Flash-DSC provides valuable insights into glass relaxation and crystallization

Abstract

Conventional differential scanning calorimeters (DSC) are widely used to study thermal responses in glasses, such as crystallization, relaxation, and glass transition. However, their cooling ($q_c$) and heating ($q_h$) rates are limited, typically ranging from 0.01 to 2 K s⁻¹. Flash-DSC overcomes this limitation by achieving much higher rates (up to ∼10⁴ K s⁻¹), allowing exploration of a wider range of experimental times, which is valuable for studying the glass transition phenomenon relevant to melts and glass industry. In this study, we utilized flash-DSC to investigate the thermal behavior of lithium disilicate (Li₂Si₂O₅) and lead metasilicate (PbSiO₃) glasses, employed here as examples of distinct fragility and glass-forming ability. We measured their limiting fictive temperatures (T’_f), onset glass transition temperatures (T_g,onset), and the shift factors, which enable the retrieval of viscosity from DSC experiments. Our findings reveal that: i) the shift factor is composition-dependent; ii) when using a fixed heating rate for glass samples made with different cooling rates and the absolute values of $q_h>q_c$, T_g,onset shifts to higher values as $q_c$ decreases, but when $q_h\le q_c$, T_g,onset shows no significant variation despite different T’_f values due to relaxation on the heating path; iii) Li₂Si₂O₅ glass exhibited non-overlapping heating curves in 8 repeated experiments after being cooled at the lowest rate, 50 K s⁻¹, suggesting partial crystallization during cooling, while PbSiO₃ exhibited overlapping heating curves, indicating its superior glass forming ability. Therefore, the critical cooling rate for vitrification of Li₂Si₂O₅ was estimated to be above 50 K s⁻¹. These findings indicate the power of flash-DSC to provide valuable insights into relaxation and crystallization phenomena.