WEB Densification of yttria by flash sintering under an AC electric fieldThursday (28.05.2020) 14:13 - 14:13 Poster Room Part of:
Flash sintering, which allows rapid densification at low furnace temperature under strong electric field, is powerful technique to consolidate oxide ceramics. For instance, Y2O3 can be densified by flash sintering at the furnace temperature of 940 °C by applying a DC field of 1000 V/cm, while that can be densified by conventional sintering at 1600 °C for three hours in air. However, DC field causes the development of significant electrical potential differences between the anodic and cathodic regions, resulting in non-uniform microstructure due to thermal and defects gradients along the gauge portion. We therefore employed AC filed, and investigated the frequency dependence on the densification behavior of Y2O3. A constant AC field of 500 V ·cm−1 with a frequency in a range of 0.05 Hz-1000 Hz was applied to a green compact, and the current limit was set to 16 mA·mm−2.
As a result, uniform, fully-densified Y2O3 body was successfully produced by the flash sintering under the AC field. The Surge of specimen current and simultaneous rapid densification, i.e. flash event took place under all frequency conditions examined. The onset flash temperatures under AC field depended on the frequency, and the onset temperature took the minimum value of 1230 ºC at 5 Hz. The final density values of the sintered bodies also depended on the frequency; the Y2O3 body exhibited the final density of higher than 99 % at 1000 Hz. The AC flash sintering was useful to produce uniform and fully-densified Y2O3 body at relatively low temperature and short sintering time.
It should be noted that the Y2O3 densified by the AC flash sintering emitted photoluminescence under ultra-violet light; blue-colored visible light with the wavelength of 411 nm (3.0 eV) was emitted under the excitation light of 254 nm (4.9 eV). The light emission was not detected in the Y2O3 which was densified by conventional sintering from the same starting powder. This result indicated that concentration of point defects was increased by the application of strong AC field.