Tape casting of alumina/zirconia suspensions containing graphene oxide

The introduction of carbon derivatives (nanotubes, graphene, etc.) as a second phase in ceramic matrices has limitations arising from their difficult processing. This paper studies the colloidal stability and the rheological behaviour of concentrated suspensions of alumina with 5 vol.% Y-TZP (AZ) and the effect of the addition of 2 vol.% of graphene oxide (AZGO) on the suspension stability, rheological behaviour and tape casting performance. The colloidal stability was studied using zeta potential measurements in terms of concentration of deflocculants and pH and homogenisation was optimised adjusting the sonication mode and time. The best results were obtained for pulsed mode. The optimum rheological properties were obtained for solid loadings of 53 vol.% and 40 vol.% for AZ and AZGO. Homogeneous, flexible tapes with thickness of ∼120 μm were obtained reaching densities of >60% of theoretical density in which secondary phases are well dispersed.