Effect of nano-Al2O3 addition on the densification of YSZ electrolytes
ABSTRACT This work investigates the effect of nanosized Al2O3 addition on the sinterability of YSZ electrolyte. (1-x)YSZ + Al2O3 ceramics with compositions x = 0 to 0.01 were prepared by the conventional mixed oxide route from a commercial powder suspension (particle size <50 nm), and sintered at 1200 to 1500 degrees C for 2 hours in air. Densification, phase evolution, and microstructure were characterized by SEM/EDS and XRD. An improvement in sintered density was observed for the samples with 0.2 to 0.5 mol% Al2O3, though depending on the sintering temperature. Only cubic zirconia was detected as crystalline phase, although XRD features suggested chemical interactions depending upon the amount of Al2O3. The grain size of YSZ was homogeneous and no second phase segregation was detected in the tested range of incorporated nano-Al2O3 and sintering temperatures.
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ABSTRACT: The sintering behaviour of conventional yttria powder was investigated, with emphasis on the effect of sintering additives such as B2O3, YF3, Al2O3, ZrO2, and TiO2, etc. at sintering temperatures from 1000 °C to 1600 °C. Powder shrinkage behaviour was analysed using a dilatometer. The powder sintering mechanisms were identified at different temperatures using powder isothermal shrinkage curves. This analysis showed that the sintering additives B2O3 and YF3 could improve yttria sintering by changing the diffusion/sintering mechanisms at certain temperatures, while sintering additives TiO2, Al2O3 and ZrO2 appeared to retard the powder densification at temperatures around 1000 °C and are more suitable when used at temperatures in excess of 1300 °C. The powder with La2O3 added had the slowest densification rate throughout the test temperatures in this experiment and was also found to be more suitable when used at temperatures higher than 1550 °C.Ceramics International 07/2013; 39(5):4791–4799. DOI:10.1016/j.ceramint.2012.11.069 · 2.09 Impact Factor
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ABSTRACT: Assembly of nanoparticles on multiple length scales and large areas is crucial for the manufacture of nanostructured devices. Nowadays, major problems in nanoparticle synthesis and their processing are the handling of waste (such as solvents, sub-products and unreacted precursors) and the search for environmental tolerable procedures. Environmental and economical pressures are now forcing the chemical community to search for more efficient ways of performing particle synthesis and processing. Thus, it would be much more efficient if both processes synthesis and processing could be realized in one sequence without isolating the intermediates. Here, we detail the results of a sustainable approach in which synthesis and the as-synthesized nanoparticles assembly are realized in one sequence without any intermediate step such as drying, sieving or centrifuging. The one pot process proposed emphasized the synergy between the mild hydrothermal synthesis of yttrium stabilized zirconia (YSZ) nanoparticles and their processing based on an electric field-driven mechanism that provides the assembly of the as-synthesized nanoparticles suspended in the synthesis mother water with low solid loading (<1 g L−1). The layer-by-layer or Frank–van-der-Merwe growth of an extremely densely packed nanoparticle-based film consolidated by green technologies was highlighted. Results suggest a fast (<1 h) and reliable shaping process that could approach a full yield. The approach is described for YSZ nanospheres, but it could be applicable to any nanoparticle and/or synthesis process offering a controlled, robust, inexpensive route for the large-scale manufacture of densely packed nanoparticle-based films. The key step of the process is the stabilization of the as-synthesized nanoparticle in the post-reaction medium using the synthesis catalyst itself, urea, and an additional dispersant, polyethyleneimine (PEI). The presence of organic modifiers in a low concentration (<2 wt% on the base of solids in the suspension) is critical and determines movement and re-arrangement of nanoparticles under the influence of an electric field during film growth.Green Chemistry 05/2014; 16(6). DOI:10.1039/C3GC42539H · 6.85 Impact Factor