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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Molecular Dynamics Simulations of the Growth Inhibiting Effect of Fe~(2+), Mg~(2+), Cd~(2+), and Sr~(2+) on Calcite Crystal Growth
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Molecular Dynamics Simulations of the Growth Inhibiting Effect of Fe~(2+), Mg~(2+), Cd~(2+), and Sr~(2+) on Calcite Crystal Growth

机译：Fe〜（2 +），Mg〜（2 +），Cd〜（2+）和Sr〜（2+）抑制方解石晶体生长的分子动力学模拟

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Molecular dynamics simulations were employed to investigate the initial stages of growth of calcium, magnesium, iron, cadmium, and strontium carbonates at two experimentally observed calcite steps. The calculated energies suggest that in a solution containing all five cations MgCO_3, FeCO_3, and SrCO_3 grow onto the steps in preference to CdCO_3 and especially CaCO_3. Initial incorporation of all impurity ions is more exothermic at the more open, obtuse step than at the acute step edge (by 44-896 kJ mol~(-1)), although growth next to an existing CaCO_3 unit occurs preferentially at the acute step. Growth of full rows of impurity carbonates is highly exothermic for the first row at -205 to -155 kJ mol~(-1) per MCO_3 depending on M (M = Mg, Fe, Cd, Sr), but is much less so for a subsequent row (-5 to -80 kJ mol~(-1) per MCO_3), due to increasing mismatch between the rows of MCO_3 at the surface and the underlying calcite lattice, especially for the large strontium ion. Calcite growth, which is a slightly endothermic process in its pure form (on average +1.8 to +3.5 kJ mol~(-1) per CaCO_3), is severely hindered by the presence of impurity ions at the step edges, when the average enthalpies of the CaCO_3 growth process increase to +15 to +75 kJ mol~(-1) per CaCO_3, depending on the type of cation decorating the step. The results of these molecular dynamics simulations therefore suggest that growth of impurity carbonates at the calcite steps is initially an energetically very favorable process, hence competing effectively with growth of pure calcite. Subsequent incorporation of impurities, however, becomes more and more endothermic, until finally the presence of steps decorated with rows of impurities inhibits further crystal growth, in agreement with experimental evidence, which shows for example that the presence of magnesium and iron ions inhibits calcite growth.
机译：分子动力学模拟被用来研究钙，镁，铁，镉和碳酸锶在两个实验观察到的方解石步骤中生长的初始阶段。计算出的能量表明，在包含所有五个阳离子的溶液中，MgCO_3，FeCO_3和SrCO_3优先于CdCO_3（尤其是CaCO_3）生长到台阶上。尽管在邻近的CaCO_3单元旁边的生长优先发生在急性步骤附近，但在较开放的钝角步骤中，所有杂质离子的初始掺入比在急性步骤边缘处的放热更大（44-896 kJ mol〜（-1））。 。取决于M（M = Mg，Fe，Cd，Sr），对于第一行，每MCO_3的全碳酸盐碳酸盐的生长是放热的，在-205至-155 kJ mol〜（-1）处，但是对于随后的一行（每个MCO_3为-5至-80 kJ mol〜（-1）），这是由于表面上的MCO_3行与下面的方解石晶格之间的失配增加，特别是对于大锶离子而言。方解石的生长是纯形式的轻微吸热过程（每CaCO_3平均+1.8至+3.5 kJ mol〜（-1）），当平均焓变时，在台阶边缘存在杂质离子会严重阻碍方解石的生长。取决于装饰步骤的阳离子的类型，每个CaCO_3的CaCO_3生长过程的时间增加到+15至+75 kJ mol〜（-1）。因此，这些分子动力学模拟的结果表明，方解石步骤中杂质碳酸盐的生长最初在能量上非常有利，因此与纯方解石的生长有效竞争。然而，随后的杂质掺入变得越来越吸热，直到最后，用成排的杂质装饰的台阶的存在抑制了进一步的晶体生长，这与实验证据相一致，例如，实验证据表明镁和铁离子的存在抑制了方解石的生长。

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