Mechanism of crystallization of Co-cordierites from stoichiometric powdered glasses

The influence of cobalt, as a divalent cation, on the crystallization behaviour of the cordierite based glasses was studied. Powdered glass specimens of stoichiometric composition 2MO 2Al2O3 5SiO2 (M=Co and/or Mg) were obtained and thermally treated at several temperatures and times, and the sequence of crystallization and their microstructural evolution were analysed by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Results on the crystallization sequence showed that the steps in the crystallization path are independent of the nature of the divalent cation. The first crystalline phase detected displayed the μ-cordierite structure, i.e. a solid solution with β-quartz structure. After further thermal treatment a phase with α-cordierite structure was formed. Cobalt μ- and α-cordierites were further characterized by infrared (IR) and UV–vis diffuse reflectance spectroscopies. The final morphology of cobalt-containing hexagonal cordierites depended on the densification degree of the precursor glass.