Mechanical Damping Spectrum for Mixed‐Alkali R ₂ O·Al ₂ O ₃ ·6SiO ₂ Glasses

Abstract

The internal friction of R 2 O·Al 2 O 3 ·6SiO 2 glasses was measured from‐180° to 700°C at 0.4 Hz. Glasses containing Li 2 O or Na 2 O 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.