Preparation of high solids content nanozirconia suspensions

A new colloidal route leading to the production of ~99% dense 3 mol% yttria stabilized zirconia nanostructured ceramics, whilst retaining a final average grain size of ~75 nm, has been developed. The process was based on the production of stable, homogeneous nanosuspensions with solids contents of up to 28 vol% (70 wt%) but viscosities less than 0.05 Pa s at any shear rate in the range of study were obtained. The suspensions were formed by the concentration and optimization of precursor, dilute (5.0 vol%) commercial nanosuspensions, the approach requiring a change of pH, from the 2.4 of the as-received suspension to 11.5, and the use of an appropriate anionic dispersant. Exposure of the nanosuspensions to ultrasound also helped to reduce the viscosity further, though it only worked when the dispersant was optimized. The nanosuspension was slip cast to form homogenous green bodies with densities of ~55% of theoretical without agglomeration in the nanostructure; these were subsequently densified using a two-step sintering technique