PARTICLE SIZE MEASUREMENTS by sensing zone analysis are based on dynamic/Stokes principles. These methods are not widely used for metal powders, but they are used for ceramic powders. The two main methods are electrozone (electrical sensing zone) size analysis and optical sensing zone size analysis.

Sensing zone methods involve the suspension of powders in a liquid medium, and there are important factors to be considered when interpreting particle size distribution results for metal powders. Most metal powders have a higher specific gravity than the particulates for which the obscuration-principle apparatus, as well as other particle size analyzers, was originally designed. As a result, a greater tendency exists for particles to settle in the sample reservoir before being sampled, thus causing the distribution to be skewed toward the fine side. This phenomenon is greater for coarser and more regularly shaped particles. Good reproducibility of a distribution does not guarantee the absence of particle settling, as settling of coarse particles also occurs and is reproducible.

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