Comparison of the micromechanical aggregate properties of nanostructured aggregates with the stress conditions during stirred media milling

Abstract

Abstact In many cases nanosized particles are produced not as single primary particles but rather as particle collectives consisting of several primary particles. For many applications the particles must be available in liquid as separately dispersed primary particles or in a certain aggregate size. Especially the micromechanical properties of nanostructured aggregates, for example the breakage energy, have a strong impact on their breaking behaviour and, thus, on the dispersion process. For the determination of the micromechanical properties of nanostructured silica aggregates different measurements with a nanoindenter have been carried out. Comparing the measured micromechanical properties with dispersion results in a stirred media mill, conclusions concerning the influence of particle interactions and solid bridges between the primary particles and the strength of aggregates and their dispersibility can be drawn. The strength of the aggregates can be changed using different primary particle sizes. Generally, the maximum achievable product fineness and the efficiency of the dispersion process increases with decrease in aggregate strength and, thus, increasing primary particle size. With the help of the calculated stress energy distribution in the stirred media mill using the discrete element method and the measured fracture distribution of the aggregates measured via nanoindentation an effective dispersion fraction can be calculated. Comparing the effective dispersion fraction with the dispersion progress in the stirred media mill a linear correlation can be obtained.