Mixed-alkaline earth effects on the network structure and properties of alkali-free aluminosilicate glasses

Alkali-free aluminosilicate glasses with different SrO/(MgO+SrO) molar ratios were prepared by the meltquenching method, and their structural evolution was characterized by Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR). The glass properties, including high-temperature viscosity, thermal expansion coefficient, density, Vicker hardness, elastic modulus, and chemical stability, were tested and analyzed. With the increasing of SrO/(MgO+SrO) molar ratios from 0 to1, the fraction of Q4 units in [SiO4] tetrahedral increased from 30.88 % to 39.06 %, and the Al3+ ions are dominated in [AlO4] groups, but small amount in [AlO5] units. In terms of comprehensive properties, the glass density and strain point temperature increased approximately linearly with the SrO/(MgO+SrO) ratios, while, the elastic modulus decreased with the SrO/(MgO+SrO) ratios. However, the high-temperature viscosity, Vickers hardness, chemical stability, and characteristic temperatures (melting temperature, working point temperature, Littleton softening temperature) deviated from linearity and exhibited the opposite mixed alkaline earth effect compared to previously reported aluminosilicate glasses. when the SrO/(MgO+SrO) molar ratio is approximately 0.25, the glass demonstrates optimal comprehensive performance.