Characterization of TiO2 nanoparticle suspensions for electrophoretic deposition

The rheology of suspensions is critically important for the successful achievement of defect-free TiO(2) deposits by electrophoretic deposition (EPD). The rheological behaviour of TiO(2) nanoparticle suspensions in acetylacetone with and without iodine was investigated over a broad solid-concentration range (0.3-2.5 wt.%) and at different shear rates (<(gamma) over dot> = 10-250 s(-1)). The influence of these parameters on the quality of TiO(2) films obtained by EPD on stainless steel substrates was assessed. The pure solvent and the 1 wt.% TiO(2) nanoparticles suspension without iodine exhibited shear-thickening flow behaviour. For other concentrations, the suspensions showed shear-thinning behaviour followed by an apparent shear-thickening effect at a critical shear rate (100 s(-1)). For the suspension with 1 wt.% TiO(2) containing iodine, a shear-thickening flow behaviour was observed over the whole shear rate range investigated. The maximum solids fraction (phi(m)) was experimentally determined from a linear relationship between solid concentration and viscosity. The estimated value was phi(m) = 7.94 wt.% for this system. Using a suspension with 1 wt.% concentration, good-quality TiO(2) deposits on stainless steel planar substrates were obtained by EPD at constant voltage condition. The influence of pH on suspension stability was determined in the range pH = 1-9, being pH approximate to 5 the optimal value for this system in terms of EPD results.