Relaxation time spectra and the peculiarities of the process of boron anhydride glass transition

For a boron anhydride glass, the pre-exponential coefficient, B α , and the activation energy, u α , of the Boltzmann-Arrhenius equation are estimated by temperature-frequency dependence of the α-process. The temperature dependence of activation energy obeys the well-known Vogel-Fulcher-Tammann equation. A standard glass transition temperature, T g, is equal to 220°C, and the corresponding activation energy is equal to 110 kJ/mol. From these data, it can be concluded that glassy B 2O 3, by contrast with fused silica, is a linear polymer. Its viscosity and the process of glass transition, as in organic linear polymers, is determined with the overcoming of intermolecular bonds and the mobility of boron-oxygen chains rather than the rupture of the chemical B O bonds. A method of calculation of the continuous relaxation time spectra is proposed based on the Kohlrausch function, commonly used to describe the relaxation characteristics in the glass transition region. The parameter b, characterizing a relaxation time spectrum width at temperatures lower than a critical one, T c = 300°C, is b = 0.5. At higher temperatures, b increases, approaching a maximum possible value b = 1, and the relaxation time spectrum transfers to a δ-function and degenerates into the spectrum with a single relaxation time. This change is explained by the fact that structural micro-inhomogeneity of the B 2O 3 liquid gradually disappears as the temperature increases. A method of evaluation of the degree of micro-inhomogeneity of inorganic glasses by b is proposed.