Calculation of Temperature Dependences of the Viscosity and Volume Relaxation Time for Oxide Glass-Forming Melts from Chemical Composition and Dilatometric Glass Transition Temperature

Abstract

The relaxation parameter K sthat is equal to the ratio of the viscosity η to the Kohlrausch volume relaxation time τ s is analyzed. It is shown that this parameter can be evaluated from the temperature T 13(corresponding to a viscosity of 1013P) and the glass transition temperature T 8 +determined from the dilatometric heating curve. The maximum error of the estimate with due regard for experimental errors is equal to ± (0.4–0.5) log K sfor “strong” glasses and ±( 0.6–0.8) log K sfor “fragile” glasses, which, in both cases, corresponds to a change in the relaxation times with a change in the temperature by ±( 8–10) K. It is revealed that the viscosity, the Kohlrausch volume relaxation time τ s , and the shear modulus Gof glass-forming materials in silicate, borate, and germanate systems satisfy the relationship log(τ s G/η) ≈ 1. The procedure for calculating the temperature dependences of the viscosity and the relaxation times in the glass transition range from the chemical composition and the T 8 +temperature for glass-forming melts in the above systems is proposed. The root-mean-square deviations between the calculated and experimental temperatures T 11and T 13are equal to ±( 6–8) K for all the studied (silicate, borate, germanate, and mixed) oxide glass-forming systems. The proposed relationships can be useful for evaluating the boundaries of the annealing range and changes in the properties and their temperature coefficients upon cooling of glass-forming melts.