Preparation and characterisation of two polydisperse, non-spherical materials as certified reference materials for particle size distribution by static image analysis and laser diffraction

Two polydisperse, non-spherical certified reference materials consisting of corundum particles with sizes between 1 μm and 8 μm and 15 μm and 80 μm were prepared. Homogeneity was assessed using a dedicated study, as well as data from the characterisation exercise and was found sufficient. The materials were characterized with respect to their particle size distribution in interlaboratory studies. Certification was performed for selected percentiles of the cumulative distribution of the number-weighted area-equivalent circular diameter by static image analysis and for selected percentiles of the cumulative distribution of the volume-weighted equivalent spherical diameter by laser diffraction. Relative expanded assigned uncertainties ranged from 1.1% to 8.9% for laser diffraction, confirming that, for the given materials, instruments of different manufacturers do not provide different results. Relative expanded assigned uncertainties for image analysis were significantly larger than for laser diffraction and ranged from 8% to 23%. These uncertainties are considerably larger than the fundamental sampling error and indicate that unaccounted effects may be attributable to sample preparation and non-sphericity of particles may have a large effect on the reliability of image analysis.