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

Effects of Structural Factors of Hydrated TiO2 on Rutile TiO2 Pigment Preparation via Short Sulfate Process

The structural factors such as crystal structure, particle size distribution and impurity content of hydrated TiO₂ had great effects on the structures and pigment properties of the rutile TiO₂. The rutile TiO₂ white pigment was prepared via the Short Sulfate Process from low concentration industrial TiOSO₄ solution. In order to produce rutile TiO₂ pigment with good structures and excellent pigment properties, the crystal size of the hydrated TiO₂ should be controlled less than 8.9 nm and as close as possible to 7.9 nm, which could effectively promote the phase transformation and crystal growth of the rutile TiO₂. The appropriate particle size distribution of hydrated TiO₂ had obvious effects on obtaining rutile TiO₂ with narrower particle size distribution and near 0.20 µm. It was best to adjust the hydrolysis conditions to reduce the specific surface area of the hydrated TiO₂ so as to reduce the iron ion impurity adsorption.

Characterisation of polyphosphate coated aluminium-doped titania nanoparticles during milling

This paper investigates the characterisation of alumina-doped titania nanoparticles, milled under high-shear over time, in the presence of sodium hexametaphosphate (SHMP) dispersant. Transmission electron microscopy (TEM) indicated that prolonged milling times led to the formation of 10 nm particle fines which were electrostatically attracted to larger particles, where no change in the crystal structure was observed. Primary particle sizes measured by dynamic light scattering (DLS) and TEM were in agreement and showed no change in primary particle size (∼250 nm) with respect to milling time, however, there was a clear reduction in the magnitude of the slow mode decay associated to aggregates. The TiO₂ was found to have an isoelectric point (iep) in the range of pH 3-4.5, where an increase in milling time led to a lower pH_iep, indicative of an increase in SHMP coverage, which was further supported by an intensification in phosphorus content measured by X-ray fluorescence (XRF). Phosphorus content and zeta potential analysis before and after centrifugal washing showed that SHMP was partially removed or hydrolysed for the longer milled pigment samples, whereas no change was observed for shorter milled samples. Relaxation NMR was also performed, where enhanced relaxation rates at longer milling times were associated partially to increases in surface area and exposure of Al sites, as well as physicochemical changes to SHMP density and structure. It is thought that extended milling times may lead to hydrolysis or other structural changes of the dispersant from the high energy milling conditions, allowing easier removal after washing for longer milled pigments.