Miscibility Gaps in Alkali‐Silicate Binaries—Data and Thermodynamic Interpretation

Measurements of the miscibility gaps in the Li 2 O‐ and Na 2 O‐SiO 2 binaries are reported and compared to data of other workers. Heat treatments by brief immersion in liquid Sn were used for measuring the properties of glasses with a strong devitrification tendency. The miscibility‐gap boundaries of both systems are successfully described by modified regular‐mixing equations based on the concept that the thermodynamic mixing processes are controlled by complex but discrete molecular structures which exist in the melt. The assumptions and implications of the model are discussed.