Mechanical Damping Spectrum for Mixed-Alkali R₂ O·Al₂ O₃·6SiO₂ Glasses

The internal friction of R2O·Al2O3·6SiO2 glasses was measured from-180° to 700°C at 0.4 Hz. Glasses containing Li2O or Na2O exhibited only the one internal friction peak characteristic of the stress-induced movement of the alkali ions. Substitution of a second alkali resulted in two significant changes in the internal friction: (1) a rapid reduction in the magnitude of the original alkali peak and (2) the appearance of a new internal friction peak whose magnitude was especially sensitive to the concentration of the second alkali. Each combination of two alkali ions resulted in a new peak, with peaks being observed for the combinations Li-Na, Na-K, and Li-K. A mechanical damping spectrum is predicted for aluminosilicate glasses containing more than two alkali ions