Graphite are including natural graphite and artificial graphite. The two have similar structures and the same physical and chemical properties, but their uses are quite different.
Natural Graphite
Natural graphite is transformed from carbon-rich organic matter under the long-term action of high-temperature and high-pressure geological environments. It is a gift from nature. The process characteristics of natural graphite are mainly determined by its crystalline form. Graphite 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 industrially divided into three categories: dense crystalline graphite, flake graphite and cryptocrystalline graphite. Dense crystalline graphite is also called lump graphite. This type of graphite has obvious crystallization and the crystals are visible to the naked eye. Particle diameter is bigger than 0.1 mm. The crystal arrangement is chaotic and has a dense block structure. The grade is very high, generally the carbon content is 60%~65%, sometimes reaching 80%~98%, but its plasticity and smoothness are not as good as flake graphite.
Natural flake graphite is a pegmatite in crystallography. It is a single crystal. It is named because its crystals are in the shape of scales. They are divided into large scales and fine scales. This kind of graphite has better lubricity and plasticity than other types of graphite, so it has the greatest industrial value. Although the grade of flake graphite ore is not high, with the carbon content generally ranging from 3% to 25%, it is one of the most floatable ores in nature. High-grade graphite concentrate can be obtained through multiple grinding and multiple selections. Cryptocrystalline graphite is also called amorphous graphite or earthy graphite. In recent years, it has begun to be called microcrystalline graphite. The crystal diameter of this kind of graphite is generally less than 1 micron. The crystal form can only be seen under an electron microscope and can be regarded as a collection of graphite crystals. Natural microcrystalline graphite is usually transformed from coal under high-temperature and high-pressure geological environments. Therefore, natural microcrystalline graphite is usually associated with coal. The transition from anthracite to natural microcrystalline graphite can often be seen in natural microcrystalline graphite ore bodies. area. This type of graphite is characterized by an earthy surface, lack of luster, lower lubricity than flake graphite and poor selectivity. But the grade is higher, the carbon content is generally 60% to 80%, and a few are as high as 90% or more.
Artificial Graphite
Artificial graphite is similar to polycrystals in crystallography. There are many types of artificial graphite, and the production processes vary widely. Broadly speaking, all graphite materials obtained by carbonization of organic matter and then graphitization and high-temperature treatment can be collectively referred to as artificial graphite, such as carbon (graphite) fiber, pyrolytic carbon (graphite), foam graphite, etc. In a narrow sense, artificial graphite usually refers to carbonaceous raw materials with low impurity content (petroleum coke, pitch coke, etc.) as aggregate and coal pitch as binder, through batching, kneading, molding, and carbonization (industry termed It is a block solid material produced by processes such as roasting) and graphitization, such as graphite electrodes, isostatic graphite, etc.
The difference and connection between natural graphite and artificial graphite
Organizational Structure
Natural flake graphite is a single crystal with a relatively simple organizational structure. It only has crystallographic defects (point defects, dislocations, stacking faults, etc.) and exhibits anisotropic structural characteristics at a macro level. The grains of natural microcrystalline graphite are small, the grains are arranged randomly and there are holes after impurities have been removed, showing isotropic structural characteristics on a macroscopic level. Artificial graphite can be regarded as a multi-phase material, including the graphite phase transformed by carbonaceous particles such as petroleum coke or pitch coke, the graphite phase transformed by the coal pitch binder wrapped around the particles, particle accumulation or coal pitch adhesive. The pores formed after heat treatment of the binder, etc.
Physical Form
Natural graphite usually exists in powder form and can be used alone, but it is usually used in combination with other materials. Artificial graphite comes in many forms, including powder, fiber and block. Artificial graphite in the narrow sense is usually in block form and needs to be processed into a certain shape when used.
Physical and Chemical Properties
Natural graphite and artificial graphite have both commonalities and differences in performance. For example, both natural graphite and artificial graphite are good conductors of heat and electricity. However, 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 and artificial graphite lowest. Graphite has good lubricity and certain plasticity. The crystals of natural flake graphite are well developed, so the friction coefficient is small, the lubricity is the best, and the plasticity is the highest, followed by dense crystalline graphite and cryptocrystalline graphite, and artificial graphite last.
Application Areas
Graphite has many excellent properties and is widely used in metallurgy, machinery, electrical, chemical, textile, national defense and other industrial sectors. The application fields of natural graphite and artificial graphite have overlaps and differences. In the metallurgical industry, natural flake graphite can be used to produce refractory materials such as magnesia carbon bricks and aluminum carbon bricks due to its good oxidation resistance. Artificial graphite can be used as steel-making electrodes, but electrodes made of natural graphite are difficult to use in steel-making electric furnaces with harsh operating conditions. In the machinery industry, graphite materials are often used as wear-resistant and lubricating materials. Natural flake graphite has good lubricity and is often used as an additive in lubricating oils. Equipment that transports corrosive media widely uses piston rings, sealing rings and bearings made of artificial graphite, and does not require the addition of lubricating oil during operation. Natural graphite and polymer resin composite materials can also be used in the above fields, but their wear resistance is not as good as artificial graphite. 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 composite materials can also be used in the above fields, but their thermal conductivity and corrosion resistance are not as good as artificial graphite.