Explain in detail the difference between carbon materials and graphite materials

Explain in detail the difference between carbon materials and graphite materials

Since carbon materials and graphite materials have many similarities in appearance and characteristics, many people do not know how to distinguish the relationship between the two in reality. This article makes a detailed introduction.

Carbon exists in three most common allotropes: amorphous carbon, graphite, and diamond.

Molecular structure and appearance of diamond

Diamond

It is a mineral composed of carbon. Diamond is the hardest substance in nature, known as the "King of Hardness" and “the King of Gems”. The angle of the diamond crystal is 54 degrees 44 minutes and 8 seconds. In the 1950s, the United States successfully produced artificial diamonds using graphite as raw material under high temperature and pressure. Today, artificial diamonds have been widely used in production and life.

Amorphous Carbon

Generally refers to charcoal, coke, bone char, sugar charcoal, activated carbon and carbon black, etc. Except for bone char, which contains about 10% carbon, the other main components are elemental carbon. Coal is naturally occurring amorphous carbon that contains some compounds composed of carbon, hydrogen, nitrogen, etc. The so-called amorphous carbon does not refer to the shape in which these substances exist, but to their internal structure. In fact, their internal structure is not a real amorphous body, but a crystal with a similar structure to graphite, but the layered structure formed by the hexagonal ring plane of carbon atoms is messy and irregular, and the crystal formation is defective. The particles are small and contain a small amount of impurities.

Most of the amorphous carbon is a graphitic layer structure in which the molecular fragments are roughly parallel to each other and piled up irregularly, which can be referred to as a turbostratic structure. The interlayers or fragments are connected by carbon atom bonds in the tetrahedral bonding mode of the diamond structure. When the proportion of carbon atoms in this tetrahedron is large, the amorphous carbon will be relatively hard, such as coke and glassy carbon.

Molecular structure and appearance of amorphous carbon

Carbon products commonly used in industry refer to carbon products purified from amorphous carbon raw materials (such as coal, petroleum coke, pitch coke, etc.). With different raw materials and processing techniques, the proportion of graphite crystal structure contained in the carbon element crystal structure in such carbon products will vary. Generally speaking, the more graphite crystal structure components are contained, the higher the purity of carbon, and the higher the performance and price.

Since the essential difference between carbon materials and graphite materials is not great, many carbon products are also called " graphite XX" . This is also the source of the confusion between the two vocabulary concepts of graphite and carbon. For example, the large electrodes commonly used in the steelmaking industry are called " graphite electrodes " . In fact, they are carbon products, not electrodes made of graphite in the true sense. In terms of appearance, common carbon products are large in size, such as electrodes for metallurgy, lining bricks (carbon blocks) for smelting furnaces, carbon radiators, and so on.

Molecular structure and appearance of graphite

Graphite

It is an allotrope of the element carbon. Each carbon atom is surrounded by three other carbon atoms (arranged in multiple hexagons in a honeycomb pattern) and combined with covalent bonds to form a covalent molecule. Since each carbon atom releases an electron, those electrons can move freely, so graphite is an electrical conductor. Graphite can be classified as natural graphite and artificial graphite. Natural graphite ore is divided into earthy graphite and flake graphite, among which flake graphite is a higher quality natural graphite.

Artificial graphite refers to graphite materials obtained by further processing carbon materials belonging to the amorphous carbon classification to improve the purity of the carbon and further increase the proportion of graphite-like crystal structure. Like carbon materials, graphite materials can be made into industrial products such as electrodes and refractory materials. However, due to its more excellent characteristics, it is used in many high-end fields. For example, high temperature resistant lubricants, coating modification of battery materials, etc.

Carbon and graphite materials are non-metallic solid materials mainly composed of carbon elements. Carbon materials are basically composed of non-graphite carbon, while graphite materials are basically composed of graphite carbon. For simplicity, carbon and graphite materials are sometimes collectively referred to as carbon materials.

Carbon products can be divided into graphite electrodes, carbon blocks, graphite anodes, carbon electrodes, pastes, electric carbons, carbon fibers, special graphites, graphite heat exchangers, etc. according to product uses. Graphite electrodes can be divided into ordinary power graphite electrodes, high power electrodes, ultra high power electrodes according to the allowable current density. Carbon blocks can be divided into blast furnace carbon blocks, aluminum carbon blocks, electric furnace blocks, etc. according to their uses.

Carbon products can be divided into carbon products, graphite products, carbon fibers and graphite fibers according to the processing depth. Carbon products can be divided into graphite products, carbon products, carbon fibers, special graphite products, etc. according to different raw materials and production processes. Carbon products can be divided into more ash products and less ash products (with ash content less than 1%) according to the size of the ash content.

Graphite is widely used in industry and is used in almost every industry. Artificial graphite is mostly used in industry, known as special graphite. According to the way it is formed, it can be divided into the following types.

1. Isostatic graphite. That is what many people call three high graphite, but three high doesn’t equal isostatic pressing.

2. Molded graphite

3. Extruded graphite, mostly electrode material.

According to the particle size of graphite, it can also be divided into : fine structure graphite, medium coarse graphite ( general particle size is around 0.8mm ) , and electrode graphite (2-4mm) .

The Chinese national technical standards and ministerial technical standards for carbon products are classified according to different uses of products and different production processes. This classification method basically reflects the different uses and production processes of products, and is also convenient for accounting, so its calculation method also adopts this classification standard. The classification and description of carbon products are introduced below.

I. Carbon and graphite products

(1) Graphite electrodes

It is mainly made of petroleum coke and needle coke, and coal tar pitch is used as a binder. It is made by calcination, batching, kneading, pressing, roasting, graphitization, and machining. It releases electric energy in the form of an electric arc in an electric arc furnace. Conductors that are heated and melted can be divided into ordinary power, high power and ultra-high power according to their quality indicators. Graphite electrodes include:

（1） Ordinary power graphite electrode. It is allowed to use graphite electrodes with a current density lower than 17A /cm2 , which are mainly used in ordinary power electric furnaces for steelmaking , silicon smelting, yellow phosphorus smelting, etc.

（2） Anti-oxidation coated graphite electrode. A graphite electrode coated with an anti-oxidation protective layer forms a protective layer that is both conductive and resistant to high-temperature oxidation, reducing electrode consumption during steelmaking.

（3） High power graphite electrode. It is allowed to use graphite electrodes with a current density of 18-25A /cm2 , which are mainly used in high-power electric arc furnaces for steelmaking.

（4） Ultra high power graphite electrode. It is allowed to use graphite electrodes with a current density greater than 25A /cm2 . Mainly used in ultra-high power steelmaking electric arc furnaces.

(2) Graphite anodes

It is mainly made of petroleum coke as raw material and coal pitch as binder, and is made through calcination, batching, kneading, pressing, roasting, impregnation, graphitization and machining. Generally used as conductive anodes for electrolysis equipment in the electrochemical industry. include:

（1） Anode plates for various chemical industries.

（2） Various anode rods.

(3) Special graphite

Mainly use high-quality petroleum coke as raw material, coal tar pitch or synthetic resin as binder, after raw material preparation, batching, kneading, tableting, crushing, re-kneading, molding, multiple roasting, multiple impregnation, purification and graphitization, Made by machine processing. Generally used in aerospace, electronics, and nuclear industry sectors.

It includes spectrally pure graphite, high-purity, high-strength, high-density and pyrolytic graphite.

(4) Graphite heat exchanger

It is an impermeable graphite product for heat exchange made by processing artificial graphite into the required shape, impregnating and solidifying it with resin. It is a heat exchange equipment processed from artificial impermeable graphite. Used in chemical industry. include:

（1） block hole heat exchanger;

（2） Radial heat exchanger;

（3） Falling film heat exchanger;

（4） Tube heat exchanger.

(5) Carbon electrodes

Using carbonaceous materials such as anthracite and metallurgical coke (or petroleum coke) as raw materials, coal tar pitch as a binder, conductive electrodes fired by compression molding without graphitization. It is not suitable for electric furnaces that melt high-grade alloy steel. include:

 (1)   Ashy electrodes (electrodes produced from anthracite, metallurgical coke, and pitch coke);

（2） Regenerative electrodes (electrodes produced from artificial graphite and natural graphite);

（3） Carbon resistance rods (i.e. carbon grid bricks);

（4） Carbon anodes (prebaked anodes produced from petroleum coke);

（5） Baking electrode blank.

(6) Carbon blocks

With anthracite and metallurgical coke as the main raw materials and coal tar pitch as the binder, it is made through raw material preparation, batching, mixing, molding, roasting and machining. Among them, blast furnace carbon blocks are used as high-temperature and corrosion-resistant materials for blast furnace linings; bottom carbon blocks, side carbon blocks, and electric furnace blocks are used in aluminum electrolytic cells and ferroalloy electric furnaces. include:

（1） Blast furnace charcoal;

（2） Aluminum tank carbon blocks (bottom carbon blocks and side carbon blocks);

（3） Electric stove charcoal.

(7) Carbon paste

It is made of petroleum coke, anthracite, and metallurgical coke as the main raw materials, and coal tar pitch as the binder. Some are used as electrode pastes for various continuous self-baking electric furnaces as conductive electrodes; some are used as anode pastes for continuous self-baking aluminum tanks as conductive anodes; some are used as fillers for blast furnace masonry and coarse refractory slurries. Seam and seam caulking. Although self-baked carbon blocks for blast furnaces have different uses, their production process is similar to that of paste products, so they are temporarily included in paste products. include:

（1） Anode paste;

（2） Electrode paste (including standard and non-standard electrode paste );

（3） Bottom paste (including more gray and less gray bottom paste );

（4） Sealing paste (including more ash and less ash sealing paste );

（5） Other pastes (including coarse seam paste, fine seam paste, self-baked carbon brick, etc.) .

(8)  Non-standard carbon and graphite products

This refers to various special-shaped carbon and graphite products made of carbon and graphite products through further processing. Including shovel-type anodes, fluorine-making anodes and various specifications of crucibles, plates, rods, blocks and other special-shaped products.

(9) impermeable graphite

This refers to various graphite special-shaped products made by impregnating and processing resins and various organic substances, including the matrix block of heat exchangers.

(10)  Electric charcoal products

This refers to carbon rods, brushes and other products.

II.  carbon fiber

It includes various carbon fibers, graphite fibers, pre-oxidized wires, carbon cloth, carbon belts, carbon ropes, carbon felts and their composite materials. Carbon fiber is a fiber with a carbon content higher than 93%. Made of polyacrylonitrile fiber, viscose yarn and pitch fiber through carbonization. The heat treatment temperature ranges from low to high, and can be made into heat-resistant fiber, carbonized fiber and graphite fiber respectively.

To sum up, in a broad sense: carbon materials are actually carbon materials containing more amorphous carbon structures. Graphite material is a carbon material mainly composed of graphite crystals. The two have many similarities, but there are also significant differences.