Title : Sintering of fully-dense nanostructured scandia-stabilized zirconia
Scandia-stabilized zirconia (ScSZ) has a great technological interest as solid electrolyte in solid oxide fuel cells since it has the highest ionic conductivity among zirconia-based ceramics. The consolidation of this ionic conductor requires high temperatures to achieve high densification due to its low sinterability. Moreover, ScSZ exhibits a complex phase diagram including an ordered rhombohedral phase with low ionic conductivity, which prevents its application as solid electrolyte. Over the last decades, full stabilization of the high ionic conductivity cubic phase at room temperature was accomplished by introducing a second dopant or by decreasing grain size to the nanoscale. In this work, fully-dense and single-phase nanostructured ScSZ specimens were produced by recently proposed Deformable-Punch Spark Plasma Sintering technique (DP-SPS). It has been postulated that the DP-SPS method inhibits grain growth due to the low processing temperatures and eliminates isolated residual pores due to high pressure application. Nanocrystalline powders were prepared by the coprecipitation method. Green pellets were sintered at temperatures varying from 700 to 900 °C and pressures from 1.4 to 2 GPa, resulting in dense microstructures with single-phase fluorite-type cubic structure within a wide range of Sc2O3 content (6–15 mol%). Microstructural characterization of thin lamellas of sintered specimens prepared by focused ion beam was performed by transmission electron microscopy. The average grain size ranged from 8 to 20 nm. Transmittance spectra confirm translucence in sintered specimens, which is consistent with full density. In order to compare, samples were conventionally sintered at 1600 °C. The results reveal that the polymorphism challenge in the zirconia-scandia system can be successfully suppressed by this consolidation technique, which allows for controlling the grain size of bulk specimens.
Improvements of sintering of ceramics will be presented and discussed.
Dense-nanostructured ceramics might be produced and engineered for a wide range of applications.
Preparation of thin lamellas for transmission electron microscopy analysis will be presented.