TheInfoList

Particle size is a notion introduced for comparing dimensions of solid particles (flecks),
liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external force. Fluids are a Phase (matter), phase of matter and incl ...
particles ( droplets), or gaseous particles ( bubbles). The notion of particle size applies to colloidal particles, particles in ecology, particles present in
granular material A granular material is a conglomeration of discrete solid Solid is one of the four fundamental states of matter (the others being liquid, gas and plasma). The molecules in a solid are closely packed together and contain the least amoun ...
(whether airborne or not), and particles that form a granular material (see also
grain size Grain size (or particle size) is the diameter In geometry Geometry (from the grc, γεωμετρία; ''wikt:γῆ, geo-'' "earth", ''wikt:μέτρον, -metron'' "measurement") is, with arithmetic, one of the oldest branches of m ...
).

# Measuring particle size

There are several methods for measuring particle size and
particle size distribution The particle-size distribution (PSD) of a powder, or granular material, or particles dispersed in fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external force ...
. Some of them are based on
light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be visual perception, perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 ...
, other on
ultrasound Ultrasound is sound waves with frequency, frequencies higher than the upper audible limit of human hearing range, hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it ...
,Dukhin, A. S. and Goetz, P. J. ''Characterization of liquids, nano- and micro- particulates and porous bodies using Ultrasound'', Elsevier, 2017 or
electric field An electric field (sometimes E-field) is the physical field that surrounds each electric charge Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. There are two ty ...
, or
gravity Gravity (), or gravitation, is a list of natural phenomena, natural phenomenon by which all things with mass or energy—including planets, stars, galaxy, galaxies, and even light—are brought toward (or ''gravitate'' toward) one another. ...
, or
centrifugation Centrifugation is a mechanical process which involves the use of the centrifugal force to separate particles from a solution according to their size, shape, density, medium viscosity and rotor speed. The more dense components of the mixture migra ...
. The use of sieves is a common measurement technique, however this process can be more susceptible to human error and is time consuming. Technology such as dynamic image analysis (DIA) can make particle size distribution analyses much easier. This approach can be seen in instruments like Retsch Technology's CAMSIZER or the Sympatec QICPIC series of instruments. They still lack the capability of inline measurements for real time monitoring in production environments. Therefore, inlie imaging devices like the SOPAT system are most efficient. Machine learning algorithms are used to increase the performance of particle size measurement. This line of research can yield low-cost and real time particle size analysis. In all methods the size is an indirect measure, obtained by a model that transforms, in abstract way, the real particle shape into a simple and standardized shape, like a sphere (the most usual) or a cuboid (when minimum bounding box is used), where the ''size'' parameter (ex. diameter of sphere) makes sense. Exception is the Granulometry (morphology), mathematical morphology approach, where no shape hypothesis is necessary. Definition of the particle size for an ensemble (collection) of particles presents another problem. Real systems are practically always polydisperse, which means that the particles in an ensemble have different sizes. The notion of
particle size distribution The particle-size distribution (PSD) of a powder, or granular material, or particles dispersed in fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external force ...
reflects this polydispersity. There is often a need for a certain average particle size for the ensemble of particles.

## Expressions for sphere size

The particle size of a spherical object can be unambiguously and quantitatively defined by its diameter. However, a typical material object is likely to be irregular in shape and non-spherical. The above quantitative definition of ''particle size'' cannot be applied to non-spherical particles. There are several ways of extending the above quantitative definition to apply to non-spherical particles. Existing definitions are based on replacing a given particle with an imaginary sphere that has one of the properties identical with the particle. ;Volume-based particle size: Volume-based particle size equals the diameter of the sphere that has the same volume as a given particle. Typically used in sieve analysis, as shape hypothesis (Mesh (scale), sieve's mesh size as the sphere diameter). :$D = 2 \sqrt\left[3\right]$ :where ::$D$: diameter of representative sphere ::$V$: volume of particle ;Area-based particle size: Area-based particle size equals the diameter of the sphere that has the same surface area as a given particle. Typically used in optical granulometry techniques. :$D = \sqrt\left[2\right]$ :where ::$D$: diameter of representative sphere ::$A$: surface area of particle

## Indirect measure expressions

In some measures the size (a length dimension in the expression) can't be obtained, only calculated as a function of another dimensions and parameters. Illustrating below by the main cases. ;Weight-based (spheroidal) particle size: Weight-based particle size equals the diameter of the sphere that has the same weight as a given particle. Useful as hypothesis in
centrifugation Centrifugation is a mechanical process which involves the use of the centrifugal force to separate particles from a solution according to their size, shape, density, medium viscosity and rotor speed. The more dense components of the mixture migra ...
and decantation, or when the number of particles can be estimated (to obtain average particle's weight as sample weight divided by the number of particles in the sample). This formula is only valid when all particles have the same density. :$D = 2 \sqrt\left[3\right]$ :where ::$D$: diameter of representative sphere ::$W$: weight of particle ::$d$: density of particle ::$g$: gravitational constant ;Aerodynamic particle size: Hydrodynamic or aerodynamic particle size equals the diameter of the sphere that has the same drag coefficient as a given particle. : Another complexity in defining ''particle size'' in a fluid medium appears for particles with sizes below a micrometre. When a particle becomes that small, the thickness of the Interface (chemistry), interface layer becomes comparable with the particle size. As a result, the position of the particle surface becomes uncertain. There is a convention for placing this imaginary surface at a certain position suggested by Gibbs and presented in many books on interface and colloid science.

# International conventions

There is an international standard on presenting various characteristic particle sizes, the ISO 9276 (Representation of results of particle size analysis). This set of various average sizes includes ''median size'', ''geometric mean size'', ''average size''. In the selection of specific small-size particles is common the use of ISO 565 and ISO 3310-1 to the choice of Mesh (scale), mesh size.

## Colloidal particle

In Materials science and Colloidal chemistry, the term colloidal particle is about a small amount of matter having size typical for colloids and with a clear phase boundary. The dispersed-phase particles have a diameter between approximately 1 and 1000 nanometre, nanometers. Colloids are heterogeneous in nature. Invisible to the naked eye, and always move in a zig-zag motion known as the Brownian motion. The scattering of light by colloidal particles is known as Tyndall effect.

# See also

*Dynamic light scattering *Micromeritics *Dispersion Technology

# References

8.ISO Standard 14644-1 Classification Airborne Particles Cleanliness {{DEFAULTSORT:Particle Size Colloidal chemistry