Influence of the heating rates on the correlation between glass-forming ability (GFA) and glass stability (GS) parameters

Abstract

It is well known that some glass stability (GS) parameters which can be used to estimate glass-forming ability (GFA) are readily obtained by means of Differential Scanning Calorimetry (DSC) or Differential Thermal Analysis (DTA) experiments. In this work, the GS parameters proposed by Hrubÿ (KH), Weinberg (KW), Lu & Liu (KLL), Long et al. (KLX) and Zhang et al. (KZW) were determined for the following silicate glasses: Li2O·2SiO2, BaO·2SiO2, Na2O·2CaO·3SiO2 and 2BaO·TiO2·2SiO2. Monolithic specimens of these glasses were placed in Pt–Rh crucibles and heated in air in a DSC furnace at different heating rates (ϕ=2, 5, 10, 15, 20, 25 and 30°C/min) from room temperature up to their respective melting temperatures. The results indicate that all the parameters under study vary significantly as a function of the heating rate, and that KH, KW and KLL increase with ϕ while KZW and KLX decrease. To evaluate the reliability of these parameters in estimating GFA, they were correlated with the critical cooling rates (RC) calculated by the continuous cooling (RCC) and “nose” (RCN) methods using experimental data of steady-state nucleation and crystal growth rates, free energy per unit of volume, and viscosity of each vitreous material investigated. It was found that the correlation between the GFA (RCC or RCN) and all the parameters studied here persists, even if the changing of the GS parameters with the heating rates is taken into account.