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The use of a small amount of MgO dopant can help to improve the performance of Na-β″-Al 2 O 3 electrolyte by enhancing the relative density, promoting the formation of homogeneous and compact microstructure, and increasing the content of β″-Al 2 O 3 phase. In this work, the effects of the amount of MgO dopant and the sintering temperature on the relative density, β″ phase content, and performance of the Na-β″-Al 2 O 3 electrolyte were studied in detail, respectively. The samples were characterized in respects of relative density, closed-cell porosity, XRD, SEM, bending strength, and AC Impedance. The results demonstrated that the addition of MgO dopant significantly improved the densification rate of Na-β″-Al 2 O 3 ceramics. The crucial temperature phase for pore elimination was 1500–1550 °C. Samples doped with 0.2–2.0 wt% MgO formed homogeneous microstructures associated with grain size refinement of the final compact at 1550 °C. Macro defects appeared when sintering temperature reached to 1580 °C. The total conductivity showed a linear dependence on the temperature (200–700 °C), which fitted well with the Arrhenius equation. Na-β″-Al 2 O 3 ceramics doped with 0.4 wt% MgO showed the best bending strength (283 MPa) and preferable ionic conductivity. [ABSTRACT FROM AUTHOR]

Doping a small amount of TiO 2 can promote the relative density, increase the content of β″-Al 2 O 3 phase and improve the microstructure of β″-Al 2 O 3 electrolyte. In this work, the influence of microstructure, relative density, content of β″ phase and performance of β″-Al 2 O 3 electrolyte were studied by adjusting the doping amount of TiO 2 and the sintering temperature. Samples were characterized with respect of density, closed-cell porosity, XRD, SEM, bending strength, AC Impedance Spectroscopy. The results demonstrated that the addition of TiO 2 can significantly improve the densification rate of β″-Al 2 O 3 ceramics. 1500–1550 °C is the key temperature section of eliminating pore process. At 1550 °C, the sample of 0.1–0.8 wt.% TiO 2 formed homogeneous microstructure associated with a refinement in the grain size of the final compact. Macro defects appeared when the sintering temperature reached to 1580 °C or the content of TiO 2 was 1.6–2.0 wt.%. The total conductivity linearly depended on the temperature and fitted well with the Arrhenius equation. β″-Al 2 O 3 ceramics showed the best bending strength and ionic conductivity at 1550 °C when the doping amount of TiO 2 is 0.4 wt.% and 0.8 wt.%, respectively. [ABSTRACT FROM AUTHOR]

Water-soluble salt core materials have high bending strength at room temperature. During high-pressure casting, water-soluble salt cores must withstand high temperatures and impact loads. To obtain a composite water-soluble salt core suitable for high-pressure casting components, sodium chloride and sodium carbonate are used as base salt materials. Ceramic particles of alumina are used as reinforcement materials in the preparation of a water-soluble composite salt core with excellent high-temperature strength via gravity casting. The microstructures of the salt core and fracture surface are observed and characterized. The use of alumina to enhance the sensitivity of the binary salt cores results in a low thermal crack sensitivity coefficient. The alumina particles dispersed in the matrix prevent crack propagation. Simulation results show that sodium aluminate has strong interfacial bonding abilities with other components in the salt core, affecting its high-temperature strength. Further results confirm that sodium aluminate formation enhances the high-temperature strength of salt cores. [ABSTRACT FROM AUTHOR]

Abstract In this study, investigations of sintering behavior and properties were performed on lithium-stabilized Na-β''-alumina (LiSBA) ceramics with and without 15 wt% 8 mol% Y 2 O 3 stabilized ZrO 2 (8YSZ) addition synthesized by solid phase reaction. Changes of phase composition, relative density, and grain size in the ceramics sintered at different temperature were analyzed. It was shown that phase transformation in sintering ceramics was controlled by relationship between the Na 2 O evaporation and Li+ ions stabilization, while microstructure evolution was controlled by pore-boundary interaction. LiSBA with YSZ addition (Zr-LiSBA) showed more significant variation of β'' phase fractions, slower grain growth and faster densification with increasing sintering temperature, which were caused by enhanced Na 2 O evaporation and gas transport by oxygen ion conductor ZrO 2 as well as the drag effect by second phase particles of YSZ in Zr-LiSBA ceramics. Zr-LiSBA specimens sintered at optimized condition achieved higher Vickers microhardness and intermediate Na+ ion conductivity. [ABSTRACT FROM AUTHOR]

The humidity property of the lithium stabilized Na-β"-alumina (LSBA) sensing material was investigated in detail on a resistivity-type sensor prepared by pasting LSBA powder on a ceramic substrate with Ag interdigitated electrodes through ac and dc analysis. Results from ac complex impedance analysis suggested that LSBA powder based sensor was highly sensitive to humidity with a six order magnitude impedance difference as relative humidity (RH) changed from 11.3% to 93.6% and good stability in 30 days. The response time and recovery time of the sensor were short at lower RH circumstance, which were 42 s and 48 s at 52.8% RH, respectively. Evidences from dc variation, ac dielectric loss and ac complex impedance spectra under different RH circumstance indicated that high humidity sensitivity of the LSBA sensor originated not only from the water molecules absorbed on the surface but also from the Na + ions in the conduction slab of the LSBA crystal. [ABSTRACT FROM AUTHOR]