Carbon-Based Nanostructures
Present chapter describes in detail carbon nanomaterials such as carbon black, fullerenes, carbon nanotubes, graphene, and nanodiamond particles. Analysis of advantages and disadvantages of these materials for application in gas sensors of various types i
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Carbon-Based Nanostructures
As mentioned earlier in Volume 1, there are no ideal sensing materials which meet all requirements. That is why research is continually being conducted to search for new sensing materials with new properties which might be used in the development of gas sensors with new and unusual functional characteristics.
1.1
Carbon Black
Carbon black (CB) is one of numerous forms of carbon (see Table 1.1). CB is a material produced by the incomplete combustion of heavy petroleum products such as FCC (fluid catalytic cracking) tar, coal tar, and ethylene cracking tar, and a small amount comes from vegetable oil. Carbon black is a form of amorphous carbon that has a high surface-area-to-volume ratio. However, in spite of that fact, carbon black, due to specific conductivity and mechanical properties, is not being used as a sensing material in gas sensors. Only activated carbon, also called activated charcoal, activated coal or carbon activates, one can find in gas sensors where CB can be used as a filter. Activated carbon is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for either adsorption or chemical reactions. Due to its high degree of microporosity, just 1 g of activated carbon has a surface area in excess of 500 m2. Other possibility for carbon black to be integrated in gas sensors is connected with using composites, where another material provides the gas-sensing properties while carbon black plays the part of filler, characterized by high conductivity and high dispersion. The key carbon black properties useful for composites design are excellent dispersion, integrity of the carbon black structure or network, consistent particle size, specific resistance, structure, and purity. As a rule, carbon black is used mainly in polymer-based composites. The carbon black endows electrical conductivity to the films, whereas the different organic polymers such as poly(vinyl acetate) (PVAc), polyethylene (PE), poly(ethyleneco-vinyl acetate) (PEVA), and poly(4-vinylphenol) (PVP) are sources of chemical diversity between elements in the sensor array. In addition, polymers function as the insulating phase of the carbon black composites. The concentration of CB in composites is varied within the range 2–40 wt%. The conductivity of these materials and their response to compression or expansion can be explained using percolation theory (McLachlan et al. 1990). The compression of a composite prepared by mixing conducting and insulating particles leads to increased conductivity, and, conversely, expansion leads to decreased conductivity. This effect is especially strong in the composites with compositions around the percolation threshold; an extremely small volume change of the phase due to an extrinsic perturbation
G. Korotcenkov, Handbook of Gas Sensor Materials, Integrated Analytical Systems, DOI 10.1007/978-1-4614-7388-6_1, © Springer Science+Business Media New York 2014
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Carbon-Based Nanostructures
Table 1.1 The propert
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