Hydro-textural and consistency surface states of humid granular media

Powder elaboration often starts with a wetting/kneading stage that generates a medium which can be formed of discontinuous agglomerates or of continuous dough. From a thermodynamic point of view, the medium can be considered as triphasic (solid/liquid/gas). All these phases, whose proportions vary according to the stresses generated by the process, interact in the medium. This first stage of wetting/kneading can be coupled with another unit operation of elaboration or of liquid extraction that can also modify the relative proportions of the three phases. The organization of the three phases depends on the process capability but also on the textural properties of these multiphasic dispersed media. The objective of this work is to propose a descriptive framework depicting all the potential states of an unsaturated wet granular medium. The phase diagram proposed in this study is consistent with that describing the "athermic" material class of the soft matter. This phase diagram is called here the "hydro-textural diagram". It allows the description of the macroscopic states resulting from the actions of formulation (solid/liquid ratio) and process (type and amplitude of stresses), the connectivity of the phases or the mechanical consistency transitions. The hydro-textural diagram is a cognitive tool for the identification of the mechanisms. It can be used to follow the transformation path of a wet granular medium throughout its elaboration process. (C) 2010 Elsevier B.V. All rights reserved.