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Investigation of the dissolution mechanism of silicate minerals at the atomic scale by using scanning probe microscopy

利用扫描探针显微镜研究原子尺度硅酸盐矿物的溶解机制

基本信息

批准号：
12640464
负责人：
KOGURE Toshihiro
金额：
$ 2.3万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

项目摘要

Weathering and dissolution processes of minerals are importan to understand the global gelogic cycle of elements. In order to understand the processes, laboratory experiments were perfoumed by many groups for the last several decades. However, these experiments were basically to mearure the concentrations of ions or elements in solutions dissolved from bulk minerals to determine mineral dissolution rates, which did not suggest basic mechanism how the elements dissolve from mineral surgaces at the atomic scale. Scanning probe microscopy (SPM) is the most suitable tool to obtain the insights for this mechanism because SPM can make atomic scale in-situ obserbation of mineral surfaces in folution. In this research, we have observed successfully the dissolution feature of some silicates, which are the most important mineral group in earth science, in strong acid solution using SPM.First, we tried to observe the surface dissolution of biotite, a sheet silicate and one of the most common rock-forming minerals, in nitric acid at pH=1. On the (001) surface, the dissolution proceeds by forming many etch-pits randomly on the top layer and by expanding these etch-pits. After the top layer dissolved completely, the next layer starts to dissolve in the same mnner. Sometimes two or three layers dissolve simultaneously with etch-pits deeper than one unit layer thicness. Probably this is related to the crystal growth mechanism of biotite.Secondly we have succeeded to observe the in-situ dissolution of (010) surface of olivine (Fo_<90>Fa_<10>), also an important rock-forming mineral, in nitric acid at pH=1. The dissolution speed depends on the dirctions in (010) surface.Beides theseresults, temperature dependence of the dissolution speed of brucite, Mg (OH)_2, was determined using a hot specimen stage for the SPM measurement.

矿物的风化和溶解过程是认识全球元素地质循环的重要内容。为了了解这些过程，许多研究小组在过去几十年里进行了实验室实验。然而，这些实验基本上都是通过测定矿物溶解溶液中离子或元素的浓度来确定矿物溶解速率，并没有从原子尺度上揭示元素从矿物中溶解的基本机理。扫描探针显微镜（SPM）是最合适的工具，以获得对这一机制的见解，因为SPM可以使原子尺度上的矿物表面在流动中原位包裹。本研究利用扫描探针显微镜（SPM）成功地观察了地球科学中最重要的矿物硅酸盐在强酸性溶液中的溶解特征。首先，我们尝试观察了最常见的造岩矿物之一的片状硅酸盐黑云母在pH = 1的硝酸溶液中的表面溶解。在（001）表面上，溶解通过在顶层上随机地形成许多蚀坑并通过扩展这些蚀坑来进行。在顶层完全溶解后，下一层开始以相同的方式溶解。有时两个或三个层同时溶解，腐蚀坑比一个单位层厚更深。其次，我们成功地观察到橄榄石（Fo_Fa_）（010）面在pH = 1的硝酸溶液中的原位溶解过程。<90><10>溶解速度取决于（010）面的方向，在此基础上，利用SPM热样品台测定了水镁石Mg（OH）_2溶解速度的温度依赖性。