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Tomography of Carbon Black for Surface Area Measurement

Currently, the morphology of carbon black is described by distributive morphological properties that are measured using two dimensional TEM projections of the carbon black aggregates. The area, perimeter and several Feret diameters of 2000 such aggregate projections are measured with an automated system and used to calculate a number of parameters including the mean primary particle diameter and the surface area of the carbon black in m2/g. Several assumptions must be made in order to carry out these calculations, the first being that the aggregates are either isotropic or randomly oriented. True random orientation is impossible due to the flat surface on which the carbon black is deposited. For relatively compact spherical, ellipsoidal and linear aggregates this assumption works fairly well. However, the more highly structured a carbon black aggregate is, the worse this assumption becomes. Studies of these types of aggregates have shown that the two dimensional projected area and perimeter can decrease up to 25% as the viewing angle is increased from 0° to 45°. The use of electron tomography to determine surface area will eliminate this problem. in addition, the use of tomographically reconstructed carbon black aggregates for the determination of surface area is a more direct measurement technique, although limitations to its accuracy do exist.