The Influence of Alumina Distributions upon Scavenging Highly Resistive Grain-boundary Phase of 8 mol% Yttria-stabilized Zirconia

The effect of concentration, size, and distribution of Al₂O₃ upon scavenging siliceous phase at grain boundary, was studied in 8 mol% yttria-stabilized zirconia (8YSZ) containing 0.2-1 mol% Al₂O₃ prepared from ball milling and ultrasonic dispersion. The grain-boundary resistivity at 400°C decreased prominently with adding Al₂O₃ to 8YSZ, which reflects the scavenging of siliceous grain-boundary phase. The uniform distribution of fine Al₂O₃ particles (0.3 μm) was more beneficial than that of coarse one (4-10 μm). However, the difference was not significant when the density is high, that is, when the connectivity between grain boundaries is good enough. As density decreases, the uniform distribution of fine Al₂O₃ particles becomes more important to decrease the grain-boundary resistivity. It explains that the scavenging reaction is assisted by rapid grain-boundary diffusion. From the ²⁸Si^- concentration map using imaging scanning secondary ion mass spectroscopy (SIMS), it was proved that the coarse Al₂O₃ scavenges the siliceous phase mainly by interfacial reaction.