Oscillatory torsion deformation experiments were performed on partially crystallized Li2O–2SiO2 glasses at 350 to 480C and 20 to 0.002Hz. 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 by using a normalized frequency. The frequency shift factor was taken as a function of temperature in Arrhenius form, yielding an activation energy of the background Q-1 which was close to the activation energy of O defect diffusion of 120kJ/mol. The master curves of real and imaginary components of shear modulus and internal friction indicated a stretched exponential shear stress relaxation with an exponent of about 0.45, characteristic of a broadened relaxation spectrum. The dynamic viscosity was estimated at 470 and 480C. The extrapolation of dynamic viscosity to zero frequency permitted the estimation of the relaxed shear viscosity. The presence of crystals increased the relaxed shear viscosity by about 0.2log(Pas)/10vol% of crystallinity.

Internal Friction Spectroscopy in Li2O–2SiO2 Partially Crystallised Glasses. K.Müller, N.S.Bagdassarov, M.James, H.Schmeling, J.Deubener: Journal of Non-Crystalline Solids, 2003, 319[1-2], 44-56