Impact of Mg/Al ratio on the structure and properties of CaO–MgO–Al₂O₃–SiO₂ glass with high MgO content

Effects of Mg/Al ratio on the structure and properties of CaO–MgO–Al 2 O 3 –SiO 2 glass with high MgO content (23–29 wt.%) were systematically investigated based on differential scanning calorimetry (DSC), infrared spectrophotometry (IR) and 27 Al magic angles spinning nuclear magnetic resonance spectra ( 27 Al MAS NMR). Results show that excess MgO introduced an abundance of free oxygen, resulting in variations in the coordination states of Al 3+ . Al 3+ predominantly existed in [AlO 4 ] and [AlO 5 ], with [AlO 4 ] accounting for a high proportion. The decrease of Mg/Al mass ratio (from 1.81 to 1.05) led to the continuous increase of [AlO 4 ] content and the degree of glass network polymerization. This trend was accompanied by an increase in thermal stability and viscosity activation energy, as well as decreases in the elastic modulus, dielectric constant, and dielectric loss. When Mg/Al ratio was 1.05, the CMAS glass presented the better comprehensive performances with the elastic modulus of 110.3 GPa, dielectric constant of 5.73, and the dielectric loss of 0.96 × 10 −3 (at 1 MHz).