Session: Crystallization Pathways: New Perspectives on Nucleation, Growth & Dissolution of Natural & Synthetic Materials:

Gypsum plaster is a hydraulic binder with calcium sulfate dihydrate being its binding phase. The development of its mechanical properties and its strength, which make it widespread and full of applications, are due to the hydraulic set that defines hydraulic binders. The hydraulic set transforms calcium sulfate hemihydrate (bassanite) crystals into a porous agglomerate made of interlocking gypsum crystals. A deep comprehension of the hydration process and the microstructure of hardened gypsum plaster is indeed fundamental for a future improvement on the properties of the material. Moreover, many studies on the nucleation of gypsum (and more in general of calcium sulfate) have been done from the end of the nineteenth century up to now. These works shed light on the crystallization of gypsum describing it as a complex multi-step process. Using a combined approach of Three Dimensional X-ray Diffraction (3DXRD) and Phase Contrast Tomography (PCT) on the hydrating calcium sulfate hemihydrate it is possible to gain both crystallographic and spatial information. The diffraction based imaging of the 3DXRD technique permits to investigate the crystallization and growth of the gypsum crystals and the possible presence of traces of the nucleation process on the final crystals. With the PCT, it is instead possible to reconstruct volumetrically the system over time following the stages of the hydration process and the development of the hardened microstructure.

Carlotta Giacobbe

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