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Crystallization Processes 105
FIGURE 9 Attachment of surfactant molecules to crystal surfaces.
and a second that does not. The part that does not lation distribution relates the number of crystals at each
fit repulses incoming growth units or causes size to the size, while the mass distribution expresses how
significant interatomic stress because of its mass is distributed over the size range. In the following
position in the crystal lattice. If such species are paragraphs, methods for describing and using distribution
purposely added to the crystallizing system to functions will be outlined.
modify crystal morphology, they are referred to as Size distribution is a major determinant of the proper-
tailor-made additives. ties of crystalline products, especially appearance, and to
downstream processing and handling of crystalline mate-
rials.Solid–liquidseparationbyfiltrationorcentrifugation
C. Crystal Size Distributions
can be straightforward with a desired CSD, but it can be
Most crystallization processes produce particles whose disastrous when an inappropriate one increases resistance
sizes cover a range of varying breadth. If the particles to liquor flow through a filter or centrifuge cake. Like-
consist of single crystals, the resulting distribution is a wise, CSD affects other downstream processing such as
crystal size distribution (CSD); on the other hand, if the the removal of impurities and mother liquor by washing,
particles consist of agglomerates or other combination of dissolution or reaction of the crystals, and transporting or
multiple crystals, the distribution is a particle size dis- storing crystals.
tribution. In either case, the distribution is expressed in Crystal size distributions may be expressed by: (1) his-
terms of either population (number) or mass. The popu- tograms, which are the amount or fraction of mass or
