Ultrahigh hardness Li₂O–MgO–Al₂O₃–SiO₂ glass–ceramics containing multiphase nanocrystals

Abstract

Li 2 O-Al 2 O 3 -SiO 2 -based glass-ceramics containing nanocrystals have attracted much attention due to their low expansion coefficient, good mechanical properties, for different applications, such as fire-safe glass, dental materials, and electronic devices protectors. In current research, ultrahigh hardness Li 2 O-MgO-Al 2 O 3 -SiO 2 glass-ceramics were prepared by conventional meltquenching and subsequent heat-treatment method. MgO was introduced via Li 2 O substitution to change glass crystallization and mechanical properties. The differential scanning calorimetry analysis indicated the glass transition and crystallization temperatures increased with MgO/Li 2 O ratio increase, for better glass network connectivity from Raman spectra analysis. In addition, the main crystal phase changed from Li 2 SiO 5 and LiAlSi 4 O 10 , to the combination of LiAlSi 2 O 6 and MgAl 2 Si 4 O 12 , and finally to MgAl 2 Si 4 O 12 . The Vickers hardness of glass-ceramics was highly dependent on MgO/Li 2 O ratios in glass components and heat-treatment temperatures, corresponding with the crystal phases in glass-ceramics. The highest hardness could reach 9.34 GPa, which was much higher than traditional silicate glass-ceramics. The scanning electron microscope images confirmed the crystal diameters that varied from 30 to 100 nm and were determined by MgO content. Transmission electron microscope images and energy-dispersive spectroscopy mapping also confirmed the precipitation of multiphase nanocrystals in glass matrix. The changes of glass structure, and corresponding crystal combinations in glass-ceramics resulting from MgO introduction, were responsible for the ultrahigh hardness glass.