Analysis of regularities in composition dependence of the viscosity for glass-forming oxide melts: I. viscosity of melts in the Na sub(2)O-RO-SiO sub(2) and Na sub(2)O-R sub(2)O-SiO sub(2) systems

The available experimental data on the composition dependence of the viscosity have been analyzed for the Na sub(2)O-RO-SiO sub(2) and Na sub(2)O-R sub(2)O-SiO sub(2) systems. It is established that, at temperatures of 900-1000 degree C and above, the influence of composition on the viscosity logarithm obeys the additivity rule. In particular, this allows a quantitative comparison of the influence of all the components entering into the composition of the studied systems on the viscosity of melts. It is demonstrated that the change in the cationic size of alkaline-earth and alkali metals upon substitution of their oxides for silica produces opposite effects on the viscosity. Certain regularities in the effect of the studied components on the viscosity of melts are revealed for temperatures below the lower boundary of the additivity. The regularities revealed are useful for the development of techniques for calculating the viscosity of multicomponent melts.