Modelling of artefacts in estimations of particle size of needle-like particles from laser diffraction measurements

TL;DR

This paper investigates how using spherical models in laser diffraction measurements causes artefacts and underestimation of particle sizes in needle-like particles, highlighting the need for shape-aware modeling.

Contribution

The study demonstrates the impact of shape assumptions on particle size estimation and shows that non-spherical particles can produce misleading results with standard spherical models.

Findings

Spherical models cause artefacts in size distributions of needle-like particles.

Using spherical assumptions leads to underestimation of true particle sizes.

False multimodal distributions can appear due to shape-related artefacts.

Abstract

Manufacturing of particulate products across many industries relies on accurate measurements of particle size distributions in dispersions or powders. Laser diffraction (or small angle light scattering) is commonly used, usually off-line, for particle size measurements. The estimation of particle sizes by this method requires the solution of an inverse problem using a suitable scattering model that takes into account size, shape and optical properties of the particles. However, laser diffraction instruments are usually accompanied by software that employs a default scattering model for spherical particles, which is then used to solve the inverse problem even though a significant number of particulate products occur in strongly non-spherical shapes such as needles. In this work, we demonstrate that using the spherical model for the estimation of sizes of needle-like particles can lead to the appearance of artefacts in the form of multimodal populations of particles with size modes much smaller than those actually present in the sample. This effect can result in a significant under-estimation of the mean particle size and in false modes in estimated particles size distributions.