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What Is The Difference Between Conductive Graphite Powder And Conductive Carbon Black

Pulished on Jan. 04, 2020

Graphite, as one of the forms of carbon, has a layered structure. Each carbon atom in the layer forms three equidistant bonds with three adjacent carbon atoms with sp2 hybrid orbitals. There is also one spz orbital that does not participate in hybridization. Solitary electrons are perpendicular to the direction of the graphite layer. The solitary electrons in the spz orbits of each carbon atom overlap each other (side by side) to form delocalized π bonds. These delocalized electrons move freely in the entire carbon atom plane, resulting in graphite Parallel to the sheet layer, there is good conductivity, and the layer-to-layer combination is based on Van der Waals force, showing high resistance.

Therefore, carbon graphite can be regarded as a two-dimensional conductor, and its transport properties are between metal and semiconductor. The two-dimensional characteristics of graphite are the key to the successful development of carbon nanotubes. Graphite sheets can be rolled into tubes, and the carbon atom layer of graphite is rolled into a cylindrical shape, forming carbon nanotubes with very small radial dimensions. Therefore, the two-dimensional transport characteristics of graphite is a hot topic in theoretical and experimental research.

Graphite Powder

Graphite Powder

The conductivity of graphite powder mainly depends on the purity (ie carbon content), the degree of graphitization (the degree of graphitization is a measure of the degree of rearrangement of carbon material from amorphous carbon through its structure, and its crystals are close to perfect graphite) and Body particle size, morphology and other factors. Generally speaking, the higher the purity of the powder, the higher the degree of graphitization, the wider the particle size distribution, and the higher the aspect ratio, the better the conductivity.

Conductive carbon black is a collective name, which generally guides the special carbon black varieties that are stronger than ordinary carbon black and pigment carbon black. According to the conductive capacity, it can be divided into conductive blacks, super conductive blacks, and extra conductive blacks from low to high. In terms of production methods, it can be divided into three categories: acetylene carbon black, heavy oil furnace carbon black, and heavy oil gas by-product carbon black.

China graphite powder is an amorphous carbon. It is a fine powder produced by incomplete combustion or thermal cracking of hydrocarbon compounds (liquid or gaseous). The main composition is carbon, which exists in the form of colloidal primary particles and aggregates similar to spheres, and also contains a small amount of hydrogen, oxygen, sulfur, ash, tar and moisture. The structure of carbon black is expressed by the degree to which carbon black particles are aggregated into a chain or grape shape.

At present, the oil absorption value is commonly used to indicate the structure. The larger the oil absorption value, the higher the structure of carbon black, which easily forms a space network channel and is not easy to destroy. High-structure carbon black has fine particles, densely packed network chains, large specific surface area, and many particles per unit mass, which is conducive to the formation of a chain conductive structure in the polymer. Carbon black particles with a wide particle size distribution are more capable of imparting conductivity to polymers than carbon black particles with a narrow distribution. Statistical methods can be used to explain this phenomenon. For carbon black with a wide particle size distribution, a small number of large diameter particles need a large number, and smaller diameter particles are compensated. Carbon black with the same average particle size distribution has a larger total number of particles than carbon black with a narrow distribution.

The so-called amorphous carbon does not refer to the shape in which these substances exist, but to its internal structure. In fact, their internal structure is not a true amorphous body, but a crystal with the same structure as graphite, except that the layered structure formed by the hexagonal ring-shaped plane of carbon atoms is disorderly and irregular, and the crystal is defective, and the crystal The grains are small and contain a small number of impurities. Most of the amorphous carbon is a graphite layer structure. The molecular fragments are roughly parallel to each other and are randomly stacked together, which can be referred to as a random layer structure.

Since the truly excellent conductivity is graphitized carbon, the higher the degree of graphitization, the better the conductivity.

So in general, the conductivity of graphite is better than carbon black (in the case of high purity of both, if the purity is not high, there is no comparable). But in plastic systems, why does carbon black add less mass to achieve better electrical conductivity than graphite?

This is because, in a polymer system, in addition to the conductivity of the conductive powder itself, the factors that play a role in electrical conductivity are also related to the distribution state of the conductive particles in the polymer. Carbon black and graphite of the same quality, because carbon black has a smaller specific gravity, it occupies a larger volume fraction in the polymer, which is beneficial to the formation of a conductive network, thereby obtaining a better conductive effect than graphite powder as a filler. However, in the highly aggregated state, the conductivity of graphite aggregates is much better than carbon black. This is why good conductive electrode materials are made of graphite, not carbon black.