Crystallization of a SiO_2-MgO-AI_2O_3-K_2O-Fe_2O_3-F Glass

摘要

The phase-separation and the crystallization of SiO_2-MgO-Al_2O_3-K_2O-Fe_2O_3-F glass were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe of microanalyzers (EPMA). The results reveal that the varieties and the morphology of crystalline phases formed depend sensitively on the thermal treatment schedules. During the isothermal treatments, the crystalline phases of mica, mica and iron oxide (FeFeO_4), and FeFeO_4 as major crystals are precipitated in the glass samples heat-treated at 900, 1000 and 1050℃ respectively. However, the two-step heat treatment beginning at 900℃ for lh and subsequently followed at 1050℃ for lh leads to the precipitation of mica crystal and no any signs of FeFeO_4 crystalline phase is observed. Also the morphology of sample is different from that of the isothermally treated glass at 1050℃, but is similar from that of sample at 900℃. A "worm"-shaped phase-separation is observed in the sample heated at 800℃ for 0.5h, which exhibits different morphology from that of droplet- or globule-shape conventionally discerned. EPMA results show that the incorporation of Fe_2O_3 accelerates accumulation of fluorine element, promoting the phase-separation and the crystallization of the present glass.