Structural evolution and mechanical properties of SiO2-Al2O3-MgO-B2O3 glasses with partial substitution of MgO by MgF2

Abstract

SiO2-Al2O3-MgO-B2O3-MgF2 glasses were prepared using a high-temperature melting method, and their amorphous nature was confirmed through X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS) and magic angle spinning nuclear magnetic resonance (MAS-NMR) were used to investigated structural changes in the glass. It is found that substituting MgO with MgF2 disrupted the Si-O and Al-O networks in the high-temperature glass melt structure, reducing the degree of glass network polymerisation and viscosity. During cooling and annealing, moderate amounts of fluoride ions (F−) promoted the linkage of a partially fragmented glass network by converting [BO3] and [AlO5] into [BO4] and [AlO4]. An increased F− content improved the mechanical properties of the glass, including flexural strength, Young's modulus, and hardness, which peaked at 157.50 MPa, 95.21 GPa, and 838.57 HV with 2 mol% MgF2 substitution. These findings advance our understanding of the behavior of MgF2-substituted glass.