Characterization and analysis of powders

Divided solids make up a significant proportion of the finished and intermediate products used in the chemical industry, and are omnipresent in our daily lives. This dossier introduces the basic concepts needed to characterize granular media: from the properties of the grain [J 2 251] to the behavioral properties [J 2 252] of powders, via the collective characteristics of particles. The aim is to enable the reader to understand and visualize the scientific bases and techniques for characterizing divided solids, which can be used as a means of process control, analysis and improvement.

A powder is an assembly of heterogeneous solid particles dispersed in a continuous gaseous phase, between which a multitude of interactions (Van der Waals, capillary, electrostatic, etc.) take place. The overall behavior of a powder depends directly on these interactions and on the characteristics of the solid particles. Thus, the characterization of a particulate system takes place at three levels [1] :

• intrinsic particle characteristics (size, density, shape, porosity, hygroscopicity, softening point, etc.);

• properties relating to a population of particles (size distribution, bulk density, homogeneity, etc.);

• behavioral properties that reflect, on a global and macroscopic scale, the interactions existing within the particulate medium or between powder particles and their environment. In other words, these are the collective characteristics that reflect the behavior of the powder in various circumstances and/or environments. The study of these properties is the subject of a second dossier [J 2 252] .