Thermodynamic and Kinetic Parameters for Glass Transition
of Alkali-Borate and Alkali-Silicate Melts

V. M. Ushakov and N. V. Borisova

Grebenshchikov Institute of Silicate Chemistry, Russian Academy of Sciences,
ul. Odoevskogo 24/2, St. Petersburg, 199155 Russia

E-mail: ushakov@isc1.nw.ru

Abstract—Differential scanning calorimetry was used to study glasses and crystals whose compositions cor-
respond to congruently melting compounds: B₂O₃, Rb₂O · nB₂O₃ (n = 2, 3, 5); Cs₂O ·nB₂O₃ (n = 3, 5, 9);
M₂O · 2B₂O₃ (M = Li, Na); and K₂O · 4SiO₂. The fictive glass-transition temperature T_f, the excess of the
entropy of glass over that of the crystal at T_f for various prehistories of the glasses (the rate of melt cooling was
varied from 0.5 to 10⁶ K/min), and the activation energies of glass transition h* were evaluated. Based on the
data obtained, the thermodynamic (the ratio of the excess of the entropy of glass over the entropy of the corre-
sponding crystal at T_f to the entropy of the melting of the crystal) and kinetic (fragility m = f(h*, T_f)) param-
eters were compared for alkali-borate and alkali-silicate melts. The thermodynamic parameter alone is insuffi-
cient to describe the process of glass transition; both parameters should be used simultaneously.

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