Study On Fractal Aggregation Of Silica Particles And Process Development Of White Carbon Black

In this paper, the effects of the sizes of silica primary particles and the structures of aggregate on the quality of silica-white were studied, and an investigation was made to develop a good process of producing silica filler. As silica particles stop growth at very small size, it is not difficult to obtain silica products with particle sizes in nanometer range. However, the reinforcing property of silica is not determined only by the size, but also by the structures of aggregate, to which only a little of attention was paid and no appropriate parameter was proposed for its description. In this work, the concept of fractal was introduced to explain the paradox between theory and practical production.At first, the laser scatting technology was employed to monitor the particles growth under varying conditions and the Smoluchowski equation was used to describe the process theoretically, in which the coagulation kernel was determined in view of fractal by using molecular reaction kinetic method. Then the set of differential equations was numerically solved by Treanor method and combination method was used to decrease the number of equations. By comparing with experimental data, the kinetic parameter k₀ and fractal dimension D were determined and the obtained D is between the limited values of diffusion and reaction controlled aggregation. In terms of k₀ of varying temperatures, the activation energies of aggregation at different pH values were obtained, and the effects of salts, additives, and concentration of reactant on process were studied. The pertinence of kernel form and necessity of using fractal were certified by the excellent fitness of experiment and numerical solution.According to the utilization performance of silica as reinforcing filler, the sedimentation diameter obtained from the falling behavior of particles under the influence of gravity was selected as a standard of product quality. In preliminary experiment, the influence on sedimentation diameter of the value of pH, concentration of reactant and salt, species of acid, agitation, and additives were studied and the maximum of diameter was found with the advent of aging. the processes of gelling and aging were analyzed from the views of fractal and qualitative explanation to experimental phenomena was made.