Trace the origin and decrypt, explore the cause
Natural graphite is a non-metallic mineral composed of carbon elements. It is the result of the combined effects of sedimentation and metamorphism during the geological history period. Its formation process mainly consists of two stages: the carbon-rich sediment accumulation stage and the metamorphic mineralization stage. The former provides a rich source of carbon for the formation of graphite, while the latter completes the transformation from carbon to graphite.
Natural graphite is formed from carbon substances in nature. The sources of carbon substances can be mainly divided into organic carbon and inorganic carbon. Among them, organic carbon dominates, mainly coming from algae plants and microfossils in the original ocean, as well as other carbon-containing residues. Inorganic carbon accounts for a relatively smaller proportion, mostly coming from carbon-containing inorganic substances such as carbonate rocks formed in the marine environment. The original organic carbon and inorganic carbon accumulate and are buried on the seabed, forming sedimentary layers rich in carbon substances.
After having sufficient sedimentary reserves, carbonaceous materials need certain temperature and pressure conditions to be transformed into graphite. This transformation process is also known as the graphitization process. During the movement of the Earth's tectonic plates, the carbon-rich sedimentary layers in the ocean gradually move to the deep part of the crust. The closed environment with high temperature and pressure enables the scattered carbonaceous materials to rapidly and orderly form graphite nuclei, and then slowly aggregate and grow to form graphite crystals. Among them, temperature and pressure are the primary conditions for the transformation of carbonaceous materials into graphite, and the crystal growth time is an important factor in the degree of graphitization.
Trace and locate; widely distributed
Natural graphite is widely distributed globally and has abundant reserves. The "2024 Mineral Commodity Summary" released by the United States Geological Survey shows that as of the end of 2022, the globally proven reserves of natural graphite were approximately 280 million tons. China's reserves were about 810 million tons, accounting for approximately one quarter of the global total. The global graphite production in 2023 was approximately 1.6 million tons, and China's production was about 1.23 million tons, accounting for approximately 77% of the world's total output, making China the world's leading producer of graphite.
Diverse in form and rich in variety
Natural graphite is jet black in color and slippery in texture. According to the differences in its crystalline form, it can be divided into crystalline graphite and amorphous graphite.
The crystalline graphite has a good crystal shape and the crystals can be seen with the naked eye. It can be further classified into flake graphite and block graphite. When single layers of graphite are orderly stacked, they form fish-scale-like flake graphite. If the arrangement is disorderly, dense block graphite will be formed.
The cryptocrystalline graphite crystals are extremely small and resemble soil-like substances. Their crystal shapes can only be clearly observed with the aid of an electron microscope, hence they are also called soil-like graphite.
The crystal form of natural graphite is closely related to its industrial value. Generally speaking, the better the crystallization degree, the higher the quality characteristics. Therefore, flake graphite often has superior properties and application value compared to other types of graphite.
Based on the classification of minerals according to their crystalline form, the graphite deposits can be further divided into three types: regional metamorphic type, contact metamorphic type, and magmatic hydrothermal type, based on the geological background and conditions during the formation of graphite.
Regional metamorphic graphite deposits are mostly formed by the regional metamorphism of ancient carbon-containing sedimentary strata due to tectonic movements. They often produce large-sized and high-quality flake graphite. Although the ore grade is relatively low, these deposits have a large scale and the industrial value is the highest.
The contact metamorphic graphite deposit is formed when magma intrudes into the coal-bearing strata and the carbon in the coal layer undergoes metamorphism. It is also known as coal-bearing graphite. The graphite crystallization degree is relatively low, presenting as microcrystalline or cryptocrystalline. The ore grade is relatively high, reaching 60% to 90%.
Magma hydrothermal graphite deposits are formed by the cooling and crystallization of carbon-containing magma fluids. They are generally of small scale, with irregular mineral bodies, significant variations in the degree of graphite crystallization, and most are medium to fine flake graphite. The ore grade is relatively low.
Distinctive personality, a gem of industry
The unique structure of natural graphite endows it with a variety of excellent properties, and also significantly expands its application scope in the industrial field.
Soft texture:Graphite possesses excellent high-temperature resistance. Its melting point is close to 4,000℃ and its boiling point reaches 4,250℃. Graphite is an atomic crystal, and the covalent single bonds between carbon atoms are very strong chemical bonds that require an extremely high amount of energy to break. Therefore, the melting point of graphite is very high, and it experiences minimal weight loss even under extremely high temperatures. Thus, in industrial sectors such as metallurgy and casting, graphite can be used to produce magnesium-carbon refractory bricks and high-temperature-resistant graphite crucibles.
Chemical resistant：Graphite possesses excellent anti-corrosion properties. It can withstand the erosion of various strong acids, strong bases and organic solutions. Moreover, graphite has an extremely low "affinity" for most chemical solutions, and its surface is not prone to scaling. It can be used in the chemical industry to manufacture high-purity corrosion-resistant devices, such as chemical pipelines, reaction tanks, combustion towers, and so on.
Good lubricity：Graphite is a solid lubricant with a long history of use. Its layered structure that is easy to slide gives it excellent lubrication properties. After adsorbing gases and water vapor in the air, the distance between graphite layers increases, making it easier to slide and further enhancing its lubrication performance. Therefore, in industries such as mechanical manufacturing, graphite can be used as a solid lubricant to help remove molds from castings, or it can be combined with other metals to make oil-free lubricating bearings and other frictional materials. It is also a commonly used lubricant in daily life for solving the rusting problem of lock cores.
Electrical conductivity：Graphite is a commonly used non-metallic conductive material, which is related to the electron arrangement structure of carbon atoms in graphite. Each carbon atom has 4 electrons in its outer layer. In the honeycomb-like layered structure of graphite, each carbon atom uses 3 electrons to connect with the other 3 carbon atoms around it to form covalent bonds. Therefore, each carbon atom will have an extra free electron to conduct electricity, which makes graphite have excellent conductivity. Thus, graphite is widely used in the electrical industry and is commonly used as the filament of high-intensity light bulbs, carbon rods, brushes, etc., or applied as electrodes in small electrode carbon tubes, positive electrodes of mercury rectifiers, welding carbon, telephone accessories and other components.
Furthermore, the stable physical and chemical properties of graphite determine its suitability as a chemical reaction retardant and a good insulator. This has enabled it to be widely utilized in cutting-edge industrial fields such as nuclear industry materials and aerospace equipment components. In the fourth-generation high-temperature gas-cooled reactors currently in commercial operation in China, stable graphite is used as the retardant for the reactors.
The differences between the two "industrial black gold" types
Natural graphite and coal are both substances composed of carbon elements, and both are known as "industrial black gold". However, they differ significantly in structural properties and formation causes, and they also have their own unique advantages in industrial applications.
From a structural perspective, natural graphite and coal differ significantly. Natural graphite is a pure mineral composed of carbon elements, with carbon atoms arranged in an orderly layer structure and a uniform crystal structure. Coal, on the other hand, is a mixture of various elements such as carbon, hydrogen, and oxygen. Carbon atoms combine with other atoms to form different organic molecules, which are randomly combined with inorganic compounds, resulting in a complex and disordered structure. Therefore, the physical and chemical properties of graphite are much more stable than those of coal. Its ignition point, melting point, and thermal conductivity are all much higher than those of coal. This is the reason why although both contain a large amount of carbon elements, coal can be used as fuel while graphite cannot.
From the perspective of causes, although both natural graphite and coal are products of the sedimentation and metamorphism of ancient plant remains, the formation of graphite requires a high-temperature and high-pressure metamorphism in the deep part of the earth's crust, where carbon can form graphite crystals. Coal only needs to undergo sedimentation in the shallow part of the earth's crust to form lignite, and undergo a low degree of metamorphism to form bituminous coal and anthracite. If the temperature and pressure continue to increase, the transformation from coal to graphite can also occur. For example, contact metamorphic coal-type graphite is formed when the anthracite layer is intruded by magma and undergoes high-temperature metamorphism.
In industrial applications, natural graphite is quite different from coal. Natural graphite is mainly used as an industrial raw material to manufacture industrial machinery parts and carbon-based materials. Coal, on the other hand, is mainly used for combustion for energy supply and the extraction of organic compounds, such as in power generation, steelmaking, and the production of methanol, crude ammonia, and so on.
New materials - promising future
The advent of the new round of global industrial revolution has brought new opportunities and challenges to the research and application of graphite. With technological progress and industrial upgrading, the advanced processing technology of graphite has continuously achieved breakthroughs, the properties of graphite have been deeply developed and utilized, and the graphite industry has begun to develop towards high-tech fields. A series of new graphite materials have emerged, such as flexible graphite, spherical graphite, graphene, and so on.
Flexible graphite is made by rapidly heating and expanding natural flake graphite through special chemical processing. Due to its expansion manufacturing process, it is also called expanded graphite. Flexible graphite not only inherits the excellent properties of natural graphite but also expands its softness, resilience, and adsorption properties. It can work under high temperatures, high pressures, or radiation conditions and can be used as a flame retardant and sealing material. Utilizing its hydrophobic and oleophilic characteristics, it can be used as an adsorbent to treat oil-based substances, often used for handling crude oil leaks and oilfield wastewater; it can also remove substances soluble in oil, such as pesticides and some organic or inorganic harmful components, or be used to remove harmful substances in industrial exhaust and vehicle exhaust gases.
Spherical graphite is obtained by using mechanical and physical methods to sphericalize the natural flake graphite. The spherical shape endows it with excellent electrical conductivity, charge and discharge capacity, and cycle life, making it a relatively ideal negative electrode material for lithium-ion batteries. In recent years, the usage of lithium-ion batteries in electronic products such as computers, communications, and entertainment has grown rapidly. With the rapid expansion of the clean and environmentally friendly electric vehicle industry, the demand for high-performance lithium-ion power batteries has continuously increased, which in turn has driven the demand and development of spherical graphite.
Among all the new types of graphite materials currently available, graphene is undoubtedly the "dark horse" of materials, triggering a new wave of applications for graphite and truly representing a new type of productive force.
Graphene is a single-layer sheet-like material composed of carbon atoms, also known as monolayer graphite. Despite its extremely thin thickness, it possesses extremely high strength, along with excellent electrical conductivity, thermal conductivity, and malleability, making it highly valued in numerous fields such as physics, chemistry, biology, and energy. By leveraging the superior properties of graphene, advanced industrial and electronic products such as graphene composite anti-corrosion coatings, heat dissipation film materials, flexible display devices, and sensing sensors can be produced. In the future, graphene will have broad prospects in areas like biomedicine, optics, electronics, and the environment, and is expected to bring about a disruptive revolution in the semiconductor field, becoming the fundamental material for next-generation circuits and supercomputers.
In the context of continuous in-depth research on graphite materials, more innovative and high-performance graphite-based materials are expected to emerge in the future, playing a significant role in promoting industrial development, enhancing energy efficiency, and protecting the environment. Current research indicates that the quality of natural graphite directly affects the performance and application scope of new materials prepared from it. The better the quality and purity of natural graphite, the greater the advantages in the preparation of new materials. In the future, the fields of new energy, new materials, national defense industry, and aerospace, which apply cutting-edge graphite materials, will have a greater demand for high-quality graphite resources. As the largest reserve and producer of natural graphite in the world, China should continue to deepen graphite exploration efforts, use multiple methods to comprehensively search for deep-seated minerals and develop high-quality resources, and rely on this, strengthen the comprehensive development and utilization of graphite resources, enhance research and technological innovation capabilities in emerging fields, and transform the advantages of graphite resources into development advantages in new fields, continuously empowering the development of new productive forces.
