Mixed alkaline‐earth effect on the mechanical and rheological properties of Ca–Mg silicate glasses

Abstract

AbstractIn this article, we investigate the mixed alkaline‐earth effect in a silicate glass series with varying the molar ratio of [MgO]/([CaO]+[MgO]). This effect manifests itself as a minimum in Vickers microhardness (HV), coefficient of thermal expansion (CTE), and isokom temperatures at 1012(Tg) and 102 Pa·s, and as a maximum in liquid fragility. To probe the structural origin of the mixed alkaline‐earth effect in CTE and Hv, we conducted the Raman measurements. In contrast to the aluminosilicate glasses, the present glass series exhibit a negative deviation of shift of peak position at ~1100 cm−1 from a linear additivity, indicating the role of the aluminum speciation in affecting the vibration modes. By fitting the Vogel–Fulcher–Tamann equation to the high‐temperature viscosity data, we found a near‐linear increase of the fractional free volume with the gradual substitution of Ca by Mg, confirming the dynamic structural mismatch model describing the mixed modifier effect. This work gives insight into the mixed modifier effect in glassy systems.