Electric field-induced softening of alkali silicate glasses

McLaren, Charles T.; Heffner, William R.; Tessarollo, R.; Raj, Rishi; Jain, Himanshu

doi:10.1063/1.4934945

Cited by 51 publications

(72 citation statements)

References 28 publications

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“…McLaren et al [123] investigated the photoemission in two lithium-sodium mixed alkali silicates (5L5NS and 2L8NS) and a single alkali sodium silicate (NS) under an applied field. The application of a DC field significantly lowered the softening temperature (T Soft ) of both glasses for fields above 50 V cm −1 .…”

Section: Polarity Induced Effectsmentioning

confidence: 99%

Review of flash sintering: materials, mechanisms and modelling

Grasso

McKinnon

et al. 2016

Advances in Applied Ceramics

392

248

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Flash sintering (FS) is an energy efficient sintering technique involving electrical Joule heating, which allows very rapid densification (<60 s) of particulate materials. Since the first publication on flash-sintered zirconia (3YSZ) in 2010, it has been intensively researched and applied to a wide range of materials. Going back more than a century ago, we have found a close similarity between FS of oxides and Nernst glowers developed in 1897. This review provides a comprehensive overview of FS and is based on a literature survey consisting of 88 papers and seven patents. It correlates processing parameters (i.e. electric field magnitude, current density, waveforms (AC, DC) and frequency, furnace temperature, electrode materials/ configuration, externally applied pressure and sintering atmosphere) with microstructures and densification mechanisms. Theorised mechanisms driving the rapid densification are substantiated by modelling work, advanced in situ analysis techniques and by established theories applied to electric current assisted/activated sintering techniques. The possibility of applying FS to a wider range of materials and its implementation in industrial scale processes are discussed.

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Section: Polarity Induced Effectsmentioning

confidence: 99%

Review of flash sintering: materials, mechanisms and modelling

Grasso

McKinnon

et al. 2016

Advances in Applied Ceramics

392

248

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“…19 EFIS is a processing technique where a compressive load is applied to a rectangular glass block inside a furnace. The furnace is then heated at a constant rate while electrodes are used to apply an external electric field across the two parallel faces of the block.…”

mentioning

confidence: 99%

Depletion Layer Formation in Alkali Silicate Glasses by Electro-Thermal Poling

McLaren

Balabajew

Gellert

et al. 2016

J. Electrochem. Soc.

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Electro-thermal poling of alkali-containing glasses has been known to enhance various physical and chemical properties due to the formation of an alkali ion depletion layer. We have investigated the role of alkali ion migration in depletion layer formation by in situ impedance spectroscopy, poling current measurements and ToF-SIMS on two binary alkali (lithium and sodium) disilicate glasses and two mixed alkali lithium-sodium disilicate glasses. Typically, the depletion layer is formed within a few minutes, reaching a thickness of the order of 100 nm while its impedance continues to increase for the duration of poling. Its electrical conductivity is six or more orders of magnitude lower than that of the bulk glass; by comparison the dielectric constant is lower, approaching the value for silica containing a few percent alkali oxide. Two processes contribute to the formation of a depletion layer: a relatively fast initial process arising from alkali ion migration, followed by a slower process of either electrolysis or gaseous oxygen evolution near the anode. Implications of electro-thermal poling for the mechanism of recently discovered electric field-induced softening of glass are discussed. Electro-thermal poling was primarily developed to induce secondorder nonlinear (SONL) optical susceptibility in glasses by application of DC electric fields. [1][2][3][4] In recent years, interest in this technique has expanded beyond SONL to enhance a variety of biological, physical and chemical properties of glass.5-18 For example, electro-thermal poling has been reported to modify a glass' affinity to atmospheric water at the anode region.18 Electro-thermal poling generally comprises of four main processing steps. First, a glass is heated to a predetermined poling temperature (T p ) below the glass transition temperature (T g ), which allows for increased ionic conductivity while retaining the preformed dimensions. Electrodes on opposite sides of the glass sample are then used to apply a DC voltage (V p ) at T p . After sufficient charge flow has occurred, the glass is then cooled to ambient while still applying the DC voltage to 'freeze' ionic displacements. Finally, the applied voltage is removed at ambient temperature where ionic conductivity is significantly lower to prevent ionic migration back toward original positions. Modification of properties is largely effected by the formation of an alkali ion depletion layer at the anode due to charge transport of ions during these steps.Recently, electric field-induced softening (EFIS) of glass was reported to reduce furnace temperature required for glass softening. 19EFIS is a processing technique where a compressive load is applied to a rectangular glass block inside a furnace. The furnace is then heated at a constant rate while electrodes are used to apply an external electric field across the two parallel faces of the block. The observed reduction in furnace temperature, compared to zero-field conditions, occurs as a result of Joule heating, electrolysis and dielectric b...

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“…Melting is an endothermic reaction, therefore local melting is associated with activation energy to initiate the melt from the crystal. In this respect, application of external fields on crystals and glasses (even with no contact electrodes) was found to enhance reorientation of the surface dipoles [48], increase the structural disorder at the surface [49], and enhance the softening of glasses [4]. The electric field-induced softening (EFIS) of the glass was related to combination of Joule heating, dielectric breakdown, and electrolysis within the glass.…”

Section: Discussionmentioning

confidence: 99%

“…If this limitation is removed, the excess Joule heat may locally melt the compact [35], or fully melt the glass (see supplement in Ref. [4]). Second, as shown and argued above, the liquid has a transient nature.…”

Section: Discussionmentioning

confidence: 99%

“…The sudden densification takes place at appropriate combinations of the electric field and temperature and accompanied by the photoluminescence flash [3]. The photoemission during the flash was related to different sources, such as electroluminescence due to electron-hole recombination [3][4][5], dielectric breakdown [6], and as incandescence emission [7]. The photoluminescence signals the transition to the nonlinear behavior of the compact's electric conductivity, which otherwise is almost linear with the increase in the temperature [8,9].…”

Section: Introductionmentioning

confidence: 99%

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On thermal runaway and local endothermic/exothermic reactions during flash sintering of ceramic nanoparticles

Chaim

Estournès

2018

J Mater Sci

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OATAO is an open access repository that collects the work of some Toulouse researchers and makes it freely available over the web where possible. ABSTRACTNumerical analysis of the heat balance at the flash event during flash sintering of granular ceramic nanoparticles was performed assuming continuum solid state as well as simultaneous surface softening/liquid formation and current percolation through the nanoparticle contacts. Assuming inter-particle radiations in the specimen volume, the electric Joule heat generated at the nanoparticle contacts partially lost by radiation from the specimen external surfaces. Considering the thermal effects due to rapid heating rate and freemolecular heat conduction regime, high-temperature gradients between the nanoparticle surfaces and the surrounding gas were developed. The attractive capillary forces, induced by the particle surface softening/liquid at the percolation threshold, lead to rapid rearrangement and densification of the nanoparticles. The excess Joule heat, already at the flash event, suffices the excess internal heat that is necessary for partial or full melting. Particle surface softening/liquid formation is a transient process, hence followed by crystallization immediate after the nanoparticle rearrangement. Thermal runaway is associated with local surface softening/melting and its solidification.

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Electric field-induced softening of alkali silicate glasses

Cited by 51 publications

References 28 publications

Review of flash sintering: materials, mechanisms and modelling

Review of flash sintering: materials, mechanisms and modelling

Depletion Layer Formation in Alkali Silicate Glasses by Electro-Thermal Poling

On thermal runaway and local endothermic/exothermic reactions during flash sintering of ceramic nanoparticles

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