Rheological and thermodynamic properties of alkaline earth oxide bearing silicate glasses: Implication of structural role of Mg 2+ in peralkaline glasses

Abstract We investigate the rheological and thermodynamic features of SiO 2 – Al 2 O 3 – Bi 2 O 3 – Na 2 O– MeO glasses (Me = Mg, Ca, Sr and Ba) using calorimetry and viscosity measurements. The results show a striking phenomenon: the glass containing MgO shows an obvious deviation in glass transition temperature T g , configurational heat capacity Δ C p and dynamic fragility m from the linear tendency of glasses containing Ca 2+ , Sr 2+ and Ba 2+ ions. It is also found that the content of non-bridging oxygen decreases accompanying a increase of bridging oxygen content when CaO is substituted by MgO from the O 1s XPS data. This implies that Mg 2+ serves as intermediate rather than network modifier like other alkaline earth cations in the studied silicate glass. Furthermore, the configurational entropy S c ( T ) based on the theories of Adam-Gibbs (AG) and iso-structural viscosity ( η iso ) shows that the structural role of Mg 2+ in the studied silicate glass does not change much with temperature. This is verified by the unique infrared absorption band (∼1055 cm −1 ) of fast-quenched glass Mg.