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 sign ificant errors can be expected. Generally, the most important errors concer n the evaluation of the fine (smaller than some microns) particle content a nd they are obtained when the particles move away from ideal conditions (wh ich are spherical particles, monophasic and isotropic material). Among the various sources of errors and inaccuracies concerning this techni que, two have been dealt with in this paper: the choice of the mathematical model and the evaluation of the optical properties of the materials analyz ed. Practical cases are presented, which permit to evaluate the consequence s of these errors, such as calculation of virtual fine particles that do no t exist. Lastly, precautionary measures are suggested to minimize the error s 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 distr ibution by this technique required substantial preliminary knowledge of the physicochemical properties of the material.