Two kinds of pottery clays (TS-1, TS-2) have been prep ared by pulverizing Amakusa pottery stone and two sorts of sericites (5-1, S-2) by elutriating the two pottery clays, respectively. Dispersion and coagulation properties of suspended pottery clays (TS-1, TS-2) and surface charge of sericites (5-1, S-2) have been studied as a function of pH on the basis of the data for zeta potential and the DLVO theory.
Two kinds of sericites showed almost the same value of zeta potential in high pH region, however, the values of 5-1 were smaller than those of S-2 at pH below 7. Surface potential, Stern layer and Guoy layer charges of S-1 and S-2 were calculated on the assumption that the edge potential was + 2 mV at pH 7. The surface potentials of S-1 and S-2 were-74 mV and-60 mV, respectively.
In the coagulation series tests, sediments in coagulated suspensions of TS-1 were more voluminous than those of TS-2 of the same solid concentration under the conditions of pH below 7 or above 12. The difference between the structures of both sediments in coagulated suspensions was analyzed by the DLVO theory including the particle size effects. It was difficult to consider that three types of association (face-to-face, face-toedge, edge-to-edge) occurred simultaneously or to the same extent, when a suspention of very thin plate-like clay minerals coagulated in water. At the early stage of coagulation, edge-to-edge association was considered to play an important role in determining the structure of sediments because a potential energy barrier of edge-to-edge association in case of the very thin particles became much lower than the average kinetic energy of particles (15kt). It was therefore concluded that thin particles exhibited voluminous coagulation than thicker particles.
