Preparation and freezing behavior of TiO2 nanoparticle suspensions

Freeze casting can prepare porous materials with high porosity, directional pores, and complex shapes. However, due to the difficulty of obtaining nanoparticle suspensions with high solids loading, the formed bodies usually experience large shrinkage and have low strength in the process of vacuum drying and heat treatment. To address these problems, we studied the zeta potential, agglomeration, and rheological property of commercial P25 TiO2 nanoparticle suspensions by adjusting the pH value and the sodium hexametaphosphate additive amount of the suspensions. Suspensions with up to 30 vol% solids loading were prepared. The water freezing process and the directional arrangement of the pores are influenced by freezing temperature gradient, and porous TiO2 samples with directional laminar structures are obtained.