Carbon Black (CB) is a specific type of elemental carbon in the form of colloidal particles that is generated or produced through incomplete combustion processes or the thermal decomposition of gaseous or liquid hydrocarbons under controlled conditions. It occurs as a black fine dusty powder that must be differentiated from the undefined byproducts soot and diesel exhaust particulates generated during coal or hydrocarbon combustion. Carbon black consists of more than 96 percent of amorphous carbon and of small quantities of oxygen, hydrogen, nitrogen, and sulfur. Most of these elements are concentrated on the surface. Subsequently oxidized carbon black may contain up to 15 percent of oxygen.
Carbon black can be tailored to the respective intended purposes, hence is characterized by a high diversity that is essentially determined by the method of production and the variation of the process parameters. Carbon black consists of chain-type or botryoidal aggregates that have coalesced during production from smallest, mostly spherical particles.While still in the reactor, these aggregates form large agglomerates. The types of carbon black that have a high specific surface and widely ramified aggregates are particularly conductive. These conductive carbon blacks are used, for example, in antistatic finishings of plastics. For many applications, the carbon blacks are subjected to aftertreatments. In paints and varnishes with high color intensities, one uses e.g. carbon blacks that have been enhanced through subsequent oxidation.
Often, the formation and sizes of the aggregates described above require thorough explanation. The end product of carbon black is frequently described to be less than 0,1 micrometers in aerodynamic diameter. As a matter of fact, carbon black is produced from small spherical particles (so-called primary particles or nodules) with sizes in the range of 15–300 nm. These particles melt into particle aggregates that are 85–500 nm in aerodynamic diameter. Due to strong electric forces, these aggregates remain closely bound, forming even large agglomerates with other aggregates. Since these latter processes occur during production and since the agglomerates, once formed, do not break apart anymore, all commercial carbon blacks consist of 1 – 100 µm sized agglomerates.
The imgae shows the different stages of carbon black structure development. To ensure easy handling and avoid the occurrence of dusts, carbon blacks have been distributed for some time as pellets sized 0,1 to 1 millimeters. The use of ultrafine primary particles is restricted to the production furnace.
More than 90 percent of all carbon black is used as filler in the rubber industry, mainly in tires and technical rubber products such as conveyor belts, flexible tubes, and sealing profiles. Moreover, carbon black is used as black pigment in printing inks, India inks, paints and varnishes, for dyeing and for UV protection of plastics as well as in special products such as mascara, flower soil, decor paper, and fibers. As conductive carbon black, it is used in the electrical industry to manufacture electrodes and carbon brushes.
Currently, carbon black is among the 50 most produced chemicals (8.1 million t/a) in the world. More than 90 percent are used in the rubber industry. In China, “lamp black”, the forerunner of today’s carbon black, was manufactured already more than 3,500 years ago .
Since the middle of the 1970s, the annual bulk of carbon black (approximately 98 percent) has been supplied by the furnace process where a hot gas with temperatures in the range of 1200 to 1800°C is generated in a furnace through combustion of natural gas or oil. Coal- and oil-based carbon black oils that are rich in aromatic compounds are injected in the produced hot gas. In addition to hydrogen and other gaseous compounds, carbon black is generated through the incomplete combustion and thermal fission (pyrolysis) of the feedstock. After an exactly defined reaction time, the reaction is stopped by abrupt cooling down (quenching) of the process gas mixture through injection of water. In baghouse filters, the product is then separated from the process gas. The furnace reactors are operated nonstop in shifts. Other carbon black production methods include gas or channel black, lamp black and thermal black procedures.