Chemistry Laboratory, Department of Science Education, Graduate School of Education, Hiroshima University, 1-1-1 Kagamiyama, Higashi-Hiroshima 739-8524, Japan.
J Phys Chem A. 2011 Sep 29;115(38):10491-501. doi: 10.1021/jp206654n. Epub 2011 Sep 8.
Monohydrocalcite (CaCO(3)·H(2)O: MHC) is similar in composition and synthetic conditions to hydrated amorphous calcium carbonate (ACC), which is focused recently as a key intermediate compound of biomineralization and biomimetic mineralization of calcium carbonate polymorphs. Detailed comparisons of the physicochemical property and reactivity of those hydrated calcium carbonates are required for obtaining fundamental information on the relevancy of those compounds in the mineralization processes. In the present study, kinetics of the thermal dehydration of spherical particles of crystalline MHC was investigated in view of physico-geometrical mechanism. The reaction process was traced systematically by means of thermogravimetry under three different modes of temperature program. A distinguished induction period for the thermal dehydration and cracking of the surface product layer on the way of the established reaction were identified as the characteristic events of the reaction. By interpreting the kinetic results in association with the morphological changes of the reactant particles during the course of reaction, it was revealed that nucleation and crystal growth of calcite regulate the overall kinetics of the thermal dehydration of MHC. In comparison with the thermal dehydration of hydrated ACC, which produces anhydrous ACC as the solid product, the kinetic characteristics of the thermal dehydration of MHC were discussed from the viewpoint of physico-geometry of the component processes.
一水合碳酸钙 (CaCO(3)·H(2)O: MHC) 在组成和合成条件上与水合无定形碳酸钙 (ACC) 相似，后者最近被作为碳酸钙多晶型物生物矿化和仿生矿化的关键中间化合物受到关注。为了获得有关这些化合物在矿化过程中相关性的基本信息，需要对这些水合碳酸钙的物理化学性质和反应性进行详细比较。在本研究中，从物理几何机理的角度研究了球形 MHC 晶体的热脱水动力学。通过在三种不同的温度程序模式下进行热重分析，系统地跟踪了反应过程。在建立反应的过程中，表面产物层的热脱水和开裂存在明显的诱导期，被确定为反应的特征事件。通过将动力学结果与反应过程中反应物颗粒的形态变化相关联进行解释，揭示了方解石的成核和晶体生长调节了 MHC 热脱水的整体动力学。与产生无水 ACC 作为固体产物的水合 ACC 的热脱水相比，从组成过程的物理几何角度讨论了 MHC 热脱水的动力学特征。
