An atomic force microscopy study of calcite dissolution in seawater
An atomic force microscopy study of calcite dissolution in seawater
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DOI：
10.1016/j.gca.2020.05.031
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发表时间：
2020-08
影响因子：
5
通讯作者：
Sijia Dong;W. Berelson;J. Adkins;N. Rollins;J. Naviaux;Sahand Pirbadian;M. El‐Naggar;H. Teng
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作者：
Sijia Dong;W. Berelson;J. Adkins;N. Rollins;J. Naviaux;Sahand Pirbadian;M. El‐Naggar;H. Teng
我们首次使用原子力显微镜(AFM)检查了方解石在海水中的溶解情况。我们量化了台阶后退速度和蚀刻坑密度，以比较低离子强度水在海水中的溶解，也比较了在AFM条件下方解石的溶解与在本体溶液实验中进行的溶解(例如，Subhas等人，2015年，董等人，2018年)。在高和中饱和状态(Ω)值时，整体溶解速率和阶跃后退速度较慢，并且在低Ω时变得与低离子强度水的速率相当。缺陷辅助腐蚀坑在海水中形成的起始温度为Ω ∼ 0.85(定义为Ω临界)，高于低离子强度水中的Ω ∼ (0.54)。在海水中，当∼降至0.7时，腐蚀坑密度急剧增加(从Ω106 cm∼2到−108 cmΩ2)，而在低离子强度水中，Ω ∼ 为0.1，这表明在海水中从缺陷辅助溶解到均匀溶解的转变更加接近平衡。在海水中，阶跃后退速度(V)与欠饱和度(1-Ω)不成线性关系，这可能表明，对于方解石等非Ω晶体，扭结速度与Ω之间存在高阶相关性，或方解石在海水中溶解时的表面络合过程。
We present the first examination of calcite dissolution in seawater using Atomic Force Microscopy (AFM). We quantify step retreat velocity and etch pit density to compare dissolution in seawater to low ionic strength water, and also to compare calcite dissolution under AFM conditions to those conducted in bulk solution experiments (e.g. Subhas et al., 2015, Dong et al., 2018). Bulk dissolution rates and step retreat velocities are slower at high and mid-saturation state (Ω) values and become comparable to low ionic strength water rates at low Ω. The onset of defect-assisted etch pit formation in seawater is at Ω ∼ 0.85 (defined as Ωcritical), higher than in low ionic strength water (Ω ∼ 0.54). There is an abrupt increase in etch pit density (from ∼106cm−2to ∼108cm−2) occurring when Ω falls below 0.7 in seawater, compared to Ω ∼ 0.1 in low ionic strength water, suggesting a transition from defect-assisted dissolution to homogeneous dissolution much closer to equilibrium in seawater. The step retreat velocity (v) does not scale linearly with undersaturation (1-Ω) across an Ω range of 0.4 to 0.9 in seawater, potentially indicating a high order correlation between kink rate and Ω for non-Kossel crystals such as calcite, or surface complexation processes during calcite dissolution in seawater.