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Zwingmann, H.*; Berger, A.*; Todd, A.*; Niwa, Masakazu; Rahn, M.*
no journal, ,
The present study investigates the influence of physical deformation via mechanical comminution and its influence on the isotope signatures of clay minerals, in a set of well-defined laboratory experiments using Rochester shale and Opalinus clay. Deformation experiments were carried out using different milling equipment, grinding force, time and temperature conditions. The integrated data obtained decipher physical deformation and temperature effects on Argon retention in clay minerals. We interpret the different radiogenic Ar loss ranges between the Rochester shale and Opalinus clay caused by different amounts of quartz and feldspar and different clay mineralogy of the starting materials. The shape and the hardness of the quartz/feldspar will influence the deformation of the clay particles inside the mill.
Yamaguchi, Akiko; Takahashi, Yoshio*; Okumura, Masahiko
no journal, ,
Chemical reactions such as adsorption, precipitation, and redox play an important role in the environmental fate of elements, and understanding the chemical state and local structure is necessary to understand changes in their behavior. Although the X-ray absorption near edge structure (XANES) method has the advantage of high element selectivity, its resolution and analytical methods have some issues. To address these issues, this study utilizes high-energy-resolution fluorescence detection (HERFD)-XANES measurements and ab initio calculations. Analysis of artificially weathered biotite samples revealed systematic oxidation of Fe(II) to Fe(III) due to weathering. In addition, detailed microstructures of the weathered biotite with cesium adsorption were also obtained.
Kobayashi, Keita; Yamaguchi, Akiko; Okumura, Masahiko
no journal, ,
Kaolinite is a basic clay mineral composed of alumina and silica. It is used in industries such as ceramics manufacturing and as an adsorbent for pollutants. It has been reported that kaolinite undergoes structural phase transitions and can stabilize in a hydrated state under high pressure. In this study, the material properties of kaolinite under high pressure were analyzed using machine learning molecular dynamics (MLMD). The MLMD simulations were able to reproduce the experimental data, including X-ray diffraction and infrared spectra, under high pressure. This indicates that MLMD is effective in understanding the complex behavior of minerals such as kaolinite in extreme environments.
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T. R.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K. M.*; Bourg, I. C.*; Okumura, Masahiko
no journal, ,
Understanding the radionuclide diffusion phenomena is crucial for the safe geological disposal of high-level radioactive waste. The diffusion in clay-water systems is particularly important for the performance of the artificial barrier made of bentonite. Numerical simulation is one of the best research methods for understanding the phenomenon at the microscopic level. Recently, large-scale molecular dynamics (MD) simulations of the systems with clay particles and water molecules were realized. In this presentation, we will show numerical simulation results of diffusion of cesium in the large system with MD. Our recent results suggest that cesium is less diffuse than sodium.
Okumura, Masahiko; Kobayashi, Keita
no journal, ,
Ice is a common substance in everyday life, but ice in extreme conditions has different physical properties from the ice we are familiar with. It is known that under high pressure, water molecules are trapped between the layers of kaolinite and that these water molecules assume an ice-like configuration by interacting with oxygen atoms in the kaolinite. However, the physical properties of this configuration remain unknown. In addition, Interstellar dust has a silicate core surrounded by amorphous ice, which is thought to play an important role in the formation of organic matter. However, its detailed physical properties are unknown. In this study, we applied machine-learning molecular dynamics to kaolinite interlayer ice and evaluated its physical properties. In addition, the process of amorphous ice formation was discussed using classical molecular dynamics simulations, in which the atomically flat surface of kaolinite is assumed as an idealized interstellar dust core surface.