Characterisation and crystallisation kinetics of glass ceramics developed from Erdemir blast furnace slags containing Cr₂O₃ and TiO₂ nucleants

Glass ceramic materials were developed from blast furnace slags doped with 5 wt-%TiO₂, 10 wt-%TiO₂, 5 wt-%Cr₂O₃ and 5 wt-%TiO₂ + 5 wt-%Cr₂O₃. Based on differential thermal analyses and optical microscopy, optimum conditions were determined as 18 h at 780°C and 20 min at 910°C, for nucleation and crystallisation respectively. X-ray diffraction investigations were carried out on the as nucleated and as crystallised samples. Akermanite (2CaO.MgO.2SiO₂) and gehlenite (2CaO.Al₂ O₃.SiO₂) in addition to nucleant phases (TiO₂ and/or Cr₂O₃) appeared in crystallised samples. Scanning electron microscopy and energy dispersive spectroscopy revealed the presence of TiO₂ rich and Cr₂O₃ rich particles in the matrix after nucleation and crystallisation. Crystalline phases and nucleant (TiO₂ or Cr₂O₃) existed only on the surface of the sample. Based on differential thermal analyses results, Avrami n values were calculated to vary between 1.04 and 1.22, indicating surface crystallisation for which activation energies were found to vary between 290 and 334 kJ mol^-1.