The Influence of Interparticle Interactions on Rheology and Stability in Stirred Media Mills

Publication Reference: 
45-02
Author Last Name: 
Sommer
Authors: 
Prof. Dr.-Ing. Karl Sommer, Dipl.-Ing. Volker Kehlenbeck
Report Type: 
ARR
Research Area: 
Powder Flow
Publication Year: 
2002
Publication Month: 
12
Country: 
Germany

The increasing inter-particle interactions with increasing fineness are a serious problem during wet grinding in stirred media mills. Because these inter-particle interactions have a big influence on the stability against agglomeration and on the rheology of the suspension. As shown in the literature [1] and in this report, a lower boundary of possible particle size is typically reached at around 1 μm. Furthermore the agglomerate size can even increase with further grinding, building larger particles than the original ones, that are strong enough to withstand the comminution process.

In this work we postulate that colloidal stability must be considered in wet grind- ing to understand there results and surmount there limitations on the production of nano- particles.

To study the grinding limits of particle sizes below 1 μm a detailed understanding of the agglomeration process and its mechanism is needed. Therefore the agglomeration process of fine particles is discussed in this report first under Brownian and later on under turbulent shear motion similar to the motion in stirred media mills. The agglomeration kinetics as function of added salt was measured using dynamic light scattering (DLS). Further information on the agglomeration process and the structure of the agglomerates give small angle neutron scattering (SANS) experiments.

Theoretical predictions on the stability ratio and the critical coagulation con- centration based on the DLVO-theory were calculated using measured values of the ζ-potential.

Furthermore an initial investigation to describe the equilibrium between break- age, agglomeration and deagglomeration in stirred media mills has been conducted. The problem is described by the population balance model, which will be solved using the moment method.