Study On Dispersion Of Ultrafine Ground Calcium Carbonate And Electrical Double Layer Interaction Of Particles

Based on colloidal dispersion stabilization theory, the mechanism of stabilization of ultrafine ground calcium carbonate aqueous dispersions is investigated in the dissertation. The purpose of the research is to provide theoretical guide and operation conditions for stabilized ultrafine ground calcium carbonate aqueous dispersions in practical applications. Starting with the foundations of DLVO theory, free energy of electrical double layers, electrical-double-layer interaction, and charge distribution in electrical double layers are investigated by using the relevant knowledge in thermodynamics, electrostatics, and mathematics. It is expected that the research tries hard to find some omitted properties relevant to colloidal interactions or shortcomings in DLVO theory. The contents of this dissertation are as follows:1 . Based on colloidal dispersion stabilization theory, by means of sedimentation volume, viscosity measurement, Zeta potential measurement etc, the mechanism of stabilization of 10wt% ultrafine ground calcium carbonate aqueous dispersions are investigated by employing polyacrylate sodium, sodium hexametaphosphate, and sodium dodecylbenzenesulfonate as dispersants. The stabilities of slurries are intensely influenced by the contents of dispersants and pH value in slurries; the higher contents of the dispersant do not the better dispersion effects, the contents of the dispersant have optimum contents. By comparison, polyacrylate sodium is an optimum dispersant for ultrafine ground calcium carbonate aqueous dispersions.2. The experimental results demonstrate that high-solid-content ultrafine ground calcium carbonate aqueous dispersions can be obtained by employing polyacrylate sodium as dispersant. The contents of polyacrylate sodium as dispersant vary with solid content, and have various optimum content ranges. The optimum contents of the dispersant rise with solid content.3. In the real electrical double layer of particles, dielectric constant s can be nonuniform. Based on the principles of electrostatics, the double-layerforce expression on a particle is obtained by direct analysis.4 . Combined with experimental results and results of theoretical calculation, by means of mathematical analysis, the charge distribution in a flat double layer is investigated. The generalized Poisson-Boltzmann equation where nonuniform dielectric constant is taken into account would better describe the real charge distribution in a double layer.5. Combined with the double-layer force expression on a particle in concentrated dispersions in the case of nonuniform dielectric constant, long-range electrostatic attractions between colloidal particles can be accounted for high surface charge density.6 . Based on the principles of electrostatics, the second law of thermodynamics, the derivation processes of the free energy of the double layer by the transferring method and the discharging method are analyzed. The transferring method and the discharging method are not suitable to determine the free energy of the double layer.7. The traditional direct calculation method of the double layer interaction force on two similar plates brings some difficulties for understanding of specific forces on plates. Based on the principles of electrostatics, the specific forces on plates are directly analyzed, and the expressions of the double layer forces on plates are obtained.