Atomistic thermodynamics and kinetics of dicalcium silicate dissolution
Atomistic thermodynamics and kinetics of dicalcium silicate dissolution
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DOI：
10.1016/j.cemconres.2022.106833
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发表时间：
2022-07
影响因子：
11.4
通讯作者：
Yong Tao;S. Zare;Fazhou Wang;M. J. A. Qomi
中科院分区：
文献类型：
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作者：
Yong Tao;S. Zare;Fazhou Wang;M. J. A. Qomi
低温水泥制造因其低环境足迹而受到学术界和工业界的关注。然而，所得到的水泥的缓慢水化动力学影响其早期强度发展。这促使基础研究解开溶解过程的机械图，并发现加速水合作用的科学途径。标准的原子模拟很少超过微秒，这使得它们在研究缓慢的溶解过程中不切实际。在这里，使用罕见事件采样技术，我们提供的钙离子溶解从一个扭结网站上的硅酸二钙表面的机械图片。Ca 2+离子溶解包括两个连续的阶段：从扭结网站打破限制，形成一个窗台吸附原子和脱离的窗台/梯田吸附原子网站进入溶液。第一阶段和第二阶段的特征自由能势垒分别为~63 kJ/mol和~ 29 kJ/mol，使得第一阶段成为整个Ca 2+溶解动力学的限速步骤。使用反应通量法，计算每个反应步骤的速率和平衡常数，得到约1.03 × 10−5的Ca 2+离子活度。扩散计算表明，表面效应降低了Ca ~（2+）离子在固-水界面的自扩散系数。
Low-temperature cement manufacturing has garnered academic and industrial attention for its low environmental footprints. However, the sluggish hydration kinetics of the resultant cement affects their early-age strength development. This motivates fundamental studies to unravel the mechanistic picture of the dissolution process and discover science-informed pathways to accelerate hydration. Standard atomistic simulations seldomly exceed a microsecond making them impractical to study slow dissolution processes. Here, using rare event sampling techniques, we provide the mechanistic picture of Ca2+ion dissolution from a kink site on the dicalcium silicate surface. The Ca2+ion dissolution is comprised of two sequential stages: breaking restraints from the kink sites to form a ledge adatom and detaching from the ledge/terrace adatom sites into the solution. The first and second stages feature free energy barriers of ~63 kJ/mol and ~ 29 kJ/mol respectively, making the first stage the rate-limiting step of the entire Ca2+dissolution kinetics. Using the reactive flux method, the rate and equilibrium constants for each reaction step are calculated, which yield the Ca2+ion activity of ~1.03 × 10−5. The diffusion calculations indicate that the surface effects lower the self-diffusion coefficient of Ca2+ions at the solid-water interface.