Mid-infrared spectroscopic study of crystallization of cubic spinel phase from metakaolin

The structural changes during thermal conversion of metakaolinite into cubic spinel phase that was in literature considered as Al–Si spinel or γ-Al₂O₃ were investigated by mid-infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC) using medium ordered kaolin with high content of kaolinite. Spectrum features were studied in the mid-infrared region from 4000 to 400 cm⁻¹ as function of fractional conversion that resulted from DSC experiments. The increasing contends of Al–O bonds in the octahedral position (AlO₆) was observed during thermal transformation. The high ratio of antisymmetric stretching of Si–O–Al and Si–O–Si bands and bands belonging to stretching of Al–O bonds in the (AlO₄) tetrahedra and (AlO₆) octahedra decreases exponentially with fractional conversion. The antisymmetric stretching band of Si–O–Si bond in the (SiO₄) tetrahedra becomes more expressive due to formation of amorphous SiO₂ phase.