6533b82efe1ef96bd12926b0

RESEARCH PRODUCT

Reactivity of gypsum faces according to the relative humidity by scanning force microscopy

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Abstract This article reports the experimental observation of the stability of the different faces of calcium sulphate dihydrate (gypsum CaSO 4 .2H 2 O) according to the relative humidity. Scanning Force Microscopy experiments were carried out with a view to discerning the topography of the surfaces, the chemical compositional domains, and in an attempt to evaluate the friction and viscoelastic properties of the surface. Our results indicate that the (010) face of gypsum is hydrophilic and very reactive contrary to the less hydrophilic (120) and (101) faces which remain stable depending on the relative humidity. It is clear from our results that a precipitation like process can be induced by the SFM tip. The dissolution of this precipitate depends on the amount of water in the meniscus between the probe and the surface. For the purpose of comparison, the cleaved surfaces of natural anhydrite (CaSO 4 ), calcite (CaCO 3 ), and muscovite mica were also observed. The Lateral Force Microscopy images provided the undisputed evidence that the process of dehydration of the (010) face actually occurs with a change of the elastic constant of the crystal.