Efficiency of silica powder milling in stirred media mill

Reference	Presenter	Authors (Institution)	Abstract
09-060	Willian Ferreira Camargo	Camargo, W.F.(Universidade de Caxias do Sul); Brunatto, M.L.(Universidade de Caxias do Sul); Cruz, R.C.(Universidade de Caxias do Sul);	In this work a study’s result of silica milling efficiency to obtain nanometric particles are presented. Milling efficiency is characterized by the achievement of a reduced particle size through lower energy consumption in a shorter operating time. The synthesis of nanoparticles has become fundamental to produce high performance components whose availability in the Brazilian market is low, which results in high import costs and justifies this type of study. A relationship boundary between ball mill and stirred media mill was established. The specific energy and the optimum milling time for each type of mill were determined. It has been shown that the particle size depends on the specific energy and colloidal stability of the suspension. The stirred media mill showed a milling time 60 times lower and a milling energy 80 times lower for the same final particle size when compared to the ball mill under the experimental conditions defined in this work. After 5.5 h of milling in stirred medium it was possible to obtain particles of 133 nm. By manipulating the pH of the suspension, the milling efficiency was increased by 18%, since it was possible to increase the repulsive forces between the particles. The dependence of specific surface area as a function of specific energy was also investigated. After 3 h of milling at controlled pH, powder was obtained with a specific surface area of 30 m2/g, equivalent to an spherical diameter of 75 nm. The surface area dependence is linearly proportional to the specific energy obtained with the colloidal milling process. The calculated equivalent spherical diameter adequately represents the set of particles with this specific surface area and serves as an indicator of the milling efficiency by a stirred media mill.
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