Abstract
Inorganic waste (municipal incinerator residue, sewage sludge ash, coal ash and mineral waste etc.) is one of the most serious social problems from the points of environmental loading, and its reuses or recycles as a starting material have been urgently required. Glass-ceramics are one of the targets of the products. In this study, the glass-ceramics in the CaO-Al2O3-SiO2 system based on inorganic waste were prepared and crystallizations were investigated using scanning electron microscope (SEM) and powder X-ray diffraction (XRD). Glass-ceramics of this CaO-Al2O3-SiO2 system were expected for the construction materials. Model batches were prepared by mixing a molar ratio of 87-141 SiO2, 0-35 Al2O3, 40-110 CaCO3, 19 Na2CO3, 2 Fe, 3 Na2SO4 and 8 C, or 87-121 SiO2, 15-35 Al2O3, 40-60 CaCO3, 9-19 Na2CO3, 2-9 Fe, 3 Na2SO4, 8 C and 0-0.6 [Ca3(PO4)2]3•Ca(OH)2, respectively. The glass samples were produced by melting the batches at 1450°C. The glass samples were reheated at 700-950°C for 1 h, to induce nucleation in the glasses. In addition, the glasses were reheated at 950-1200°C for 1-4 h, to form glass-ceramics. The results of the SEM photographs and powder X-ray diffraction patterns of the glass-ceramics showed that the main crystalline phases, prismatic crystals of Wollastonite (CaO•SiO2) and Anorthite (CaO•Al2O3•2SiO2), were precipitated homogeneously by bulk crystallization. It was found that Nepheline (Na2O•Al2O3•2SiO2) and/or Gehelenite (2CaO•Al2O3•SiO2) were also precipitated.
