|
|
Seminarium Instytutowego Seminarium Mechaniki im. W. Olszaka i A. SawczukaNano-micro-macro-analysis for claysprof. Yasuaki Ichikawa, Okayama University, Japan |
Clays are micro-inhomogeneous materials consisting of nano-scale platelet minerals, which are chemically active. They have number of applications including engineered buffers for the entrapment of radionuclides that can be released in deep geological disposal of high-level nuclear waste, slurry walls used to support temporary excavations for construction and in chemical engineering as a starter material for synthesizing new intercalation compounds. Clays consists of minerals which frequently form stacks together with fluids (mainly water and air). Typical examples of clay are bentonite and kaolinite. These clays show very different characteristics. For example, bentonite can swell with the addition of water, whereas kaolinite leads to strong mineral-based surface tension which works as an internal force under unsaturated conditions. These processes are governed by their molecular characteristics. This behaviour is examined by applying molecular dynamics (MD) simulations and multi-scale upscaling analyses. This lecture deals with the microscopic characterization of clays and the diffusion behaviour of cations including sorption, and dissolution of clay minerals under high pH condition. The development of surface tension in kaolinite is also discussed.
The next step follows a modelling of moisture transport in a clay starting with the characteristic nano-scale distribution of water viscosity in the neighborhood of a smectite clay surface. The modelling is achieved by appeal to molecular dynamics (MD) simulations and a multiscale homogenization analysis (HA). The seepage behavior is well-simulated by a multi-level up-scaling of Stokes' equations. A transport theory of chemical species is discussed on a basis of the mixture theory, and the seepage and consolidation phenomena are treated on the same framework. A series of in-situ X-ray diffraction (XRD) experiments are used to verify the MD/HA simulations.