Infrared and Raman Spectroscopy of Mullite Ceramics Synthesized from Fly Ash and Kaolin

Infrared spectroscopy and Raman spectroscopy were used to characterize mullite ceramics prepared from fly ash and kaolin by annealing at 1000 °C, 1100 °C, 1200 °C, and 1300 °C. IR spectroscopy confirmed the presence of SiO4 tetrahedra and AlO6 octahedra in samples. The presence of mullite has been confirmed at all temperatures. The presence of quartz has been confirmed up to a temperature of 1100 °C, and the presence of an amorphous form of SiO2 has been confirmed at temperatures of 1200 °C and 1300 °C. The transformation of quartz into the amorphous form of SiO2 at temperatures above 1100 °C is assumed. Transformation was performed on the percentage intensity decrease of the bending vibration of Si-O-Si (at about 450 cm−1) and Al-O-Si (at about 550 cm−1). Raman spectroscopy confirmed the presence of mullite at different stages of structural ordering (a well-ordered structure at a temperature of 1100 °C and a disordered structure at a temperature of 1300 °C).