Non-Newtonian Flow Behaviour Of A Phosphate Glass Melt At A Viscosity Close To The Working Point

The dependence of both the shear and the extensional viscosity of the glass melt, namely, NaPoLi melt (Na20.Li20.2P205), on the shear and extensional rate, respectively, was studied by means of a capillary method at a low shear viscosity near the working point at ns=103 Pa s. To accurately calculate shear viscosities, the Bagley end correction ws made by determining the pressure drop at the entrance of the capillary. The extensional viscosity measurement was estimated using the Cogswell model. It was found that a dilatant flow behaviour occurred at low shear rates, whereas a shear-thinning flow behaviour did at high shear rates. At the same time, an extension-thinning flow took place.