Diffusion-controlled processes in glass forming melts

Schaeffer, Helmut A.

doi:10.1016/0022-3093(84)90138-8

Cited by 53 publications

(24 citation statements)

References 11 publications

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“…This may be explained by the proposal (e.g., Muehlenbachs & Schaeffer) that these experiments involve trans port of physically dissolved O 2 gas. This interpre tation is consistent with the low activation energy (-20kcalmole" 1 )forthe process (Muehlenbachs & Schaeffer, 1977;Schaeffer & Muehlenbachs, 1978;Schaeffer, 1984). The Eyring equation pre dicts the diffusivity of Si in silicate melts (see Fig.…”

Section: Atomistic Originsupporting

confidence: 75%

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Relaxation in silicate melts

Dingwell¹,

Webb²

1990

ejm

423

259

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Abstract:The glass transition is a kinetic barrier that divides the behavior of silicate melts into two types, liquid and glassy. Liquid behavior is the equilibrium response of a melt to an applied perturbation, resulting in the determination of an equilibrium liquid property. The equilibrium may be stable (superliquidus) or metastable (subliquidus). Glassy behavior occurs when the timescale of the perturbation is too short for melt equilibration. This can occur when the frequency of an applied sinusoidal perturbation is too high or when the observation time of an experiment is too short. The time-or frequency-dependent response of the structure and properties of a melt to a perturbation is termed relaxation. Liquid and glassy behavior are relaxed and unrelaxed behavior, respectively.Linear viscoelastic theory provides mechanical models for the prediction of the isothermal transition from liquid to glassy behavior. A simple series combination of Hookean spring and Newtonian dashpot (a Maxwell element) is capable of predicting the timescale corresponding to the glass transition from the ratio of the relaxed viscosity to the infinite frequency elastic modulus. We review some experimental work on silicate melts that can be used to constrain the location of the glass transition in time-temperature space at 1 atm pressure (e.g., ultrasonic wave propagation, fiber elongation, torsional testing, scanning calorimetry).The microscopic origin of the glass transition in silicate melts is related to the exchange ofSi-O bonds. Recent" Si NMR work indicates that the Si-O bond exchange frequency matches the timescale of the glass transition. This explains the Newtonian viscosity of silicate liquids. No extended species (e.g., "polymers") can exist at higher temperatures and longer timescales than the lifetime of the fundamental Si-O bond. Silicate melts, however, become non-Newtonian as the strain rate approaches the equilibration rate of the Si-O bonds. Such a correlation between Si-O bond exchange and the viscous flow mechanism, in turn, explains the success of the Eyring relationship in relating high temperature oxygen and silicon self-diffusion to viscosity.Knowledge of the structural relaxation timescale is important in extracting equilibrium information from studies of the structure and properties of quenched glasses. Quench rate-dependent speciation data for glasses imply a temperature-dependence of the species equilibrium in the liquid state. Estimation of the relaxation times associated with the quench rates allows reconstruction of the temperature-dependence of homogeneous equilibria in liquids.Experimental work on silicate melts should consider the location of the experimental method in time-temperature space, with respect to the glass transition. Diffusivity measurements, for example, are influenced by the glass transition. When the duration of a diffusivity experiment crosses the volume relaxation time, an inflection in the temperature-dependence of diffusivity of cations is observed. A second "transition" in diff...

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Section: Atomistic Originsupporting

confidence: 75%

“…These data appear to indicate that Si diffusivity is controlled by the exchange frequency of Si-O bonds. The case for oxygen diffusion is complicated by the presence of physically dissolved oxygen in the melts which participates in bulk oxygen diffusion at relatively high O 2 pressures (Williams, 1965;Schaeffer, 1984).…”

Section: With Increasingmentioning

confidence: 99%

Relaxation in silicate melts

Dingwell¹,

Webb²

1990

ejm

423

259

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“…This induced Si content fluctuations achieved by diffusion. As Si content increased in some places, at these places the structure stabilized into silica-germania glass increasing the driving force for Si to increase its concentration (since it is known that SiO 2 adopts vitreous state easily Nevertheless, it is known that Cu diffuses much faster than Si in vitreous matter [22,23]. We thus think that ordered fiber distribution in our case is a self-organization relevant from Turing structures.…”

Section: Now One Has To Find An Answer To Three Questions In Order Tmentioning

confidence: 65%

Elaboration of a Specific Class of Metamaterial: Glass in Single Crystal

Poumellec¹,

Lancry²,

Ani-Joseph³

et al. 2012

Crystallization and Materials Science of Modern Artificial and Natural Crystals

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“…In silicate melts all cations are bonded to oxygen. The Eyring diffusivity is controlled by the exchange frequency of Si-O bonds (see Revesz and Schaeffer, 1982;Schaeffer, 1984 for discussion of SiO2). During such jumps the bonds to cations are temporarily broken and the cation is free to diffuse.…”

Section: Observation Time-scale (%)mentioning

confidence: 99%

Effects of structural relaxation on cationic tracer diffusion in silicate melts

Dingwell

1990

Chemical Geology

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Dingwell, D.B., 1990. Effects of structural relaxation on cationic tracer diffusion in silicate melts. Chem. Geol., 82:209-216.The glass transition in silicate melts is a curve in time-temperature space marking the transition of the melt structure from an unrelaxed, disequilibrium glass to a relaxed, equilibrium liquid. Tracer diffusivity data obtained in glasses vs. liquids cannot be compared without consideration of the effects of this transition. For tracer diffusivity experiments, two time scales are important, the time duration of the experiment (~d) and the inverse of the jump frequency (vp) of the tracer.When the time duration of the experiments reaches the relaxation time-scale (~d = rs) of the melt a transition occurs from diffusion in an unrelaxed matrix (undergoing vibrational thermal expansion) to diffusion in a relaxed matrix (undergoing equilibrium, configurational and elastic, thermal expansion). At this transition, an inflection is observed in the temperature dependence of cationic tracer diffusivity. At temperatures below the inflection, the diffusivity is Arrhenian whereas at temperatures above the diffusivity is non-Arrhenian.At high temperatures the tracer diffusivities of the cations approach the value of diffusivity obtained from the Eyring relation ( rp = ~s). The contrasting, high-temperature, composition dependence of Na and Li vs. Co, Cs, Sr, Ba, Eu, Fe and C diffusivities can be explained in terms of the Eyring (network 0 and Si) diffusivity influencing the latter group. The contrasting high-vs. low-temperature, composition dependence of Ba and Sr diffusivities can be similarly explained. These latter observations indicate that all cationic diffusivities will be within a loglo unit of the Eyring oxygen diffusivity in melts with viscosities below 10 P.

show abstract

Diffusion-controlled processes in glass forming melts

Cited by 53 publications

References 11 publications

Relaxation in silicate melts

Relaxation in silicate melts

Elaboration of a Specific Class of Metamaterial: Glass in Single Crystal

Effects of structural relaxation on cationic tracer diffusion in silicate melts

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