Mixed Alkali Effect in Na₂O-Li₂O-Si O₂ Glasses Studied by Isothermal Mechanical Spectroscopy

Abstract
Several studies of internal friction have been performed on silicate glasses. This work has the specificity to refer to isothermal mechanical spectroscopy over a large frequency range and for temperatures between 290 K and 520 K. Experiments were carried out with a single alkali silicate glass and two mixed alkali silicate glasses in order to observe the mixed alkali effect, to follow its evolution versus alkali ratio and to deepen the knowledge of the mechanisms involved. According to this, internal friction spectra were shown to be dependent on the measurement temperature and the relaxation parameters were determined with greater accuracy. We also proved that non bridging oxygens peak is still present in mixed alkali glasses and that the relaxation mechanism for mixed alkali effect is related to couples made by the two alkali oxides.