Carbon Black
Soot that is produced with a special purpose under controlled conditions and is specified both physically and chemically is referred to as carbon black. In comparison, diesel exhaust particulates or soot from chimneys are undefined by-products of coal or hydrocarbon combustion. Carbon black consists of more than 96 % amorphous carbon without ordered structure and small parts of oxygen, hydrogen, nitrogen, and sulfur. Most of these elements are concentrated on the surface. The oxygen content of carbon black that is oxidized at a later stage may be as high as 15 %.
Production
Carbon black is mainly produced using the furnace process (worldwide 98 %) where a hot gas in the temperature range of 1200 to 1800 °C is produced through combustion of natural gas or oil in a furnace and is then enhanced injecting soot oils from coal or oil that are rich in aromatic compounds. Carbon black forms in addition to hydrogen and other gaseous compounds through incomplete combustion and thermal decomposition (pyrolysis) of the raw material. After an exactly defined reaction time, the process gas mixture is cooled down abruptly (quenched) by injection of water to stop the reaction. Subsequently, the product is separated from the process gas using baghouse filters. The furnace reactors are operated “non-stop” in shifts. The gas, channel, lamp and thermal black procedures are known as further carbon black production methods.
Properties
The properties of the different types of carbon black can be tailored to the diverse needs by selecting specific production methods and varying the respective process parameters. Carbon black consists of chain- or cluster-type aggregates that have coalesced from small, mostly globular particles during the production process. While in the reactor, these aggregates “agglutinate” forming large agglomerates. Types of carbon black with a high specific surface and widely ramified aggregates are particularly conductive. Such conductivity soots are used for e.g., giving plastics antistatic properties. For many applications, soots are after-treated to obtain specific properties. The types of carbon black that are intended for use in varnishes with a high color depth, for example, are enhanced through subsequent oxidation.
Use
More than 90% of carbon black is used as filler in the rubber industry mainly in automobile tires and technical rubber products such as conveyor belts, flexible tubes, and rubber profiles. In addition, carbon black serves as black pigment in printing inks, India ink, and varnishes as well as for dyeing and UV protection of plastics. Carbon black pigments are also used in special products such as mascara, flower soil, decor paper, and fibers. The electrical industry uses conductivity soot for manufacturing electrodes and carbon brushes.
