Liquid Film Capillary Mechanism for Densification of Ceramic Powders during Flash Sintering

Chaim, R.

doi:10.3390/ma9040280

Cited by 78 publications

(52 citation statements)

References 41 publications

(59 reference statements)

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“…As was previously suggested [15,44] and experimentally reported [2,5,44], thermal runaway in the powder compact, which is subjected to flash sintering, may lead to local melting at the particle contact points. The present energy balance during the transient flash event confirms that particle surfaces subjected to thermal runaway may partially melt/soften at their contact points, and wet the particle to provide a preferred pass for current percolation.…”

Section: Discussionmentioning

confidence: 68%

“…Recently, an invasive percolating model was used to relate the rapid densification during flash sintering to the attractive capillary forces formed at the particle contacts, due to their local melting [15]. The percolative nature of flash sintering is confirmed due to the electrochemical character of the process [16,17,18], the asymmetric flash ‘ignition’ at one end of the specimen [1,2], as well as different microstructures formed at the cathode and anode [18], and the formation of dense and porous ‘islands’ at interrupted flash experiments [16].…”

Section: Analysis and Discussionmentioning

confidence: 99%

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Particle Surface Softening as Universal Behaviour during Flash Sintering of Oxide Nano-Powders

Chaim

2017

Materials

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The dissipated electric power in oxide powder compacts, subjected to flash sintering, is several hundreds of W·cm−3. This power is analyzed considering local softening/melting and transient plasma/liquid formation at the particle contacts due to thermal runaway. The sudden increase in compact electric conductivity and dissipated power referred to current percolation through the softening/liquid formed at the particle contacts, at the percolation threshold. The energy-balance and heat transfer considerations during the transient flash event are consistent with the local heating of the nanoparticle contacts to the ceramic melting temperature, or above it. The formation of the plasma by field emission of electrons is also considered.

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Section: Discussionmentioning

confidence: 68%

Section: Analysis and Discussionmentioning

confidence: 99%

Particle Surface Softening as Universal Behaviour during Flash Sintering of Oxide Nano-Powders

Chaim

2017

Materials

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“…They include nucleation of Frenkel pairs under the applied field [9], electrical boundary resistance [10], stress-induced generation of electric fields [11], and interaction between the external field and the space charge field [12]. Recently, a liquid film capillary model was discussed as a mechanism of rapid densification during flash sintering [13]. A similar mechanism of grain boundary softening has been proposed to explain the rapid densification under SPS [14].…”

Section: Introductionmentioning

confidence: 99%

On the Mechanism of Microwave Flash Sintering of Ceramics

et al. 2016

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The results of a study of ultra-rapid (flash) sintering of oxide ceramic materials under microwave heating with high absorbed power per unit volume of material (10–500 W/cm3) are presented. Ceramic samples of various compositions—Al2O3; Y2O3; MgAl2O4; and Yb(LaO)2O3—were sintered using a 24 GHz gyrotron system to a density above 0.98–0.99 of the theoretical value in 0.5–5 min without isothermal hold. An analysis of the experimental data (microwave power; heating and cooling rates) along with microstructure characterization provided an insight into the mechanism of flash sintering. Flash sintering occurs when the processing conditions—including the temperature of the sample; the properties of thermal insulation; and the intensity of microwave radiation—facilitate the development of thermal runaway due to an Arrhenius-type dependency of the material’s effective conductivity on temperature. The proper control over the thermal runaway effect is provided by fast regulation of the microwave power. The elevated concentration of defects and impurities in the boundary regions of the grains leads to localized preferential absorption of microwave radiation and results in grain boundary softening/pre-melting. The rapid densification of the granular medium with a reduced viscosity of the grain boundary phase occurs via rotation and sliding of the grains which accommodate their shape due to fast diffusion mass transport through the (quasi-)liquid phase. The same mechanism based on a thermal runaway under volumetric heating can be relevant for the effect of flash sintering of various oxide ceramics under a dc/ac voltage applied to the sample.

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“…Many other reports were published applying this technique to other materials [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30], studying the dependence on the amplitudes of the electric field and current density [31], on the average particle size [32], on the porosity [33], and searching for an explanation of such events [34][35][36][37][38][39][40].…”

Section: Introductionmentioning

confidence: 99%

Electrical Behavior and Microstructural Features of Electric Field-Assisted and Conventionally Sintered 3 mol% Yttria-Stabilized Zirconia

Carvalho¹,

Muccillo²,

Muccillo

2018

Ceramics

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ZrO 2 : 3 mol % Y 2 O 3 (3YSZ) polycrystalline pellets were sintered at 1400 • C and by applying an alternating current (AC) electric field at 1000 • C. An alumina sample holder with platinum wires for connecting the sample to a power supply was designed for the electric field-assisted sintering experiments. The apparent density was evaluated with the Archimedes technique, the grain size distribution by analysis of scanning electron microscopy images, and the electrical behavior by the impedance spectroscopy technique. Sintering with the application of AC electric fields to 3YSZ enhances its ionic conductivity. An explanation is proposed, based on the dissolution back to the bulk of chemical species, which are depleted at the grain boundaries, leading to an increase in the oxygen vacancy concentration. For the enhancement of the grain boundary conductivity, an explanation is given based on the diminution of the concentration of depleted chemical species, which migrate to the bulk. This migration leads to a decrease of the potential barrier of the space charge region, known to be responsible for blocking the oxide ions through the intergranular region. Moreover, the heterogeneity of the distribution of the grain sizes is ascribed to the skin effect, the tendency of the AC current density to be largest near the surface, decreasing towards the bulk.

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Liquid Film Capillary Mechanism for Densification of Ceramic Powders during Flash Sintering

Cited by 78 publications

References 41 publications

Particle Surface Softening as Universal Behaviour during Flash Sintering of Oxide Nano-Powders

Particle Surface Softening as Universal Behaviour during Flash Sintering of Oxide Nano-Powders

On the Mechanism of Microwave Flash Sintering of Ceramics

Electrical Behavior and Microstructural Features of Electric Field-Assisted and Conventionally Sintered 3 mol% Yttria-Stabilized Zirconia

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