Li₂O•Al₂O₂•2SiO₂ glass fibers were ion-exchanged from 1 to 300 minutes in a sodium nitrate bath at 366ºC. The internal friction was measured along with the lithium and sodium concentration profiles. As sodium progressively replaced lithium, the alkali internal friction peak became smaller while a new peak (mixed alkali peak) appeared and increased in magnitude. These changes in the internal friction are similar to those that occur upon the addition of a second alkali to glasses prepared by conventional melting. The magnitude of both internal friction peaks in ion exchanged glasses was dependent on the overall glass composition. The magnitude of the alkali peak depended upon the unexchanged glass core, whereas that of the mixed alkali peak depended upon the exchanged layer on the glass surface. Dissolving the exchanged surface layer led to the restoration of the original alkali peak and the disappearance of the mixed alkali peak. Changing the alkali distribution did not affect much the mixed alkali peak, but caused the alkali peak to shift to higher temperatures and become smaller. The activation energy for both peaks remained essentially constant during ion exchange of the chilled fibers and this is attributed to the rigid network structure at 366ºC. The height of the alkali peak can be used to determine the maximum depth of penetration of the second alkali --Abstract, pages iv-v
