Viscosity of strong and fragile glass-forming liquids investigated by means of principal component analysis

The Vogel-Fulcher-Tammann-Hesse (VFTH) equation has been the most widespread tool for describing the temperature dependence with viscosity for strong, moderate and fragile glass-forming liquids. In this work, the VFTH equation was applied over a wide temperature range (between the glass transition temperature, T, and the melting point, T,) for 38 oxide glasses, considering simple, binary and ternary compositions of silicate and borate systems. The Levenberg-Marquart non-linear fitting procedure was used to assess VFTH viscosity parameters B and T-0, maintaining A = -5 fixed (in Pa . s) to reduce the number of adjustable parameters. Regarding this restriction, the VFTH formula has shown to adjust very well to experimental data in a wide temperature range. Previous assertions revealed that there is statistical correlation between B and To. Principal component analysis (PCA) was used in the present study to verify the correlation between the B and To parameters [J. F. Mano, E. Pereira, J. Phys. Chem. A 108 (2004) 10824], as well as between T, and T,,,. In brief, PCA is a mathematical method aimed at reorganizing information from data sets. The results have shown that it is possible to map either borate (and almost fragile) or silicate (usually strong up to near fragile) systems. As a statistical tool, PCA justifies the use of B, T-0 and T-g as the main parameters for the fragility indexes m = d(log(10)eta)/d(T-g/T)vertical bar(T=Tg) and D = B/T-0, where eta is the viscosity and T the absolute temperature. (c) 2006 Elsevier Ltd. All rights reserved.