Izadifar Mohammadreza, Ukrainczyk Neven, Salah Uddin Khondakar Mohammad, Middendorf Bernhard, Koenders Eduardus
Institute of Construction and Building Materials, Technical University of Darmstadt, Franziska-Braun-Str. 3, 64287 Darmstadt, Germany.
Department of Structural Materials and Construction Chemistry, University of Kassel, Mönchebergstraße 7, 34125 Kassel, Germany.
Materials (Basel). 2022 Feb 15;15(4):1442. doi: 10.3390/ma15041442.
Portlandite, as a most soluble cement hydration reaction product, affects mechanical and durability properties of cementitious materials. In the present work, an atomistic kinetic Monte Carlo (KMC) upscaling approach is implemented in MATLAB code in order to investigate the dissolution time and morphology changes of a hexagonal platelet portlandite crystal. First, the atomistic rate constants of individual Ca dissolution events are computed by a transition state theory equation based on inputs of the computed activation energies (Δ) obtained through the metadynamics computational method (Part 1 of paper). Four different facets (100 or 1¯00, 010 or 01¯0, 1¯10 or 11¯0, and 001 or 001¯) are considered, resulting in a total of 16 different atomistic event scenarios. Results of the upscaled KMC simulations demonstrate that dissolution process initially takes place from edges, sides, and facets of 010 or 01¯0 of the crystal morphology. The steady-state dissolution rate for the most reactive facets (010 or 01¯0) was computed to be 1.0443 mol/(s cm); however, 0.0032 mol/(s cm) for 1¯10 or 11¯0, 2.672 × 10 mol/(s cm) for 001 or 001¯, and 0.31 × 10 mol/(s cm) for 100 or 1¯00 were represented in a decreasing order for less reactive facets. Obtained upscaled dissolution rates between each facet resulted in a huge (16 orders of magnitude) difference, reflecting the importance of crystallographic orientation of the exposed facets.
氢氧化钙作为水泥水化反应中最易溶解的产物，会影响胶凝材料的力学性能和耐久性。在本研究中，为了研究六方片状氢氧化钙晶体的溶解时间和形态变化，在MATLAB代码中实现了一种原子动力学蒙特卡洛（KMC）粗粒化方法。首先，基于通过元动力学计算方法（论文第一部分）获得的计算活化能（Δ）输入，利用过渡态理论方程计算单个钙溶解事件的原子速率常数。考虑了四个不同的晶面（100或1¯00、010或01¯0、1¯10或11¯0以及001或001¯），共产生16种不同的原子事件场景。KMC模拟结果表明，溶解过程最初发生在晶体形态的边缘、侧面以及010或01¯0的晶面上。计算得出最活泼晶面（010或01¯0）的稳态溶解速率为1.0443 mol/(s·cm)；然而，对于1¯10或11¯0为0.0032 mol/(s·cm)，对于001或001¯为2.672×10 mol/(s·cm)，对于100或1¯00为0.31×10 mol/(s·cm)，这些较不活泼晶面的溶解速率按降序排列。各晶面间获得的粗粒化溶解速率存在巨大差异（达16个数量级），这反映了暴露晶面晶体取向的重要性。
