Adhesion energy between mica surfaces: Implications for the frictional coefficient under dry and wet conditions
Adhesion energy between mica surfaces: Implications for the frictional coefficient under dry and wet conditions
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DOI：
10.1002/2013jb010550
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发表时间：
2013-12-01
影响因子：
3.9
通讯作者：
Sakuma, Hiroshi
中科院分区：
文献类型：
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作者：
Sakuma, Hiroshi
断层的摩擦强度是断层持续滑动和地震发生的关键因素。片状结构粘土矿物的存在会降低摩擦强度。在这项研究中，两个重要的因素影响矿物的摩擦系数定量分析的基础上，结合第一性原理研究和热力学的新发展的计算方法。有助于降低摩擦系数的一个因素是在干燥条件下层之间的低粘附能。当云母表面的钾离子与高浓度的卤化钠溶液接触时，很容易与钠离子交换。我们发现，与钠离子的表面离子交换降低了粘附能，表明在干燥条件下可以降低摩擦系数。另一个因素是在潮湿条件下矿物表面上的吸附水膜引起的润滑。云母表面的钾和钠离子对水分子有很强的亲和力。为了去除限制在云母表面之间的吸附水分子，在室温下需要几十吉帕斯卡量级的压差应力。这些水分子抑制矿物表面之间的直接接触并降低摩擦系数。我们的研究结果表明，摩擦系数可以通过与流体接触，根据其盐的组成进行修改。断层形成矿物之间的低粘附能和吸附水膜的存在是在连续断层滑动带处观察到的低摩擦系数的可能原因。
The frictional strength of faults is a critical factor that contributes to continuous fault slip and earthquake occurrence. Frictional strength can be reduced by the presence of sheet-structured clay minerals. In this study, two important factors influencing the frictional coefficient of minerals were quantitatively analyzed by a newly developed computational method based on a combination of first-principles study and thermodynamics. One factor that helps reduce the frictional coefficient is the low adhesion energy between the layers under dry conditions. Potassium ions on mica surfaces are easily exchanged with sodium ions when brought into contact with highly concentrated sodium-halide solutions. We found that the surface ion exchange with sodium ions reduces the adhesion energy, indicating that the frictional coefficient can be reduced under dry conditions. Another factor is the lubrication caused by adsorbed water films on mineral surfaces under wet conditions. Potassium and sodium ions on mica surfaces have a strong affinity for water molecules. In order to remove the adsorbed water molecules confined between mica surfaces, a differential compressive stress of the order of tens of gigapascals was necessary at room temperature. These water molecules inhibit direct contact between mineral surfaces and reduce the frictional coefficient. Our results imply that the frictional coefficient can be modified through contact with fluids depending on their salt composition. The low adhesion energy between fault-forming minerals and the presence of an adsorbed water film is a possible reason for the low frictional coefficient observed at continuous fault slip zones.