Influence of non-homologous substitutions of chemical components on rheological properties and on isochomal workability of silicate glass melts

The glass melts of a non-homologous series were investigated with respect to flow behaviour and stress generation behaviour as well as to workability by means of the cylinder compression method. The results show that the competition between the gross viscosity effect and the bonding strength of the dynamic glass melt structure extremely determines the high-temperature tensile strength, sigma(ts) the critical deformation rate h(c), and by that the isochomal workability. The larger h(c) values are not always connected to a larger non-Newtonian flow effect or to a larger gross viscosity effect as it is usually the case for homologous series. However, the rule for homologous series that smaller E(max) moduli, i.e. smaller stiffness and brittleness of a glass melt, are coupled to a better isochomal workability is also valid for non-homologous series. The special connections between sigma(ts), h(c) and deformation, Delta h/h(0), are analyzed.