Particle size

Particle size describes the dimensions of discrete particles in a powder or dispersed material. It may be expressed as a diameter, length, or equivalent spherical diameter, depending on particle shape and measurement method.

Particle size distribution: A description of how particle sizes are distributed across a population of particles. A size measurement across a sample usually yields a distribution, not one representative dimension.
Equivalent spherical diameter: The diameter of a sphere that matches a nonspherical particle according to a specified physical property. Many instruments report irregular particles as spheres equivalent under a chosen measurement principle.
Powder flow: The ability of a powder to move under gravity or applied forces. Fine particles often experience stronger cohesive forces relative to their weight, changing flow behavior.
Aerodynamic diameter: The diameter of a unit-density sphere with the same settling behavior as an airborne particle. It predicts airborne transport rather than directly describing geometric dimensions.
Laser diffraction: A particle-sizing method that infers size distributions from the angles of light scattered by particles. This widely used method estimates equivalent spherical sizes from a powder’s scattering pattern.
Particle shape: The geometric form and surface characteristics of an individual particle. Different dimensions of a nonspherical particle can produce different reported sizes.
Dissolution: The process by which a substance enters solution in a solvent. Reducing particle size can increase exposed surface area and accelerate dissolution.
Hydrodynamic diameter: The effective diameter of a particle moving through a fluid, including effects of its surface and surroundings. It can exceed a particle’s imaged core size because it reflects motion through liquid.
Dynamic light scattering: A method that estimates suspended particle size from fluctuations in scattered light caused by Brownian motion. It sizes particles in suspension by linking their motion to hydrodynamic diameter.
Agglomeration: The joining of primary particles into larger clusters held together by physical forces or binding material. An instrument may measure clusters rather than the smaller particles from which they formed.

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