Graphite can be divided into natural graphite and artificial graphite, the two structures are similar, similar physical and chemical properties, but there is a big difference in use. In many studies, some researchers did not notice the difference between the two and generally referred to as graphite. The result of the confusion between the two has caused a lot of misleading, even the wrong decision-making, resulting in a great waste of resources and economic losses. In this paper, from the perspective of the structure and properties of natural graphite and artificial graphite, the characteristics and differences between them are discussed.
1 Graphite classification and characteristics:
1.1 natural graphite
Natural graphite is carbon rich organic matter in the geological environment of high temperature and pressure for a long time under the action of the formation of the transformation, is the crystallization of nature. The technological characteristics of natural graphite mainly depend on its crystalline morphology. Crystalline forms of different minerals with different industrial values and uses. There are many kinds of natural graphite, according to different crystal morphology, will be divided into natural graphite industry compact crystalline graphite, graphite and aphanitic graphite three. Our country mainly aphanitic graphite flake graphite and two categories.
1.2 synthetic graphite
Multi crystal graphite is similar to the crystallographic. A wide variety of artificial graphite, different production processes. Broadly speaking, all organic compounds obtained by carbonization and then graphitised after high temperature treatment of graphite materials can be referred to as artificial graphite like carbon (graphite) fiber, pyrolytic carbon (graphite), graphite foam etc.. While in a narrow sense of artificial graphite usually refers to the impurity content of low carbon raw materials (petroleum coke and pitch coke etc.) as aggregate, coal tar as the binder, after mixing, kneading, molding and carbonization (industry called roasting) bulk solid material and graphite and other processes in the system. Such as graphite electrode, hot isostatic graphite etc..
2 natural graphite and artificial graphite
In view of the natural graphite as the raw material to prepare the general is the narrow sense of artificial graphite, only to analyze and discuss the difference between natural graphite and narrow artificial graphite.
2.1 crystal structure
Natural graphite: crystal development is more perfect, the scale graphite graphitization degree is more than 98%, and the natural microcrystalline graphite graphitization degree is usually below 93%.
Synthetic graphite: crystal growth depends on the raw materials and heat treatment temperature. In general, the higher the heat treatment temperature, the higher the degree of graphitization. At present, the industrial production of artificial graphite, the degree of graphitization is usually less than 90%.
2.2 organizational structure
Natural flake graphite is a kind of crystal structure is relatively simple, only the defects on Crystallography (such as point defects, dislocations, stacking faults, etc.) characterized by macroscopic anisotropy. 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 kind of heterogeneous material, including petroleum coke and pitch coke and carbon particles into the coating, Shi Moxiang transformation in coal asphalt binder particles around the graphite phase, particles or coal asphalt binder formed by heat treatment such as pores.
2.3 physical form
Natural graphite: usually in the form of powder, can be used alone, but often combined with other materials after the use of.
Artificial graphite: more forms, both powder, but also fiber and block, and the narrow sense of artificial graphite is usually a block, the need to be processed into a certain shape.
2.4 physical and chemical properties
In terms of physical and chemical properties, natural graphite and artificial graphite have both generality and difference in performance. Such as natural graphite and artificial graphite is a good conductor of heat and electricity, but for the same purity graphite powder and particle size, natural flake graphite, conductive heat transfer performance and the best performance of natural graphite, artificial graphite minimum. The graphite has good lubricity and certain plasticity, development of natural flake graphite crystal is perfect, the friction coefficient is small, the best lubrication, the highest plasticity, and dense crystalline graphite and the aphanitic graphite, artificial graphite.
3 natural graphite and artificial graphite
Graphite has many excellent properties, so it is widely used in metallurgical, mechanical, electrical, chemical, textile, national defense and other industrial sectors. 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 because of good oxidation resistance can be used for production of refractory materials and aluminum carbon brick and magnesia carbon brick. The artificial graphite can be used as the electrode of the steel making, and the electrode made of the natural graphite is difficult to be used in the electric furnace with the harsh conditions.
3.2 mechanical industry
In the mechanical industry, graphite materials are usually used as wear-resistant and lubricating materials. Natural flake graphite has good lubricity and is often used as additive in lubricating oil. The equipment used for conveying corrosive medium is made of synthetic graphite made of piston ring, sealing ring and bearing. Natural graphite and polymer resin composite material can also be used in the field, but not as good as artificial graphite.
3.3 chemical industry
Synthetic graphite has the advantages of corrosion resistance, good thermal conductivity, low permeability and so on. It is widely used in chemical industry, such as heat exchanger, reaction tank, absorption tower, filter and so on. Natural graphite and polymer resin composite material can also be used in the above fields, but the thermal conductivity, corrosion resistance as artificial graphite.