Efeito da estabilização de suspensões de sílica a eficiência de moagem em moinho agitador de esferas

Abstract

The milling of ceramic particles in water suspensions in stirred media mills is a high energy process indicated to obtain materiais in submicron and nanometric scales, and is presented as an alternative to chemical processes for powders synthesis. During milling, the particle size distribution, PSD, is shifted to smaller and smaller sizes. Electrostatic stabilization contrais the balance between repulsive and attractive forces and prevents agglomeration for particles under 1 µm. ln this work the particle size distribution evaluation for silica suspensions comminuted in stirred media mill was performed both in repulsive and attractive electrostatic interactions with the particles and the milling medium. The measurement of suspensions PSD and 􀀏 potential are imperative as measuring parameters for the evaluation of milling efficiency. Electroacoustic spectroscopy, dynamic light scattering and static light scattering were choosed for particle size characterization. During milling, samples of suspensions at different pH were analyzed at different times in order to monitor the sílica particles comminution. Measurements parameters for each characterization technique were changed in order to verify its effect in the measured PSD. lt was possible to observe that the results, obtained by the electroacoustic method, are dependent and sensitive to the variation in the suspension solids concentration. The results obtained by the static light scattering method indicated that the ultrasound application after addition of the sample generates perturbations in the PSD. The identification of the measurement limits for each experimental technique of PSD characterization was necessary to discern about the relative importance and effects of each parameter. The used particle size characterization techniques were not robust enough to state which pH enables the production of nanometric particles. The determination of the particles specific surface area was presented as an alternative technique to overcome the limitations of the prior used techniques, since the applicability of a nanometric powder can be measured by its surface reactivity. Volumetric and numerical distributions by AES and SLS provided lower equivalent diameters at pH 9, while DLS and SSA analysis by BET method indicated lower equivalent diameters, i.e., better milling efficiency at pH 5.