Direct coagulation casting of nano-8YSZ powder suspensions using nano-MgO as coagulating agent

New colloidal techniques such as direct coagulation casting (DCC) arise to manufacture dense, homogeneous and nanocrystalline advanced ceramics. In this work, it was possible to obtain a high solid content (72 wt%) aqueous suspension from nano-8YSZ (15-50 nm) using a suitable PAA-NH4 dispersant. Moreover, coagulation was reached by increasing ionic strength mechanism, with an optimized amount of 0.25 wt% nano-MgO (~20 nm) maintaining a low initial viscosity (~60 mPa s at 100 s−1), which corresponds to a suitable rheological behavior for direct casting. An attenuated coagulation rate was found, along a 30-min window process, due to the nanosized MgO particles. The nanosuspension was then successfully cast into a non-porous PVC mould at 25 °C producing a dense structure without cracks after 6 h. High density (~96% T.D.) samples were obtained at 1350 °C/5 h with mean grain sizes of ~800 nm and a cubic phase corresponding to 8 mol% Y2O3 according to XRD analysis.