In operando study of gypsum crystal growth through in-cell environmental SEM

Abstract

Thanks to their setting ability, hydraulic binder materials (e.g., cements, plasters) are used for a wide variety of applications (e.g., construction, medical). The setting reaction occurs through a dissolution–precipitation mechanism during which initial particles dissolve releasing ionic species from which new crystals precipitate. The development of such a microstructure governs the final properties of the material and are thus of uttermost interest.In this paper, the in operando study of the precipitation of gypsum crystals from the dissolution of bassanite particles using a specific cell for scanning electron microscope (SEM) observation is presented. Image analysis based on segmentation enabled to give quantitative results on the growth of crystals at global and local scales. Single crystal facets are indexed based on crystallography and literature results, which enables the quantification of crystal growth rates for the indexed crystallographic planes. Different growth regimes are identified; they are attributed to the transition from unfavored to the most favored crystal facets known for gypsum. The {111} and {110} planes were the fastest growing planes, whereas the {120} and {010} planes were the most stable and grew slowly.