深入了解无定形碳酸钙 (ACC) → ikaite → 方解石转化,CrystEngComm

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深入了解无定形碳酸钙 (ACC) → ikaite → 方解石转化
CrystEngComm ( IF 2.6 ) Pub Date : 2022-12-19 , DOI: 10.1039/d2ce01444k
Anett Lázár _{1,

2} , Zsombor Molnár ₃ , Attila Demény ₁ , László Kótai ₂ , László Trif ₂ , Kende Attila Béres _{2,

4} , Eszter Bódis ₂ , Gábor Bortel ₅ , László Előd Aradi ₆ , Máté Karlik ₁ , Máté Zoltán Szabó ₁ , Áron Pekker ₅ , Gergely Németh ₅ , Katalin Kamarás ₅ , Laurence A. J. Garvie ₇ , Péter Németh _{1,

3}

Affiliation

无定形碳酸钙 (ACC) 是一种前体材料，在碳酸盐的多晶型选择和结晶中起着关键作用。它参与低温碳酸盐钾沸石 (CaCO ₃ ·6H ₂O)，但人们对 ACC 在这种室温亚稳态材料转变过程中的作用知之甚少。我们报告了两种 ACC 类型的出现，它们在形成模式、形态、粒径、含水量和稳定性方面有所不同。ACC 在低于 5 °C 的溶液中沉淀，称为 ACC (I)，是无定形的，形成约 100 nm 大小的球体，含有 1.12 mol 吸附水和 0.26 mol 化学键合水。ACC (I) 在寒冷条件下老化 25 分钟会形成自形方解石，而方解石在室温下会在 10 分钟内形成。我们的研究结果表明，ACC (I) 是两种晶型的相同前体相，它们的选择可以仅通过温度来控制。在室温下通过有机溶剂和真空泵以及通过在 1 分钟内将温度从 5 °C 升高到 30 °C 使钾沸石快速脱水，形成无定形碳酸盐，称为 ACC (II)。ACC (II) 由保持 kaite 颗粒形态的微米级多孔颗粒组成，包含 0.42 mol 物理吸附水和 0.35 mol 化学键合水。在 25 和 350 °C 之间进行的温度依赖性研究表明，尽管 ACC (I) 含水量较高，但它比 ACC (II) 更稳定。在 300–350 °C，ACC (I) 可以脱水成含有 0.03 mol 水的无定形物质，其在没有过渡无水相的情况下结晶成方解石。不同的 ACC 类型对材料科学应用具有吸引力。

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Insights into the amorphous calcium carbonate (ACC) → ikaite → calcite transformations

Amorphous calcium carbonate (ACC) is a precursor material that plays a key role in polymorph selection and crystallization of carbonates. It is involved in the formation of the cryogenic carbonate ikaite (CaCO₃·6H₂O), but the role of ACC during the transformation of this room-temperature-metastable material is poorly understood. We report the occurrence of two ACC types that differ in their mode of formation, morphology, particle size, water content and stability. ACC precipitated in solution below 5 °C, referred to as ACC (I), is amorphous, forms as ∼100 nm sized spheres, and contains 1.12 mol adsorbed and 0.26 mol chemically bonded water. Aging of ACC (I) for 25 min under cold conditions forms euhedral ikaite, whereas calcite forms within 10 min at room temperature. Our findings suggest that ACC (I) is the same precursor phase for both crystalline forms and their selection can be controlled by temperature alone. Rapid dehydration of ikaite by organic solvents and vacuum pumping at room temperature and by increasing the temperature from 5 to 30 °C within 1 min forms amorphous carbonate, referred to as ACC (II). ACC (II) consists of micron-sized, porous grains that preserve the ikaite grain morphology and contains 0.42 mol physically adsorbed and 0.35 mol chemically bonded water. Temperature-dependent investigations performed between 25 and 350 °C indicate that ACC (I) is more stable than ACC (II) despite its higher water content. At 300–350 °C ACC (I) can be dehydrated to an amorphous material containing 0.03 mol water, which crystallizes to calcite without a transitional anhydrous phase. The different ACC types can be attractive for materials science applications. The finding of an amorphous phase during the ikaite → calcite transition suggests the alteration of the original geochemical signal and thus has implications for interpreting paleoclimatological data.

更新日期：2022-12-19

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