Carbon black is a form of amorphous carbon that is commercially produced from the partial combustion of petroleum products such as natural gas or coal tar. Most carbon blacks are used as pigments or fillers but its unique electrical properties have led to its use as a conductive additive in applications like batteries, films, and molded electronic devices.
History and Production of Carbon Black
The industrial production of carbon black can be traced back to the late 19th century when it first started to be manufactured as a pigment and rubber reinforcing filler. While earlier processes burned petroleum or natural gas in low oxygen environments, modern production utilizes the furnace black method. In this process, heavy petroleum oil or natural gas is pyrolyzed in temperature-controlled rotary kilns at temperatures between 1200-1400°C under a limited supply of combustion supporting gas like oxygen or steam. Control over production conditions allows manufacturers to tailor carbon blacks for specific properties and applications.
Structure and Morphology
On an atomistic level, carbon black is composed purely of carbon atoms. However, it does not exist as a pure crystalline form of carbon but instead as an amorphous, quasi-graphitic material. Its structure can be described as spheroidal particles consisting of fused, structured graphene sheets only a few nanometers in diameter. High resolution microscopy reveals carbon blacks have a grape-like morphology with the sheets fused into a three-dimensionalnetwork. Increasing the pyrolysis temperature or decreasing the combustion supporting gases results in higher structural ordering, greater dimensionality and larger particle sizes.
Electrical Properties
Besides its use as pigments and fillers, one of the key properties enabling new applications for carbon black is its ability to conduct electricity. This is due to delocalized pi-electrons available for conduction that are generated through disruption of the graphene sheets during manufacture. The electrical conductivity depends strongly on production parameters and pretreatments and can range from semi-conducting to highly conductive. Conductive grades contain a network of electron-conducting pathways through physical contact between the spheroidal particles and chains of fused primary particles. Additional treatments like gas or chemical activation can introduce surface functional groups and further enhance conductivity.
Applications in Batteries
One area benefiting greatly from Conductive Carbon Blacks is energy storage technologies. In lithium-ion batteries, carbon black is often used as the anode material due to its high surface area, conductivity, stability, and low cost. It provides active sites for Li+ intercalation while maintaining excellent cycling performance. Advanced Si-based anodes are also combined with carbon black to accommodate large volume changes during charging. In supercapacitors, high surface area carbon blacks in electrode formulations help provide rapid charge propagation within electrochemical double layers, translating to higher power capabilities. When doped with nitrogen or other heteroatoms, their capacitance can be further improved by additional fast faradaic reactions. Overall, conductive carbon blacks enable the development of lighter, longer lasting batteries and supercapacitors for electric vehicles and portable devices.
Carbon Black Composites
The unique percolating network structure of conductive carbon blacks makes them valuable fillers for enhancing composite materials. Polymer composites containing carbon black display significantly increased electrical and thermal conductivities even at low loadings. This has led to uses in conductive plastics for applications such as antistatic packaging, EMI shielding, sensors and printed electronics. Carbon black is also combined with metals, semiconductors and ceramics to form multifunctional composites exhibiting properties such as electromagnetic interference suppression, heat diffusion and piezoresistivity. Advanced automotive applications exploit these to enable technologies like resistive heating films, strain and pressure sensors. Overall, the development of advanced carbon black-based composites continues to be an active area of research.
Additional Applications
Beyond energy storage and composites, conductive carbon blacks are enabling new technologies through their unique set of physical properties. When three-dimensionally structured into aerogels or foams, they can serve as high surface area substrates for catalysts, water purification media or sensing platforms. As fullerene-like molecules, novel carbon blacks act as excellent dry lubricants or radiation shields. Their electrical conductivity also allows functionalization into versatile printable inks and pastes for applications like transparent heaters and biosensors. With continued advancements, carbon blacks are well positioned to usher in the next generation of electronic devices from flexible circuits to implantable biomedical tools.
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