Relation of Alkali Mobility and Mechanical Relaxation in Mixed‐Alkali Silicate Glasses

Internal friction and Na and K self‐diffusion coefficients for (I–X)Na 2 OXK 2 O‐3SiO 2 glasses were measured. Alkali diffusion was measured between 300° and 500°C using radioactive isotopes and a thin‐sectioning technique; internal friction was determined at room temperature to 500°C at 0.1 to 2000 Hz. Comparison of the data for alkali diffusion and internal friction in Na‐K glasses with those for other mixed‐alkali glasses shows that the mixed‐alkali peak is related to alkali mobility. It is concluded that the mechanism of mixed‐alkali internal friction is cooperative rearrangement of dissimilar alkali ions, with the slower‐moving ion controlling the rate of reorientation.