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 gamma-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. (C) 2011 Elsevier Inc. All rights reserved.