Heat Capacity and Structural Relaxation of Mixed‐Alkali Glasses

Moynihan, Cornelius T.; Easteal, Allan J.; Tran, D. C.; Wilder, J. A.; Donovan, E. P.

doi:10.1111/j.1151-2916.1976.tb09450.x

Cited by 97 publications

(64 citation statements)

References 17 publications

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“…The results of the present study are consistent with literature data within the same temperature interval. The differences in heat capacity observed across the glass transition temperature are consistent with the data of Moynihan et al (1976) and Bershtein et al (1980). The non-linear composition dependence of the heat capacity of the supercooled liquids indicates that multi-linear fits of heat capacity will have only limited success in predicting the thermal properties of such systems.…”

Section: Heat Capacitysupporting

confidence: 81%

Non-linear properties of supercooled liquids in the system Na2OSiO2

et al. 1994

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The physical properties, viscosity, density, heat capacity and thermal expansivity, of relaxed supercooled liquids in the temperature range just above the glass transition have been determined for ten compositions along the compositional binary Na20-SiO2, in the range of 2-45 mole% Na20, by a combination of scanning calorimetry, dilatometry and micropenetration viscometry. The viscosity, density, heat capacity and thermal expansivity in the glassy state have also been determined.The heat capacities illustrate a linear composition dependence for the glassy state and a smooth but strongly non-linear composition dependence for the supercooled liquid state. The thermal expansivities were determined by dilatometry up to the glass transition and, by a normalized comparison of relaxation behavior in the glass transition interval, to temperatures ~ 50 °C above the glass transition. The expansivity is a linear function of the molar composition in the glass but a strongly non-linear function of molar composition in the supercooled liquid.The viscosity data just above the glass transition temperature, combined with data from high temperature using the concentric cylinder method, illustrate that the composition dependence of viscosity is strongly non-linear and exhibits an inflection as a function of composition. The glass transition temperature, taken as the peak temperature of the calorimetric measurements, is not in general an isokom in this system.The data for these property determinations in the Na20-SiO2 system provide much improved constraints on the partial molar properties of SiO2 liquid and partial molar properties of the SiO 2 component in silicate melts. The complex behavior of the transport properties, i.e. the glass transition temperature and the viscosity, point to complexities in viscous flow beyond that of simple binary mixing of the Na20 and SiO2 components.

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Section: Heat Capacitysupporting

confidence: 81%

Non-linear properties of supercooled liquids in the system Na2OSiO2

et al. 1994

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“…While the model is known to describe successfully the evolution of many macroscopic quantities in the glass transition region [49][50][51][52][53] , it fails to reproduce the XPCS data, predicting relaxation times several orders of magnitude longer than the measured ones. The model assumes indeed that the aging takes place on a time scale comparable to the structural relaxation time, and this is usually the case for macroscopic observables.…”

Section: Resultsmentioning

confidence: 95%

“…The parameters x ¼ 0.7 and b ¼ 0.66 are fixed to the results of calorimetric measurements reported by Moynihan et al 52 The thermal protocol is composed of temperature changes at a constant cooling rate followed by annealing intervals of a few hours, during which the XPCS correlation functions are collected (see Methods). While the model is known to describe successfully the evolution of many macroscopic quantities in the glass transition region [49][50][51][52][53] , it fails to reproduce the XPCS data, predicting relaxation times several orders of magnitude longer than the measured ones.…”

Section: Resultsmentioning

confidence: 99%

Revealing the fast atomic motion of network glasses

Baldi²,

et al. 2014

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Still very little is known on the relaxation dynamics of glasses at the microscopic level due to the lack of experiments and theories. It is commonly believed that glasses are in a dynamical arrested state, with relaxation times too large to be observed on human time scales. Here we provide the experimental evidence that glasses display fast atomic rearrangements within a few minutes, even in the deep glassy state. Following the evolution of the structural relaxation in a sodium silicate glass, we find that this fast dynamics is accompanied by the absence of any detectable aging, suggesting a decoupling of the relaxation time and the viscosity in the glass. The relaxation time is strongly affected by the network structure with a marked increase at the mesoscopic scale associated with the ion-conducting pathways. Our results modify the conception of the glassy state and asks for a new microscopic theory.

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“…Such a behaviour of To with X may be attributed to the MAE. Although similar trends in the variation of experimental glass transition temperature, T, with the ion fraction of either of the alkali ions were reported for mixed alkali systems in hydrate (12, 13) as well as anhydrous melts (2,20), to date no report of To of mixed alkali system varying in this fashion with composition has been made. However, it may be pointed out that since in the temperature ranges of this study the conductance varies by only factors of 3 to 6 the computed values of the To parameter may not be very precise.…”

Section: Conductance Propertymentioning

confidence: 83%

Mixed alkali effect in sodium thiosulfate pentahydrate melt

Islam¹,

Ismail²

1988

Can. J. Chem.

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SHAKIRA S. ISLAM and KOCH~ ISMAIL. Can. J. Chem. 66, 242 (1988).Density and electrical conductance measurements of 0.35[XNaN03 + (I -X)KN03] + 0.65Na2S203.5H20 melt were made as functions of temperature and X. Molar volume, V, is found to be additive. The percent deviation of V,,, (extrapolated V of the pure solute from the plot of V vs. total added alkali ion fraction) from VcaI (calculated V of the pure solute from its high temperature density data) increases monotonically as the amount of NaNO, in the hydrate melt increases, thereby manifesting a "structure-forming" tendency of NaNO,. The non-Arrhenius temperature dependence of molar conductance, A is analyzed in terms of the Vogel-Tammann-Fulcher (VTF) equation. Mixed alkali effect (MAE) has been observed on A and To (ideal glass transition temperature). A competitive polarization model has been used to explain the MAE on A . On a effectut des mesures de densitt et de conductivitt Clectrique sur des mtlanges fondus de 0,35[XNaN03 + (I -X)KNO,] + 0,65Na2S2O3. 5H20, en fonction de la temptrature et de la valeur de X. On a trouvt que le volume molaire, V, est une proprittt additive. Le pourcentage de dtviation de la valeur V,,, (la valeur de V du solutt pur extrapolte a I'aide du courbe de V en fonction de la fraction totale des ions alcalins ajoutts) par rapport a la valeur VcaI (la valeur V calculte du solutt pur obtenue partir de ses donntes de densitt a haute temptrature) augmente d'une fason monotone avec I'augmentation de la quantitt de NaN0, dans la phase hydratte fondue; ces rtsultats suggkrent que le NaN0, a tendance a former des structures. La relation entre conductivitt molaire, A , et la temptrature ne suit pas la loi d'Arrhtnius; on analyse ce fait en fonction de l'tquation de Vogel-Tamman-Fulcher (VTF). On a observt l'effet des sels alcalins mixtes (EAM) sur A et sur To (temptrature de transition vitreuse idtale). On a utilist un modkle de polarisation compktitive pour expliquer I'EAM sur A .[Traduit par la revue]

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Heat Capacity and Structural Relaxation of Mixed‐Alkali Glasses

Cited by 97 publications

References 17 publications

Non-linear properties of supercooled liquids in the system Na2OSiO2

Non-linear properties of supercooled liquids in the system Na2OSiO2

Revealing the fast atomic motion of network glasses

Mixed alkali effect in sodium thiosulfate pentahydrate melt

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