Glass viscosity at crystallization temperature: an approach

In this work glasses which crystallize by surface or volume were selected and produced with the aim of studying the behavior of their viscosities at the crystallization temperature, using the equation proposed by Vogel–Fulcher–Tammann (VFT). The viscosity curves, determined from the VFT equation, included some modifications in the equation parameters. However, the characteristic temperatures such as half-sphere, glass transition, dilatometric softening and melting were always used. The temperatures corresponding to these phenomena were determined by dilatometric analysis (optic and contact dilatometry) and differential thermal analysis, which were used to determine the crystallization temperature of the glasses. From the analysis of the obtained experimental viscosity curves and the ones found in the literature for the studied compositions among other glasses, which show the same mechanisms of crystallization, it was found that there is a standard behavior of the parent glasses regarding their viscosities in the crystallization temperature. These viscosities are shown to be near to 104.28 ± 0.41 Pa s for surface crystallization and 106.37 ± 0.51 Pa s for volume crystallization.