lon-exchanged versus as-melted mixed alkali glasses

Abstract

Assuming that the glass network structure containing Channels for ionic migration is established at the glass transition temperature during cooling and is perfectly rigid below this temperature, the properties of ion-exchanged and as-melted mixed alkali glasses are compared. Alkali ions introduced by ion exchange below the glass transition temperature bring the glass matrix into a State of internal strain by elastic expansion or contraction of ionic sites. In an as-melted mixed alkali glass, an ion-channel mismatch produces a similar strained State, resulting in large internal friction and the so-called thermometer effect. The change in molar volumes due to ion exchange is calculated on the basis of Eshelby's misfitting sphere theory. The molar volumes of ion-exchanged glasses calculated are close to those observed for as-melted mixed alkali glasses. The mixed alkali effect is also expected in ionexchanged mixed alkali glasses from the Standpoint of the ion-channel match model.