Scope

This guide sets out the general approach to the particle size distribution measurement of powders, suspensions, or slurries using an appropriate wet or dry methodology by the laser diffraction technique. It is recommended for use in measurements of broad particle size distributions.

The guide provides guidelines to the parameters that should be specified and a generalized guideline to reasonable and acceptable tolerances for points in the volume-based distribution curve such as x10 (Dv10), x50 (Dv50), x90 (Dv90), and D[4, 3] (volume moment mean). It is noted that ISO prefers the term x for particle size as opposed to other usage of d or D (implying diameter).

Significance and Use

The technique of laser diffraction for particle size distribution analysis is extensively used in industry and academia both for on-line control and laboratory needs. Guidance is obviously useful in this regard.

This guide can be used to develop methods of particle size analysis where well-established analysis procedures do not already exist. See Guide B821 for similar guidance and useful procedures for wet dispersion of metal powders and related compounds.

Summary of Guide

This guide provides a general overview of the methodologies involved with the development of wet and dry dispersion techniques for measuring the particle size distribution of powdered systems. Specific details are provided to the approach taken when a powder is either measured directly with dry dispersion or wetted in a liquid for wet dispersion.

Reagents

In general, no reagents specific to the laser diffraction technique are necessary. For dry measurement the dispersant ‘fluid’ is usually dry, particulate-matter-free air. However, in the wet methodology, dispersing, and stabilizing agents can be used for a specific test sample in order to preserve stability during the measurement. A suitable diluent is used to achieve a particle concentration appropriate for a laser diffraction measurement (typically 0.001 – 0.1 volume %). Particle size may undergo change on dilution, as the ionic environment within which the particles are dispersed, changes in nature or concentration. The apparent particle size may change in line with increased concentration (obscuration), especially with particles smaller than around 2 μm, due to multiple scattering.

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