We investigated two earths sent to the Institute for Glass and Ceramics at the Technical University in Prague by the Inspectorate for Research and Mining at Presov in Slovakia. The earth from the region of Kuzmice is a “metabentonite.”
In the literature there has as yet been no mention of the abnormal properties of suspensions of such clays. We found that suspensions with a concentration of over 15 per cent (measured by volume) behave as a gel with a very low limit of flow. This is the reason why no signs of thixotropy show themselves. Between certain limits the viscosity does not rise with increasing concentration above the 15 per cent mentioned above, which we explain as a consequence of structural flow of the gel. At lower concentrations the particles are rather distant from one another so that they can move freely (rotate) when flow takes place and the viscosity increases with the concentration of the suspension. Above 15 per cent the particles draw so near to one another that their swollen and easily deformable surface layers can touch one another. Such particles deform during their motion; they orientate themselves in the direction of the flow and they glide over one another so that the viscosity does not increase. The limit of flow being very low, the gel has not got such a strength as is necessary to solidify perfectly; this is the reason for the absence of signs of thixotropy.