抄録
The viscosities of mixed-alkali lead silicate glasses were measured by the penetration viscometer in the softening range approximately from the flow point to the softening point. The densities of glasses at room temperature were also determined by the buoyancy method. The results obtained are summarized as follows:
(1) The minimum of viscosity appears at the molar concentration ratio of about 0.5 for the Na-K glasses and at the Na2O-rich side for the Li-Na glasses. For the K-Li glasses, on the other hand, the viscosity decreases with increasing Li2O content.
(2) The apparent molar volume-composition curve indicates a negative deviation from linearity for all the Li-Na, Na-K, and K-Li glasses.
(3) The compositional dependency of viscosity and that of the apparent activation energy of viscous flow show the same tendency for all the mixed-alkali glasses.
(4) The correlation between the minimum of viscosity and the largest negative deviation of molar volume in the Na-K glasses was interpreted in terms of the assumption of the increase in alkali-oxygen bond strengths based on the interaction between dissimilar alkali ions.
