Effect of operational parameters and stress energies on the particle size distribution of TiO2 pigment in stirred media milling

Titanium dioxide with a particle size of approximately 0.3 μm is widely used as a pigment because of its notably high refractive index and significant scattering properties. To achieve optimum scattering in the visible range (400–700 nm), it is important to obtain a narrow particle size distribution, between 0.2 μm and 0.4 μm. TiO2 particles are usually finely ground to the desired particle size range using a wet-stirred media mill. In the present case this fine grinding was performed in the multiple passage mode using a laboratory-scale stirred media mill. Optimum values for the operational parameters were determined, and the stress energies were varied to obtain different stress mechanisms, and thus different particle size distributions. The narrowest particle size distribution around the target of 0.3 μm was achieved with operational parameters resulting in the lowest stress energy and the lowest specific energy consumption. The operational parameters at this point included a 255 μm Zirconium oxide grinding media, a stirrer tip speed of 9.2 m/s, and a solid concentration of 52 wt.% and a filling ratio of 70 vol.%. Comminution was expected to largely follow a compressive stress mechanism when this optimal combination was employed.