Effect of Bi2O3 addition on the sintering and microstructural development of gadolinia-doped ceria ceramics

Ethanol solutions of bismuth nitrate were added to ethanol suspensions of Gd-doped ceria powder (Ce0.9Gd0.1O1.95) with particle size of 0.38 micron, dried and calcined at 700 C, to obtain ceria doped with 0.2-2.0 wt% Bi2O3. Isostatically-pressed specimens were sintered in air by dilatometer, to a maximum temperature of 1600 C; and isothermally sintered at 1400 C for 0-8 h. Specimens were characterised by density measurements and microstructural studies. The calcined powders were also heat treated at 1200-1400 C for 2 h and studied by XRD to determine the influence of Bi2O3 additions on crystallinity. Further XRD studies were performed on ceria-B2O3 50:50 mixtures heat treated at 850-1200 C. The Bi2O3 doping enhanced ceria sinterability, reducing the sintering temperature by approximately 250-300 C. Enhanced densification was attributed to liquid phase-assisted sintering. The grain size of the doped material increased with increasing Bi2O3 content up to 1.0 wt%, then decreased with further additions, attributed to poor wettability by the liquid phase. The solubility limit of Bi2O3 in the doped ceria structure was approximately 0.8 wt% over the temperature range 1200-1400 C. 20 refs.