This standard specifies a method for determining the particle size and size distribution of powders using an optical microscope. It covers the apparatus, sample preparation, measurement procedure, and the calculation of results for particles typically in the 1 to 150 micrometre range.
Determination of particle size of powders by optical microscope method
Quick Reference Values
Applicable particle size range1 to 150 micrometres (µm)
Minimum number of particles to be measured for routine analysis625 particles
Maximum number of particles per field of view for countingapproximately 60 particles
Recommended number of particles for high accuracy work2500 particles
Required microscope magnificationSuch that the image of the particle is at least 10 divisions of the eyepiece graticule
Key Formulas
Arithmetic Mean Diameter (d_mean) = (Σ n_i * d_i) / Σ n_i, where n_i is the number of particles of size d_i
Practical Notes
Proper sample dispersion on the slide is critical to prevent particle agglomeration, which leads to inaccurate, oversized measurements. Using a suitable dispersing agent is often necessary.
The choice of mounting medium should ensure good optical contrast and chemical inertness, so it does not react with or dissolve the powder particles.
A statistically significant number of particles (typically over 600) must be measured across multiple fields of view to obtain a representative size distribution.