Carbon black appears as a light, fluffy, and very fine black powder on the surface, but its specific surface area is very large. It is a product of incomplete combustion or thermal decomposition of organic substances under conditions of insufficient air. Carbon black plays an important role in our daily lives, and is used in products such as ink, paint, and especially rubber products for reinforcement.
Chemical Composition:
Carbon black is a fine powder produced by incomplete combustion of carbon-containing raw materials (mainly petroleum). It has a pure black appearance and can be in the form of fine particles or powders. The color depth, particle fineness, and specific gravity vary depending on the raw materials used and the manufacturing methods. Carbon black is insoluble in water, acids, and alkalis, and can be burned into carbon dioxide in the air. The main component of carbon black is carbon, with small amounts of hydrogen, oxygen, sulfur, ash, tar, and water.
Structure:
The structure of carbon black is expressed by the degree of aggregation of carbon black particles into chain or grape-like structures. Carbon black composed of aggregates of particles with different sizes, shapes, and numbers in each aggregate is called high-structure carbon black. Currently, the structure is commonly represented by the oil absorption value, with higher values indicating higher structure, making it easy to form a spatial network channel and less likely to be destroyed. High-structure carbon black has fine particles, tight mesh-like stacking of chain structures, a large specific surface area, and a high number of particles per unit weight, which is conducive to forming a chain-like conductive structure in polymers. Among the many types of carbon black, acetylene carbon black is the best. Carbon black particles with a wider particle size distribution can endow polymers with electrical conductivity more effectively than those with a narrower distribution, and this phenomenon can be explained by statistical methods. In carbon black with a wider particle size distribution, a large number of a few large diameter particles compensate for the smaller diameter particles, resulting in a larger total number of particles than carbon black with a narrower particle size distribution, with the same average particle size distribution.
Insulating carbon black: Surface chemistry
The production method of carbon black results in different surface chemistry properties. The surface of carbon black has different oxygen-containing functional groups (such as carboxyl, olefin, phenol, carbonyl, etc.). Generally, carbon black with higher oxygen-containing functional groups has higher volatiles and better tinting strength, as well as higher flowability. The volatiles of carbon black are expressed in weight loss per hundred weight of carbon black when heated to 825 ± 25oC. The more oxygen-containing groups in carbon black, the greater the volatiles.
Insulating carbon black: Structure
Carbon black particles not only exist in the form of primary particles but also agglomerate into cohesive bodies during production. This agglomerate is formed by chemical bonding of primary particles. In the process of agglomeration, carbon black composed of primary agglomerates with a large number of chain branches is called high-structure carbon black. Carbon black composed of primary particles with fewer chain branches is called low-structure carbon black.
The function of carbon black is relatively obvious, as it has good reinforcing and insulation properties. Therefore, when purchasing carbon black, it is necessary to carefully identify it. Generally, the blacker and finer the carbon black product, the better the quality. Similarly, we can touch it with our hands or put it in water to determine its quality.