Experimental and theoretical investigations of the coating of capsules with titanium dioxide

Titanium dioxide is a ceramic material which is widely used as a white pigment and catalyst. In the present work the precipitation of TiO2 by the thermal hydrolysis of titanium oxysulphate was studied in terms of the homogeneous precipitation and the coating of capsules. Experimental work and simulations have been done to describe the precipitation in 0.1 M aqueous solutions while in some experiments sulphuric acid was added to increase the reaction time. In the experimental part of this work, gravimetric and spectroscopic measurements were performed to determine the time-dependent precipitation of the material and particle size measurements to characterize the time-dependent size distribution of the precipitated particles. In the theoretical part different mechanisms of the precipitation process like nucleation, growth and agglomeration were considered using semi-empirical equations. For the transfer of the effects of the individual particle scale to the whole population of particles population balance equations (PBEs), one for the colloidal and one for the deposited phase, were used. Finally, the theoretical results were compared to the experimental ones and the limitations of the model were discussed. (C) 2010 Elsevier B.V. All rights reserved.