Handling of powders Physical principles of divided solids

Most of the products used in the chemical industry or in our daily lives are in powder form at some stage in their life cycle. Controlling and optimizing the use properties of these products, and the processes that give them these properties, requires a better understanding of the behavior of divided solids. Nevertheless, despite their industrial and economic importance, the physics of granular media is not yet sufficiently well established, and the behavior of powders during the various processing or shaping operations remains poorly understood. This difficulty in describing the behavior of granular media is essentially due to the divided nature of the systems concerned, which gives them specific features, even singularities, that clearly distinguish them from conventional continuous gas, liquid or solid media. These peculiarities have even led some scientists to consider the "divided solids" state as a (fourth) state of matter in its own right. However, knowledge of these distinctive features, described in this article, is an essential prerequisite for better control of powder processing techniques, as well as informed interpretation of the results of certain characterization tests. More specifically, it covers the fundamental principles of granular media statics, as well as the solid-solid or solid-fluid interactions that may be present within these media. The main objectives and challenges of powder characterization are also presented.