Internal friction spectroscopy in Li2O–2SiO2 partially crystallised glasses

Abstract

Oscillatory torsion deformation experiments were performed on partially crystallised Li 2 O-2SiO 2 glasses in the temperature range 350-480°C and with frequencies between 20 and 0.002 Hz. The experiments were carried out in a torsion deformation apparatus exerting a small strain on cylindrical samples. Data obtained at varying temperatures and frequency were reduced to master plots using a normalised frequency. The frequency shift factor has been taken as a function of temperature in an Arrhenian form, yielding an activation energy of a background Q À1 close to the activation energy of oxygen defect diffusion ( ¼ 120 kJ/mol). The master curves of real and imaginary components of shear modulus and internal friction indicate a stretched exponential shear stress relaxation with a an exponent of %0.45, characteristic of a broadened relaxation spectrum. The dynamic viscosity was estimated at temperatures of 470 and 480°C. The extrapolation of dynamic viscosity to zero frequency allowed estimation of the relaxed shear viscosity. The presence of crystals increases the relaxed shear viscosity by %0:2 logðPa sÞ/10 vol.% of crystallinity. Dependence of the relative shear viscosity of partially crystallised lithium disilicate melts on crystal content is discussed.

Experimental investigation of magma rheology at 300 MPa: From pure hydrous melt to 76 vol.% of crystals

“…However, although most natural magmas are crystal suspensions, studies on the effect of crystals on the rheological properties of magmas have long been scarce [16][17][18][19] until the late nineties [20][21][22][23][24][25][26][27][28][29]. Despite these new data, the existence, significance and importance of some rheological thresholds are still under debate [30][31][32] and a unified model for predicting the viscosity of magmas over their whole range of crystallisation is still to be proposed.…”

Effects of crystallization and bubble nucleation on the seismic properties of magmas

“…However, the amplitude of this variation decreases with increasing crystal content. Microstructure is also a fundamental parameter in determining the elastic properties [e.g., Müller et al ., ; Hier‐Majumder , ; Schmeling , ; Mavko , 1980]. The nonlinear increase of seismic wave velocities by increasing the crystal fraction is a direct result of the formation of a continuous crystal network [ Caricchi et al ., ].…”