| Research Abstract |
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.
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