Flash Sintering (FS) is a promising field assisted sintering technique, first developed by Raj and co-workers in 2010. When ceramics with negative temperature coefficient (NTC) are heated under an electric field, the abrupt increase of electrical conductivity at the so-called onset temperature leads to almost instantaneous densification at greatly reduced furnace temperatures. In the context of FS as an energy-efficient method, research efforts have been devoted to further decrease the onset temperature by applying very strong electric fields or using reductive atmospheres. However, issues such as limited sintering and preferential current path formation usually arise in these cases. Thus, a compromise between reduced temperatures and proper, homogeneous densification is needed for the effective implementation of FS.
This work proposes a multi-phase configuration to reduce the flash-onset temperature in ceramic materials while avoiding the aforementioned problems. Three or more electrodes are equidistantly placed over the edges of the sample and connected to a multi-phase power supply, creating a rotating electric field across the entire sample. In contrast to traditional FS, which involves uni- or bi-directional current flow, the more uniform electric field distribution in MPFS results in higher delivered power for a given voltage at a certain temperature (Figure 1a). This way, the flash-onset can be triggered not only at lower temperatures but also using lower applied voltages, thus mitigating undesired localization phenomena and promoting thermal uniformity.
It is shown that specimens of materials with different types of electrical conduction mechanisms (ZnO and 8-mol% Yttria-Stabilized ZrO2) can be homogeneously sintered in a matter of seconds at furnace temperatures lower than those used in conventional FS under the same voltage. Figure 1b shows the consistent displacement of the flash-onset towards decreased temperatures for different values of applied voltage. It is remarkable that 8YSZ can be flash-sintered at voltages as low as 20 V using the MPFS technique, but the flash cannot be activated below 30 V under a conventional DC-FS configuration.
All in all, MPFS can be considered an enhanced version of FS and an interesting methodology for industrial applications due to its effectiveness and smaller energy footmark in comparison to traditional sintering techniques and even to conventional FS.

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