Determination of complex-specific heat and fragility of sodium borate glasses by temperature-modulated DSC

摘要

The frequency dependences of the complexspecific heat of the sodium borate glasses, xNa_2O.(100 - x)B_2O_3, where x denotes molar concentration of Na_2O, have been investigated by temperature-modulated DSC. The temperature dependences of α-relaxation time have been analyzed in Angell plot, and the fragility index has been determined. The composition dependence of the fragility index has been discussed on the basis of the variations of the structural units of the borate network. The origin of the fragility of the borate system relates to the distribution of the coordination number of boron atom.