Institute of Low Temperature Science, Hokkaido University, Kita-19, Nishi-8, Kita-ku, Sapporo, 060-0819, Japan.
Faraday Discuss. 2022 Jul 14;235(0):81-94. doi: 10.1039/d1fd00125f.
Several different building blocks or precursors play an important role in the early stages of the crystallization of calcium carbonate (CaCO). Many studies have been conducted over a long period to elucidate the fundamental processes involved in this crystallization. Here, we report the role of an amorphous phase and embryo at the beginning of the nucleation of CaCO from solutions of relatively low supersaturation. Prenucleation crystals formed in amorphous calcium carbonate (ACC) at a significantly large formation rate of 2 × 10 m s, suggesting that a low interfacial energy exists between the ACC and crystals. Only one calcite crystal exceeded the size for a critical nucleus (∼10 molecules) in 150 pre-nucleation crystals. Each pre-nucleation crystal might consist of a different polymorph, and ACCs have a similar composition and structure. A particle-detection algorithm, used in conjunction with machine learning, suggested that an embryo with a characteristic structure exists in solution and might play a crucial role in nucleation. No similar embryonic structure could be observed immediately after the dissolution of pre-nucleation particles, implying that their dissolution process is not simply the reverse process of their growth. This method should provide a new approach to understanding nucleation processes.
几种不同的结构单元或前体在碳酸钙（CaCO）结晶的早期阶段起着重要作用。为了阐明这一结晶过程中的基本过程，人们进行了长期的研究。在这里，我们报告了在相对较低过饱和度的溶液中从 CaCO 成核的初始阶段无定形相和晶核的作用。在无定形碳酸钙（ACC）中以 2×10^-9 m s^-1 的显著大形成速率形成了预成核晶体，这表明 ACC 和晶体之间存在低界面能。在 150 个预成核晶体中，只有一个方解石晶体的尺寸超过了临界核（约 10 个分子）。每个预成核晶体可能由不同的多晶型组成，并且 ACC 具有相似的组成和结构。与机器学习结合使用的粒子检测算法表明，溶液中存在具有特征结构的晶核，可能在成核中起着关键作用。在预成核颗粒溶解后立即无法观察到类似的胚胎结构，这意味着它们的溶解过程不仅仅是其生长的逆过程。这种方法应该为理解成核过程提供一种新方法。
