New developments in particle characterization by laser diffraction: size and shape

Laser diffraction has become a popular technique in many fields for measuring particle size distributions (PSDs). It is not only one of the standard techniques for laboratory measurements but is also gaining importance for on-line process monitoring and process control. This article reports some developments of this technique while recognizing the potential that still exists. In this report both particle size and shape are taken into account. For optimum results, both effective sensing and analysis of the diffraction pattern are required. This is the goal of our present study with a special interest in on-line application. In this paper, a statistical approach - principal component analysis (PCA) - to the scattered Light signals from a conventional detector array is shown to improve the sensitivity to a few large particles relative to the main size distribution. For determining particle shape, a wedge-type photo-detector for sensing the azimuthal Light intensity has been applied together with the procedures of cross-correlation, sweep selection for single particle presence and Fourier analysis. Finally, a novel light scattering sensor is presented, which enables the measurement of both size and shape and which offers even more promising applications for on-line process control. (C) 2000 Elsevier Science S.A. All rights reserved.