Controlled current-rate AC flash sintering of uranium dioxide

Neto, Rubens Roberto Ingraci; McClellan, Kenneth J.; Byler, Darrin D.; Kardoulaki, Erofili

doi:10.1016/j.jnucmat.2021.152780

Cited by 11 publications

(6 citation statements)

References 64 publications

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“…The significance of the heating rate in flash experiments arises when data from many oxides 26 are plotted in the Arrhenius form (akin to Figure 2B). They include semiconductors, for example, cobalt manganese oxide 27,28 and ZnO, 29 carbides, 30 and borides, 31 ionic conductors for fuel cell applications, for example, yttria‐stabilized zirconia of the cubic phase, 32 composites of ceria with various transition metal and rare‐earth oxides, 33 Gd‐doped ceria, 34,35 and electronic conductors, such as titanium oxide, 36 ferroelectrics, and dielectric ceramics, for example, barium titanate, 37,38 strontium titanate, 39 KNN, 40 nuclear materials, 41 and, most recently, metals 42 . Flash experiments have included not only powder‐pressed samples but also dense polycrystals and 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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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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“…The ability of flash sintering to reduce the activation energy for densification was also reported on uranium dioxide (UO 2 ), where the apparent activation energy was decreased from 380 to 108 kJ mol −1 . [ 70 ] Additionally, the reduction of the apparent activation energy for sintering was also observed in other sintering techniques with high heating rate, such as FAST/SPS, [ 70,71 ] microwave sintering, [ 72 ] and UHS. [ 35,73 ] Although different sintering methods use different sintering aids (pressure, electric field, electromagnetic field, etc.…”

Section: Discussionmentioning

confidence: 79%

Experimental and Numerical Studies of Densification and Grain Growth of 8YSZ during Flash Sintering

et al. 2023

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As a promising sintering technique, flash sintering utilizes high electric fields to achieve rapid densification at low furnace temperatures. Various factors can influence the densification rate during flash sintering, such as ultrahigh heating rates, extra‐high sample temperatures, and electric field. However, the determining factor of the densification rate and the key mechanism during densification are still under debate. Herein, the densification and grain growth kinetic during flash sintering of 8 mol% Y2O3‐stabilized ZrO2 (8YSZ) is studied experimentally and numerically using finite element method (FEM). The roles of Joule heating and heating rate on the densification are investigated by comparing flash sintering with conventional sintering. An apparently smaller activation energy for the material transport resulting in densification is obtained by flash sintering ( =424 kJ mol−1) compared to the conventional sintering ( = 691 kJ mol−1). In addition, a constitutive model is implemented to study both the densification and the grain growth during flash and conventional sintering. Furthermore, the effect of electrical polarity on the density and the grain size evolution during flash sintering of 8YSZ is also investigated. The simulation results of average density and grain size inhomogeneity agree well with the experimental data.

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“…RFS tests were performed in a dilatometer (DIL 402C from Netzsch) that was adapted by inserting two platinum electrodes into its furnace chamber, as described elsewhere 47,48 . Two power supplies were used in this study, one for DC fields (N5772A from Keysight) and another for AC fields set at 16 Hz (AST1501 from California Instruments).…”

Section: Methodsmentioning

confidence: 99%

“…The RFS tests were performed using the controlled current‐rate approach. This approach contributes to the grain size homogeneity between electrodes and minimizes the current localization and thermal shock 19,48 . After the sample was preheated, the maximum electric field was applied and the current permitted through the sample was increased linearly at a predefined rate.…”

Section: Methodsmentioning

confidence: 99%

“…The actual temperatures of the pellets were probably a couple hundred degrees lower than the estimates, since the aspect ratio of the pellets (4:3 – diameter vs. length) was different from the traditional dog‐bone shaped samples from the literature (1:8 thickness vs. length 16 ). It is also known that a fraction of the heat will be dissipated by thermal conduction through the top and bottom of the pellet in contact with the electrodes 48 . Yet, the black body radiation model offers a good approximation when the pellet temperature during RFS and the furnace temperature are not too different, since thermal radiation would still be the dominant heat transfer mechanism.…”

Section: Methodsmentioning

confidence: 99%

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The influence of the processing parameters on the reactive flash sintering of ZrO₂‐CeO₂

2022

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Reactive flash sintering (RFS) is a method that was recently developed to produce dense single‐phase bulk ceramic parts through solid‐state reactions in a single‐step that only takes a few minutes. The influence of the RFS parameters on the phase purity of a simple mixed oxide, (Zr0.8,Ce0.2)O2, was investigated. Parameters such as furnace temperature, furnace atmosphere, electric current density, and alternating current (AC) or direct current (DC) were examined. It was found that (Zr0.8,Ce0.2)O2 pellets with high densities, above 90% of its theoretical density, can be produced by RFS in a few minutes when RFS occurs under oxidizing atmospheres, AC fields with current densities of 100 mA·mm−2, and at a furnace temperature of 1200°C. Reducing conditions such as Ar‐H2 atmosphere and DC fields, low furnace temperatures, and low current densities resulted in phase impurities and poor reactions between the ZrO2 and the CeO2 powders. These results show that RFS is a useful method to produce mixed oxides, but it is very sensitive to the processing parameters. This is the first time that the influence of most of the RFS processing parameters has been studied systematically. Thus, the present work aims to provide guidelines on selecting the right processing parameters when exploring RFS.

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Controlled current-rate AC flash sintering of uranium dioxide

Cited by 11 publications

References 64 publications

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

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

Experimental and Numerical Studies of Densification and Grain Growth of 8YSZ during Flash Sintering

The influence of the processing parameters on the reactive flash sintering of ZrO₂‐CeO₂

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Controlled current-rate AC flash sintering of uranium dioxide

Cited by 11 publications

References 64 publications

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

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

Experimental and Numerical Studies of Densification and Grain Growth of 8YSZ during Flash Sintering

The influence of the processing parameters on the reactive flash sintering of ZrO2‐CeO2

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The influence of the processing parameters on the reactive flash sintering of ZrO₂‐CeO₂