A novel way to vary the structure of precipitated silica and calcium carbonate aggregates in a wide range by using grinding media during the precipitation process

Certain characteristics of the product quality particularly the aggregate structure of precipitated nano- und micro-particles are relevant depending on the application of precipitated solids. This structure depends on the physicochemical properties of the material as well as on the operating and formulation parameters of the precipitation process and the following process steps. In most of the cases large aggregates are produced by precipitation processes. These aggregates have to be redispersed in a subsequent dispersion step to produce colloidal systems with the desired product properties. In this study the effect of grinding media on the formation of aggregates in a precipitation process was investigated by implementing a basket mill in the precipitation reactor instead of a stirrer. This enables simultaneous precipitation and stirred media milling. The aggregate size range by this method was considerably smaller compared to the one obtained by standard precipitation and dispersion processes. During the following drying step, these aggregates aggregate further forming larger tertiary structures consisting of secondary aggregates. Therefore, compared to the secondary particles obtained from the precipitation process at standard conditions, a new product with a novel tertiary aggregate structure and different micromechanical properties, which can be characterized qualitatively via nanoindentation, was developed. A correlation between the maximum product fineness at the end of the precipitation process and the number of stress events according to the stress model for grinding and dispersing with stirred media mills has been observed.

► Aggregate structure depends on operating and formulation parameters of the particle synthesis.
► Effect of stirred media milling during the precipitation process was investigated.
► In contrast to the standard precipitation process we obtained a novel aggregate structure.
► The novel aggregate structure shows different micromechanical aggregate properties.
► The product fineness can be correlated with the stress model of stirred media milling.