and characteristics of natural graphite and using appropriate processes, routes and methods to produce artificial graphite products with special structures, properties and uses.