Topography and surface properties of clay minerals analyzed by atomic force microscopy

摘要

The specific surface area (SSA) of natural particles is an important parameter to quantify surface processes such as dissolution and adsorption. In this study, the SSA of illite and montmorillonite particles was determined by N_2 gas adsorption (BET),the EGME method and atomic force microscopy (AFM). By AFM it was possible to analyze additionally the specific basal surface area (BSA) and the specific edge surface area (ESA). For the calculation of the surface area from the AFM data we used three different approaches, which yielded similar values. Furthermore, there was a strong correlation between the specific surface area and the particles' height. For illite BET estimated a SSA of 46 m~2/g, while 54 AFM images resulted in a mean SSA of 64 m~2/g.For montmorillonite we found a SSA of 79 m~2/g by BET and of 246 m~2/g by AFM (n=42). We assume that the commonly used preparation method for AFM samples causes delamination of clay minerals, leading to particles with a thickness of only 4 to 10 unit layers.