Effect of Europium Ion on Pseudoboehmite Phase Transition and Microstructure

After doping Eu(NO3)3 into pseudoboehmite sol suspension, europium-doped pseudoboehmite xerogel was prepared by a spray-drying process. Effects of Eu3+ ions on pseudoboehmite phase transition and microstructure were investigated by differential thermal gravimetric analysis, X-ray powder diffraction and field emission transmission electron microscopy. Results show that upon doping of Eu3+ ions into pseudoboehmite, the phase transition temperatures of γ-Al2O3→θ-Al2O3 and θ-Al2O3→α-Al2O3 increase by 172 oC and 13 oC, respectively. It is found that Eu3+ ions entirely enter γ-Al2O3 or θ-Al2O3 crystal lattices, and the crystallinity of γ-Al2O3 is improved, resulting in increasing of the phase transition temperature of γ-Al2O3→θ-Al2O3. When α-Al2O3 is generated in the phase transition process, all of Eu3+ ions exist among α-Al2O3 grain boundaries in the form of compound EuA112O19, which will hinder the bulk diffusion of Al3+ resulting in an increase of phase transformation temperature of θ-Al2O3→α-Al2O3 process.