Calculation of temperature dependences of the viscosity and volume relaxation time for oxide glass-forming melts from chemical composition and dilatometric glass transition temperature

摘要

The relaxation parameter K_s that is equal to the ratio of the viscosity #eta# to the Kohlrausch volume relaxation time #tau#_s is analyzed. It is shown that htis parameter can be evaluated from the temperature T_(13) (corresponding to a viscosity of 10~(13) P) and the glass transition temperature T_g~+ determined from the dilatometric heting curve. The maximum error of the estimate with due regard for experimental errors is equal to +-(0.4-0.5)logK_s for "strong"glasses and +-(0.6-0.8)logK_s for "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 #tau#_s, and the shear modulus G of glass-forming materials in silicate, borate, and germanate systems satisfy the relationship log(#tau#_sG/#eta#)approx=1. The procedure for calculating the temperatur edependences of the viscosity and the relaxation times in the glass transition range from the chemical composition and the T_g~+ temperature for glass-forming melts in the above systems is proposed. The root-meansquare deviations between the calculated and experimental temperatures T_(11) and T_(13) are 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.