The flash effect in electronic conductors: The case of amorphous carbon fibers

Neto, Rubens Roberto Ingraci; Raj, Rishi

doi:10.1016/j.scriptamat.2020.01.003

Cited by 8 publications

(12 citation statements)

References 33 publications

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“…In a recent paper, Bechteler et al 20 showed that the optical spectra from a graphite furnace heated to 1200 • C also show electroluminescent spectra. They have failed to recognize a recent publication showing the flash phenomenon in carbon fibers, 21 with electroluminescent spectra resembling those from flash experiments in ceramics. Even more recent work from our laboratory has shown that even metals, such as tungsten, flash and exhibit electroluminescence.…”

Section: Discussionmentioning

confidence: 98%

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

Jalali

Raj

2023

J Am Ceram Soc.

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This is the second report on the retention of electronic conductivity in yttriastabilized zirconia at room temperature after cooling down from the state of flash . In the first report, the specimens (which were flashed in air) were quenched by in-flash immersion into liquid nitrogen. Now we show that if the specimens are flashed in Ar in a glove box (O 2 < 1 ppm), then they remain electronic conductors under nominal cooling. Indeed, the conductivity of the Ar-flashed specimens is higher than the conductivity of LN 2 -quenched samples. In both instances, their conductivity increases with flash current. In contrast, specimens flashed in air, and then air-cooled, become insulating akin to their original condition. We propose a possible pathway for such a reaction. In addition, we report measurements of the interface resistance at the anode and the cathode by the four-point technique. In air, the resistance at anode is higher than at the cathode, and the sum of the interface resistances is about one half of the total end-to-end resistance.

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Section: Discussionmentioning

confidence: 98%

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

Jalali

Raj

2023

J Am Ceram Soc.

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“…The question arises whether or not the transition is a result of unconstrained Joule heating produced by the negative coefficient of resistance with temperature. However, the simulations of thermal runaway 45 are contraindicated by experiments of flash in electronic conductors such as carbon 46 and brand new results on tungsten carbide, 47 which have a positive temperature coefficient. Additionally, local heating at particle–particle interfaces, 48 and even melting at grain boundaries, 49 is not consistent with experiments with single crystals 43 .…”

Section: Significance Of the Heating Rate In Flash Experimentsmentioning

confidence: 99%

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

et al. 2023

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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.

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“…have shown sintering of tungsten carbide with electrical activation. Graphitization of amorphous carbon under flash was demonstrated by Ingraci and Raj 25 …”

Section: Discussionmentioning

confidence: 99%

“…Graphitization of amorphous carbon under flash was demonstrated by Ingraci and Raj. 25 Although ceramics require furnace heating to initiate flash sintering, metals do not. They can be sintered without a furnace by direct injection of current.…”

Section: Discussionmentioning

confidence: 99%

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

Bamidele,

Jalali,

Weimer

et al. 2023

J Am Ceram Soc.

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Sintering of tungsten nominally requires several hours at ultrahigh temperatures. We show this refractory metal can be sintered quickly by direct injection of current into dog bone shaped specimens. The current rate was varied from 10 A s−1 (fast) to 0.1 A s−1 (slow), leading to sintering in 2–200 s, respectively. Sintering occurred at the same current density, regardless of the current rate. In all instances, the samples sintered when they reached 1000°C. The phenomenological behavior of flash sintering of metals is described by three stages: an incubation time followed by electroluminescence, and finally by abrupt sintering to full density. It is conjectured that rapid sintering is instigated by the formation of Frenkel pairs (vacancies and interstitials), as well as electrons and holes. The point defects accelerate mass transport, whereas electrons and holes recombine to form photons. Calorimetric measurements show an endothermic reaction attributed to the creation of defects. Estimates suggest an unusually large concentration of Frenkel pairs. PS: Flash sintering is different than electro‐discharge‐sintering where a capacitor is discharged in a few milliseconds to sinter a metal. Here, instead of dumping large amount of energy at once, a power supply is programed to control the rate of current injection.

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The flash effect in electronic conductors: The case of amorphous carbon fibers

Cited by 8 publications

References 33 publications

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

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

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

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

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