Phase and morphology evolution of calcium carbonate precipitated by carbonation of hydrated lime
Phase and morphology evolution of calcium carbonate precipitated by carbonation of hydrated lime
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DOI：
10.1007/s10853-012-6535-7
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发表时间：
2012-08-01
影响因子：
4.5
通讯作者：
Van Balen, Koenraad
中科院分区：
文献类型：
--
作者：
Cizer, Ozlem;Rodriguez-Navarro, Carlos;Van Balen, Koenraad
研究了Ca(OH)(2) + CO2 -> CaCO3 + H2O在不同条件下(60% RH和93% RH条件下，pco_2（2) /千分之一10(-3.5)atm）碳化石灰膏过程中沉淀的CaCO3的物相和形态演变；用XRD、FTIR、TGA、SEM等方法测定了在93% RH下pCO(2) = 1atm。利用PHREEQC程序对不同碳化阶段和碳化条件下的孔隙溶液化学进行了模拟，以研究体系的化学演变。结果表明，在过量的Ca2+离子作用下，初始析出的无定形碳酸钙（ACC）转变为方解石。由于它们的极性特性，与非极性菱形面（F型）相比，尺度面（S型）与过量Ca2+的相互作用更强，这种效应最终有利于面的稳定。随着Ca2+离子的充分消耗和二氧化碳的进一步溶解导致孔隙溶液的pH值下降，scalenhedron被溶解。这最终导致菱角体在接近中性的ph值下重新沉淀。这种结晶顺序在碳化深度中进行，强烈依赖于暴露于CO2的程度，这是由控制CO2扩散的碳化孔隙结构控制的。在高RH和高pCO(2)条件下，碳酸化过程和斜面体向斜面体的转变在动力学上都是有利的。过饱和对CaCO3晶体的成核密度和尺寸起关键作用。这些结果对于理解古代和现代石灰砂浆在建筑遗产保护中的应用具有重要意义。
Phase and morphology evolution of CaCO3 precipitated during carbonation of lime pastes via the reaction Ca(OH)(2) + CO2 -> CaCO3 + H2O has been investigated under different conditions (pCO(2) a parts per thousand 10(-3.5) atm at 60 % RH and 93 % RH; pCO(2) = 1 atm at 93 % RH) using XRD, FTIR, TGA, and SEM. Simulations of the pore solution chemistry for different stages and conditions of carbonation were performed using the PHREEQC code to investigate the evolution of the chemistry of the system. Results indicate initial precipitation of amorphous calcium carbonate (ACC) which in turn transforms into scalenohedral calcite under excess Ca2+ ions. Because of their polar character, scalenohedral faces (type S) interact more strongly with excess Ca2+ than non-polar rhombohedral faces (type F), an effect that ultimately favors the stabilization of faces. Following the full consumption of Ca2+ ions and further dissolution of CO2 leading to a pH drop of the pore solution, scalenohedra are subjected to dissolution. This eventually results in re-precipitation of rhombohedra at close-to-neutral pH. This crystallization sequence progresses through the carbonated depth with a strong dependence on the degree of exposure to CO2, which is controlled by the carbonated pore structure governing the diffusion of CO2. Both the carbonation process and the scalenohedral-to-rhombohedral transformation are kinetically favored under high RH and high pCO(2). Supersaturation plays a critical role on the nucleation density and size of CaCO3 crystals. These results have important implications in understanding the behavior of ancient and modern lime mortars for applications in architectural heritage conservation.