Parametric study of sodium aluminosilicate glasses using the non-reversing heat flow method of MDSC

Modulated differential scanning calorimetry (MDSC) has received much attention to study the relaxation behavior of different glasses but, due to equipment limitations, has almost exclusively been used on non-oxide and low-T_g compositions. While MDSC allows for the deconvolution of overlapping kinetic and thermodynamic signals, the addition of a sinusoidal modulation to the heating rate introduces more experimental parameters that are non-trivial to determine. Additionally, the relaxation of sodium aluminosilicate glasses, which are important in industrial applications, has not been thoroughly studied, especially by MDSC. In this paper, we propose best practices based on our own analysis of the non-reversing heat flow method that include erasing the thermal history of glass samples prior to MDSC, accounting for user error of the area integration by performing at least three separate analyses and plotting the enthalpy of relaxation with error bars, and standardizing the area integration by matching the shapes of the enthalpy integrals as closely as possible. We also report the enthalpy of relaxation calculated from the non-reversing heat flow from MDSC for variety of modulation parameters and for three different frequency correction methods. We find that the locations of minima in relaxation vary greatly with different frequency correction methods and parameters and for the modulation parameters with the best linearity, there was no discernible relaxation minimum across the compositions. Overall, this study suggests that the non-reversing heat flow method is not suitable for high-T_g oxide glasses or that there may be other modulation parameters that could provide better linearity.