Table of contents 1 Why is particle size important?

particle through a viscous medium, with the other particles and/or the container

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Particle Guidebook 09-2019

SHAPE FACTOR
Performing a particle size analysis is the best way to answer the question: What size are those particles Once the analysis is complete the user has

particle through a viscous medium, with the other particles and/or the container
walls tending to slow their movement. Flaky or plate-like particles will orient to
maximize drag while sedimenting, shifting the reported particle size in the smaller
direction. A light scattering device will average the various dimensions as the
particles flow randomly through the light beam, producing a distribution of sizes
from the smallest to the largest dimensions.
The only techniques that can describe particle size using multiple values are
microscopy or automated image analysis. An image analysis system could
describe the non-spherical particle seen in Figure 1 using the longest and shortest
diameters, perimeter, projected area, or again by equivalent spherical diameter.
When reporting a particle size distribution the most common format used even for
image analysis systems is equivalent spherical diameter on the x axis and percent
on the y axis. It is only for elongated or fibrous particles that the x axis is typically
displayed as length rather than equivalent spherical diameter.
DIAMETER
VERTICAL
PROJECTION
HORIZONTAL
PROJECTION
figure 1
|
SHAPE FACTOR
Many techniques make the
general assumption that every
particle is a sphere and report the
value of some equivalent
diameter. Microscopy or
automated image analysis are the
only techniques that can describe
particle size using multiple values
for particles with larger aspect
ratios.
2

Performing a particle size analysis is the best way to answer the question:
What size are those particles? Once the analysis is complete the user has
a variety of approaches for reporting the result. Some people prefer a single
number answer—what is the average size? More experienced particle scientists
cringe when they hear this question, knowing that a single number cannot describe
the distribution of the sample. A better approach is to report both a central point of
the distribution along with one or more values to describe the width of distribution.
Other approaches are also described in this document.

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