On the confluence of ultrafast high‐temperature sintering and flash sintering phenomena

Abstract

Ultrafast high-temperature sintering (UHS) and flash sintering are novel methods for rapid sintering of ceramics, often completed in just a few seconds. Here, we show that both also share two additional features: an abrupt rise in electrical conductivity, which is electronic, and electroluminescence. More fundamentally, both are related to phonon physics where MD calculations have shown that proliferation of phonons at the edge of the Brillouin zone can induce Frenkel pairs without the application of electrical fields. Here, we show that, indeed, heating without the application of electric field, can also induce flash: Rapid heating processes of thin films of an oxide-salt deposited on silk fibers, with a propane torch, are shown to induce electronic conductivity, electroluminescence, and rapid sintering of the oxide. The discussion in this article harkens back to two inventions, more than a century ago, which can now be related to flash and UHS: (i) the Nernst glow lamp circa 1900, made from zirconia, and (ii) the Welsbach mantle, constituted from ceria doped thorium oxide, in the late nineteenth century. Thus, the confluence between high heating rate and electric field induced flash phenomena links the past to the new. The emerging question is how injection of phonons that has been shown to create Frenkels can further induce high electronic conductivity and electroluminescence in oxides. Both electronic conductivity and luminescence are likely related to the generation of electron-hole pairs.

Flash in argon atmosphere yields electronically conducting yttria‐stabilized zirconia at ambient temperature

“…The role of defects in flash experiments is starting to emerge, starting with the generation of Frenkel pairs with phonon proliferation 22,23 . The relationship between ultrafast heating rate sintering and flash sintering 24 also points toward a role for phonons in defect generation. How the generation of Frenkel pairs can evolve into electrons and holes is not known.…”

Innovations in Electric Current-Assisted Sintering for SOFC: A Review of Advances in Flash Sintering and Ultrafast High-Temperature Sintering

“…This helps to minimize temperature differences between the center and surface of the sample. Additional techniques include non-contact FS to avoid the need for direct contact between the electrode and sample, as well as multi-step current-limiting FS to regulate the flow of current and prevent the occurrence of localized high temperatures [117][118][119].…”

Flash sintering of tungsten at room temperature (without a furnace) in <1 min by injection of electrical currents at different rates

“…Two other advanced processing methods, ultrafast heating rate, 8 and cold sintering, 9 have emerged. Interestingly, the equivalence between ultrafast heating rate experiments and flash sintering was recently demonstrated in experiments with thin layers made from fine powders could be heated at a rapid rate with a propane torch 10 …”

“…recently demonstrated in experiments with thin layers made from fine powders could be heated at a rapid rate with a propane torch. 10 The design of flash experiments enables open access to the specimens. In this way, in-operando measurements are enabled: Sintering is measured with a rapid-rate camera, 4 the temperature with a pyrometer, 11 and the optical emission spectrum with a spectrometer.…”