Characterizing the pathways by which crystals form remains a significant challenge, particularly when multiple pathways operate simultaneously. Here, an imaging-based strategy is introduced that exploits confinement effects to track the evolution of a population of crystals in 3D and to characterize crystallization pathways. Focusing on calcium sulfate formation in aqueous solution at room temperature, precipitation is carried out within nanoporous media, which ensures that the crystals are fixed in position and develop slowly. The evolution of their size, shape, and polymorph can then be tracked in situ using synchrotron X-ray computed tomography and diffraction computed tomography without isolating and potentially altering the crystals. The study shows that bassanite (CaSO₄ 0.5H₂O) forms via an amorphous precursor phase and that it exhibits long-term stability in these nanoscale pores. Further, the thermodynamically stable phase gypsum (CaSO₄ 2H₂O) can precipitate by different pathways according to the local physical environment. Insight into crystallization in nanoconfinement is also gained, and the crystals are seen to grow throughout the nanoporous network without causing structural damage. This work therefore offers a novel strategy for studying crystallization pathways and demonstrates the significant impact of confinement on calcium sulfate precipitation, which is relevant to its formation in many real-world environments.

中文翻译：

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利用限制研究硫酸钙的结晶途径

表征晶体形成的途径仍然是一个重大挑战，特别是当多个途径同时运作时。在这里，引入了一种基于成像的策略，该策略利用限制效应来跟踪 3D 中晶体群的演化并表征结晶途径。专注于室温下水溶液中硫酸钙的形成，在纳米多孔介质中进行沉淀，确保晶体固定在位并缓慢发展。然后可以使用同步加速器 X 射线计算机断层扫描和衍射计算机断层扫描原位跟踪它们的大小、形状和多晶型的演变，而无需分离和潜在地改变晶体。研究表明，贝桑石（CaSO ₄ 0.5H ₂O) 通过无定形前体相形成，并且在这些纳米级孔中表现出长期稳定性。此外，热力学稳定相石膏（CaSO ₄ 2H ₂ O）可以根据当地的物理环境通过不同的途径沉淀。还可以深入了解纳米限制中的结晶，并且可以看到晶体在整个纳米多孔网络中生长，而不会造成结构损坏。因此，这项工作为研究结晶途径提供了一种新策略，并证明了限制对硫酸钙沉淀的显着影响，这与其在许多现实世界环境中的形成有关。