Chemical controls on the propagation rate of fracture in calcite
Chemical controls on the propagation rate of fracture in calcite
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DOI：
10.1038/s41598-018-34355-1
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发表时间：
2018-11-07
影响因子：
4.6
通讯作者：
Jungjohann, K. L.
中科院分区：
文献类型：
--
作者：
Ilgen, A. G.;Mook, W. M.;Jungjohann, K. L.
方解石（CaCO3）是地壳中最丰富的矿物之一，它容易受到亚临界化学驱动压裂的影响。了解单个裂缝尖端的化学过程，以及它们如何控制地下裂缝和裂缝网络的发展，对于碳和核废料储存、资源开采以及地震预测至关重要。控制方解石亚临界断裂的化学过程尚不清楚。我们展示了一种新的方法来量化亚临界断裂的耦合化学-力学效应。方解石表面的压痕使用维氏几何压痕尖端，导致可重复的微米级裂缝从压痕扩展。单个的凹痕样品被浸泡在一系列的含水流体中，并使用光学显微镜在原位跟踪断裂的生长。裂缝扩展速率从1.6 × 10(-8) ms（-1）到2.4 × 10(-10) ms（-1）不等。该速率取决于存在的水配体的类型，而与方解石的测定溶解速率或ζ电位趋势无关。我们假设方解石中断裂尖端的化学络合作用控制了亚临界断裂的生长。以往的研究间接指出ζ电位是最关键的因素，而我们的工作表明ζ电位的变化具有次要影响。
Calcite (CaCO3) is one of the most abundant minerals in the Earth's crust, and it is susceptible to subcritical chemically-driven fracturing. Understanding chemical processes at individual fracture tips, and how they control the development of fractures and fracture networks in the subsurface, is critical for carbon and nuclear waste storage, resource extraction, and predicting earthquakes. Chemical processes controlling subcritical fracture in calcite are poorly understood. We demonstrate a novel approach to quantify the coupled chemical-mechanical effects on subcritical fracture. The calcite surface was indented using a Vickers-geometry indenter tip, which resulted in repeatable micron-scale fractures propagating from the indent. Individual indented samples were submerged in an array of aqueous fluids and an optical microscope was used to track the fracture growth in situ. The fracture propagation rate varied from 1.6 x 10(-8) ms(-1) to 2.4 x 10(-10) ms(-1). The rate depended on the type of aqueous ligand present, and did not correlate with the measured dissolution rate of calcite or trends in zeta-potential. We postulate that chemical complexation at the fracture tip in calcite controls the growth of subcritical fracture. Previous studies indirectly pointed to the zeta-potential being the most critical factor, while our work indicates that variation in the zeta-potential has a secondary effect.