Formation of crystalline phases in (SiO2-CaO-Fe2O3)-TiO2 based glasses

Glass ceramics were obtained by annealing of the SiO2-CaO-Fe2O3 system, and the devitrifying effect of adding TiO2 was compared with Fe2O3. In spite of its higher field strength, TiO2 was unable to accelerate the devitrifying kinetics as could be seen in the TTT diagrams between 825 and 1000 °C. In both kinds of composition, a strong increase in electric conductivity was observed by SEM as crystalline phases appeared in heat-treated glass, which corresponded to a redistribution of iron oxide in the matrix material. XRD showed the presence of wollastonite and haematite, as well as amorphous silica, and energies of activation (Ea) were calculated with respective values of 210 and 450 kJ/mol for wollastonite and haematite.