Effects of B2O3 and TiO2 on Crystallization Behavior of Slags in Al2O3-CaO-MgO-Na2O-SiO2 System

Nowadays, there are increasing demands for developing mould fluxes without fluoride due to environmental concerns. Slag bearing titanium oxide and/or boron oxide proved to be promising substitute for traditional mould fluxes with fluoride. In the present work, Crystallization behaviors of some slags in Al2O3-CaO-MgO-Na2O-SiO2-B2O3-TiO2 system were investigated using single hot thermocouple technique (SHTT), differential thermal analysis (DTA), and X-ray diffraction (XRD) technique. It was found that liquidus temperature of slag decreases with increases of B2O3 content. The XRD analysis on the crystallized samples shows that crystallization products are perovskite, gehlenite, and wollastonite. Time-temperature-transformation diagrams (TTT) for various slags have been constructed using SHTT technique. It was found that B2O3 can significantly increase the incubation time for crystallization of slags. Incubation time for crystallization of slags at nose temperature decreases with increase of titanium oxide content from 5% to 10%. The morphology of crystals was also investigated using SHTT technique. At higher temperature, dendrites and columnar crystal tend to form and grow with time progress, while at lower temperature, small crystals appear and the amount of crystal increase with time increasing.