Mechanism of cordierite formation in MgO-Al2O3-SiO2 glass-ceramic prepared by the sol- gel method

Sol-gel is chemical method for synthesis of nanometric powder that has been proposed in recent years. In the present investigation, synthesis of amorphous and nanometric powder with stoichiometric composition of cordierite in MgO-Al2O3-SiO2 system was prepared by tetraethyl orthosilicate and magnesium and aluminium chlorides. Particle size distribution of synthesised powder investigated by laser method. Structural investigation of gel derived powder at 100ºC and 1385ºC were characterized by FT-IR. The mechanism of cordierite formation was also studied using DTA and XRD techniques to follow the reactions occurring during gel heat treatment up to full cordierite conversion (1385ºC). XRD analysis revealed that spinel and cristobalite are formed at the beginning of heat treatment and then α-cordierite formed as the main crystalline phase in the sintered glass-ceramic by the reaction between spinel and cristobalite at crystallization peak temperature. The transformation of µ-cordierite to α-cordierite and a direct crystallization of α-cordierite from glass also occurred.