Characterization of TiO2 nanoparticle suspensions for electrophoretic deposition

Abstract

The rheology of suspensions is critically important for the successful achievement of defect-free TiO2 deposits by electrophoretic deposition (EPD). The rheological behaviour of TiO2 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 ( $$ \dot \gamma $$ = 10–250 s−1). The influence of these parameters on the quality of TiO2 films obtained by EPD on stainless steel substrates was assessed. The pure solvent and the 1 wt.% TiO2 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.% TiO2 containing iodine, a shear-thickening flow behaviour was observed over the whole shear rate range investigated. The maximum solids fraction (ϕm) was experimentally determined from a linear relationship between solid concentration and viscosity. The estimated value was ϕm = 7.94 wt.% for this system. Using a suspension with 1 wt.% concentration, good-quality TiO2 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 ≈ 5 the optimal value for this system in terms of EPD results.