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Swelling pressure of montmorillonite with multiple water layers at elevated temperatures and water pressures: A molecular dynamics study
Applied Clay Science ( IF 5.6 ) Pub Date : 2021-02-01 , DOI: 10.1016/j.clay.2020.105924
Yafan Yang , Rui Qiao , Yifeng Wang , Shuyu Sun

Abstract The swelling of clay at high temperature and pressure is important for applications including nuclear waste storage but is not well understood. A molecular dynamics study of the swelling of Na montmorillonite in water at several temperatures (T = 298, 400, and 500 K) and water environment pressures (Pe = 5 and 100 MPa) is reported here. Adopting a rarely used setup that enables swelling pressure to be resolved with an accuracy of ~1 MPa, the swelling pressure was computed at basal spacings 1.6–2.6 nm (or 2–5 water layers between neighboring clay sheets), which has not been widely studied before. At T = 298 K and Pe = 5 MPa, swelling pressure Ps oscillates at d-spacing d smaller than 2.2 nm and decays monotonically as d increases. Increasing T to 500 K but keeping Pe at 5 MPa, Ps remains oscillatory at small d, but its repulsive peak at d = 2.2 nm shifts to ~2.0 nm and Ps at different d-spacings can grow more attractive or repulsive. At d > 2.0 nm, Ps is weakened greatly. Keeping T at 500 K and increasing Pe to 100 MPa, Ps recovers toward that at T = 298 K and Pe = 5 MPa, however, the repulsive peak at d = 2.0 nm remains the same. The opposite effects of increasing temperature and pressure on the density and dielectric screening of water, which control ion correlations and thus double layer repulsion, are essential for understanding the observed swelling pressure at elevated temperatures and its response to environment pressures.

中文翻译:

具有多个水层的蒙脱石在升高的温度和水压下的膨胀压力:分子动力学研究

摘要 粘土在高温高压下的膨胀对于包括核废料储存在内的应用很重要,但尚未得到很好的理解。本文报道了 Na 蒙脱石在几种温度(T = 298、400 和 500 K)和水环境压力(Pe = 5 和 100 MPa)下在水中溶胀的分子动力学研究。采用一种很少使用的设置,能够以 ~1 MPa 的精度解决膨胀压力,在 1.6-2.6 nm(或相邻粘土片之间的 2-5 个水层)的基础间距处计算膨胀压力,这尚未被广泛使用之前研究过。在 T = 298 K 和 Pe = 5 MPa 时,溶胀压力 Ps 在 d 间距 d 小于 2.2 nm 处振荡,并随着 d 的增加单调衰减。将 T 增加到 500 K 但将 Pe 保持在 5 MPa,Ps 在小 d 时保持振荡,但其在 d = 2.2 nm 处的排斥峰移至 ~2.0 nm,并且不同 d 间距下的 Ps 会变得更具吸引力或排斥性。在 d > 2.0 nm 处,Ps 大大减弱。将 T 保持在 500 K 并将 Pe 增加到 100 MPa,Ps 在 T = 298 K 和 Pe = 5 MPa 时恢复到该值,但是,d = 2.0 nm 处的排斥峰保持不变。增加温度和压力对水的密度和介电屏蔽的相反影响,控制离子相关性,从而控制双层排斥,对于理解在升高的温度下观察到的膨胀压力及其对环境压力的响应至关重要。Ps 在 T = 298 K 和 Pe = 5 MPa 时恢复到该值,然而,d = 2.0 nm 处的排斥峰保持不变。增加温度和压力对水的密度和介电屏蔽的相反影响,控制离子相关性,从而控制双层排斥,对于理解在升高的温度下观察到的膨胀压力及其对环境压力的响应至关重要。Ps 在 T = 298 K 和 Pe = 5 MPa 时恢复到该值,然而,d = 2.0 nm 处的排斥峰保持不变。增加温度和压力对水的密度和介电屏蔽的相反影响,控制离子相关性,从而控制双层排斥,对于理解在升高的温度下观察到的膨胀压力及其对环境压力的响应至关重要。
更新日期:2021-02-01
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