Diffusive motion in alkali silicate melts: An NMR study at high temperature

Liu, S.-B.; Stebbins, Jonathan F.; Schneider, E.; Pines, Alexander

doi:10.1016/0016-7037(88)90108-1

Cited by 96 publications

(96 citation statements)

References 44 publications

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“…Recent 29 Si NMR studies of relaxation in Silicate melts (Na 2 Si 2 0 5 [Liu et al, 1988] and K 2 Si 4 0 9 [Stebbins, 1988]) have resulted in the determination of timescales for the exchange of Si-0 bonds. This time scale corresponds to the macroscopic structural relaxation time scale obtained from the Maxwell relation.…”

Section: Microscopic Considerationsmentioning

confidence: 99%

Non‐Newtonian rheology of igneous melts at high stresses and strain rates: Experimental results for rhyolite, andesite, basalt, and nephelinite

Webb¹,

Dingwell²

1990

J. Geophys. Res.

258

182

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The stress‐strain rate relationships of four silicate melt compositions (high‐silica rhyolite, andesite, tholeiitic basalt, and nephelinite) have been studied using the fiber elongation method. Measurements were conducted in a stress range of 10–400 MPa and a strain rate range of 10−6 to 10−3 s−1. The stress‐strain rate relationships for all the melts exhibit Newtonian behavior at low strain rates, but non‐Newtonian (nonlinear stress‐strain rate) behavior at higher strain rates, with strain rate increasing faster than the applied stress. The decrease in calculated shear viscosity with increasing strain rate precedes brittle failure of the fiber as the applied stress approaches the tensile strength of the melt. The decrease in viscosity observed at the high strain rates of the present study ranges from 0.25 to 2.54 log10 Pa s. The shear relaxation times τ of these melts have been estimated from the low strain rate, Newtonian, shear viscosity, using the Maxwell relationship τ = ηs/G∞. Non‐Newtonian shear viscosity is observed at strain rates ( trueε˙=time−1 ) equivalent to time scales that lie 3 log10 units of time above the calculated relaxation time. Brittle failure of the fibers occurs 2 log10 units of time above the relaxation time. This study illustrates that the occurrence of non‐Newtonian viscous flow in geological melts can be predicted to within a log10 unit of strain rate. High‐silica rhyolite melts involved in ash flow eruptions are expected to undergo a non‐Newtonian phase of deformation immediately prior to brittle failure.

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Section: Microscopic Considerationsmentioning

confidence: 99%

Non‐Newtonian rheology of igneous melts at high stresses and strain rates: Experimental results for rhyolite, andesite, basalt, and nephelinite

Webb¹,

Dingwell²

1990

J. Geophys. Res.

258

182

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“…The viscosity data used are from references in Richet (1984) for (SiO2, ABalbite, AN-anorthite, DI-diopside): Astin (1962: 710-soda lime SRM 710) and calculated using the method of Shaw (1972: R1A rhyolite). Other sources of data relating to relaxation times are discussed in the text, including volume relaxation of densified SiO 2 (H6fler and Seifert 1984); fiber elongation (Simmons et al 1982); high-temperature 298i NMR (Liu et al 1988); normal (Dingwell, unpubl. ) and high torque (Spera et al 1988) concentric cylinder viscometry; ultrasonics (Sato and Manghnani 1985); shock wave (Rigden et al 1988) to demonstrate (via Equation 8) that z s is a strong function of composition (and temperature).…”

Section: Temperature-and Composition-dependence Ofmentioning

confidence: 99%

“…Additional evidence relating to the basic viscous flow process comes from high-temperature static 29Si NMR work of Liu et al (1988). Liu et al (1988) studied the static 29Si NMR spectrum of Na2Si205 melt as a function of temperature.…”

Section: Microscopic Insightsmentioning

confidence: 99%

Structural relaxation in silicate melts and non-Newtonian melt rheology in geologic processes

1989

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Abstract. The timescale of structural relaxation in a silicate melt defines the transition from liquid (relaxed) to glassy (unrelaxed) behavior. Structural relaxation in silicate melts can be described by a relaxation time, z, consistent with the observation that the timescales of both volume and shear relaxation are of the same order of magnitude. The onset of significantly unrelaxed behavior occurs 2 loglo units of time above z. In the case of shear relaxation, the relaxation time can be quantified using the Maxwell relationship for a viscoelastic material; Zs=r/s/G~ (where Zs is the shear relaxation time, G~ is the shear modulus at infinite frequency and t/s is the zero frequency shear viscosity). The value of Go is known for SiO 2 and several other silicate glasses. The shear modulus, Go, and the bulk modulus, K~, are similar in magnitude for every glass, with both moduli being relatively insensitive to changes in temperature and composition. In contrast, the shear viscosity of silicate melts ranges over at least ten orders of magnitude, with composition at fixed temperature, and with temperature at fixed composition. Therefore, relative to qs, Go may be considered a constant (independent of composition and temperature) and the value of %, the relaxation time, may be estimated directly for the large number of silicate melts for which the shear viscosity is known.For silicate melts, the relaxation times calculated from the Maxwell relationship agree well with available data for the onset of the frequency-dependence (dispersion) of acoustic velocities, the onset of non-Newtonian viscosities, the scan-rate dependence of the calorimetric glass transition, with the timescale of an oxygen diffusive jump and with the Si-O bond exchange frequency obtained from 298i NMR studies.Using data obtained over a range of frequencies and strain-rates we illustrate the significance of relaxed versus unrelaxed behavior in laboratory experiments on silicate melts. Similarly, using strain-rate estimates for magmatic processes we evaluate the significance of the liquid-glass transition in igneous petrogenesis.

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“…Because the time scale of structural relaxation has been identified with the inverse of the jump frequency of oxygen in Si-O bonds (Liu et al, 1988;Stebbins, 1988). The volume relaxation time-scale, macroscopically derived, can be used to estimate 0 and Si diffusivity, rate-limited by this mechanism (Dingwell and Webb, 1989).…”

Section: Structural Relaxationmentioning

confidence: 99%

“…Recent 29Si NMR studies on the spin-spin relaxation of Si in silicate melts (Liu et al, 1988;Stebbins, 1988) have demonstrated that the lifetime of a Si-O bond in a silicate liquid corresponds to the macroscopically defined glass transition (i.e. the time-scale of relaxation of the melt structure to changes in density, shear stress, temperature).…”

Section: Introductionmentioning

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.

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Diffusive motion in alkali silicate melts: An NMR study at high temperature

Cited by 96 publications

References 44 publications

Non‐Newtonian rheology of igneous melts at high stresses and strain rates: Experimental results for rhyolite, andesite, basalt, and nephelinite

Non‐Newtonian rheology of igneous melts at high stresses and strain rates: Experimental results for rhyolite, andesite, basalt, and nephelinite

Structural relaxation in silicate melts and non-Newtonian melt rheology in geologic processes

Effects of structural relaxation on cationic tracer diffusion in silicate melts

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