Suspension preparation of alumina whiskers for spray granulation

Whisker presence in a ceramic matrix could increase mechanical strength and reduce thermal conductivity due to phonon scattering. Therefore it is a potential reinforcement in TBCs, However, due to difficult handling and lack of homogenous distribution, their usage is limited. In this study, semi-flowing granules of alumina whiskers were prepared by spray dryer suitable for plasma spraying method. Suspensions of alumina whiskers and nanoparticles were prepared; rheological properties of the slurries were studied using spin rheometer, zeta-sizer and observing the sedimentation height. Two different slurries were prepared; the first one comprises alumina whiskers and the second one comprise 70% wt alumina whiskers- 30% wt alumina nanoparticles as filler. Both slurries were prepared with the same condition of pH, solid content and binder then granulated using a spray dryer. Morphology of the obtained granules was analyzed by FE-SEM and OM, also flow properties were investigated. The results showed that the granules from both slurries were hollow with semi-spherical morphology. However, the powder contained alumina nanoparticles had a thicker shell and smoother surface, because nanoparticles have been filled the gaps between whiskers; therefore it has the better flowability.