Каковы различия между натуральным графитом и синтетическим графитом?

Classification and Characteristics of Graphite:

Graphite can be classified into natural graphite and synthetic (or artificial) graphite. Although they share similar structures and physicochemical properties, their applications vary significantly.

Natural Graphite:

Natural graphite is formed through the long-term transformation of carbon-rich organic matter under high-temperature and high-pressure geological conditions, representing a crystallization of nature. Its technological characteristics are primarily determined by its crystalline form. Minerals with different crystalline forms possess distinct industrial values and applications. There are several types of natural graphite, and industrially, they are categorized into three main types based on their crystalline form: dense crystalline graphite, flake graphite, and cryptocrystalline graphite. In China, the primary types are flake graphite and cryptocrystalline graphite.

Synthetic (Artificial) Graphite:

Synthetic graphite resembles a polycrystal in crystallography. There is a wide variety of synthetic graphite types, and their production processes vary greatly. Broadly speaking, all graphite materials obtained through the carbonization of organic matter followed by high-temperature graphitization treatment can be collectively referred to as synthetic graphite, such as carbon (graphite) fibers, pyrolytic carbon (graphite), and foam graphite. In a narrower sense, synthetic graphite typically refers to block solid materials prepared through processes such as batching, kneading, molding, carbonization (industrially referred to as roasting), and graphitization, using low-impurity carbonaceous raw materials (such as petroleum coke and pitch coke) as aggregates and coal tar pitch as a binder. Examples include graphite electrodes and hot isostatically pressed graphite.

Differences and Connections between Natural and Synthetic (Artificial) Graphite:

Given that the preparation of synthetic graphite in its narrower sense often starts with natural graphite as a raw material, this article will only analyze and discuss the differences and connections between natural graphite and synthetic graphite in its narrower sense.

Physicochemical Properties:

Natural graphite and synthetic graphite share common properties but also exhibit performance differences. For example, both natural and synthetic graphite are good conductors of heat and electricity. However, for graphite powders of the same purity and particle size, natural flake graphite exhibits superior thermal and electrical conductivity, followed by natural microcrystalline graphite, with synthetic graphite having the lowest conductivity.

Graphite also possesses good lubricity and certain plasticity. Natural flake graphite, with its well-developed crystal structure, has a low friction coefficient, excellent lubricity, and high plasticity. Dense crystalline graphite and cryptocrystalline graphite follow in these properties, while synthetic graphite has relatively poor performance.

Applications:

Graphite's many excellent properties make it widely used in industries such as metallurgy, machinery, electrical engineering, chemicals, textiles, and defense. The application fields of natural and synthetic graphite overlap in some areas but also differ in others.

In metallurgical industries, natural flake graphite, due to its good oxidation resistance, is used in the production of refractory materials such as magnesia-carbon bricks and alumina-carbon bricks.

Synthetic graphite can be used as a steel-making electrode, whereas electrodes made from natural graphite are difficult to use in steel-making electric furnaces with harsh operating conditions.

In the machinery industry, graphite materials are commonly used as wear-resistant and lubricating materials. Natural flake graphite, with its good lubricity, is often used as an additive in lubricating oils.

Piston rings, seals, and bearings made from synthetic graphite are widely used in equipment that transports corrosive media, requiring no lubricating oil during operation.

Natural graphite-polymer composites can also be used in these fields but have inferior wear resistance compared to synthetic graphite.

Synthetic graphite, with its corrosion resistance, good thermal conductivity, and low permeability, is widely used in the chemical industry for making heat exchangers, reaction tanks, absorption towers, filters, and other equipment.

Natural graphite-polymer composites can also be used in these fields but have inferior thermal conductivity and corrosion resistance compared to synthetic graphite.

Development of Synthetic Graphite from Natural Graphite:

In fact, the development of new graphite products by drawing on the preparation processes of synthetic graphite is not a new topic in the synthetic graphite industry. Many carbon-graphite products have been prepared using natural graphite as the main or auxiliary raw material according to synthetic graphite production processes, with some even forming large industries.

Zinc-Manganese Battery Carbon Rods: Carbon rods for zinc-manganese batteries (commonly known as dry batteries) produced through processes such as kneading, extrusion molding, roasting, machining, and wax impregnation using natural microcrystalline graphite and coal tar pitch as main raw materials.

These rods primarily utilize the high electrical conductivity and low cost of natural microcrystalline graphite, with less stringent requirements for ash content but stricter requirements for iron and sulfur impurities.

Natural Graphite Brushes: Electric motor brushes produced through processes such as kneading, rolling, grinding, molding, roasting (and graphitization treatment if necessary), and machining using natural flake graphite and coal tar pitch as main raw materials.

These brushes primarily utilize the high electrical conductivity and high orientation of natural flake graphite, requiring low iron and sulfur impurity content and an ash content not exceeding 2%. Attention must be paid to the orientation of flake graphite during machining.