Understanding the difference between natural graphite and artificial graphite: how to develop artificial graphite products with natural graphite
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. The technological properties of natural graphite mainly depend on its crystalline form. Graphite minerals with different crystalline forms have different industrial values and uses. There are many kinds of natural graphite, which can be divided into compact crystalline graphite, flake graphite and APHANITIC graphite. There are two kinds of flake graphite and APHANITIC graphite in China. Compact crystalline graphite is also called bulk graphite. This kind of graphite crystallizes obviously, the crystal is visible to the naked eye. Particle diameter greater than 0.1 mm. The crystals are arranged in a haphazard, dense block-like structure. High Grade, the general carbon content is 60% ~ 65% , sometimes 80% ~ 98% , but its plasticity and smoothness is not as good as flake graphite. Natural Flake graphite belongs to the pegmatite in crystallography. It is a kind of single crystal. It is named for its flake-like crystal. This kind of graphite is superior to other types of graphite in lubricity and plasticity, so its industrial value is the biggest. Although the grade of flake graphite ore is not high, the carbon content is generally between 3% and 25% , but it is one of the best floatable ores in nature. APHANITIC graphite, also called Amorphous graphite or earthy graphite, has been called microcrystalline graphite in recent years. This graphite crystal diameter is generally less than 1 Micron, only in the electron microscope to see the crystal shape, can be seen as a collection of graphite crystals. Natural microcrystalline graphite is usually converted from coal under high temperature and high pressure. Therefore, natural microcrystalline graphite is usually associated with coal, the transition zone from anthracite to natural microcrystalline graphite can often be seen in natural microcrystalline graphite ore bodies. This kind of graphite is characterized by earthy surface, lack of luster, lubricity is lower than that of flake graphite and poor selectivity. But high grade, carbon content is generally 60% ~ 80% , a few as high as 90% . 2 artificial graphite artificial graphite is similar to polycrystal in crystallography. There are many kinds of artificial graphite, and the production process varies greatly. In a broad sense, all graphite materials obtained by carbonization and graphitization of organic matter, such as carbon (graphite) fiber, pyrolytic carbon (graphite) , foam graphite, etc. . In a narrow sense, artificial graphite usually refers to the carbonaceous raw materials (petroleum coke, pitch coke, etc.) with low impurity content as aggregate and coal tar as binder, bulk solid materials, such as graphite electrode and isostatic pressing graphite, are prepared by batching, kneading, molding, carbonization (known as calcination in industry) and graphitization. The difference and connection between natural graphite and artificial graphite in the narrow sense of artificial graphite is usually prepared from natural graphite, so this paper only analyses and discusses the difference and connection between natural graphite and artificial graphite in the narrow sense. The Crystal Structure of natural graphite is well developed, the graphitization degree of natural flake graphite is usually above 98% , and the graphitization degree of natural microcrystal graphite is usually below 93% . The degree of crystal development of artificial graphite depends on raw material and heat treatment temperature. Generally speaking, the higher the heat treatment temperature is, the higher the degree of graphitization is. At present, the degree of graphitization of manufactured graphite is usually less than 90% . The structure of natural flake graphite is a kind of single crystal, the structure is simple, there are only crystallographic defects (point defects, dislocation, stacking fault, etc. . The grain size of natural microcrystalline graphite is small, the grains are arranged in disorder and there are holes after impurity removal. Artificial graphite can be regarded as a multiphase material, including carbonaceous particles such as petroleum coke or asphalt coke, the graphite phase transformed by particles, the graphite phase transformed by coal tar pitch binder wrapped around the particles, the accumulation of particles or the pores formed by heat treatment of Coal Tar Pitch Binder, etc. . Physical form natural graphite usually exists in powder form and can be used alone, but it is usually compounded with other materials. There are many forms of artificial graphite, such as powder, fiber and block, and the narrow sense of artificial graphite is usually block, when used to be processed into a certain shape. The physical and chemical properties of natural graphite and artificial graphite have both similarities and differences in performance. For example, natural graphite and artificial graphite are both good conductors of heat and electricity, but for graphite powder with the same purity and granularity, natural flake graphite has the best heat transfer and electric conductivity, natural microcrystalline graphite is next, and artificial graphite is the lowest. Graphite has better lubricity and certain plasticity, the crystal of natural flake graphite is more perfect, the friction coefficient is smaller, the lubricity is the best, the plasticity is the highest, and the dense crystalline graphite and aphanitic graphite are the second, artificial graphite is poor. Graphite is widely used in metallurgy, machinery, electric, chemical, textile, national defense and other industrial sectors because of its many excellent properties. The application fields of natural graphite and artificial graphite have both overlap and difference. In metallurgical industry, natural flake graphite can be used to produce MGO-C bricks and al-c bricks due to its good oxidation resistance, Refractory. Artificial graphite can be used as steel-making electrode, but the electrode made of natural graphite can not be used in steel-making electric furnace. In the mechanical 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 oil. Corrosion medium transport equipment, widely made of artificial graphite piston rings, seals and bearings, work without adding lubricating oil. Natural graphite and polymer resin composites can also be used in the above fields, but the wear resistance is not as good as artificial graphite. Man-made graphite is widely used in chemical industry for making heat exchanger, reaction tank, absorption tower, filter and so on. Natural graphite and polymer resin compound, composite materials can also be used in the above areas, but thermal conductivity, corrosion resistance than artificial graphite. In fact, using natural graphite as raw material to develop new graphite products is not a new topic in the field of artificial graphite. Many carbon and graphite products have been prepared with natural graphite as the main raw material or auxiliary raw material according to the production technology of artificial graphite, some of which have even formed a large industry. Zinc-manganese Battery Carbon Rod: The Carbon Rod of zinc-manganese battery (commonly called dry battery) is produced with natural microcrystalline graphite and coal pitch as the main raw materials by the processes of kneading, extruding forming, roasting, machining and dipping wax. Because of its high conductivity and low price, natural microcrystalline graphite is not required for ash content, but for impurities such as iron and sulfur. Natural Graphite Brush: the brush is made from natural flake graphite and coal tar pitch by mixing, rolling, grinding, molding, roasting (graphitizing if necessary) and machining. Based on the characteristics of high conductivity and orientation of natural flake graphite, it is necessary to pay attention to the orientation of flake graphite when machining. Carbon and graphite materials for machinery: The bulk materials produced by mixing, rolling, grinding, molding and roasting with natural graphite and coal tar pitch as the main raw materials need to be processed by precision machine according to the requirements of use. Natural graphite is mainly used for its lubricity, high temperature resistance and corrosion resistance, and high ash content and impurity content are required. As can be seen from the above examples, compared with the narrow sense of artificial graphite, natural graphite is used as the main raw material or auxiliary raw material, carbon graphite products prepared by artificial graphite production process have the following differences in production process and product properties: (1) the former usually needs to be graphitized above 2500 °C to obtain the required physical and chemical properties; The latter can be graphitized or not graphitized. In order to reduce the cost of production, graphitization is not usually carried out, so there is binder asphalt in its structure
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