Morphology and Internal Structure of Soot and Carbon Blacks
From the viewpoint of morphology and internal structure soot collected in exhaust gases of engines and carbon blacks are identical materials. They are made of aggregates of pseudospherical particles; the size of individual particles goes from ca. 10 to 500 nm; a single aggregate can include several tens of particles.
The morphology (size and shape) of aggregates can be characterized by electron microscopy, scattering and absorption of light, ultracentrifugation and also adsorption of gases and liquids (pure liquids and solutions).
Electron microscopy has been used to give a two dimensional description of aggregates; the development of Quantimets permitted a quantitative description of soot. The third dimension of carbon black aggregates can be investigated by using electron microscopy combined with stereoscopic methods (observation under two different angles).
Scattering and absorption of light allow one to compute equivalent diameters of aggregated particles.
Ultracentrifugation, carried out on suspensions in water, gives equivalent Stokes diameter distributions of carbon blacks.
A convenient technique has become standard; it is based on the absorption of oil or dibutyl-phthalate in the voids between the particles constituting the aggregates.
Specific surface areas and porosity of soot are currently determined by gas adsorption (essentially nitrogen at the temperature of liquid nitrogen). Iodine adsorption from iodine solution in water has also become standard practice.
The internal structure of carbon blacks (i.e. the crystalline organization of carbon inside the material) has been systematically studied by X-ray diffraction, electron microscopy of oxidized particles, dark field and phase contrast electron microscopy.
The crystalline structure is essentially graphitic (turbostratic). Layer planes of carbon are the basic building blocks of carbon black; they are partially oriented parallel to the surface but also around centers inside the particles.
External layer planes are continuous from one particle to its neighbors. Therefore, in the final material, individual particles have no real existence; the aggregate is the constituent unit of soot.
KeywordsCarbon Black Dark Field Soot Particle Layer Plane Carbon Black Particle
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