Abstract
This is the first study to conduct the flash sintering of 3 mol% yttria-stabilized zirconia (3YSZ) ceramics at room temperature (25 °C) under a strong electric field, larger than 1 kV/cm. At the standard atmospheric pressure (101 kPa), the probability of successful sintering is approximately half of that at low atmospheric pressure, lower than 80 kPa. The success of the proposed flash sintering process was determined based on the high electric arc performance at different atmospheric pressures ranging from 20 to 100 kPa. The 3YSZ samples achieved a maximum relative density of 99.5% with a grain size of ∼200 nm. The results showed that as the atmospheric pressure decreases, the onset electric field of flash sintering decreases, corresponding to the empirical formula of the flashover voltage. Moreover, flash sintering was found to be triggered by the surface flashover of ceramic samples, and the electric arc on the sample surfaces floated upward before complete flash sintering at overly high pressures, resulting in the failure of flash sintering. This study reveals a new method for the facile preparation of flash-sintered ceramics at room temperature, which will promote the application of flash sintering in the ceramic industry.
Highlights
Flash sintering is a novel field-assisted sintering technique (FAST) discovered by Cologna et al [1] in 2010
Downs and Sglavo [17] succeeded in flash sintering cubic 8% mol yttriastabilized zirconia (8YSZ) at 390 °C under a 2.25 kV/cm DC field and a 120 mA current; the linear shrinkage of the sintered samples reached only 8.5%
According to Liu et al [31], the dielectric breakdown under AC can trigger the flash sintering of zinc oxide at room temperature, and they reported the highest relative density of sintered zinc oxide of 99% [31,32]. These results indicate that flash sintering induced by AC dielectric breakdown is likely to facilitate the formation of dense Yttria-stabilized zirconia (YSZ) ceramic samples at furnace temperature lower than their Debye temperature [18]
Summary
Flash sintering is a novel field-assisted sintering technique (FAST) discovered by Cologna et al [1] in 2010. Yttria-stabilized zirconia (YSZ) has a wide range of applications such as electrolytes and barriers [10–15]. It is the most widely studied material in flash sintering research. DC power is more commonly used than AC for the flash sintering of YSZ. Many researchers have attempted to lower the onset temperature of YSZ by increasing the electric field power in both DC and AC flash sintering [16]. Steil et al [20] sintered 8YSZ pellets to 80% relative density with a 300 V/cm AC field at 800 °C, while the electric field strength in other AC flash sintering experiments of YSZ is lower than 200 V/cm [10,21–27]. The Debye temperature is still regarded as the lower bound of flash sintering for YSZ [28]. Far, there have been no reports on flash sintering of YSZ at room temperature
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