Water film thickness in the clay-water system

The permeable press experiment was performed for aqueous clay mineral systems to understand the relationship between the water film thickness and the applied permeable pressure. Water film thickness between particles was calculated from the particle size and the linear drying shrinkage of pressed bodies. The permeable press experimental results were compared to the calculated total interaction pressures between particles using the DLVO theory.; The kaolinite and the metakaolinite had the same particle shape. Kaolinite particles were crystalline, and metakaolinite particles were short-range order. The kaolinite had the point of zero net charge, PZNC, at pH 5.7. However, the kaolinite showed multi-cross points at pHs 4.6, 5.7, 6.2, and 7.2. These multi-cross points were in agreement with the theoretical titration using the two-site surface complex reaction model by Carroll-Webb and Walther. On other hand, the metakaolinite had the PZNC at pH 7.2 as a common intersection point. If the zeta potential at pHpzNc is identical to the silica basal surface potential, the silica surface charge densities are calculated as −2.6 μC cm−2 for the kaolinite and −2.7 μC cm −2 for the metakaolinite, respectively. The calculated surface charge density is equivalent to one aluminum atom substituted in 54 silicon atoms in the silica tetrahedral layer.; The total interaction pressures using the DLVO theory corresponded to the permeable press experimental results of the metakaolinite-0.1 M NaCl systems. The surface of the metakaolinite was estimated to have immobile water layers between 5 and 8 molecules thick. The metakaolinite samples cracked in experiments when the applied permeable pressure increased. This phenomenon can be explained by a vanishing capillary pressure: contacting immobile layers. The permeable press experimental results of all the kaolinite systems were significantly higher than the calculated total interaction pressures. The slope of the natural log of the permeable pressure and the water film thickness of the kaolinite systems indicated the existence of a longer-range repulsive pressure than that of the metakaolnite systems. The DLVO theory cannot explain the kaolinite systems because the nature of materials, such as an atomic configuration of the surface, which induces the structural forces, is not considered.