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Salt creeping is a phenomenon where salt crystals continue to precipitate far from an evaporating salt solution by a self-amplifying mechanism. Due to multiple nucleation sites of crystallization at the evaporation front , the spreading of the salt solution is enhanced well beyond the initial liquid/air front and creates a self-amplifying process[1]. The process results in three-dimensional crystalline networks at macroscopic distances from the salt solution . Such crystallization process can initiate and grow on flat surfaces and on the surface of porous materials such as soil or stones, known as salt efflorescence. The latter poses significant challenges in cultural heritage conservation, materials degradation such as frescoes or wall paintings and soil sodification, due to the ability of salt solutions to infiltrate porous materials through capillary rise from groundwater, followed by evaporation and crystallization as efflorescence at the surface of the porous material. Here we investigate the mechanisms for the formation of NaCl efflorescence focusing on the emergence of self-similar, cauliflower-shaped structures [2-3]. Through controlled evaporation experiments of salt creeping and micro-scale analysis of the resulting salt deposit, our results reveal a hierarchical organization of cubical micro crystals within the efflorescence structure making a porous structure. Scanning electron microscopy images, X-ray microtomography results, and fractal dimension analysis reveal the intricate structure and self-similar patterns at different scale enhancing the capillary rise in the efflorescence cluster. Our finding reveals that salt creeping crystallization height are primarily governed by the initial salt mass available, rather than by the competition between capillary and viscous effects within the porous efflorescence structure. Our findings shed some light on how mineral precipitation and growth from evaporative salt solutions self-organizes into macroscopic hierarchical structures such as salt efflorescence on top of porous materials. The phenomenon can also lead to spectacular macroscopic salt deposit structures, such as desert roses in arid desert regions or salt pillars near saline lakes in nature.
| References | 1- Qazi, M. J., Salim, H., Doorman, C. A. W., Jambon-Puillet, E., & Shahidzadeh, N. (2019). Salt creeping as a self-amplifying crystallization process. Science advances, 5(12), eaax1853. 2- Wijnhorst, R. J., Prat, M., & Shahidzadeh, N. (2025). Self-similarity in creeping salt crystallization. arXiv preprint arXiv:2508.18779. 3- Wijnhorst , R., Salt Crystallization in Cultural Heritage. From Fundamentals to Deterioration, PhD manuscript 2024. |
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| Country | The Netherlands |
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