Sinter-crystallization in air and inert atmospheres of a glass from pre-treated municipal solid waste bottom ashes

Glass powders, obtained after vitrification and milling of iron-rich Municipal Solid Waste Bottom Ashes (MSWA), were studied towards manufacture of sintered glass-ceramic material. The crystallization kinetics was investigated both in air and argon atmospheres by non-isothermal Differential Thermal Analysis (DTA). The densification behaviors at different temperatures were studied with optical dilatometry. The formed crystal phases were evaluated with X-ray diffraction (XRD) and the microstructure of samples were observed by scanning electron microscopy (SEM). The investigated composition is characterized with a high crystallization trend and formation of pyroxene solid solutions and melilite solid solutions. Due to additional nucleation process and lower viscosity (because of the lack of Fe2+ oxidation) the phase formation in inert atmosphere is accelerated and is carried out at lower temperature. In the interval 800–900 °C the densification in both atmospheres is inhibited by the intensive phase formation. However, after increasing the sintering temperature up to 1120–1130 °C secondary densification is carried out, resulting in material with zero water absorption, low closed porosity and high crystallinity. Some decreasing of sintering temperature and finer crystal structure are predicted at densification in inert atmosphere.