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Description
The study of the crystallization of one or more salts resulting from evaporation from a porous medium has motivated numerous works, see [1] and references therein. However, a systematic study of the impact of the evaporation conditions and the mean pore size of the porous medium is still lacking. In order to fill this gap, we are performing an experimental campaign for aqueous solutions of sodium chloride where both factors are varied. As illustrated in Fig.1, the considered evaporation process typically leads to the formation of a salt structure developing at the evaporative surface of the porous sample. This type of salt structure is referred to as a salt efflorescence [1, 2]. The developed experimental set-up allows us to determine the drying kinetics, to characterize the growth of the efflorescence and to get insights into the internal structure of the efflorescence via X-ray microtomography (Fig.1). The drying kinetics is typically characterized by two main stages. In the first stage, the evaporation rate is comparable to the one for pure water. In the second stage, the evaporation rate becomes much lower. These two stages can be correlated to the efflorescence growth with also exhibits two main stages with a first stage of fast growth compared to the second stage of much slower growth. As illustrated in Fig.1, a remarkable feature in these experiments is that the efflorescence is not only itself a porous medium but also a hollow structure, referred to as a dome structure. The features, i.e., the drying kinetics, the efflorescence growth and the dome formation will be discussed in relation with the various experiments performed and recent results in the literature discussing the efflorescence detachment process [3].
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