Abstract
The viscosities and densities of a series of ternary sodium aluminogermanate melts with the Na2O/Al2O3 ratio equal to unity have been determined for temperatures between 1200° and 1500°C. The viscosity and expansion coefficient evidence suggests that aluminum (III) takes part in network formation in the form of AlO4 tetrahedra. The molar‐volume data can best be interpreted in terms of a model that involves GeO4 and AlO4 tetrahedra as well as Na2O increase that is positively related to the Al2O3 content. Crystal‐structure and binary‐melt data were used to suggest likely coordination‐polyhedra types and partial molar volumes for the models discussed.

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