Electric field-induced softening of alkali silicate glasses (original) (raw)
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DC-electro softening in soda lime silicate glass: An electro-thermal analysis
Scripta Materialia, 2018
DC-electric field-induced softening was investigated in soda lime glass. The application of a DC current causes a migration of Na ions towards the cathode resulting in the formation of a sodium depleted layer close to the anode where a localized voltage drop ignites electrical arcs through the glass. This effect is strongly asymmetric with respect to the applied DC polarity and, at the anode, it induces strong photoemission (optical transition of alkali elements) sharp rise in temperature and increased electrical resistance. It appears that electrolytic effects and sodium migration play a fundamental role as triggering mechanisms of DC-electric field-induced softening.
Electrode Material Effect on the Flash Ignition in Soda-Lime Silicate Glass
2021
The need for sustainable solutions to reduce the carbon footprint of the ceramics and glass industry leads towards the development of new electric current-assisted technologies. Flash sintering-like processes in glasses allow a reduction of the softening temperature and could pave the way for new shaping technologies. Herein, we investigated the flash transition in soda-lime silicate glass using two different electrode materials, silver, and platinum. The high dielectric strength registered on samples tested with platinum electrodes undergoes a significant reduction when silver is used. In other words, in the case of silver electrodes, the flash ignition takes place at a lower onset field. Moreover, the Joule heating developed during the process can be turned from being highly inhomogeneous with Pt electrodes to homogeneous when Ag electrodes are used.
Viscous flow flash sintering of porous silica glass
Journal of Non-Crystalline Solids, 2017
For the first-time compacts of porous glass particles (95 wt% SiO 2 , 2.3% Na 2 O, 1.6% Al 2 O 3) exhibiting macro-, meso-and micro-pores were densified by flash sintering, using DC electric field in the range 1000-3000 V cm − 1. The results point out the applicability of this sintering technology to glasses characterized by viscous flow sintering mechanisms. Excluding the anodic region, the specimens resulted well densified using a current limit of 2 mA mm − 2 and a dwelling time of 30 s. The obtained microstructure at the anode and at the cathode side is asymmetric, the former being characterized by the formation of Na-enriched region, the latter by the local formation of large pores (hundreds of microns). The mechanism, which triggers the flash event, appears to be associated to dielectric breakdown. 2. Materials, methods and calculations 2.1. Glass preparation and characterization Sodium borosilicate glass with composition (wt%) 65.6 SiO 2 − 27.8
Mechanical and dielectric behaviour of some ionic glasses
Solid state ionics, 1998
Mechanical and electrical relaxation processes are compared on identical superionic glasses in which the glassy matrix AgPO was doped with various kinds of salt dopant. It was found that the same values characterize the a.c. conductivity as 3 well as the mechanical spectra. Above T¯10K there are two different activated contributions to the acoustic absorption: one, dominant at high temperatures / low frequencies is characterized by a linear decrease of the activation energy as the salt dopant is increased; the second, dominant at intermediate temperatures / frequencies is characterized by activation energy values one order of magnitude smaller. At the same time the log-log representation of the experimental a.c. conductivity vs. frequency shows a double power law behaviour. Two different relaxing processes can account for the activation energy values and for the double power law behaviour of the a.c. conductivity.
Ac conductivity and dielectric relaxation in ionically conducting soda–lime–silicate glasses
Journal of Non-crystalline Solids, 2008
The frequency dependent conductivity and dielectric relaxation of alkali ions in some soda-lime-silicate (Na 2 O-CaO-SiO 2 ) glasses are investigated over a frequency range from 50 Hz to 1 MHz and in a temperature range from room temperature to 603 K by using alternating current impedance spectroscopy. The conductivity isotherms show a transition from frequency independent dc region to dispersive region where the conductivity continuously increases with increasing frequency. The electric modulus representation has been used to provide comparative analysis of the ion transport properties in these glasses. The scaling behavior of imaginary part of electric modulus indicates that all dynamical processes occurring at different frequencies give the same activation energy.
Electrode-dependent Joule heating in soda lime silicate glass during flash processes
Scripta Materialia, 2020
Electric current-assisted technologies stand as a promising route to reduce the carbon footprint of the 21 st century industry. Nevertheless, recent activities on flash sintering have shown that electrically-induced DC Joule heating in silicate glasses is highly inhomogeneous under the effect of a direct electric field, thus limiting further developments and industrial applications. In this work, we have shown that the Joule heating in soda lime silicate glass can be tailored and controlled by changing the material used as electrode. The highly inhomogeneous temperature profile developed using platinum electrodes turns into a well-homogenous distribution by employing molten NaNO 3 electrodes.
Influence of SiO2 on the structural and dielectric properties of ZnO∙Bi2O3∙SiO2 glasses
Glasses having composition 20ZnO∙(80-x)Bi2O3∙xSiO2 (0 ≤ x ≤ 50 mol%) were prepared by the conventional meltquench technique. Conduction and relaxation mechanism in these glasses were studied using impedance spectroscopy in the frequency range from 10Hz to 7MHz and in the temperature range from 473K to 703 K. The complex impedance plots show depressed semicircles that shift towards origin with increase in temperature which reveals the migration of charge carrier ions in glass matrix is thermally stimulated. The ac and dc conductivities, activation energy for dc conduction (Edc) and relaxation (Eτ) were extracted from the impedance spectra. The compositional variation in conductivity has been attributed to the presence of mixed glass former effect in these glasses. Similar values of Edc and Eτ for each glass composition indicate that the charge carrier ions have to overcome the same energy barrier during conduction as well as relaxation processes. The perfect overlapping of normalized plots of electrical modulus on a single ‘master curve’ for all temperatures reveals that the conductivity relaxation occurring at different frequencies exhibit temperature independent dynamical processes. IR spectra reveals that in these glasses, Bi2O3 acts as both network former with [BiO3] pyramidal units and as modifier with [BiO6] octahedral units. The compositional dependence of density, molar volume and glass transition temperature were analyzed and correlated with the structural changes occurring in the glasses.
Applied Surface Science, 2012
A scanning electron microscope (SEM) is employed to investigate the temperature effect on the charging behaviour of alkali-silicate glasses under electron beam irradiation using electrostatic influence method (EIM). A modified special arrangement adapted to the SEM allows to study charging mechanisms and charge transport characteristics of these glasses using the simultaneous measurement of displacement and leakage currents. The trapping process during continuous electron irradiation can be directly determined by the EIM. The experimental results reveal that the charging ability of glasses decreases with increasing temperature. The variation of charge process has been confirmed by measuring the surface potential in response to the sample temperature. In this report, we introduce also the secondary electron emission (SEE) yield. It was found the strong dependence of the SEE yield on the temperature variation. The higher is the temperature and the lower is the SEE yield. The trapping ability is analyzed taking into account the regulation mechanisms involved under electron irradiation.
Journal of Non-Crystalline Solids, 2014
The ion exchange process for chemical strengthening of glass involves an inter-diffusion of alkali ions between the glass and a molten salt bath. In most commercial glasses, this comprises an exchange of Na + ions in the glass for larger K + ions from the salt bath. The stuffing of K + ions into sites previously occupied by Na + in the glass results in the formation of a compressive stress profile in the glass. In the absence of stress relaxation, this compressive stress profile largely follows the concentration profile of the K + ions. Any subsequent migration of K + ions within the glass would result in a change in this stress profile, which could lead to different mechanical behaviors of the glass. In particular, a reduction of the surface compressive stress could lead to a compromise in the retained strength of the glass, making it more susceptible to failure. Recent work has shown that chemically strengthened glass can be used as an effective substrate material for organic thin film transistors (TFTs), since the temperatures involved with organic TFT deposition are low enough to avoid any compromise in the compressive stress profile. This opens the possibility of fabricating high strength organic TFT displays. However, the question remains as to whether the exposure of the glass to an electric field may lead to the diffusion of the alkali ions and a corresponding alteration of the stress profile, which could compromise the strength of the organic TFT device. In this paper, we demonstrate that there is no change in the stress profile of Corning® Gorilla® Glass 3 after subjecting the glass to much higher voltage dc fields compared to the maximum field that would be exhibited in an organic TFT device. The stress profile is modified only after treating the glass at sufficiently high temperature, where alkali migration becomes thermally activated.
Chemistry of Materials, 2007
Molecular dynamics simulations and energy-minimization techniques have been applied for the first time to determine the whole set of elastic properties (Young's modulus, shear modulus, bulk modulus, and Poisson's ratio) of alkali silicate glasses with different ion modifiers (Li, Na, and K) in the range 0-30 mol % alkaline oxide. Excellent agreement has been found between the simulation results and the experimental data. The peculiar behavior of the Li-containing glasses with respect to the Na and K ones is extensively discussed in terms of the glass structural features. It is found that the elastic property variation as a function of alkali addition can be explained by three concurrent factors: (1) depolymerization of the silica network; (2) increasing the cohesion of the glass by the establishment of alkali-NBO bonds; and (3) decreasing the free volume with consequent increasing of the glass packing density.