From atom level to macroscopic scale: structural mechanism of gypsum dehydration

Florian Beaugnon, Joao G. D. Preturian, Florian Fusseis, Emmanuelle Gouillart, Sara Quiligotti, Gilles Wallez

Research output: Contribution to journalArticlepeer-review

Abstract

Plaster, made of calcium sulfate hemihydrate (CaSO4•½H2O) and/or γ-anhydrite (CaSO4) is obtained by dehydration of gypsum (CaSO4·2H2O) at 100–200 °C. When mixed with water, it dissolves while new gypsum crystals precipitate. Plaster's microstructures affect its reactivity and setting properties, but are poorly understood due to confusion between crystals and polycrystalline structures in the literature. Through a multi-scale approach combining X-ray microtomography, optical and scanning electron microscopy, we revealed size, morphology and orientation of pores and crystals formed by dehydrating single crystals at T = 105–130 °C and pH2O = 0–40 hPa. The expulsion of water from the (010) interlayers results in a three-level fragmentation: cracks form parallel to (010), then the solid is divided into [101] polycrystalline needles (5–10 x 30–300 μm) formed of micron-sized crystals arranged in a fishbone pattern. The same behavior is observed whatever T and pH2O, however the crystallites size increases with pH2O.
Original languageEnglish
Article number106845
JournalSolid state sciences
Volume126
Early online date26 Feb 2022
DOIs
Publication statusPublished - 1 Apr 2022

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