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Communication Dans Un Congrès Année : 2018

Hopper growth of salt crystals

Résumé

In nature, crystals generally are rarely found only in their equilibrium state; instead, many minerals and salts appear as clusters of interconnected crystalline regions known as hopper crystals. The latter results from an anisotropic growth in which the edges of a crystal grow faster than the centers of its faces. Although, such hopper crystals is common to many substances and minerals little experimental work has been done to understand the mechanism of their formation. Here we investigate experimentally their growth by performing evaporation experiments on small volumes of sodium chloride solutions, the most abundant salt on the earth. We show that sodium chloride crystals that grow very fast from a highly supersaturated solution form a peculiar form of hopper crystal consisting of a series of connected miniature versions of the original cubic crystal. We report for the first time that the transition between cubic and hopper growth happens at a well-defined supersaturation of 1.45 which corresponds to the point where the growth speed of the cubic crystal reaches a maximum (~6.5±1.8 µm/s). Above this threshold, since cubic growth is limited by the incorporation of ions into the surface, the only way to incorporate more ions from the supersaturated solution is then to create new surfaces. The overall growth rate order of the hopper morphology is found to be 3, confirming that a new mechanism, controlled by surface integration of new molecules, induces the new mechanism of skeletal growth of cubic crystals in cascade. The results are in immediate importance for our understanding of salt nucleation and growth in general and for gaining a better control over the crystal structure. In addition, since the crystal morphology dictates the dissolution rate, it has a significant impact on various applications such as pharmacology, for the food industry and for weathering of cultural heritage due to salt crystallization.
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Dates et versions

hal-02392076 , version 1 (06-12-2019)

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  • HAL Id : hal-02392076 , version 1

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Julie Desarnaud, Hannelore Derluyn, Jan Carmeliet, Daniel Bonn, Noushine Shahidzadeh. Hopper growth of salt crystals. Sixth European Conference on Crystal Growth, Sep 2018, Varna, Bulgaria. ⟨hal-02392076⟩

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