Analysis of regularities in composition dependence of the viscosity for glass-forming oxide melts: II. Viscosity of ternary alkali aluminosilicate melts

The data available in the literature on the viscosity of alkali aluminosilicate melts are collected and analyzed using the SciGlass information system. It is established that there are two composition regions in which the composition dependences of the viscosity logarithm at a constant temperature (above 1000degreesC are adequately described by linear equations. The largest amount of data is available for the composition region with an alkali oxide concentration exceeding the aluminum oxide concentration ([R2O] > [Al2O3]) In this region, the viscosity of melts is predominantly affected by two factors, namely, the concentration of alkali oxide uncombined into the alkali aluminate complex and the nature of alkali cations. At a constant concentration of unbound alkali oxide, the replacement of SiO2 by AIRO(2) is accompanied by a noticeable decrease in the viscosity of lithium aluminosilicate melts, a very weak decrease in the viscosity of sodium aluminosilicate melts, and a considerable increase in the viscosity of potassium aluminosilicate melts. In the second composition region ([R2O] < [Al2O3]), the replacement of SiO2 by AlO1.5 at a constant alkali metal content is attended by a decrease in the viscosity. In this region, the viscosity increases when changing over from Li2O to K2O upon complete substitution of one alkali oxide for another. Different variants of structural interpretation of the regularities revealed are discussed.