<i>In Situ</i> X-ray Microscopy Unraveling the Onset of Salt Creeping at a Single-Crystal Level

Salt creeping, the precipitation of salt crystals ahead of the liquid front of an evaporating salt solution, poses severe challenges to agriculture, buildings and structures, maritime field, and art conservation while holding significant promise for wastewater treatment and mineral extraction. Despite their critical role, insights into the key mechanisms of salt creeping remain elusive. Here, we leverage <i>in situ</i> X-ray microscopy to unravel the onset of salt creeping at a single-crystal level. Notably, we directly image the first salt crystal pinned on the solid-liquid interface, which penetrates the liquid meniscus and initiates a cascading crystallization process. New salt crystals precipitate from the extended meniscus created by the initial salt crystal. Combining X-ray imaging with thermodynamic analysis, we demonstrate that the formation of the first pinned crystal is associated with a critical contact angle of the liquid meniscus. This work elucidates the microscopic origin of salt creeping, shedding light on the effective manipulation of salt crystallization for various applications.