Optimization of Slip Casting Parameters of Alumina Yttria Nanocomposite Powder for Obtaining Transparent Yttrium Aluminum Garnet Ceramics

In this study, Spark Plasma Sintering (SPS) of both slip casted and powder specimens of alumina/ yttria core-shell nanocomposite were utilized for fabricating transparent Yttrium Aluminum Garnet (YAG) ceramics. Phase evolution, optical transmittance and the microstructure of sintered samples were compared. In slip casting process, Dolapix CE64 was used as a dispersant for preparing the stable aqueous slurry of this nanocomposite powder. The effect of Dolapix concentration and pH value on the stability of the suspension was described, and the viscosity diagrams were investigated at different pH value and different weight percents of Dolapix. The rheological behavior of the nanocomposite powder slipped at 60-70 wt% solid loading was studied by measuring their viscosity and shear stress as a function of shear rate of the slurry. The results showed that, the suspension has a minimum viscosity at pH of 10 by addition of 2.5 wt% Dolapix. Also, the slurry with solid loading of 60 wt% showed the Newtonian behavior and this rheological behavior was preserved even above this solid loading values. Slip casting technique caused the uniform size and pores distribution as well as eliminating large pores in the green body. Consequently, transparent YAG ceramic with 60% optical transmittance was achieved after SPS process of slip casted green body which was much higher than that of nanocomposite powder, i.e. about 30% at the same sintering conditions.