Silicon oxynitride glasses produced by ammonolysis from colloidal silica

Silicon oxynitride glasses have been obtained by nitridation of two commercial colloidal silicas (Cab-O-Sil and Microsilica) and a SiO2–Na2O gel. The nitridation kinetics and the temperature influence over the nitridation process were studied. Crystallization and densification phenomena inhibit nitridation of SiO2–Na2O gel and Microsilica, while in the as-received Cab-O-Sil a maximum of nitridation around Tg, along with an increase in Tg with nitrogen were observed. The highest nitrogen contents obtained in Cab-O-Sil up to 19 wt% N are justified by its higher initial specific surface area Se. From this maximum nitrogen percentage, crystallization of α- and β-Si3N4 occurs, and the powder maintains Ss higher than 125 m2 g−1, corresponding to crystalline nanoparticles.