Flash sintering scaling-up challenges: Influence of the sample size on the microstructure and onset temperature of the flash event

Campos, João V.; Lavagnini, Isabela R.; Silva, João G. Pereira da; Ferreira, Julieta Adriana; Sousa, Rafael Vieira de; Mücke, Robert; Guillon, Olivier; Pallone, Elíria Maria de Jesus Agnolon

doi:10.1016/j.scriptamat.2020.04.022

Cited by 34 publications

(24 citation statements)

References 21 publications

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“…The reported measurements of in-situ conductivity of single and polycrystalline samples fall in debatable accuracy issues, for two main reasons: the dissimilar scale of single crystals (mm) and polycrystalline pellets (cm) and the densification degree of each: fully dense for SCs, and 35% to 37% porosity in compacts. Issues with scaling of the applied potential for a constant electric field in different sized samples are known [ 25 ], as well as the detrimental effects of air (in porous compacts) for conductivity measurements.…”

Section: Resultsmentioning

confidence: 99%

Particle Characteristics’ Influence on FLASH Sintering of Potassium Sodium Niobate: A Relationship with Conduction Mechanisms

et al. 2021

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The considerable decrease in temperature and time makes FLASH sintering a more sustainable alternative for materials processing. FLASH also becomes relevant if volatile elements are part of the material to be processed, as in alkali-based piezoelectrics like the promising lead-free K0.5Na0.5NbO3 (KNN). Due to the volatile nature of K and Na, KNN is difficult to process by conventional sintering. Although some studies have been undertaken, much remains to be understood to properly engineer the FLASH sintering process of KNN. In this work, the effect of FLASH temperature, TF, is studied as a function of the particle size and impurity content of KNN powders. Differences are demonstrated: while the particle size and impurity degree markedly influence TF, they do not significantly affect the densification and grain growth processes. The conductivity of KNN FLASH-sintered ceramics and KNN single crystals (SCs) is compared to elucidate the role of particles’ surface conduction. When particles’ surfaces are not present, as in the case of SCs, the FLASH process requires higher temperatures and conductivity values. These results have implications in understanding FLASH sintering towards a more sustainable processing of lead-free piezoelectrics.

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Section: Resultsmentioning

confidence: 99%

Particle Characteristics’ Influence on FLASH Sintering of Potassium Sodium Niobate: A Relationship with Conduction Mechanisms

et al. 2021

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“…This NTC phenomenon, combined with the specimen cooling at the boundaries, tends to amplify the temperature gradients and may generate highly unstable heating regions. 27,28 These so-called hot spots can be detected in samples after sintering through microstructural features, including local melting, 3 and abnormal grain growth. 29 Grain core-boundary temperature differences are minimal and unlikely to contribute significantly to the temperature gradients.…”

Section: Thermal Inhomogeneities and Gradientsmentioning

confidence: 99%

“…The microscope images show examples of these effects for (a) cross-sectional differences in regions in a flash sintered sample of 8 mol% yttria-stabilized zirconia 25 and (b) differences between core, surface, and electrode regions of a flash sintered sample of 3 mol% yttria-stabilized zirconia. 27 On the right (c) is an example of a thermal imaging measurement of the thermal gradient in soda lime silicate glass during flash sintering. 28 dependent on geometry), and thermal conductivity (material property).…”

Section: Geometry and Electrode Contact Effectsmentioning

confidence: 99%

“…The small height minimizes any gradient between the sample center and the electrode region, but also facilitates the formation of hot spots and radial gradients. 43 Common sizes of disk vary, but most used in FS experiments are less than 10 mm in diameter, [44][45][46] the exception being flash-SPS where larger disk diameters are more common [47][48][49][50][51] When "pellet" samples are used (i.e., cylindrical-shaped samples with similar diameter to height), 27 geometry effects lie between the two extremes of the dogbone (low diameter-to-height ratio) and the disk (high diameter-to-height ratio).…”

Section: Geometry and Electrode Contact Effectsmentioning

confidence: 99%

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Promoting microstructural homogeneity during flash sintering of ceramics through thermal management

Jones

Biesuz

et al. 2021

MRS Bulletin

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Flash sintering (FS) is a novel field-assisted sintering technology, where the ceramic is heated internally by the Joule effect. While FS promises a tremendous reduction of ceramic firing time and furnace temperature, it has been applied only at the laboratory scale to date. The key limitation of scaling up the technique to the industrial manufacturing level is the intrinsic difficulty managing the heat generation and obtaining homogenous microstructures in components of industrial interest. Heterogeneous regions primarily originate from the different types of thermal gradients that develop during FS; therefore, the management of heat generation is crucial to achieve uniformity. In this article, we discuss the advantages of controlling the microstructural homogeneity of ceramics during FS, and the technical routes to achieve this. The origin and formation mechanisms of thermal gradients upon flash sintering are outlined. Possible approaches to reduce thermal and microstructural gradients are identified. The opportunities and challenges in scale-up of FS are discussed from both industrial and scientific perspectives.

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“…One of the drawbacks of FS is the development of hot-spots during the flash transition due to the electric power spike [35]. These hot-spots can lead to nonhomogenous microstructures [36]. In order to reduce hot-spots formation, some authors developed flash processes where the current limit is raised stepwise during the process [37][38][39].…”

Section: Introductionmentioning

confidence: 99%

Flash sintering of zircon: rapid consolidation of an ultrahigh bandgap ceramic

Martínez

Biesuz

Dong

et al. 2021

Journal of Asian Ceramic Societies

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Flash sintering scaling-up challenges: Influence of the sample size on the microstructure and onset temperature of the flash event

Cited by 34 publications

References 21 publications

Particle Characteristics’ Influence on FLASH Sintering of Potassium Sodium Niobate: A Relationship with Conduction Mechanisms

Particle Characteristics’ Influence on FLASH Sintering of Potassium Sodium Niobate: A Relationship with Conduction Mechanisms

Promoting microstructural homogeneity during flash sintering of ceramics through thermal management

Flash sintering of zircon: rapid consolidation of an ultrahigh bandgap ceramic

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