LASER DIFFRACTION SPECTROSCOPY - INFLUENCE OF PARTICLE-SHAPE AND A SHAPE ADAPTATION TECHNIQUE

The evaluation algorithm employed in laser diffraction spectroscopy is usually based on the Fraunhofer diffraction theory for spheres. As th is evaluation theory is limited to spheres only, the measurement of ir regularly shaped particles results in errors in the evaluated particle size distribution. To determine the influence of the particle shape, measurements of arbitrarily shaped particles were simulated, evaluated and compared with results for spherical particles of the same project ed area. The detailed investigations showed that the particle's micros tructure, i.e. its surface roughness, has almost no or only a negligib le effect on the measurement result. In contrast to this advantageous outcome, the particle's microstructure, i.e. its axis ratio, affects t he measurement result greatly and must be taken into account in the ev aluation method. Based on these results, particles were considered to be ellipsoids with specific (but negligible) surface structures and a mathematical adaptation method was developed by extending the evaluati on theory from spheres to randomly in space oriented ellipsoids. Simul ations and experiments with reticles verified the need for this adapta tion technique and its efficiency when applied.