Effect of BaO addition on the structure and microstructure of SiO2–Al2O3–Na2O–K2O–MgO glass–ceramic composites

We examined the influence of barium oxide addition on the structure and properties of SiO2–Al2O3–Na2O–K2O–MgO glass–ceramics. Glass–ceramics were prepared with constant SiO2/Al2O3 and Na2O/K2O ratios of 6.5 and 1.04, respectively, and the MgO content was maintained at 10.56 wt%. The barium oxide content was set at 4 wt%, 9 wt%, and 14 wt%. The weight ratios were recalculated from the BaCO3 added. To determine the microstructure of the glassy materials, scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS), X-ray diffraction (XRD), medium (MIR) and far infrared analysis (FIR), and Raman spectroscopy were used. Significant differences were observed in the phase composition and in the silica–alumina-oxide network of the glassy phase, which could be related to changes in the amount of barium oxide. The characteristic temperatures (beginning of sintering, sphere, half-sphere and melting), which were measured by using hot stage microscopy and dilatometry, also showed changes.