Development of etch pit size distributions on dissolving minerals
Development of etch pit size distributions on dissolving minerals
复制标题
溶解矿物的蚀坑尺寸分布的发展
DOI：
10.1016/0009-2541(93)90117-2
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发表时间：
1993
期刊：
影响因子：
3.9
通讯作者：
S. Brantley
中科院分区：
文献类型：
--
作者：
I. MacInnis;S. Brantley
将晶体尺寸分布理论应用于溶蚀矿物蚀刻坑尺寸分布的演化。基于蚀坑的成核、生长和湮灭，导出了种群平衡方程。PSD图logn（每个区域每个尺寸的坑数）vs.W（蚀刻坑宽度）用于比较蚀刻坑的数量。我们用PSD分析研究了方解石在旋转圆盘实验（远离平衡，25°C，初始pH = 8.6, 0.7MKCl）中腐蚀坑的形成。在溶解的早期阶段，PSD图上存在一个最大值，并且似乎是在有限的时间间隔内，在初始劈裂表面的所有可用位置上的凹坑成核的结果。随着凹坑变大，变成平底并湮灭，峰值移动到更大的尺寸，并在17.5小时后减小到不显著。0.5小时后，PSD图在小坑宽处变为线性，标志着种群平衡，新坑在平坦的坑内成核，变大，变平，最终湮灭。这些短暂的、小的（< 100μm）蚀刻坑可能是由点缺陷或杂质团簇的成核造成的。长寿命、较大凹坑的线性PSD出现在17.5小时，可能反映了位错处的蚀刻凹坑。由于这两个种群，17.5小时的整体PSD图是相互关联的。根据PSD系数计算的方解石溶解速率在溶液化学测量的溶解速率的两倍之内。如果溶蚀的持续时间不大大超过蚀坑的平均寿命，这样的估计将更加准确。从风化了12,500年的黄土土壤中得到的角闪石和微斜粒的PSD图与方解石实验的PSD图相似。角闪石PSD呈峰状，微斜岩PSD呈线状或可能呈扭结状。从PSD计算出的颗粒的整体溶解速率比在实验室中测量到的这些矿物质的速率要慢。根据PSD系数估算的角闪石和微斜岩土壤颗粒的溶解速率分别比相应的实验室速率慢3-4个数量级和1-2个数量级。
We have applied the theory of crystal size distributions to the evolution of etch pit size distributions (PSD's) on dissolving minerals. Population-balance equations are derived based on nucleation, growth and annihilation of etch pits. PSD plots of logn(number of pits per size per area) vs.W(etch pit width) are used to compare etch pit populations. We have used PSD analysis to study the development of etch pits on calcite dissolved in a rotating disk experiment (far from equilibrium, 25°C, initial pH = 8.6, 0.7MKCl). A maximum is present on the PSD plot in the early stages of dissolution and appears to result from nucleation of pits at all available sites on the initial cleaved surface over a finite time interval. As pits grow larger, become flat-bottomed and annihilate, the peak moves to larger sizes and decreases in magnitude to become insignificant after 17.5 hr. After 0.5 hr, the PSD plots become linear at small pit widths marking a population balance as new pits nucleate within flat pits, grow larger, become flat-bottomed and finally annihilate. This population of short-lived, small (< 100μm) etch pits possibly results from nucleation at point-defect or impurity clusters. A linear PSD for long-lived, larger pits appears at 17.5 hr, possibly reflecting etch pits at dislocations. The overall PSD plot at 17.5 hr is kinked due to these two populations. Calcite dissolution rates calculated from the coefficients of the PSD are within a factor of two of the dissolution rate measured from solution chemistry. Such estimates will be more accurate if the duration of dissolution does not greatly exceed the mean lifetime of etch pits.PSD plots for hornblende and microcline grains from a loess soil that has weathered for 12,500 yr show similarities to the PSD's from our calcite experiments. The hornblende PSD shows a peak and the microcline PSD is linear or possibly kinked. Bulk dissolution rates for the grains calculated from the PSD's are slower than rates measured for these minerals in the laboratory. Dissolution rates estimated from the PSD coefficients for the hornblende and microcline soil grains are 3–4 and 1–2 orders of magnitude slower, respectively, than the corresponding laboratory rates.