Sintered glass-ceramics and foams by metallurgical slag with addition of CaF2

The possibilities for the production of self-glazed sintered glass-ceramics or/and glass-ceramic foams using metallurgical slag are discussed. The effect of CaF2 addition on the glass melting, the densification and the foaming is also studied. The sintering and the bloating trends are evaluated by hot stage microscopy and the phase formation is estimated by X-ray diffraction spectroscopy. The structure of the obtained samples is studied with scanning electron microscopy and with computed tomography. The results demonstrate a good sinter ability of the used glass powders in the interval 800-950 degrees C and a subsequent intensive bloating behaviour of the sintered samples in the range 1050-1150 degrees C. The addition of a certain amount of CaF2 in the glass batches leads to a noticeable decrease of both the melting and the sintering temperatures as well as to some increase of the crystallinity. As a result, self-glazed glass-ceramics with high percentage of CaF2 and with an improved micro-hardness and crystallinity can be obtained using finer glass powders, moderate heating rates and holding temperatures of 950-1000 degrees C. At the same time, glass-ceramic foams with closed porosity of about 80 vol % can be synthesized using glass powders with a modest addition of CaF2 by applying higher heating rates and holding temperatures of 1100-1150 degrees C.