Particle size distribution of fine powders by LASER diffraction spectrometry. Case of cementitious materials.

LASER diffraction spectrometry is one of the most widespread techniques for particle sizing, but it must be used with many precautions, otherwise significant errors can be expected. Generally, the most important errors concern the evaluation of the fine (smaller than some microns) particle content and they are obtained when the particles move away from ideal conditions (which are spherical particles, monophasic and isotropic material). Among the various sources of errors and inaccuracies concerning this technique, two have been dealt with in this paper: the choice of the mathematical model and the evaluation of the optical properties of the materials analyzed. Practical cases are presented, which permit to evaluate the consequences of these errors, such as calculation of virtual fine particles that do not exist. Lastly, precautionary measures are suggested to minimize the errors and thus to increase the degree of confidence in the results. In all the cases studied, it was seen that a correct evaluation of particle size distribution by this technique required substantial preliminary knowledge of the physicochemical properties of the material.